| 1. |
- Burstedt, Marie S I, et al.
(author)
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Retinal function in Bothnia dystrophy. An electrophysiological study.
- 2003
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In: Vision Research. - 0042-6989 .- 1878-5646. ; 43:24, s. 2559-2571
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Journal article (peer-reviewed)abstract
- Using prolonged dark adaptometry, standard dark adaptation (DA) and prolonged DA full-field electroretinograms (ERGs), we analysed the retinal function in patients with Bothnia dystrophy (BD), a variant of recessive retinitis punctata albescens (RPA). A compromised rod and cone function, a likely dysfunction of the Müller cells, and indications of disturbed neuronal function of the inner retina, were found. With prolonged DA, a gradual increase in retinal sensitivity to light and an improvement of the ERG components occurred. The findings indicate a prolonged synthesis of photopigments, retardation of the visual process in the retinal pigment epithelium (RPE), and a loss of retinal cells, probably starting at a relatively early age in BD.
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| 2. |
- Nilsson, Ulla L, et al.
(author)
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Patients with AMD and a large absolute central scotoma can be trained successfully to use eccentric viewing, as demonstrated in a scanning laser ophthalmoscope
- 2003
-
In: Vision Research. - 0042-6989 .- 1878-5646. ; 43:16, s. 1777-1787
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Journal article (peer-reviewed)abstract
- Twenty patients with age-related macular degeneration, an absolute central scotoma and a mean visual acuity of 0.04 (20/475) were studied. A scanning laser ophthalmoscope (SLO) was used for microperimetry and determination of preferred retinal locus, often located to the left of the retinal lesion (corresponding to a location to the left of the visual field scotoma), which is considered unfavorable for reading. All 20 patients were trained to use a new and more favorable retinal locus for reading, above (or occasionally below) the retinal lesion (corresponding to a location below or above the visual field scotoma), first by reading scrolled text under simultaneous fixation monitoring and instruction in the SLO and then by reading printed text, using high magnification (mean 14.3╫). For the 18 patients who learned to use eccentric viewing, reading speed with adequate magnification prior to training was 9.0▒5.8 words/min. With training (mean 5.2 hours), it increased significantly (p<0.001) to 68.3▒19.4 words per min. Training of eccentric reading has thus proved to be very successful.
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| 3. |
- Poom, Leo
(author)
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Inter-attribute tilt effects and orientation analysis in the visual brain
- 2000
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In: Vision Research. - : Elsevier. - 0042-6989 .- 1878-5646. ; 40:20, s. 2711-2722
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Journal article (peer-reviewed)abstract
- A test grating appears to be tilted away from an inducing grating for small angular separations (repulsion), but towards the inducing grating for larger angular separations (attraction). Previous research on luminance gratings suggests that repulsion is caused by local inhibition in cortical areas V1 and/or V2, and that the attraction involves global interactions beyond V1, in extrastriate areas. Experiments reported here demonstrate attribute invariant attraction and repulsion effects for gratings specified by luminance, motion, and disparity contrasts. A frame surrounding the inducing grating abolishes only the attraction effect, but a spatial frequency difference, or a small gap between the inducer and test gratings, abolishes only the repulsion effect, irrespective of the attributes that specify the gratings. It is proposed that detectors selectively sensitive to attribute invariant orientation and size exist in early cortical sites such as V1 and/or V2.
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| 4. |
- Poom, Leo
(author)
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Visual binding of luminance, motion, and disparity edges
- 2002
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In: Vision Research. - 0042-6989 .- 1878-5646. ; 42:23, s. 2577-2591
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Journal article (peer-reviewed)abstract
- Visual binding of edge segments embedded in noise and created by luminance, motion and disparity contrasts were studied in three experiments. The results showed that path formation was limited by the same rules across all attributes tested. The first experiment showed that binding could be accomplished with either attribute used in isolation. The second experiment showed that closed paths were easier to detect than open paths irrespectively of the attributes used to create the path elements. No additive effects were found in either Experiment 1 or 2 when the path elements were created with several attributes superimposed on the same positions, compared to when only one attribute was used along the path. In Experiment 3 it was found that when another attribute was added between the positions of the first attribute along the path, so that two attributes alternated along the path, the performance of path detection was better than expected by probability summation estimated from the single attribute conditions. These results provide evidence for attribute-invariant Gestalt laws and provide clues about the underlying neural mechanisms.
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| 5. |
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| 6. |
- Abalo, Xesus, 1976-, et al.
(author)
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Circadian regulation of phosphodiesterase 6 genes in zebrafish differs between cones and rods : Implications for photopic and scotopic vision
- 2020
-
In: Vision Research. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0042-6989 .- 1878-5646. ; 166, s. 43-51
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Journal article (peer-reviewed)abstract
- A correlation is known to exist between visual sensitivity and oscillations in red opsin and rhodopsin gene expression in zebrafish, both regulated by the clock gene. This indicates that an endogenous circadian clock regulates behavioural visual sensitivity, apart from the regulation exerted by the pineal organ. However, the specific mechanisms for cones (photopic vision) and rods (scotopic vision) are poorly understood. In this work, we performed gene expression, cosinor and immunohistochemical analyses to investigate other key genes involved in light perception, encoding the different subunits of phosphodiesterase pde6 and transducin G alpha(T), in constant lighting conditions and compared to normal light-dark conditions. We found that cones display prominent circadian oscillations in mRNA levels for the inhibitory subunit gene pde6ha that could contribute to the regulation of photopic sensitivity by preventing overstimulation in photopic conditions. In rods, the mRNA levels of the inhibitory subunit gene pde6ga oscillate under normal conditions and dampen down in constant light but continue oscillating in constant darkness. There is an increase in total relative expression for pde6gb in constant conditions. These observations, together with previous data, suggest a complex regulation of the scotopic sensitivity involving endogenous and non-endogenous components, possibly present also in other teleost species. The G alpha(T) genes do not display mRNA oscillations and therefore may not be essential for the circadian regulation of photosensitivity. In summary, our results support different regulation for the zebrafish photopic and scotopic sensitivities and suggest circadian regulation of pde6ha as a key factor regulating photopic sensitivity, while the regulatory mechanisms in rods appear to be more complex.
