| 1. |
- Bergman, Monica, et al.
(författare)
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Dangerous Waters : The Impact of the 2004 Indian Ocean Tsunami on Survivor Dream Content
- 2023
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Ingår i: Dreaming (New York, N.Y.). - : American Psychological Association (APA). - 1053-0797 .- 1573-3351. ; 33:4, s. 369-387
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Tidskriftsartikel (refereegranskat)abstract
- Episodic memories of emotionally salient and personally significant events are often incorporated into dreams, although rarely replayed identically to the original waking event except in replicative posttraumatic nightmares. We investigated, in five Swedish female 2004 Indian Ocean tsunami survivors, how episodic memories of the catastrophe were reflected in their dreams after trauma, both in retrospectively recalled nightmares and bad dreams, and in prospective dream diaries completed several months after the catastrophe. We also assessed whether the emotional and threatening dream content differed between the trauma and a matched control group. Based on the threat simulation theory, we predicted that the trauma group dreams would portray notable similarities with elements related to the original tsunami trauma, and that the trauma group would demonstrate a higher prevalence of negative emotional states, and a higher frequency of threatening dream events as well as more severe threats in their dreams. Only the first hypothesis was partially supported, with retrospective nightmares bearing higher similarity to the trauma experience than the prospective dream diary dreams. However, we observed no statistically significant differences in emotional or threatening dream content between the groups, suggesting that the trauma group participants were not suffering from significant posttraumatic dreaming at the time of systematic dream data collection. Yet, specific features of the trauma group dreams might be interpreted as remnants of episodic tsunami-related memories: Their dreams had a higher percentage of life-threatening events depicting realistic but improbable threats, and an analysis of water-related themes evidenced stressful themes related to waves.
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| 2. |
- Bergman, Monica, et al.
(författare)
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The Holocaust as a Lifelong Nightmare : Posttraumatic Symptoms and Dream Content in Polish Auschwitz Survivors 30 Years After World War II
- 2020
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Ingår i: American Journal of Psychology. - : University of Illinois Press. - 0002-9556 .- 1939-8298. ; 133:2, s. 143-167
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Tidskriftsartikel (refereegranskat)abstract
- Posttraumatic symptoms, including nightmares, are more prevalent in World War II survivors than in the general population, but how war experiences have affected subsequent dream content in specific survivor populations remains less explored. In the present study, we used self -reports collected in 1973 from Polish Auschwitz survivors (N = 150; 45 women) to investigate the prevalence of posttraumatic symptoms, classified according to the DSM-5 diagnostic criteria for posttraumatic stress disorder (PTSD). Furthermore, we classified main themes, central emotions, and threatening events in the dreams (N = 632) of the survivors, comparing dreams recalled from before, during, and after the war. Of the respondents, 12.7% described experiencing all diagnostic criteria for PTSD. War-related themes were less common in dreams dreamt before than during the war but were most common after the war. Themes related to family and freedom were most likely to appear in dreams dreamt during than before or after the war. The most often occurring emotion was fear, and dreams from after the war were likely to contain more negative and less positive emotions than dreams dreamt during the war. The likelihoods of reporting threatening events and threats involving aggression were higher in dreams dreamt during than before the war and in dreams dreamt after than during the war. In conclusion, PTSD symptoms were common in Polish Auschwitz survivors 30 years after World War II, and the themes, emotions, and threatening events in their dreams seem to reflect lifelong posttraumatic dreaming. We interpret the results as lending support for the threat simulation theory of dreaming.
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| 3. |
- Eklund, Rasmus, 1989-
(författare)
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Electrophysiological correlates of consciousness
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- How does the brain enable us to experience seeing or hearing a stimulus? If a stimulus is repeatedly presented at the awareness threshold, subjects will report that they are aware of the stimulus on half of the presentations. Electroencephalography (EEG) can be used to non-invasively record neural activity as event-related potentials (ERPs). The contrastive analysis of neural activity to trials rated as aware minus neural activity to trials rated as unaware reveals the neural correlates of consciousness (NCC). Research on the NCC in vision has resulted in two ERPs: an early negative difference wave (visual awareness negativity, VAN) and a subsequent late positivity (LP). Visual awareness may be reflected by one or both of these ERPs. However, the contrastive analysis (aware minus unaware) may not isolate the NCC because it arguably compares aware processing with a combination of unaware processing and no processing. In support, previous research that tried to isolate a comparison between aware processing and unaware processing found that LP was the only NCC. However, subsequent replications suggested VAN and LP as NCC. Because of these mixed results, we followed up on these studies in Study I with a preregistered design that manipulated stimulus size. Results showed VAN and LP as NCC. The findings provide evidence for VAN as an early NCC.Another main goal of this thesis was to investigate auditory awareness. In Study II, an auditory threshold task was used, and the contrastive analysis revealed an early negative difference wave (auditory awareness negativity, AAN) and LP. These ERPs are comparable to VAN and LP in vision. Because post-perceptual processes related to responding may confound the NCC in contrastive analysis, no-response tasks can be used to isolate awareness-related activity. In vision, a previous study in which the manual response requirement was manipulated showed effects on LP but not on VAN. In Study III, we used a similar task with auditory stimuli at the awareness threshold. Results suggested that AAN and LP are unaffected by the response manipulation. However, the present no-response task may not be optimal for removing post-perceptual processing because subjects need to reflect on their experience even if they do not need to respond manually. Additional analyses that attempted source localization of the AAN suggested that it is generated in auditory cortex.From a theoretical perspective, one view of these results is that VAN and AAN reflect local recurrent processing and that this is the neural signature of awareness, whereas LP reflects global recurrent processing that enables reporting. Other views suggest that VAN and AAN merely reflect preconscious processes, whereas LP and global recurrent processing reflect consciousness. The studies described in this thesis do not support one theory over the other but provide robust evidence for early neural correlates of visual and auditory awareness.
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| 4. |
- Filimonov, Dmitri, et al.
(författare)
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Is auditory awareness graded or dichotomous : Electrophysiological correlates of consciousness at different depths of stimulus processing
- 2024
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Ingår i: Consciousness and Cognition. - : Elsevier. - 1053-8100 .- 1090-2376. ; 123
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Tidskriftsartikel (refereegranskat)abstract
- The level-of-processing (LoP) hypothesis postulates that transition from unaware to aware visualstimuli is either graded or dichotomous depending on the depth of stimulus processing. Humanscan be progressively aware of the low-level features, such as colors or shapes, while the high-levelfeatures, such as semantic category, enter consciousness in an all-or none fashion. Unlike invision, sounds always unfold in time, which might require mechanisms dissimilar from visualprocessing. We tested the LoP hypothesis in hearing for the first time by presenting participantswith words of different categories, spoken in different pitches near the perceptual threshold. Wealso assessed whether different electrophysiological correlates of consciousness, the auditoryawareness negativity (AAN) and late positivity (LP), were associated with LoP. Our findingsindicate that LoP also applies to the auditory modality. AAN is an early correlate of awarenessindependent of LoP, while LP was modulated by awareness, performance accuracy and the levelof processing.
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| 5. |
- Filimonov, Dmitri, et al.
(författare)
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Modality-specific and modality-general electrophysiological correlates of visual and auditory awareness : Evidence from a bimodal ERP experiment
- 2022
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Ingår i: Neuropsychologia. - : Elsevier. - 0028-3932 .- 1873-3514. ; 166
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Tidskriftsartikel (refereegranskat)abstract
- To date, most studies on the event-related potential (ERP) correlates of conscious perception have examined a single perceptual modality. We compared electrophysiological correlates of visual and auditory awareness in the same experiment to test whether there are modality-specific and modality-general correlates of conscious perception. We used near threshold stimulation and analyzed event-related potentials in response to aware and unaware trials in visual, auditory and bimodal conditions. The results showed modality-specific negative amplitude correlates of conscious perception between 200 and 300 ms after stimulus onset. A combination of these auditory and visual awareness negativities was observed in the bimodal condition. A later positive amplitude difference, whose early part was modality-specific, possibly reflecting access to global workspace, and later part shared modality-general features, possibly indicating higher level cognitive processing involving the decision making, was also observed.