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| 7. |
- Albonico, Andrea, et al.
(author)
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Perceptual efficiency and the inversion effect for faces, words and houses
- 2018
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In: Vision Research. - : Pergamon Press. - 0042-6989 .- 1878-5646. ; 153, s. 91-97
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Journal article (peer-reviewed)abstract
- Face and visual word recognition are two key forms of expert visual processing. In the domain of object recognition, it has been suggested that expert processing is characterized by the use of different mechanisms from the ones involved in general object recognition. It has been suggested that one traditional marker of expert processing is the inversion effect. To investigate whether face and word recognition differ from general object recognition, we compared the effect of inversion on the perceptual efficiency of face and visual word recognition as well as on the recognition of a third, non-expert object category, houses. From the comparison of identification contrast thresholds to an ideal observer, we derived the efficiency and equivalent input noise of stimulus processing in both upright and inverted orientations. While efficiency reflects the efficacy in sampling the available information, equivalent input noise is associated with the degradation of the stimulus signal within the visual system. We hypothesized that large inversion effects for efficiency and/or equivalent input noise should characterize expert high-level processes, and asked whether this would be true for both faces and words, but not houses. However, we found that while face recognition efficiency was profoundly reduced by inversion, the efficiency of word and house recognition was minimally influenced by the orientation manipulation. Inversion did not affect equivalent input noise. These results suggest that even though faces and words are both considered expert processes, only the efficiency of the mechanism involved in face recognition is sensitive to orientation.
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| 8. |
- Berry, Richard P., et al.
(author)
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Form vision in the insect dorsal ocelli: An anatomical and optical analysis of the dragonfly median ocellus
- 2007
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In: Vision Research. - : Elsevier BV. - 1878-5646 .- 0042-6989. ; 47:10, s. 1394-1409
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Journal article (peer-reviewed)abstract
- Previous work has suggested that dragonfly ocelli are specifically adapted to resolve horizontally extended features of the world, such as the horizon. We investigate the optical and anatomical properties of the median ocellus of Hemicordulia tau and Aeshna mixta to determine the extent to which the findings support this conclusion. Dragonfly median ocelli are shown to possess a number of remarkable properties: astigmatism arising from the elliptical shape of the lens is cancelled by the bilobed shape of the inner lens surface, interference microscopy reveals complex gradients of refractive index within the lens, the morphology of the retina results in zones of high acuity, and the eye has an exceedingly high sensitivity for a diurnal terrestrial invertebrate. It is concluded that dragonfly ocelli employ a number of simple, yet elegant, anatomical and optical strategies to ensure high sensitivity, fast transduction speed, wide fields of views and a modicum of spatial resolving power. (C) 2007 Elsevier Ltd. All rights reserved.
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| 9. |
- Berry, Richard P., et al.
(author)
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Form vision in the insect dorsal ocelli: An anatomical and optical analysis of the Locust Ocelli
- 2007
-
In: Vision Research. - : Elsevier BV. - 1878-5646 .- 0042-6989. ; 47:10, s. 1382-1393
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Journal article (peer-reviewed)abstract
- The dorsal ocelli are commonly considered to be incapable of form vision, primarily due to underfocused dioptrics. We investigate the extent to which this is true of the ocelli of the locust Locusta migratoria. Locust ocelli contain thick lenses with a pronounced concavity on the inner surface, and a deep clear zone separating retina and lens. In agreement with previous research, locust ocellar lenses were found to be decidedly underfocused with respect to the retina. Nevertheless, the image formed at the level of the retina contains substantial information that may be extractable by individual photoreceptors. Contrary to the classical view it is concluded that some capacity for resolution is present in the locust ocelli.
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| 10. |
- Dewhurst, Richard, et al.
(author)
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How task demands influence scanpath similarity in a sequential number-search task
- 2018
-
In: Vision Research. - : Elsevier BV. - 1878-5646 .- 0042-6989. ; , s. 9-23
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Journal article (peer-reviewed)abstract
- More and more researchers are considering the omnibus eye movement sequence—the scanpath—in their studies of visual and cognitive processing (e.g. Hayes, Petrov, & Sederberg, 2011; Madsen, Larson, Loschky, & Rebello, 2012; Ni et al., 2011; von der Malsburg & Vasishth, 2011). However, it remains unclear how recent methods for comparing scanpaths perform in experiments producing variable scanpaths, and whether these methods supplement more traditional analyses of individual oculomotor statistics. We address this problem for MultiMatch (Jarodzka et al., 2010; Dewhurst et al., 2012), evaluating its performance with a visual search-like task in which participants must fixate a series of target numbers in a prescribed order. This task should produce predictable sequences of fixations and thus provide a testing ground for scanpath measures. Task difficulty was manipulated by making the targets more or less visible through changes in font and the presence of distractors or visual noise. These changes in task demands led to slower search and more fixations. Importantly, they also resulted in a reduction in the between-subjects scanpath similarity, demonstrating that participants’ gaze patterns became more heterogenous in terms of saccade length and angle, and fixation position. This implies a divergent strategy or random component to eye-movement behaviour which increases as the task becomes more difficult. Interestingly, the duration of fixations along aligned vectors showed the opposite pattern, becoming more similar between observers in 2 of the 3 difficulty manipulations. This provides important information for vision scientists who may wish to use scanpath metrics to quantify variations in gaze across a spectrum of perceptual and cognitive tasks. © 2018 Elsevier Ltd
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| 11. |
- Fagard, Jacqueline, et al.
(author)
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The role of the corpus callosum in the perception of reversible figures in children
- 2008
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In: Vision Research. - : Elsevier BV. - 0042-6989 .- 1878-5646. ; 48, s. 2451-2455
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Journal article (peer-reviewed)abstract
- To test the role of interhemispheric competition through the corpus callosum in the perceptual alternation of reversible figures, we compared children with callosal pathology and typically developing children on a bistable stimulus task. The children with corpus callosum pathology reported significantly less changes of percepts per minute than the age-matched typically developing children. In addition, older typically developing children reported significantly more changes of percepts than the younger ones. These results support the hypothesis that the rate of reversal between two interpretations of a bistable stimulus may be partly mediated by the corpus callosum.
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| 12. |
- Fermuller, C, et al.
(author)
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Uncertainty in visual processes predicts geometrical optical illusions
- 2004
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In: Vision Research. - : Elsevier BV. - 1878-5646 .- 0042-6989. ; 44:7, s. 727-749
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Journal article (peer-reviewed)abstract
- It is proposed in this paper that many geometrical optical illusions, as well as illusory patterns due to motion signals in line drawings. are due to the statistics of visual computations. The interpretation of image patterns is preceded by a step where image features such as lines, intersections of lines, or local image movement must be derived. However, there are many sources of noise or uncertainty in the formation and processing of images, and they cause problems in the estimation of these features; in particular, they cause bias. As a result, the locations of features are perceived erroneously and the appearance of the patterns is altered. The bias occurs with any visual processing of line features; under average conditions it is not large enough to be noticeable, but illusory patterns are Such that the bias is highly pronounced. Thus, the broader message of this paper is that there is a general uncertainty principle which governs the workings of vision systems, and optical illusions are an artifact of this principle.
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| 13. |
- Gagnon, Yakir, et al.
(author)
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Adjusting a light dispersion model to fit measurements from vertebrate ocular media as well as ray-tracing in fish lenses.
- 2010
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In: Vision Research. - : Elsevier BV. - 1878-5646 .- 0042-6989. ; 50:9, s. 850-853
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Journal article (peer-reviewed)abstract
- Color dispersion, i.e., the dependency of refractive index of any transparent material on the wavelength of light, has important consequences for the function of optical instruments and animal eyes. Using a multi-objective goal attainment optimization algorithm, a dispersion model was successfully fitted to measured refractive indices of various ocular media and the longitudinal chromatic aberration determined by laser-scanning in the crystalline lens of the African cichlid fish, Astatotilapia burtoni. The model describes the effects of color dispersion in fish lenses and may be applicable to the eyes of other vertebrates as well.
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| 14. |
- Garm, Anders, et al.
(author)
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Unique structure and optics of the lesser eyes of the box jellyfish Tripedalia cystophora
- 2008
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In: Vision Research. - : Elsevier BV. - 1878-5646 .- 0042-6989. ; 48:8, s. 1061-1073
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Journal article (peer-reviewed)abstract
- The visual system of box jellyfish comprises a total of 24 eyes. These are of four types and each probably has a special function. To investigate this hypothesis the morphology and optics of the lesser eyes, the pit and slit eyes, were examined. The pit eyes hold one cell type only and are probably mere light meters. The slit eyes, comprising four cell types, are complex and highly asymmetric. They also hold a lens-like structure, but its optical power is minute. Optical modeling suggests spatial resolution, but only in one plane. These unique and intriguing traits support strong peripheral filtering.
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| 15. |
- Gislén, Anna, et al.
(author)
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The accommodative pupil responses of children and young adults at low and intermediate levels of ambient illumination
- 2008
-
In: Vision Research. - : Elsevier BV. - 0042-6989 .- 1878-5646. ; 48:8, s. 989-993
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Journal article (peer-reviewed)abstract
- Accommodative pupil constrictions were compared between 27 children (9-10 years) and 13 young adults (22-26 years) in order to clarify the issue whether or not children have such a response. Accommodative stimuli of 4 and 7 diopters were used to elicit the response and experiments were performed at 5 and 100 lux in order to investigate whether the level of ambient light has different effects on developing and mature visual systems. The accommodative pupil response is present in children, but weaker than in adults. Different levels of ambient light lead to only minor additional differences between children and adults. The weaker accommodative pupil response of children may be a consequence of their superior accommodative ranges, which make it unnecessary to close the pupil to increase depth of field. Adults, in contrast, may do better with smaller pupils that reduce accommodative demand because of increased depth of field. A mature human visual system may furthermore be better tuned to handle dimmer and thus noisier images in the photopic range than the developing visual system of a child. (C) 2008 Elsevier Ltd. All rights reserved.
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| 16. |
- Gislén, Anna, et al.
(author)
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Visual training improves underwater vision in children
- 2006
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In: Vision Research. - : Elsevier BV. - 1878-5646 .- 0042-6989. ; 46:20, s. 3443-3450
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Journal article (peer-reviewed)abstract
- Children in a tribe of sea-gypsies from South-East Asia have been found to have superior underwater vision compared to European children. In this study, we show that the improved underwater vision of these Moken children is not due to better contrast sensitivity in general. We also show that European children can achieve the same underwater acuity as the Moken children. After I month of underwater training (I I sessions) followed by 4 months with no underwater activities, European children showed improved underwater vision and distinct bursts of pupil constriction. When tested 8 months after the last training session in an outdoor pool in bright sunlight-comparable to light environments in South-East Asia-the children had attained the same underwater acuity as the sea-gypsy children. The achieved performance can be explained by the combined effect of pupil constriction and strong accommodation. (c) 2006 Elsevier Ltd. All rights reserved.
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| 17. |
- Grönqvist, Helena, et al.
(author)
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Developmental asymmetries between horizontal and vertical tracking
- 2006
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In: Vision Research. - : Elsevier BV. - 0042-6989 .- 1878-5646. ; 46:11, s. 1754-1761
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Journal article (peer-reviewed)abstract
- The development of the asymmetry between horizontal and vertical eye tracking was investigated longitudinally at 5, 7, and 9 months of age. The target moved either on a 2D circular trajectory or on a vertical or horizontal 1D sinusoidal trajectory. Saccades, smooth pursuit, and head movements were measured. Vertical tracking was found to be inferior to horizontal tracking at all age levels. The results also show that the mechanisms responsible for horizontal and vertical tracking mutually influence one another in the production of 2D visual pursuit. Learning effects were observed within-trials but no transfer between trials was found.