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| 6. |
- Filimonov, Dmitri, et al.
(författare)
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The influence of feature-based attention and response requirements on ERP correlates of auditory awareness
- 2024
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Ingår i: Neuroscience of Consciousness. - : Oxford University Press. - 2057-2107. ; 2024:1
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Tidskriftsartikel (refereegranskat)abstract
- In search for the neural correlates of consciousness (NCCs), it is important to isolate the true NCCs from their prerequisites, consequences, and co-occurring processes. To date, little is known about how attention affects the event-related potential (ERP) correlates of auditory awareness and there is contradictory evidence on whether one of them, the late positivity (LP), is affected by response requirements. By implementing a GO-NOGO design with target and nontarget stimuli, we controlled for feature-based attention and response requirements in the same experiment, while participants rated their awareness using a perceptual awareness scale. The results showed a prolonged auditory awareness negativity (AAN) for aware trials, which was influenced neither by attention nor by response requirement. The LP was affected by both attention and response requirements. Consistent with the levels of processing hypothesis, the LP was related to consciousness as a correlate of the processing of higher-level stimulus features, likely requiring access to a "global workspace." Our findings further suggest that AAN is a proper ERP correlate of auditory consciousness and thus a true NCC in the auditory modality.
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| 7. |
- Fingelkurts, Andrew, et al.
(författare)
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Cortex Functional Connectivity as a Neurophysiological Correlate of Hypnosis : an EEG Case Study
- 2007
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Ingår i: Neuropsychologia. - : Elsevier. - 0028-3932 .- 1873-3514. ; 45:7, s. 1452-1462
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Tidskriftsartikel (refereegranskat)abstract
- Cortex functional connectivity associated with hypnosis was investigated in a single highly hypnotizable subject in a normal baseline condition and under neutral hypnosis during two sessions separated by a year. After the hypnotic induction, but without further suggestions as compared to the baseline condition, all studied parameters of local and remote functional connectivity were significantly changed. The significant differences between hypnosis and the baseline condition were observable (to different extent) in five studied independent frequency bands (delta, theta, alpha, beta, and gamma). The results were consistent and stable after 1 year. Based on these findings we conclude that alteration in functional connectivity of the brain may be regarded as a neuronal correlate of hypnosis (at least in very highly hypnotizable subjects) in which separate cognitive modules and subsystems may be temporarily incapable of communicating with each other normally
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| 8. |
- Fingelkurts, Alexander, et al.
(författare)
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Hypnosis Induces Reorganization in the Composition of Brain Oscillations in EEG : A case study
- 2007
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Ingår i: Contemporary Hypnosis. - : John Wiley & Sons. - 0960-5290 .- 1557-0711. ; 24:1, s. 3-18
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Tidskriftsartikel (refereegranskat)abstract
- Cognitive functions associated with the frontal lobes of the brain may be specifically involved in hypnosis. Thus, the frontal area of the brain has recently been of great interest when searching for neural changes associated with hypnosis. We tested the hypothesis that EEG during pure hypnosis would differ from the normal non-hypnotic EEG especially above the frontal area of the brain. The composition of brain oscillations was examined in a broad frequency band (1-30 Hz) in the electroencephalogram (EEG) of a single virtuoso subject. Data was collected in two independent data collection periods separated by one year. The hypnotic and non-hypnotic conditions were repeated multiple times during each data acquisition session. We found that pure hypnosis induced reorganization in the composition of brain oscillations especially in prefrontal and right occipital EEG channels. Additionally, hypnosis was characterized by consistent right-side-dominance asymmetry. In the prefrontal EEG channels the composition of brain oscillations included spectral patterns during hypnosis that were completely different from those observed during non-hypnosis. Furthermore, the EEG spectral patterns observed overall during the hypnotic condition did not return to the pre-hypnotic baseline EEG immediately when hypnosis was terminated. This suggests that for the brain, the return to a normal neurophysiological baseline condition after hypnosis is a time-consuming process. The present results suggest that pure hypnosis is characterized by an increase in alertness and heightened attention, reflected as cognitive and neuronal activation. Taken together, the present data provide support for the hypothesis that in a very highly hypnotizable person (a hypnotic virtuoso) hypnosis as such may be accompanied by a changed pattern of neural activity in the brain. Copyright © 2007 British Society of Experimental & Clinical Hypnosis. Published by John Wiley & Sons, Ltd.
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| 9. |
- Förster, Jona, et al.
(författare)
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ERP and MEG correlates of visual consciousness : The second decade
- 2020
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Ingår i: Consciousness and Cognition. - : Elsevier. - 1053-8100 .- 1090-2376. ; 80
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Tidskriftsartikel (refereegranskat)abstract
- The first decade of event-related potential (ERP) research had established that the most consistent correlates of the onset of visual consciousness are the early visual awareness negativity (VAN), a posterior negative component in the N2 time range, and the late positivity (LP), an anterior positive component in the P3 time range. Two earlier extensive reviews ten years ago had concluded that VAN is the earliest and most reliable correlate of visual phenomenal consciousness, whereas LP probably reflects later processes associated with reflective/access consciousness. This article provides an update to those earlier reviews. ERP and MEG studies that have appeared since 2010 and directly compared ERPs between aware and unaware conditions are reviewed, and important new developments in the field are discussed. The result corroborates VAN as the earliest and most consistent signature of visual phenomenal consciousness, and casts further doubt on LP as an ERP correlate of phenomenal consciousness.
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| 10. |
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| 11. |
- Grassini, Simone, et al.
(författare)
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Pattern matters : Snakes exhibiting triangular and diamond-shaped skin patterns modulate electrophysiological activity in human visual cortex
- 2019
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Ingår i: Neuropsychologia. - : Elsevier. - 0028-3932 .- 1873-3514. ; 131, s. 62-72
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Tidskriftsartikel (refereegranskat)abstract
- The neural and perceptual mechanisms that support the efficient visual detection of snakes in humans are still not fully understood. According to the Snake Detection Theory, selection pressures posed by snakes on early primates have shaped the development of the visual system. Previous studies in humans have investigated early visual electrophysiological activity in response to snake images vs. various alternative dangerous or non-dangerous stimuli. These studies have shown that the Early Posterior Negativity (EPN) component is selectively elicited by snake or snake-like images. Recent findings yielded the complementary/alternative hypothesis that early humans (and possibly other primates) evolved an aversion especially for potentially harmful triangular shapes, such as teeth, claws or spikes. In the present study we investigated the effect of triangular and diamond-shaped patterns in snake skins on the ERP correlates of visual processing in humans. In the first experiment, we employed pictures of snakes displaying either triangular/diamond-shaped patterns or no particular pattern on their skins, and pictures of frogs as control. Participants observed a random visual presentation of these pictures. Consistent with previous studies, snakes elicited an enhanced negativity between 225 and 300 ms (EPN) compared to frogs. However, snakes featuring triangular/diamond-shaped patterns on their skin produced an enhanced EPN compared to the snakes that did not display such patterns. In a second experiment we used pictures displaying only skin patterns of snakes and frogs. Results from the second experiment confirmed the results of the first experiment, suggesting that triangular snake-skin patterns modulate the activity in human visual cortex. Taken together, our results constitute an important contribution to the snake detection theory.
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| 12. |
- Grassini, Simone, et al.
(författare)
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Processing of natural scenery is associated with lower attentional and cognitive load compared with urban ones
- 2019
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Ingår i: Journal of Environmental Psychology. - : Academic Press. - 0272-4944 .- 1522-9610. ; 62, s. 1-11
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Tidskriftsartikel (refereegranskat)abstract
- Environmental psychology has provided evidence for psychologically favorable effects of exposure to natural settings, by means of controlled laboratory experiments as well as outdoor field studies. Most of these studies have employed subjective rating scales to assess processes and outcomes of exposure to nature, while only few of them have used physiological measures to assess the neural correlates of these benefits. The present study used electroencephalography (EEG) to explore how the brain engages in processing of images of natural vs. urban scenery. During EEG recording, the participants (n = 32) were presented with a series of photos depicting urban or natural scenery. Participants rated the sceneries for their subjective relaxing value. Images of natural scenery were rated as more relaxing compared to the images of urban scenery. Event related potentials suggested a lower attentional demand for images of natural scenery compared to urban ones. Signal spectral analyses revealed differences in brain activity level and cognitive demand between natural and urban scenery. Our data suggest that the visual perception of natural environments calls for less attentional and cognitive processing, compared with urban ones. © 2019 Elsevier Ltd
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| 13. |
- Grassini, Simone, et al.