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| 18. |
- Haller, Nicola, et al.
(author)
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Stimulus motion improves spatial contrast sensitivity in budgerigars (Melopsittacus undulatus).
- 2014
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In: Vision Research. - : Elsevier BV. - 1878-5646 .- 0042-6989. ; 102, s. 19-25
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Journal article (peer-reviewed)abstract
- Birds are generally thought to have excellent vision with high spatial resolution. However, spatial contrast sensitivity of birds for stationary targets is low compared to other animals with similar acuity, such as mammals. For fast flying animals body stability and coordination are highly important, and visual motion cues are known to be relevant for flight control. We have tested five budgerigars (Melopsittacus undulatus) in behavioural discrimination experiments to determine whether or not stimulus motion improves contrast sensitivity. The birds were trained to distinguish between a homogenous grey field and sine-wave gratings of spatial frequencies between 0.48 and 6.5 cycles/degree, and Michelson contrasts between 0.7% and 99%. The gratings were either stationary or drifting with velocities between 0.9 and 13 degrees/s. Budgerigars were able to discriminate patterns of lower contrast from grey when the gratings were drifting, and the improvement in sensitivity was strongest at lower spatial frequencies and higher drift velocities. Our findings indicate that motion cues can have positive effects on visual perception of birds. This is similar to earlier results on human vision. Contrast sensitivity, tested solely with stationary stimuli, underestimates the sensory capacity of budgerigars flying through their natural environments.
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| 19. |
- Hemstrom, Jennifer, et al.
(author)
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Visual search for complex objects: Set-size effects for faces, words and cars
- 2019
-
In: Vision Research. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0042-6989 .- 1878-5646. ; 162
-
Journal article (peer-reviewed)abstract
- To compare visual processing for different object types, we developed visual search tests that generated accuracy and response time parameters, including an object set-size effect that indexes perceptual processing load. Our goal was to compare visual search for two expert object types, faces and visual words, as well as a less expert type, cars. We first asked if faces and words showed greater inversion effects in search. Second, we determined whether search with upright stimuli correlated with other perceptual indices. Last we assessed for correlations between tests within a single orientation, and between orientations for a single object type. Object set-size effects were smaller for faces and words than cars. All accuracy and temporal measures showed an inversion effect for faces and words, but not cars. Face-search accuracy measures correlated with accuracy on the Cambridge Face Memory Test and word-search temporal measures correlated with single-word reading times, but car search did not correlate with semantic car knowledge. There were cross-orientation correlations for all object types, as well as cross-object correlations in the inverted orientation, while in the upright orientation face search did not correlate with word or car search. We conclude that object search shows effects of expertise. Compared to cars, words and faces showed smaller object set-size effects, greater inversion effects, and their search results correlated with other indices of perceptual expertise. The correlation analyses provide preliminary evidence supporting contributions from common processes in the case of inverted stimuli, object-specific processes that operate in both orientations, and distinct processing for upright faces.
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| 20. |
- Hooge, Ignace, et al.
(author)
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The art of braking : post saccadic oscillations in the eye tracker signal decrease with increasing saccade size
- 2015
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In: Vision Research. - : Elsevier BV. - 1878-5646 .- 0042-6989. ; 112, s. 55-67
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Journal article (peer-reviewed)abstract
- Abstract in Undetermined Recent research has shown that the pupil signal from video-based eye trackers contains post saccadic oscillations (PSOs). These reflect pupil motion relative to the limbus (Nyström, Hooge, & Holmqvist, 2013). More knowledge about video-based eye tracker signals is essential to allow comparison between the findings obtained from modern systems, and those of older eye tracking technologies (e.g. coils and measurement of the Dual Purkinje Image-DPI). We investigated PSOs in horizontal and vertical saccades of different sizes with two high quality video eye trackers. PSOs were very similar within observers, but not between observers. PSO amplitude decreased with increasing saccade size, and this effect was even stronger in vertical saccades; PSOs were almost absent in large vertical saccades. Based on this observation we conclude that the occurrence of PSOs is related to deceleration at the end of a saccade. That PSOs are saccade size dependent and idiosyncratic is a problem for algorithmic determination of saccade endings. Careful description of the eye tracker, its signal, and the procedure used to extract saccades is required to enable researchers to compare data from different eye trackers.
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| 21. |
- Höglund, Julia, et al.
(author)
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Owls lack UV-sensitive cone opsin and red oil droplets, but see UV light at night : Retinal transcriptomes and ocular media transmittance
- 2019
-
In: Vision Research. - : Elsevier BV. - 0042-6989 .- 1878-5646. ; 158, s. 109-119
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Journal article (peer-reviewed)abstract
- Most diurnal birds have cone-dominated retinae and tetrachromatic colour vision based on ultra-violet/violet-sensitive UV/V cones expressing short wavelength-sensitive opsin 1 (SWS1), S cones expressing short wavelength-sensitive opsin 2 (SWS2), M cones expressing medium wavelength-sensitive opsin (RH2) and L cones expressing long wavelength-sensitive opsin (LWS). Double cones (D) express LWS but do not contribute to colour vision. Each cone is equipped with an oil droplet, transparent in UV/V cones, but pigmented by carotenoids: galloxanthin in S, zeaxanthin in M, astaxanthin in L and a mixture in D cones. Owls (Strigiformes) are crepuscular or nocturnal birds with rod-dominated retinae and optical adaptations for high sensitivity. For eight species, the absence of functional SWS1 opsin has recently been documented, functional RH2 opsin was absent in three of these. Here we confirm the absence of SWS1 transcripts for the Long-eared owl (Asio otus) and demonstrate its absence for the Short-eared owl (Asio flammeus), Tawny owl (Strix aluco) and Boreal owl (Aegolius funereus). All four species had transcripts of RH2, albeit with low expression. All four species express all enzymes needed to produce galloxanthin, but lack CYP2J19 expression required to produce astaxanthin from dietary precursors. We also present ocular media transmittance of the Eurasian eagle owl (Bubo bubo) and Short-eared owl and predict spectral sensitivities of all photoreceptors of the Tawny owl. We conclude that owls, despite lacking UV/V cones, can detect UV light. This increases the sensitivity of their rod vision allowing them, for instance, to see UV-reflecting feathers as brighter signals at night.
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| 22. |
- Johansson, Kjell, et al.
(author)
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Structural changes in the developing retina maintained in vitro.
- 2005
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In: Vision Research. - : Elsevier BV. - 1878-5646 .- 0042-6989. ; 45:25-26, s. 3235-3243
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Journal article (peer-reviewed)abstract
- The present study examined the emergence of structural remodeling in explanted neonatal rat retina. Immunohistochemical analysis demonstrated signs of glial and neuronal remodeling after I I days in vitro and included the activation of Muller cells, the formation of ectopic neuropil areas and sprouting of photoreceptor terminals. We also observed that cholinergic and GABA-ergic amacrine cells displayed signs of disorganized laminations. These results demonstrate that retinal culturing initiates structural changes that show morphological similarities to glial and neuronal remodeling identified in retinitis pigmentosa retinas and experimentally detached retinas.
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| 23. |
- Kato, Masaharu, et al.
(author)
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Sensitivity to second-order motion in 10-month-olds
- 2008
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In: Vision Research. - : Elsevier BV. - 0042-6989 .- 1878-5646. ; 48:10, s. 1187-1195
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Journal article (peer-reviewed)abstract
- Ten-month-old infants' sensitivity to first-order motion (FOM) defined by luminance and second-order motion (SOM) defined by flickering was measured in an eye-tracking paradigm. We used a small single disc or gratings moving horizontally. Although infants could track the SOM of a small disc, they failed to exhibit smooth pursuit eye movements. They also failed to track SOM gratings with smooth pursuit. However, the gain of tracking based on slow eye movement was influenced by the motion direction of SOM in cases when both FOM and SOM were presented simultaneously, suggesting some sensitivity to SOM.
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| 24. |
- Khorramshahi, Omid, et al.
(author)
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A complex system of ligaments and a muscle keep the crystalline lens in place in the eyes of bony fishes (teleosts).
- 2008
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In: Vision Research. - : Elsevier BV. - 1878-5646 .- 0042-6989. ; 48:13, s. 1503-1508
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Journal article (peer-reviewed)abstract
- The suspension of the crystalline lens in the eye was studied in 11 species of teleost (bony fish) from 10 families and 7 orders by light and electron microscopy. In all species there were 4-5 ligaments in about the equatorial plane of the eye, in which also the tendon of the retractor lentis muscle attaches to the lens. In two cichlid species two additional ligaments were found running from the mid-posterior surface of the lens to the optic nerve head, where they attach to the falciform process. Lens suspension in teleosts is more complex than previously described and well-suited to firmly keep the heavy spherical lens in position for well-focused vision.
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| 25. |
- Kröger, Ronald, et al.
(author)
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Compensation for longitudinal chromatic aberration in the eye of the firefly squid, Watasenia scintillans
- 2004
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In: Vision Research. - : Elsevier BV. - 1878-5646 .- 0042-6989. ; 44:18, s. 2129-2134
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Journal article (peer-reviewed)abstract
- The camera eyes of fishes and cephalopods have come forth by convergent evolution. In a variety of vertebrates capable of color vision, longitudinal chromatic aberration (LCA) of the optical system is corrected for by the exactly tuned longitudinal spherical aberration (LSA) of the crystalline lens. The LSA leads to multiple focal lengths, such that several wavelengths can be focused on the retina. We investigated whether that is also the case in the firefly squid (Watasenia scintillans), a cephalopod species that is likely to have color vision. It was found that the lens of W. scintillans is virtually free of LSA and uncorrected for LCA. However, the eye does not suffer from LCA because of a banked retina. Photoreceptors sensitive to short and long wavelengths are located at appropriate distances from the lens, such that they receive well-focused images. Such a design is an excellent solution for the firefly squid because a large area of the retina is monochromatically organized and it allows for double use of the surface area in the dichromatically organized part of the retina. However, it is not a universal solution since compensation for LCA by a banked retina requires that eye size and/or spectral separation between photopigments is small. (C) 2004 Elsevier Ltd. All rights reserved.
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| 26. |
- Kröger, Ronald, et al.
(author)
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Space-saving advantage of an inverted retina.
- 2009
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In: Vision Research. - : Elsevier BV. - 1878-5646 .- 0042-6989. ; 49:18, s. 2318-2321
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Journal article (peer-reviewed)abstract
- Vertebrate eyes are of the simple or camera type with a single optical system that creates an image on the retina in the back of the eye. There, the visual information is encoded as nervous signals by photoreceptors, processed by retinal neurons, and then sent to the brain via the optic nerve. Surprisingly at first sight, the retinal neurons are located between the lens and the light-sensitive parts of the photoreceptors. The tissue scatters some light, which leads to loss of light and image blur. The inverted retina has, therefore, long been regarded as inferior. Here, we provide evidence that the inverted retina actually is a superior space-saving solution, especially in small eyes. The inverted retina has most likely facilitated the evolution of image-forming eyes in vertebrates, and it still benefits especially small and highly visual species.
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| 27. |
- Lee, Young-Lim, et al.
(author)
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Object recognition using metric shape
- 2012
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In: Vision Research. - : Elsevier BV. - 0042-6989 .- 1878-5646. ; 69, s. 23-31
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Journal article (peer-reviewed)abstract
- Most previous studies of 3D shape perception have shown a general inability to visually perceive metric shape. In line with this, studies of object recognition have shown that only qualitative differences, not quantitative or metric ones can be used effectively for object recognition. Recently. Bingham and Lind (2008) found that large perspective changes (>= 45 degrees) allow perception of metric shape and Lee and Bingham (2010) found that this, in turn, allowed accurate feedforward reaches-to-grasp objects varying in metric shape. We now investigated whether this information would allow accurate and effective recognition of objects that vary in respect to metric shape. Both judgment accuracies (d') and reaction times confirmed that, with the availability of visual information in large perspective changes, recognition of objects using quantitative as compared to qualitative properties was equivalent in accuracy and speed of judgments. The ability to recognize objects based on their metric shape is, therefore, a function of the availability or unavailability of requisite visual information. These issues and results are discussed in the context of the Two Visual System hypothesis of Milner and Goodale (1995, 2006).