(författare)
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Subjective ratings of fear are associated with frontal late positive potential asymmetry, but not with early brain activity over the occipital and centro-parietal cortices
- 2020
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Ingår i: Psychophysiology. - : John Wiley & Sons. - 0048-5772 .- 1469-8986. ; 57:12
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Tidskriftsartikel (refereegranskat)abstract
- The human frontal cortex is asymmetrically involved in motivational and affective processing. Several studies have shown that the left-frontal hemisphere is related to positive and approach-related affect, whereas the right-frontal hemisphere is related to negative and withdrawal-related affect. The present study aimed to investigate whether evolutionarily threatening stimuli modulate asymmetrical frontal activity. We examined hemispheric differences in frontal late positive potentials (f-LPP asymmetry) and frontal alpha power activation (frontal alpha asymmetry, FAA) in response to images depicting snakes, spiders, butterflies, and birds. Results showed that the late component of f-LPP asymmetry, but not FAA, was modulated by the category of stimuli. Specifically, threatening stimuli (snakes and spiders) evoked a relatively large late f-LPP over the right-frontal hemisphere than non-threatening stimuli (birds and butterflies). Moreover, this relatively great right-frontal activity was positively associated with the subjective ratings of fear. Importantly, the subjective ratings of fear were not associated with early brain activity over the occipital or centro-parietal cortices. These results suggest that late f-LPP asymmetry may reflect higher order affective processes, specifically the subjective appraisal of threatening stimuli and the subjective experience of fear, that are independent of the fast and automatic processing of evolutionarily significant and affectively arousing stimuli.
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| 14. |
- Grassini, Simone, et al.
(författare)
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Visual features and perceptual context modulate attention towards evolutionarily relevant threatening stimuli : Electrophysiological evidence
- 2019
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Ingår i: Emotion. - : American Psychological Association (APA). - 1528-3542 .- 1931-1516. ; 19:2, s. 348-364
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Tidskriftsartikel (refereegranskat)abstract
- The snake detection hypothesis claims that predatory pressure from snakes has shaped the primate visual system, but we still know very little about how the brain processes evolutionarily important visual cues, and which factors are crucial for quick detection of snakes. We investigated how visual features modulate the electrophysiological markers of early attentional processes. In Experiment 1, we compared snake, rope, gun, and bird images to isolate the effects due to curvilinearity of the stimuli. The results showed that both snake and rope images elicited enhanced P1 and N1 event-related potential components as well as early posterior negativity (EPN). In Experiment 2, we studied whether nonthreatening curvilinear images (i.e., ropes) still elicit the enhanced electrophysiological responses when snake images are not presented as stimuli, and therefore the context does not provoke top-down attention to curvilinear shapes. Rope images still evoked an enhanced EPN, suggesting that curvilinear shapes are preferably captured by attentional processes. However, this effect was smaller than in Experiment 1, in which snake images were present. Thus, our results hint to the possibility that the perceptual context may interact with processing of shape information, drawing attention to curvilinear shapes when the presence of snakes is expectable. Furthermore, we observed that spatial frequency of the visual stimuli modulated especially the early electrophysiological responses, and decreased the differences between stimulus categories in EPN without completely eliminating them. The findings suggest that low-level and high-level mechanisms interact to give an attentional priority to potentially threatening stimuli.
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| 15. |
- Haarala, Christian, et al.
(författare)
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Electromagnetic field emitted by 902 MHz phones shows no effects on children's cognitive function
- 2005
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Ingår i: Bioelectromagnetics. - : Wiley-Liss. - 0197-8462 .- 1521-186X. ; 26:S7, s. S144-S150
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Tidskriftsartikel (refereegranskat)abstract
- The present study investigated the potential effects of a standard 902 MHz global system for mobile communication (GSM) mobile phone on 10–14 years old children’s cognitive function. A total of 32 children (16 boys, 16 girls) participated with their own and parental consent. The subjects were 10– 14 years old (mean 12.1 years, SD 1.1). They performed a battery of cognitive tests twice in a counterbalanced order: once while exposed to an active mobile phone and once during exposure to an inactive phone. The tests were selected from those we used earlier with adults. The statistical analyses showed no significant differences between the mobile phone off and on conditions in reaction times and accuracy over all tests or in any single test. It was concluded that a standard mobile phone has no effect on children’s cognitive function as measured by response speed and accuracy. The present results challenge some earlier findings suggesting that the electromagnetic field (EMF) created by an active mobile phone would facilitate cognitive functioning.
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| 16. |
- Hurme, Mikko, et al.
(författare)
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Early processing in primary visual cortex is necessary for conscious and unconscious vision while late processing is necessary only for conscious vision in neurologically healthy humans
- 2017
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Ingår i: NeuroImage. - : Elsevier. - 1053-8119 .- 1095-9572. ; 150, s. 230-238
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Tidskriftsartikel (refereegranskat)abstract
- The neural mechanisms underlying conscious and unconscious visual processes remain controversial. Blindsight patients may process visual stimuli unconsciously despite their VI lesion, promoting anatomical models, which suggest that pathways bypassing the VI support unconscious vision. On the other hand, physiological models argue that the major geniculostriate pathway via VI is involved in both unconscious and conscious vision, but in different time windows and in different types of neural activity. According to physiological models, feedforward activity via VI to higher areas mediates unconscious processes whereas feedback loops of recurrent activity from higher areas back to VI support conscious vision. With transcranial magnetic stimulation (TMS) it is possible to study the causal role of a brain region during specific time points in neurologically healthy participants. In the present study, we measured unconscious processing with redundant target effect, a phenomenon where participants respond faster to two stimuli than one even when one of the stimuli is not consciously perceived. We tested the physiological feedforward-feedback model of vision by suppressing conscious vision by interfering selectively either with early or later VI activity with TMS. Our results show that early VI activity (60 ms) is necessary for both unconscious and conscious vision. During later processing stages (90 ms), VI contributes selectively to conscious vision. These findings support the feedforward-feedback-model of consciousness.
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| 17. |
- Hurme, Mikko, et al.
(författare)
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V1 activity during feedforward and early feedback processing is necessary for both conscious and unconscious motion perception
- 2019
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Ingår i: NeuroImage. - : Elsevier. - 1053-8119 .- 1095-9572. ; 185, s. 313-321
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Tidskriftsartikel (refereegranskat)abstract
- The study of blindsight has revealed a seminal dissociation between conscious vision and visually guided behavior: some patients who are blind due to V1 lesions seem to be able to employ unconscious visual information in their behavior. The standard assumption is that these findings generalize to the neurologically healthy. We tested whether unconscious processing of motion is possible without the contribution of V1 in neurologically healthy participants by disturbing activity in V1 using transcranial magnetic stimulation (TMS). Unconscious processing was measured with redundant target effect (RTE), a phenomenon where participants respond faster to two stimuli than to one stimulus, when the task is just to respond as fast as possible when one stimulus or two simultaneous stimuli are presented. We measured the RTE caused by a motion stimulus. V1 activity was interfered with different stimulus onset asynchronies (SOA) to test whether TMS delivered in a specific time window suppresses conscious perception (participant reports seeing only one of the two stimuli) but does not affect unconscious processing (RTE). We observed that at each SOA, when TMS suppressed conscious perception of the stimulus, the RTE was also eliminated. However, when visibility of the redundant target was suppressed with a visual mask, we found unconscious processing of motion. This suggests that unconscious processing of motion depends on V1 in neurologically healthy humans. We conclude that the neural mechanisms that enable motion processing in blindsight are modulated by neuroplastic changes in connectivity between subcortical areas and the visual cortex after the V1 lesion. Neurologically healthy observers cannot process motion unconsciously without functioning of V1.