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| 28. |
- Lewis, Peter, 1971-, et al.
(author)
-
Resolution of static and dynamic stimuli in the peripheral visual field
- 2011
-
In: Vision Research. - : Elsevier BV. - 0042-6989 .- 1878-5646. ; 51:16, s. 1829-1834
-
Journal article (peer-reviewed)abstract
- In a clinical setting, emphasis is given to foveal visual function, and tests generally only utilize static stimuli. In this study, we measured static (SVA) and dynamic visual acuity (DVA) in the central and peripheral visual field on healthy, young emmetropic subjects using stationary and drifting Gabor patches. There were no differences between SVA and DVA in the peripheral visual field; however, SVA was superior to DVA in the fovea for both velocities tested. In addition, there was a clear naso-temporal asymmetry for both SVA and DVA for isoeccentric locations in the visual field beyond 10 degrees eccentricity. The lack of difference in visual acuity between static and dynamic stimuli found in this study may reflect the use of drift-motion as opposed to displacement motion used in previous studies.
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| 29. |
- Lind, Olle, et al.
(author)
-
Avian colour vision: Effects of variation in receptor sensitivity and noise data on model predictions as compared to behavioural results.
- 2009
-
In: Vision Research. - : Elsevier BV. - 1878-5646 .- 0042-6989. ; 49, s. 1939-1947
-
Journal article (peer-reviewed)abstract
- Colour vision models require measurement of receptor noise and the absorbance of visual pigments, oil droplets, and ocular media. We have studied how variation in these parameters influences colour matching, spectral sensitivity, and colour discrimination predictions in four bird species. While colour match predictions are sensitive to variation in visual pigment and oil droplet absorbance data, discrimination predictions are mostly sensitive to variation in receptor noise. Ocular media transmittance influences only modelled spectral sensitivities at short wavelengths. A comparison between predicted and measured spectral sensitivities in domestic fowl and duck revealed large discrepancies, likely because of influences from achromatic mechanisms.
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| 30. |
- Lisney, Thomas J., et al.
(author)
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Behavioural assessment of flicker fusion frequency in chicken Gallus gallus domesticus
- 2011
-
In: Vision Research. - : Elsevier BV. - 0042-6989 .- 1878-5646. ; 51:12, s. 1324-1332
-
Journal article (peer-reviewed)abstract
- To interact with its visual environment, an organism needs to perceive objects in both space and time. High temporal resolution is hence important to the fitness of diurnally active animals, not least highly active aerial species such as birds. However, temporal resolution, as assessed by flicker fusion frequency (FFF; the stimulus frequency at which a flickering light stimulus can no longer be resolved and appears continuous) or critical flicker fusion frequency (CFF; the highest flicker fusion frequency at any light intensity) has rarely been assessed in birds. In order to further our understanding of temporal resolution as a function of light intensity in birds we used behavioural experiments with domestic chickens (Gallus gallus domesticus) from an old game breed 'Gammalsvensk dvarghona' (which is morphologically and behaviourally similar to the wildtype ancestor, the red jungle fowl, G. gallus), to generate an 'Intensity/FFF curve' (I/FFF curve) across full spectrum light intensities ranging from 0.2 to 2812 cd m(-2). The I/FFF curve is double-branched, resembling that of other chordates with a duplex retina of both rods and cones. Assuming that the branches represent rod and cone mediated responses respectively, the break point between them places the transition between scotopic and photopic vision at between 0.8 and 1.9 cd m(-2). Average FFF ranged from 19.8 Hz at the lowest light intensity to a CFF 87.0 Hz at 1375 cd m(-2). FFF dropped slightly at the highest light intensity. There was some individual variation with certain birds displaying CFFs of 90-100 Hz. The FFF values demonstrated by this non-selected breed appear to be considerably higher than other behaviourally derived FFF values for similar stimuli reported for white and brown commercial laying hens, indicating that the domestication process might have influenced temporal resolution in chicken.
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| 31. |
- Lisney, Thomas J., et al.
(author)
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Using electroretinograms to assess flicker fusion frequency in domestic hens Gallus gallus domesticus
- 2012
-
In: Vision Research. - : Elsevier BV. - 0042-6989 .- 1878-5646. ; 62, s. 125-133
-
Journal article (peer-reviewed)abstract
- The assessment of flicker fusion frequency (FFF), the stimulus frequency at which a flickering light stimulus can no longer be resolved and appears continuous, and critical flicker fusion frequency (CFF; the highest frequency at any light intensity that an observer can resolve flicker) are useful methods for comparing temporal resolution capabilities between animals. Behavioural experiments have found that average CFFs in domestic chickens (Gallus gallus domesticus) are in the range of ca. 75-87 Hz, measured in response to full spectrum (i.e. white light plus UV) stimuli. In order to examine whether the chicken retina is able to detect flicker at higher frequencies, we used electroretinograms (ERGs) to assess FFF/CFF in adult hens from two commercial genotypes, Lohmann Selected Leghorns (LSLs) and Lohmann Browns (LBs). ERGs were recorded in response to flickering light at ten full spectrum light intensities ranging from 0.7 to 2740 cd m(-2). Two methods were used to determine FFF/CFF from the ERG recordings and these methods yielded very similar results, with average FFF ranging from ca. 20 Hz at 0.7 cd m(-2) to an average CFF of ca. 105 Hz at 2740 cd m(-2). In some individuals, CFFs of 118-119 Hz were recorded. The Intensity/FFF (I/FFF) curves are double-branched with a break point representing the rod-cone transition occurring between 2.5 and 5.9 cd m(-2). No significant differences in the I/FFF curves were found between the two genotypes. At stimulus light intensities >250 cd m(-2), the ERG-derived FFF and CFF values are all higher than those from behavioural studies using the same stimuli. Although hens do not appear to be able to consciously perceive flicker above approximately 90 Hz, the finding that the ERG responses are able to remain in phase with light flickering at frequencies >100 Hz means that the retinae of domestic poultry housed in artificial light conditions may be able to resolve flicker from fluorescent lamps. As range of detrimental effects have been reported in humans as a result of exposure to such "invisible flicker", the possibility exists that flicker from fluorescent lamps also acts as stressor in domesticated birds.