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| 18. |
- Intaite, Monika, et al.
(författare)
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Perceptual reversals of Necker stimuli during intermittent presentation with limited attentional resources
- 2013
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Ingår i: Psychophysiology. - : Wiley-Blackwell. - 0048-5772 .- 1469-8986. ; 50:1, s. 82-96
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Tidskriftsartikel (refereegranskat)abstract
- During prolonged viewing of ambiguous stimuli, such as Necker cubes, sudden perceptual reversals occur from one perceptual interpretation to another. The role of attention in such reversals is not clear. We tested whether perceptual reversals depend on attentional resources by manipulating perceptual load and recording event-related potentials (ERPs) during intermittent presentation of Necker stimuli. The results did not reveal any influence for perceptual load on the frequency of reversals. The ERPs showed that perceptual load influenced electrophysiological activity over parieto-central areas in the P1 time window (110–140 ms), but load did not modify the early enhancements of positivity (30–140 ms), which correlated with perceptual reversals at occipito-temporal sites. We conclude that disambiguation of ambiguous figures is based on early mechanisms that can work efficiently with only a minimal amount of attentional resources.
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| 19. |
- Intaité, Monika, et al.
(författare)
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Reversal negativity and bistable stimuli : Attention, awareness, or something else?
- 2010
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Ingår i: Brain and Cognition. - : Elsevier. - 0278-2626 .- 1090-2147. ; 74:1, s. 24-34
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Tidskriftsartikel (refereegranskat)abstract
- Ambiguous (or bistable) figures are visual stimuli that have two mutually exclusive perceptual interpretations that spontaneously alternate with each other. Perceptual reversals, as compared with non-reversals, typically elicit a negative difference called reversal negativity (RN), peaking around 250 ms from stimulus onset. The cognitive interpretation of RN remains unclear: it may reflect either bottom-up processes, attentional processes that select between the alternative views of the stimulus, or it may reflect the change in the contents of subjective awareness. In the present study, event-related potentials in response to endogenous unilateral and bilateral reversals of two Necker lattices were compared with exogenously induced reversals of unambiguous lattices. The RN neither resembled the attention-related N2pc response, nor did it correlate with the content of subjective visual awareness. Thus, we conclude that RN is a non-attentional ERP correlate of the changes in the perceptual configuration of the presented object.
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| 20. |
- Johanson, Mirja, et al.
(författare)
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Alterations in the contents of consciousness in partial epileptic seizures
- 2008
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Ingår i: Epilepsy & Behavior. - : Elsevier. - 1525-5050 .- 1525-5069. ; 13:2, s. 366-371
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Tidskriftsartikel (refereegranskat)abstract
- Epilepsy research suffers from a deficiency of systematic studies concerning the phenomenology of the contents of consciousness during seizures, partially because of the lack of suitable research methods. The Phenomenology of Consciousness Inventory (PCI), a standardized, valid, and reliable questionnaire, was used here to study which dimensions of the contents of consciousness are distorted during partial epileptic seizures compared with baseline. Further, the similarity of the altered pattern of subjective experiences across recurring seizures was also explored. Our results indicate that patients with epilepsy report alterations on most dimensions of the contents of consciousness in conjunction with seizures, but individual seizure experiences remain similar from one seizure to another. The PCI was found suitable for the assessment of subjective experiences during epileptic seizures and could be a valuable tool in providing new information about phenomenal consciousness in epilepsy in both the research and clinical settings.
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| 21. |
- Johanson, Mirja, et al.
(författare)
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Content analysis of subjective experiences in partial epileptic seizures
- 2008
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Ingår i: Epilepsy & Behavior. - : Elsevier. - 1525-5050 .- 1525-5069. ; 12:1, s. 170-182
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Tidskriftsartikel (refereegranskat)abstract
- A new content analysis method for systematically describing the phenomenology of subjective experiences in connection with partial epileptic seizures is described. Forty patients provided 262 descriptions of subjective experience relative to their partial epileptic seizures. The results revealed that subjective experiences during seizures consist mostly of sensory and bodily sensations, hallucinatory experiences, and thinking. The majority of subjective experiences during seizures are bizarre and distorted; nevertheless, the patients are able to engage in adequate behavior. To the best of our knowledge, this is the first study for which detailed subjective seizure descriptions were collected immediately after each seizure and the first study in which the content of verbal reports of subjective experiences during seizures, including both the ictal and postictal experiences, has been analyzed in detail.
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| 22. |
- Johanson, Mirja, et al.
(författare)
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How to assess ictal consciousness?
- 2011
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Ingår i: Behavioural Neurology. - : Hindawi Publishing Corporation. - 0953-4180 .- 1875-8584. ; 24:1, s. 11-20
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Tidskriftsartikel (refereegranskat)abstract
- Despite the complexity and methodological difficulties in defining the concept consciousness, it is a central concept in epileptology, and should thus be tractable for scientific analysis. In the present article, a two-dimensional model consisting of concepts related to the level and the contents of consciousness will be presented. This model has been found to be well suited for the description of seizure-induced alterations of consciousness, and is supported both by findings from neuroimaging and electrophysiological studies as well as from phenomenological studies. Further, we will review both traditional introspective methods as well as methods that have recently been developed or utilized in epilepsy research, summarize the main findings concerning first person experiences during epileptic seizures acquired with some of these methods, and discuss their strengths and weaknesses.
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| 23. |
- Kallio, Sakari, et al.
(författare)
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Altering the state of the altered state debate : reply to commentaries
- 2005
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Ingår i: Contemporary Hypnosis. - : John Wiley & Sons. - 0960-5290 .- 1557-0711. ; 22:1, s. 46-55
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Tidskriftsartikel (refereegranskat)abstract
- The main point of our article Hypnotic phenomena and altered states of consciousness: A multilevel framework of description and explanation was to clarify, explicate and reveal the differences between current theoretical viewpoints in explaining hypnosis. Furthermore, we wanted to present a research programme and propose some experiments that if carried out, might lend decisive support to either the Nonstate View (NSV) or the State View (SV) approaches to hypnosis. The commentaries revealed that the concept of altered state of consciousness (ASC) still lacks a commonly accepted definition and is in need of further clarification. The controversy between NSV and SV of hypnosis seems to boil down to the question concerning the explanatory power of the neural level and especially to what the results at this level tell us. In this reply we further clarify the multilevel framework of explanation, the problems associated with the concept of ASC, and we explain the rationale for our proposal of using virtuosos as a model system in hypnosis research. Copyright © 2005 British Society of Experimental and Clinical Hypnosis
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| 24. |
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| 25. |
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| 26. |
- Kallio, Sakari, et al.
(författare)
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Hypnotic phenomena and altered states of consciousness : A multilevel framework of description and explanation
- 2003
-
Ingår i: Contemporary Hypnosis. - : Wiley. - 0960-5290 .- 1557-0711. ; 20:3, s. 111-164
-
Tidskriftsartikel (refereegranskat)abstract
- There is currently agreement that, in addition to the changes in external behaviour, suggestions presented in a hypnotic context may give rise to changes in subjective experience. Yet, there is no general agreement about the theoretical framework within which these changes in experience should be explained. Though different theories about hypnosis overlap in many respects, there is still disagreement on whether reference to a specific internal state of the individual is necessary in order to explain these changes. We place the explanatory task in the context of a multilevel framework of explanation, which reveals that the disagreement between the state and nonstate view is about the level of description at which the phenomenon hypnosis should be conceptualized. We propose a novel approach using the multilevel explanation which helps to formulate empirically testable hypotheses about the nature of hypnosis. We will outline the basic elements of such an approach and hope that our proposition will help hypnosis research to integrate with the multidisciplinary research on other phenomena of consciousness.
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| 27. |
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| 28. |
- Kallio, Sakari, et al.
(författare)
-
The observer remains hidden
- 2005
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Ingår i: Contemporary Hypnosis. - : John Wiley & Sons. - 0960-5290 .- 1557-0711. ; 22:3, s. 138-143
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Tidskriftsartikel (refereegranskat)abstract
- The concept of hidden observer is one of the most controversial issues in hypnosis research. Green, Page, Handley and Rasekhy (this issue) approach it by using an ideomotor task which has not previously been used in association with the hidden observer. We regard their experiment as interesting; however, there are conceptual and methodological problems that hamper the impact of their study. In our commentary, we take the opportunity to point out some problems in their paper as well as to stress the importance to integrate concepts used in hypnosis research to mainstream cognitive neuroscience and consciousness research. Copyright © 2005 British Society of Experimental & Clinical Hypnosis. Published by John Wiley & Sons, Ltd.
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| 29. |
- Kallionpää, Roosa E., et al.
(författare)
-
Alpha band frontal connectivity is a state-specific electroencephalographic correlate of unresponsiveness during exposure to dexmedetomidine and propofol
- 2020
-
Ingår i: British Journal of Anaesthesia. - : Elsevier. - 0007-0912 .- 1471-6771. ; 125:4, s. 518-528
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Tidskriftsartikel (refereegranskat)abstract
- Background herent alpha electroencephalogram (EEG) rhythms in the frontal cortex have been correlated with the hypnotic effects of propofol and dexmedetomidine, but less is known about frontal connectivity as a state-specific correlate of unresponsiveness as compared with long-range connectivity. We aimed to distinguish dose- and state-dependent effects of dexmedetomidine and propofol on EEG connectivity. thods rty-seven healthy males received either dexmedetomidine (n=23) or propofol (n=24) as target-controlled infusion with stepwise increments until loss of responsiveness (LOR). We attempted to arouse participants during constant dosing (return of responsiveness [ROR]), and the target concentration was then increased 50% to achieve presumed loss of consciousness. We collected 64-channel EEG data and prefrontal–frontal and anterior–posterior functional connectivity in the alpha band (8–14 Hz) was measured using coherence and weighted phase lag index (wPLI). Directed connectivity was measured with directed phase lag index (dPLI). sults efrontal–frontal EEG-based connectivity discriminated the states at the different drug concentrations. At ROR, prefrontal–frontal connectivity reversed to the level observed before LOR, indicating that connectivity changes were related to unresponsiveness rather than drug concentration. Unresponsiveness was associated with emergence of frontal-to-prefrontal dominance (dPLI: –0.13 to –0.40) in contrast to baseline (dPLI: 0.01–0.02). Coherence, wPLI, and dPLI had similar capability to discriminate the states that differed in terms of responsiveness and drug concentration. In contrast, anterior–posterior connectivity in the alpha band did not differentiate LOR and ROR. nclusions cal prefrontal–frontal EEG-based connectivity reflects unresponsiveness induced by propofol or dexmedetomidine, suggesting its utility in monitoring the anaesthetised state with these agents. inical trial registration
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| 30. |
- Kallionpää, Roosa E., et al.
(författare)
-
Single-subject analysis of N400 event-related potential component with five different methods
- 2019
-
Ingår i: International Journal of Psychophysiology. - : Elsevier. - 0167-8760 .- 1872-7697. ; 144, s. 14-24
-
Tidskriftsartikel (refereegranskat)abstract
- There are several different approaches to analyze event-related potentials (ERPs) at single-subject level, and the aim of the current study is to provide information for choosing a method based on its ability to detect ERP effects and factors influencing the results. We used data from 79 healthy participants with EEG referenced to mastoid average and investigated the detection rate of auditory N400 effect in single-subject analysis using five methods: visual inspection of participant-wise averaged ERPs, analysis of variance (ANOVA) for amplitude averages in a time window, cluster-based non-parametric testing, a novel Bayesian approach and Studentized continuous wavelet transform (t-CWT). Visual inspection by three independent raters yielded N400 effect detection in 85% of the participants in at least one paradigm (active responding or passive listening), whereas ANOVA identified the effect in 68%, the cluster-method in 59%, the Bayesian method in 89%, and different versions of t-CWT in 22–59% of the participants. Thus, the Bayesian method was the most liberal and also showed the greatest concordance between the experimental paradigms (active/passive). ANOVA detected significant effect only in cases with converging evidence from other methods. The t-CWT and cluster-based method were the most conservative methods. As we show in the current study, different analysis methods provide results that do not completely overlap. The method of choice for determining the presence of an ERP component at single-subject level thus remains unresolved. Relying on a single statistical method may not be sufficient for drawing conclusions on single-subject ERPs.
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| 31. |
- Kallionpää, R. E., et al.
(författare)
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Spoken words are processed during dexmedetomidine-induced unresponsiveness
- 2018
-
Ingår i: British Journal of Anaesthesia. - : Elsevier. - 0007-0912 .- 1471-6771. ; 121:1, s. 270-280
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Tidskriftsartikel (refereegranskat)abstract
- Background: Studying the effects of anaesthetic drugs on the processing of semantic stimuli could yield insights into how brain functions change in the transition from wakefulness to unresponsiveness. Here, we explored the N400 event-related potential during dexmedetomidine- and propofol-induced unresponsiveness. Methods: Forty-seven healthy subjects were randomised to receive either dexmedetomidine (n = 23) or propofol (n = 24) in this open-label parallel-group study. Loss of responsiveness was achieved by stepwise increments of pseudo-steady-state plasma concentrations, and presumed loss of consciousness was induced using 1.5 times the concentration required for loss of responsiveness. Pre-recorded spoken sentences ending either with an expected (congruous) or an unexpected (incongruous) word were presented during unresponsiveness. The resulting electroencephalogram data were analysed for the presence of the N400 component, and for the N400 effect defined as the difference between the N400 components elicited by congruous and incongruous stimuli, in the time window 300-600 ms post-stimulus. Recognition of the presented stimuli was tested after recovery of responsiveness. Results: The N400 effect was not observed during dexmedetomidine- or propofol-induced unresponsiveness. The N400 component, however, persisted during dexmedetomidine administration. The N400 component elicited by congruous stimuli during unresponsiveness in the dexmedetomidine group resembled the large component evoked by incongruous stimuli at the awake baseline. After recovery, no recognition of the stimuli heard during unresponsiveness occurred. Conclusions: Dexmedetomidine and propofol disrupt the discrimination of congruous and incongruous spoken sentences, and recognition memory at loss of responsiveness. However, the processing of words is partially preserved during dexmedetomidine-induced unresponsiveness.
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| 32. |
- Kantonen, Oskari, et al.
(författare)
-
Decreased thalamic activity is a correlate for disconnectedness during anesthesia with Propofol, Dexmedetomidine and Sevoflurane but not S-ketamine
- 2023
-
Ingår i: Journal of Neuroscience. - : Society for Neuroscience. - 0270-6474 .- 1529-2401. ; 43:26, s. 4884-4895
-
Tidskriftsartikel (refereegranskat)abstract
- Establishing the neural mechanisms responsible for the altered global states of consciousness during anesthesia and dissociating these from other drug-related effects remains a challenge in consciousness research. We investigated differences in brain activity between connectedness and disconnectedness by administering various anesthetics at concentrations designed to render 50% of the subjects unresponsive. One hundred and sixty healthy male subjects were randomized to receive either propofol (1.7 μg/ml; n = 40), dexmedetomidine (1.5 ng/ml; n = 40), sevoflurane (0.9% end-tidal; n = 40), S-ketamine (0.75 μg/ml; n = 20), or saline placebo (n = 20) for 60 min using target-controlled infusions or vaporizer with end-tidal monitoring. Disconnectedness was defined as unresponsiveness to verbal commands probed at 2.5-min intervals and unawareness of external events in a postanesthesia interview. High-resolution positron emission tomography (PET) was used to quantify regional cerebral metabolic rates of glucose (CMRglu) utilization. Contrasting scans where the subjects were classified as connected and responsive versus disconnected and unresponsive revealed that for all anesthetics, except S-ketamine, the level of thalamic activity differed between these states. A conjunction analysis across the propofol, dexmedetomidine and sevoflurane groups confirmed the thalamus as the primary structure where reduced metabolic activity was related to disconnectedness. Widespread cortical metabolic suppression was observed when these subjects, classified as either connected or disconnected, were compared with the placebo group, suggesting that these findings may represent necessary but alone insufficient mechanisms for the change in the state of consciousness.