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| 32. |
- Ma, Wei Ji, et al.
(author)
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Requiem for the max rule?
- 2015
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In: Vision Research. - : Elsevier BV. - 0042-6989 .- 1878-5646. ; 116:Pt B, s. 179-193
-
Journal article (peer-reviewed)abstract
- In tasks such as visual search and change detection, a key question is how observers integrate noisy measurements from multiple locations to make a decision. Decision rules proposed to model this process have fallen into two categories: Bayes-optimal (ideal observer) rules and ad-hoc rules. Among the latter, the maximum-of-outputs (max) rule has been the most prominent. Reviewing recent work and performing new model comparisons across a range of paradigms, we find that in all cases except for one, the optimal rule describes human data as well as or better than every max rule either previously proposed or newly introduced here. This casts doubt on the utility of the max rule for understanding perceptual decision-making.
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| 33. |
- Maethger, Lydia M., et al.
(author)
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The W-shaped pupil in cuttlefish (Sepia officinalis): Functions for improving horizontal vision
- 2013
-
In: Vision Research. - : Elsevier BV. - 1878-5646 .- 0042-6989. ; 83, s. 19-24
-
Journal article (peer-reviewed)abstract
- The eyes of cuttlefish (Sepia officinalis) have a modified horizontal slit-pupil with a distinctive W-shape in bright light, while in darkness the pupil is circular. Two suggestions have previously been made for a function of the W-shape: (1) camouflaging the eye; (2) providing distance information. Since neither of these suggestions can fully explain the function of this pupil across the entire visual field, particularly the frontal and caudal periphery, we re-addressed the question of its functional significance. We took infra-red images of the eyes of live S. officinalis at different light intensities and from different viewing angles. This allowed us to determine the shape and light-admitting area of the pupil for different parts of the visual field. Our data show that the W-shaped pupil projects a blurred "W" directly onto the retina and that it effectively operates as vertical slits for the frontal and caudal parts of the visual field. We also took images of the natural habitat of S. officinalis and calculated the average vertical brightness distribution in the visual habitat. Computing a retinal illumination map shows that the W-shaped pupil is effective in balancing a vertically uneven light field: The constricted pupil reduces light from the dorsal part of the visual field significantly more than it reduces light from the horizontal band. This will cut the amount of direct sunlight that is scattered by the lens and ocular media, and thus improve image contrast particularly for the dimmer parts of the scene. We also conclude that the pupil provides even attenuation along the horizontal band, whereas a circular pupil would attenuate the image relatively more in the important frontal and caudal periphery of the visual field. (C) 2013 Elsevier Ltd. All rights reserved.
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| 34. |
- Marcos, S., et al.
(author)
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Vision science and adaptive optics, the state of the field
- 2017
-
In: Vision Research. - : Elsevier BV. - 0042-6989 .- 1878-5646. ; 132, s. 3-33
-
Journal article (peer-reviewed)abstract
- Adaptive optics is a relatively new field, yet it is spreading rapidly and allows new questions to be asked about how the visual system is organized. The editors of this feature issue have posed a series of question to scientists involved in using adaptive optics in vision science. The questions are focused on three main areas. In the first we investigate the use of adaptive optics for psychophysical measurements of visual system function and for improving the optics of the eye. In the second, we look at the applications and impact of adaptive optics on retinal imaging and its promise for basic and applied research. In the third, we explore how adaptive optics is being used to improve our understanding of the neurophysiology of the visual system.
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| 35. |
- Mönestam, Eva, et al.
(author)
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Associations between subjective and objective visual function in patients with unilateral macular holes
- 2008
-
In: Vision Research. - : Elsevier BV. - 0042-6989 .- 1878-5646. ; 48:1, s. 104-108
-
Journal article (peer-reviewed)abstract
- Forty-six patients with uniocular macular holes and unaffected, fellow eyes were studied to evaluate inter- and intraocular associations between various objective tests of visual function and perceived visual ability. The affected eye had significant associations between visual acuity (VA) and the fovea threshold test, but for the fellow eye only VA and low-contrast VA 10% were associated. The reduction in visual acuity under low-contrast conditions relative to high-contrast did not differ between the affected eye and the healthy eye. Subjective visual ability seems to depend more on the visual acuity of the affected eye than the healthy eye.
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| 36. |
- Nyström, Marcus, et al.
(author)
-
Post-saccadic oscillations in eye movement data recorded with pupil-based eye trackers reflect motion of the pupil inside the iris
- 2013
-
In: Vision Research. - : Elsevier BV. - 1878-5646 .- 0042-6989. ; 92, s. 59-66
-
Journal article (peer-reviewed)abstract
- Abstract in UndeterminedCurrent video eye trackers use information about the pupil center to estimate orientation and movement of the eye. While dual Purkinje eye trackers suffer from lens wobble and scleral search coils may be influenced by contact lens slippage directly after saccades, it is not known whether pupil-based eye trackers produces similar artifacts in the data. We recorded eye movements from participants making repetitive, horizontal saccades and compared the movement in the data with pupil- and iris movements extracted from the eye images. Results showed that post-saccadic instabilities clearly exist in data recorded with a pupil-based eye tracker. They also exhibit a high degree of reproducibility across saccades and within participants. While the recorded eye movement data correlated well with the movement of the pupil center, the iris center showed only little post-saccadic movement. This means that the pupil moves relative to the iris during post-saccadic eye movements, and that the eye movement data reflect pupil movement rather than eyeball rotation. Besides introducing inaccuracies and additional variability in the data, the pupil movement inside the eyeball influences the decision of when a saccade should end and the subsequent fixation should begin, and consequently higher order analyses based on fixations and saccades.