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| 33. |
- Kantonen, Oskari, et al.
(författare)
-
Decreased Thalamic Activity Is a Correlate for Disconnectedness during Anesthesia with Propofol, Dexmedetomidine and Sevoflurane But Not S-Ketamine
- 2023
-
Ingår i: Journal of Neuroscience. - : Society for Neuroscience. - 0270-6474 .- 1529-2401. ; 43:26, s. 4884-4895
-
Tidskriftsartikel (refereegranskat)abstract
- Establishing the neural mechanisms responsible for the altered global states of consciousness during anesthesia and dissociating these from other drug-related effects remains a challenge in consciousness research. We investigated differences in brain activity between connectedness and disconnectedness by administering various anesthetics at concentrations designed to render 50% of the subjects unresponsive. One hundred and sixty healthy male subjects were randomized to receive either propofol (1.7 μg/ml; n = 40), dexmedetomidine (1.5 ng/ml; n = 40), sevoflurane (0.9% end-tidal; n = 40), S-ketamine (0.75 μg/ml; n = 20), or saline placebo (n = 20) for 60 min using target-controlled infusions or vaporizer with end-tidal monitoring. Disconnectedness was defined as unresponsiveness to verbal commands probed at 2.5-min intervals and unawareness of external events in a postanesthesia interview. High-resolution positron emission tomography (PET) was used to quantify regional cerebral metabolic rates of glucose (CMRglu) utilization. Contrasting scans where the subjects were classified as connected and responsive versus disconnected and unresponsive revealed that for all anesthetics, except S-ketamine, the level of thalamic activity differed between these states. A conjunction analysis across the propofol, dexmedetomidine and sevoflurane groups confirmed the thalamus as the primary structure where reduced metabolic activity was related to disconnectedness. Widespread cortical metabolic suppression was observed when these subjects, classified as either connected or disconnected, were compared with the placebo group, suggesting that these findings may represent necessary but alone insufficient mechanisms for the change in the state of consciousness.
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| 34. |
- Koivisto, Mika, et al.
(författare)
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A Preconscious Neural Mechanism of Hypnotically Altered Colors : A Double Case Study
- 2013
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Ingår i: PLOS ONE. - : Public Library of Science. - 1932-6203. ; 8:8
-
Tidskriftsartikel (refereegranskat)abstract
- Hypnotic suggestions may change the perceived color of objects. Given that chromatic stimulus information is processed rapidly and automatically by the visual system, how can hypnotic suggestions affect perceived colors in a seemingly immediate fashion? We studied the mechanisms of such color alterations by measuring electroencephalography in two highly suggestible participants as they perceived briefly presented visual shapes under posthypnotic color alternation suggestions such as "all the squares are blue''. One participant consistently reported seeing the suggested colors. Her reports correlated with enhanced evoked upper beta-band activity (22 Hz) 70-120 ms after stimulus in response to the shapes mentioned in the suggestion. This effect was not observed in a control condition where the participants merely tried to simulate the effects of the suggestion on behavior. The second participant neither reported color alterations nor showed the evoked beta activity, although her subjective experience and event-related potentials were changed by the suggestions. The results indicate a preconscious mechanism that first compares early visual input with a memory representation of the suggestion and consequently triggers the color alteration process in response to the objects specified by the suggestion. Conscious color experience is not purely the result of bottom-up processing but it can be modulated, at least in some individuals, by top-down factors such as hypnotic suggestions.
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| 35. |
- Koivisto, Mika, et al.
(författare)
-
Comparison of event-related potentials in attentional blink and repetition blindness
- 2008
-
Ingår i: Brain Research. - : Elsevier B.V.. - 0006-8993 .- 1872-6240. ; 1189, s. 115-126
-
Tidskriftsartikel (refereegranskat)abstract
- Attending to the first target in rapid serial visual presentation (RSVP) interferes with processing of the second target so that the participants fail to recognize the second target if the targets are separated by a stimulus onset asynchrony of 200–500 ms. This phenomenon is attentional blink (AB). Repetition blindness (RB) is an additional difficulty to recognize the second occurrence of the same stimulus in RSVP. A controversial issue in studies of both deficits is the processing level at which they occur. To compare the timing and mechanisms of AB and RB directly during the same RSVP stream, we recorded event-related potentials (ERPs) in response to repeated and unrepeated targets. Comparable to earlier ERP studies on visual awareness, the results showed for both types of targets a negative amplitude difference between ERPs to consciously recognized and unrecognized targets during 250-350 ms from stimulus onset, suggesting that both AB and RB are associated with deficits of conscious perception, occurring at earlier stages than access to working memory. However, the perceptual deficit in RB is more severe, which may be related to higher overall negativity in response to repeated targets observed 150–300 ms after stimulus onset, suggesting stronger cortical baseline activation and higher perceptual threshold for repeated targets as compared with unrepeated ones.
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| 36. |
- Koivisto, Mika, et al.
(författare)
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Different Electrophysiological Correlates of Visual Awareness for Detection and Identification
- 2017
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Ingår i: Journal of cognitive neuroscience. - : MIT Press. - 0898-929X .- 1530-8898. ; 29:9, s. 1621-1631
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Tidskriftsartikel (refereegranskat)abstract
- Detecting the presence of an object is a different process than identifying the object as a particular object. This difference has not been taken into account in designing experiments on the neural correlates of consciousness. We compared the electrophysiological correlates of conscious detection and identification directly by measuring ERPs while participants performed either a task only requiring the conscious detection of the stimulus or a higher-level task requiring its conscious identification. Behavioral results showed that, even if the stimulus was consciously detected, it was not necessarily identified. A posterior electrophysiological signature 200-300 msec after stimulus onset was sensitive for conscious detection but not for conscious identification, which correlated with a later widespread activity. Thus, we found behavioral and neural evidence for elementary visual experiences, which are not yet enriched with higher-level knowledge. The search for the mechanisms of consciousness should focus on the early elementary phenomenal experiences to avoid the confounding effects of higher-level processes.
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| 37. |
- Koivisto, Mika, et al.
(författare)
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Electrophysiological correlates of visual consciousness and selective attention
- 2007
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Ingår i: NeuroReport. - : Lippincott Williams & Wilkins. - 0959-4965 .- 1473-558X. ; 18:8, s. 753-756
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Tidskriftsartikel (refereegranskat)abstract
- It is not clear whether attention is necessary or not for consciousness. We studied the relationship between attention and consciousness by tracking their electrophysiological correlates. The participants attended to visual targets, ignored nontargets in the prespecified visual field and ignored all stimuli in the opposite field. Visual consciousness was varied by masking. Our results showed that the earliest electrophysiological correlate of consciousness emerged independent of the manipulations of spatial and nonspatial attention. Conversely, the electrophysiological correlate of attention, selection negativity, was elicited regardless of the presence or absence of consciousness. Only the correlates of later, higher-level conscious processes strongly depended on attention. Thus, the electrophysiological brain responses reflecting visual consciousness and attention are initially independent of each other.
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| 38. |
- Koivisto, Mika, et al.
(författare)
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Event-related brain potential correlates of visual awareness
- 2010
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Ingår i: Neuroscience and Biobehavioral Reviews. - : Elsevier. - 0149-7634 .- 1873-7528. ; 34:6, s. 922-934
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Forskningsöversikt (refereegranskat)abstract
- Electrophysiological recordings during visual tasks can shed light on the temporal dynamics of the subjective experience of seeing, visual awareness. This paper reviews studies on electrophysiological correlates of visual awareness operationalized as the difference between event-related potentials (ERPs) in response to stimuli that enter awareness and stimuli that do not. There are three candidates for such a correlate: enhancement of P1 around 100 ms, enhancement of early posterior negativity around 200 ms (visual awareness negativity, VAN), and enhancement of late positivity (LP) in the P3 time window around 400 ms. Review of studies using different manipulations of awareness suggests that VAN is the correlate of visual awareness that most consistently emerges across different manipulations of visual awareness. VAN emerges also relatively independent of manipulations of nonspatial attention, but seems to be dependent on spatial attention. The results suggest that visual awareness emerges about 200 ms after the onset of visual stimulation as a consequence of the activation of posterior occipitotemporal and parietal networks.
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| 39. |
- Koivisto, Mika, et al.
(författare)
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How meaning shapes seeing
- 2007
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Ingår i: Psychological Science. - : Sage Publications. - 0956-7976 .- 1467-9280. ; 18:10, s. 845-849
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Tidskriftsartikel (refereegranskat)abstract
- yInattentional blindness refers to the failure to see an unexpected object that one may be looking at directly when one's attention is elsewhere. We studied whether a stimulus whose meaning is relevant to the attentional goals of the observer will capture attention and escape inattentional blindness. The results showed that an unexpected stimulus belonging to the attended semantic category but not sharing physical features with the attended stimuli was detected more often than a semantically unrelated stimulus. This effect was larger when the unexpected stimuli were words than when they were pictures. The results imply that the semantic relation between the observer's attentional set and the unexpected stimulus plays a crucial role in inattentional blindness: An unexpected stimulus semantically related to the observer's current interests is likely to be seen, whereas unrelated unexpected stimuli are unseen. Attentional selection may thus be driven by purely semantic features: Meaning may determine whether or not one sees a stimulus.
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| 40. |
- Koivisto, Mika, et al.
(författare)
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Recurrent processing enhances visual awareness but is not necessary for fast categorization of natural scenes
- 2014
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Ingår i: Journal of cognitive neuroscience. - : MIT Press. - 0898-929X .- 1530-8898. ; 26:2, s. 223-231
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Tidskriftsartikel (refereegranskat)abstract
- Humans are rapid in categorizing natural scenes. Electrophysiological recordings reveal that scenes containing animals can be categorized within 150 msec, which has been interpreted to indicate that feedforward flow of information from V1 to higher visual areas is sufficient for visual categorization. However, recent studies suggest that recurrent interactions between higher and lower levels in the visual hierarchy may also be involved in categorization. To clarify the role of recurrent processing in scene categorization, we recorded EEG and manipulated recurrent processing with object substitution masking while the participants performed a go/no-go animal/nonanimal categorization task. The quality of visual awareness was measured with a perceptual awareness scale after each trial. Masking reduced the clarity of perceptual awareness, slowed down categorization speed for scenes that were not clearly perceived, and reduced the electrophysiological difference elicited by animal and nonanimal scenes after 150 msec. The results imply that recurrent processes enhance the resolution of conscious representations and thus support categorization of stimuli that are difficult to categorize on the basis of the coarse feedforward representations alone.
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| 41. |
- Koivisto, Mika, et al.
(författare)
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Recurrent Processing in V1/V2 Contributes ot Categorization of Natural Scenes
- 2011
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Ingår i: Journal of Neuroscience. - : Society for Neuroscience. - 0270-6474 .- 1529-2401. ; 31:7, s. 2488-2492
-
Tidskriftsartikel (refereegranskat)abstract
- Humans are able to categorize complex natural scenes very rapidly and effortlessly, which has led to an assumption that such ultra-rapid categorization is driven by feedforward activation of ventral brain areas. However, recent accounts of visual perception stress the role of recurrent interactions that start rapidly after the activation of V1. To study whether or not recurrent processes play a causal role in categorization, we applied fMRI-guided transcranial magnetic stimulation on early visual cortex (V1/V2) and lateral occipital cortex (LO) while the participants categorized natural images as containing animals or not. The results showed that V1/V2 contributed to categorization speed and to subjective perception during a long activity period before and after the contribution of LO had started. This pattern of results suggests that recurrent interactions in visual cortex between areas along the ventral stream and striate cortex play a causal role in categorization and perception of natural scenes.
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| 42. |
- Koivisto, Mika, et al.
(författare)
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Subjective visual awareness emerges prior to P3
- 2016
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Ingår i: European Journal of Neuroscience. - : Wiley-Blackwell. - 0953-816X .- 1460-9568. ; 43:12, s. 1601-1611
-
Tidskriftsartikel (refereegranskat)abstract
- Studies on the neural basis of visual awareness, the subjective experience of seeing, have found several potential neural corre- lates of visual awareness. Some of them may not directly correlate with awareness but with post-perceptual processes, such as reporting one’s awareness of the stimulus. We dissociated potential electrophysiological correlates of visual awareness from those occurring during response selection and thus co-occurring with post-perceptual processing. The participants performed two GO-NOGO conditions. In the aware-GO condition they responded with a key press when they were aware of the stimulus and withheld responding when they were unaware of it. In the unaware-GO condition they withheld responding when they were aware and responded when they were not aware of the stimulus. Thus, event-related potentials could be measured to aware and una- ware trials when responding was required and when not required. The results revealed that the N200 amplitude (180–280 ms) over the occipital and posterior temporal cortex was enhanced in aware trials as compared with trials without awareness. This effect (visual awareness negativity, VAN) did not depend on responding. The amplitude of P3 (350–450 ms) also was enhanced in aware trials as compared with unaware trials. In addition, the amplitudes in the P3 time window depended on responding: they were greater when awareness was mapped to GO-response than when not, suggesting that P3 reflects post-perceptual process- ing, that is, it occurs after awareness has emerged. These findings support theories of visual awareness that assume a relatively early onset of visual awareness before P3.
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| 43. |
- Koivisto, Mika, et al.
(författare)
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The earliest electrophysiological correlate of visual awareness?
- 2008
-
Ingår i: Brain and Cognition. - : Elsevier Inc.. - 0278-2626 .- 1090-2147. ; 66:1, s. 91-103
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Tidskriftsartikel (refereegranskat)abstract
- To examine the neural correlates and timing of human visual awareness, we recorded event-related potentials (ERPs) in two experiments while the observers were detecting a grey dot that was presented near subjective threshold. ERPs were averaged for conscious detections of the stimulus (hits) and nondetections (misses) separately. Our results revealed that hits, as compared to misses, showed a negativity around 180–350 ms at occipital and posterior temporal sites. It was followed by a positive wave after 400–500 ms, peaking at parietal sites. These correlates were not affected by a manipulation of attention. The early negativity, called ‘visual awareness negativity’ (VAN), may be a general, primary electrophysiological correlate of visual awareness. The present data show that it can be observed in response to appearance of a stimulus in visual awareness and that it generalizes across different manipulations of stimulus visibility.
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| 44. |
- Koivisto, Mika, et al.
(författare)
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The effects of perceptual load on semantic processing under inattention
- 2009
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Ingår i: Psychonomic Bulletin & Review. - : The Psychonomic Society, Inc.. - 1069-9384 .- 1531-5320. ; 16:5, s. 864-868
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Tidskriftsartikel (refereegranskat)abstract
- Inattentional blindness refers to a failure to consciously detect an irrelevant object that appears without any expectation when attention is engaged with another task. The perceptual load theory predicts that task-irrelevant stimuli will reach awareness only when the primary task is of low load, which allows processing resources to spill over to processing task-irrelevant stimuli as well. We studied whether perceptual load has an effect on inattentional blindness for a task-irrelevant stimulus whose meaning is or is not relevant to the attentional goals of the observer. In the critical trial, a word appeared without any expectation in the center of a display of attended pictures. The results showed that, under both high and low load, unexpected words belonging to the attended semantic category were detected more often than semantically unrelated words. These results imply that task-irrelevant stimuli, whose meanings are relevant to the observer’s task, enter awareness irrespective of perceptual load.
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| 45. |
- Koivisto, Mika, et al.
(författare)
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The relationship between awareness and attention : Evidence from ERP responses
- 2009
-
Ingår i: Neuropsychologia. - : Elsevier. - 0028-3932 .- 1873-3514. ; 47:13, s. 2891-2899
-
Tidskriftsartikel (refereegranskat)abstract
- The relationship between attention and awareness is complex, because both concepts can be understood in different ways. Here we review our recent series of experiments which have tracked the independent contributions of different types of visual attention and awareness to electrophysiological brain responses, and then we report a new experiment focusing on spatial attention, nonspatial selection of objects, and visual consciousness at the same time. The results indicate that the earliest electrophysiological correlate of consciousness, assumed to correlate with “phenomenal consciousness”, was dependent on spatial attention, suggesting that spatial attention is a prerequisite for the internal representations of space that provide the medium for phenomenal experience. The correlate of phenomenal consciousness emerged independent of nonspatial selection of objects, but its later part was modified by it. By contrast, the correlate of access to later conscious processing stages (“reflective consciousness”) that take the selected contents of phenomenal consciousness as input for conceptual thought and working memory, was dependent on both spatial attention and nonspatial selection. These results imply that one should distinguish between different types of attention and different forms of awareness, when describing the relationship between attention and awareness.
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| 46. |
- Koivisto, Mika, et al.
(författare)
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The role of selective attention in visual awareness of stimulus features : Electrophysiological studies
- 2008
-
Ingår i: Cognitive, Affective, & Behavioral Neuroscience. - : Psychonomic Society, Inc.. - 1530-7026 .- 1531-135X. ; 8:2, s. 195-210
-
Tidskriftsartikel (refereegranskat)abstract
- Attention and awareness are closely related, but the nature of their relationship is unclear. The present study explores the timing and temporal evolution of their interaction with event-related potentials. The participants attended to specific conjunctions of spatial frequency and orientation in masked (unaware) and unmasked (aware) visual stimuli. A correlate of awareness appeared 100-200 msec from stimulus onset similarly to both attended and unattended features. Selection negativity (SN), a correlate of attentional selection, emerged in response to both masked and unmasked stimuli after 200 msec. This double dissociation between correlates of awareness and SN suggests that the electrophysiological processes associated with feature-based attentional selection and visual awareness of features can be dissociated from each other at early stages of processing. In a passive task, requiring no attention to the stimuli, early electrophysiological responses (before 200 msec) related to awareness were attenuated, suggesting that focal attention modulates visual awareness earlier than does selective feature-beased attention.
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| 47. |
- Koivisto, Mika, et al.
(författare)
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The role of unattended distractors in sustained inattentional blindness
- 2008
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Ingår i: Psychological Research. - : Springer. - 0340-0727 .- 1430-2772. ; 72:1, s. 39-48
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Tidskriftsartikel (refereegranskat)abstract
- When participants are attending to a subset of visual targets or events and ignore irrelevant distractors ("selective looking"), they often fail to detect the appearance of an unexpected visual object or event even when the object is visible for several seconds ("sustained inattentional blindness"). An important factor influencing detection rates in selective looking is the attentional set of the participant: the more similar the features of the unexpected object are to the attended ones, the more probably it will be detected. We examined the possible contribution of active ignoring to this similarity effect by studying the role of the distractor objects in sustained inattentional blindness. First we showed the similarity effect for chromatic colors and then we manipulated the similarity of the unexpected object in relation to the distractor objects and did not find any effects. Moreover, we found that inattentional blindness was present even when the displays did not contain any irrelevant to-be-ignored objects. We conclude that attending to target items on the bais of attentional set, but not active ignoring of nontargets items, is sufficient for the occurrence of sustained inattentional blindness.
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| 48. |
- Koivisto, Mika, et al.
(författare)
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TMS-EEG reveals hemispheric asymmetries in top-down influences of posterior intraparietal cortex on behavior and visual event-related potentials
- 2017
-
Ingår i: Neuropsychologia. - : Elsevier. - 0028-3932 .- 1873-3514. ; 107, s. 94-101
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Tidskriftsartikel (refereegranskat)abstract
- Clinical data and behavioral studies using transcranial magnetic stimulation (TMS) suggest right-hemisphere dominance for top-down modulation of visual processing in humans. We used concurrent TMS-EEG to directly test for hemispheric differences in causal influences of the right and left intraparietal cortex on visual event-related potentials (ERPs). We stimulated the left and right posterior part of intraparietal sulcus (IPS1) while the participants were viewing and rating the visibility of bilaterally presented Gabor patches. Subjective visibility ratings showed that TMS of right IPS shifted the visibility toward the right hemifield, while TMS of left IPS did not have any behavioral effect. TMS of right IPS, but not left one, reduced the amplitude of posterior N1 potential, 180–220 ms after stimulus-onset. The attenuation of N1 occurred bilaterally over the posterior areas of both hemispheres. Consistent with previous TMS-fMRI studies, this finding suggests that the right IPS has top-down control on the neural processing in visual cortex. As N1 most probably reflects reactivation of early visual areas, the current findings support the view that the posterior parietal cortex in the right hemisphere amplifies recurrent interactions in ventral visual areas during the time-window that is critical for conscious perception.
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| 49. |
- Koivisto, Mika, et al.
(författare)
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Transcranial magnetic stimulation of early visual cortex suppresses conscious representations in a dichotomous manner without gradually decreasing their precision
- 2017
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Ingår i: NeuroImage. - : Elsevier BV. - 1053-8119 .- 1095-9572. ; 158, s. 308-318
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Tidskriftsartikel (refereegranskat)abstract
- Transcranial magnetic stimulation (TMS) of early visual cortex can suppresses visual perception at early stages of processing. The suppression can be measured both with objective forced-choice tasks and with subjective ratings of visual awareness, but there is lack of objective evidence on how and whether the TMS influences the quality of representations. Does TMS decrease the precision of representations in graded manner, or does it lead to dichotomous, "all-or-nothing" suppression. We resolved this question by using a continuous measure of the perceptual error: the observers had to perceive the orientation of a target (Landort-C) and to adjust the orientation of a probe to match that of the target. Mixture modeling was applied to estimate the probability of guess trials and the standard deviation of the non-guess trials. TMS delivered 60-150 ms after stimulus-onset influenced only the guessing rate, whereas the standard deviation (i.e., precision) was not affected. This suggests that TMS suppressed representations dichotomously without affecting their precision. The guessing probability correlated with subjective visibility ratings, suggesting that it measured visual awareness. In a control experiment, manipulation of the stimulus contrast affected the standard deviation of the errors, indicating that contrast has a gradual influence on the precision of representations. The findings suggest that TMS of early visual cortex suppresses perception in dichotomous manner by decreasing the signal-to-noise ratio by increasing the noise level, whereas reduction of the signal level (i.e., contrast) decreases the precision of representations.
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| 50. |
- Koivisto, Mika, et al.
(författare)
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Unconscious response priming by shape depends on geniculostriate visual projection
- 2012
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Ingår i: European Journal of Neuroscience. - : Wiley-Blackwell. - 0953-816X .- 1460-9568. ; 35:4, s. 623-633
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Tidskriftsartikel (refereegranskat)abstract
- It has been suggested that unconscious visual processing of some stimulus features might occur without the contribution of early visual cortex (V1/V2). In the present study, the causal role of V1/V2 in unconscious processing of simple shapes in intact human brain was studied by applying transcranial magnetic stimulation (TMS) on early visual cortex or lateral occipital cortex (LO) while observers performed a metacontrast-masked response priming task with arrow figures as visual stimuli. Magnetic stimulation of V1/V2 impaired masked priming 3090 ms after the onset of the prime. Stimulation of LO reduced the magnitude of masked priming at 90120 ms, but this effect occurred only in the early parts of the priming experiment. A control task measuring the visibility of masked primes indicated that the orientation of masked primes could not be consciously discriminated and that TMS did not influence the conscious visibility of the primes indirectly by reducing the effectiveness of the mask in the critical time windows. We conclude that feedforward sweep of processing from V1/V2 (3090 ms) to LO (90 ms and above) is necessary for unconscious priming of shape, whereas conscious perception requires also the contribution of recurrent (feedback) processing.
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