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| 37. |
- Nyström, Marcus, et al.
(author)
-
Pupil size influences the eye-tracker signal during saccades
- 2016
-
In: Vision Research. - : Elsevier BV. - 1878-5646 .- 0042-6989. ; 121, s. 95-103
-
Journal article (peer-reviewed)abstract
- While it is known that scleral search coils-measuring the rotation of the eye globe-and modern, video based eye trackers-tracking the center of the pupil and the corneal reflection (CR)-produce signals with different properties, the mechanisms behind the differences are less investigated. We measure how the size of the pupil affects the eye-tracker signal recorded during saccades with a common pupil-CR eye-tracker. Eye movements were collected from four healthy participants and one person with an aphakic eye while performing self-paced, horizontal saccades at different levels of screen luminance and hence pupil size. Results show that pupil-, and gaze-signals, but not the CR-signal, are affected by the size of the pupil; changes in saccade peak velocities in the gaze signal of more than 30% were found. It is important to be aware of this pupil size dependent change when comparing fine grained oculomotor behavior across participants and conditions.
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| 38. |
- Nyström, Marcus, et al.
(author)
-
Searching for monocular microsaccades - a red Hering of modern eye trackers?
- 2017
-
In: Vision Research. - : Elsevier BV. - 1878-5646 .- 0042-6989. ; 140, s. 44-54
-
Journal article (peer-reviewed)abstract
- Despite early reports and the contemporary consensus on microsaccades as purely binocular phenomena, recent work has proposed not only the existence of monocular microsaccades, but also that they serve functional purposes. We take a critical look at the detection of monocular microsaccades from a signal perspective, using raw data and a state-of-the-art, video-based eye tracker. In agreement with previous work, monocular detections were present in all participants using a standard microsaccade detection algorithm. However, a closer look at the raw data invalidates the vast majority of monocular detections. These results again raise the question of the existence of monocular microsaccades, as well as the need for improved methods to study small eye movements recorded with video-based eye trackers.
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| 39. |
- Nyström, Marcus, et al.
(author)
-
The influence of crystalline lens accommodation on post-saccadic oscillations in pupil-based eye trackers
- 2015
-
In: Vision Research. - : Elsevier BV. - 1878-5646 .- 0042-6989. ; 107, s. 1-14
-
Journal article (peer-reviewed)abstract
- It is well known that the crystalline lens (henceforth lens) can oscillate (or 'wobble') relative to the eyeball at the end of saccades. Recent research has proposed that such wobbling of the lens is a source of post-saccadic oscillations (PSOs) seen in data recorded by eye trackers that estimate gaze direction from the location of the pupil. Since the size of the lens wobbles increases with accommodative effort, one would predict a similar increase of PSO-amplitude in data recorded with a pupil based eye tracker. In four experiments, we investigated the role of lens accommodation on PSOs in a video-based eye tracker. In Experiment 1, we replicated previous results showing that PSO-amplitudes increase at near viewing distances (large vergence angles), when the lens is highly accommodated. In Experiment 2a, we manipulated the accommodative state of the lens pharmacologically using eye drops at a fixed viewing distance and found, in contrast to Experiment 1, no significant difference in PSO-amplitude related to the accommodative state of the lens. Finally, in Experiment 2b, the effect of vergence angle was investigated by comparing PSO-amplitudes at near and far while maintaining a fixed lens accommodation. Despite the pharmacologically fixed degree of accommodation, PSO-amplitudes were systematically larger in the near condition. In summary, PSOs cannot exhaustively be explained by lens wobbles. Possible confounds related to pupil size and eye-camera angle are investigated in Experiments 3 and 4, and alternative mechanisms behind PSOs are probed in the discussion.
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| 40. |
- Nyström, Marcus, et al.
(author)
-
Why have microsaccades become larger? Investigating eye deformations and detection algorithms
- 2016
-
In: Vision Research. - : Elsevier BV. - 1878-5646 .- 0042-6989. ; 118, s. 17-24
-
Journal article (peer-reviewed)abstract
- Abstract in UndeterminedThe reported size of microsaccades is considerably larger today compared to the initial era of microsaccade studies during the 1950s and 1960s. We investigate whether this increase in size is related to the fact that the eye-trackers of today measure different ocular structures than the older techniques, and that the movements of these structures may differ during a microsaccade. In addition, we explore the impact such differences have on subsequent analyzes of the eye-tracker signals. In Experiment I, the movement of the pupil as well as the first and fourth Purkinje reflections were extracted from series of eye images recorded during a fixation task. Results show that the different ocular structures produce different microsaccade signatures. In Experiment II, we found that microsaccade amplitudes computed with a common detection algorithm were larger compared to those reported by two human experts. The main reason was that the overshoots were not systematically detected by the algorithm and therefore not accurately accounted for. We conclude that one reason to why the reported size of microsaccades has increased is due to the larger overshoots produced by the modern pupil-based eye-trackers compared to the systems used in the classical studies, in combination with the lack of a systematic algorithmic treatment of the overshoot. We hope that awareness of these discrepancies in microsaccade dynamics across eye structures will lead to more generally accepted definitions of microsaccades.
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| 41. |
- Poom, Leo, et al.
(author)
-
Dissociations between slant-contrast and reversed slant-contrast
- 2007
-
In: Vision Research. - : Elsevier BV. - 0042-6989 .- 1878-5646. ; 47:6, s. 746-754
-
Journal article (peer-reviewed)abstract
- A vertical test probe is misperceived as slanted in the opposite direction to an inducer when disparity specifies the inducer slant while monocular cues specify a frontoparallel surface (slant-contrast). In reversed cue conditions with vertical axis slant the test probe is misperceived as slanted in the same direction as the inducer (reversed slant-contrast). We found reliable slant-contrast and reversed slant-contrast with inducers having horizontal-axis slant. The reversed slant-contrast was not influenced when the inducer and probe were separated in the frontal plane or in disparity depth whereas slant contrast was degraded, especially in the latter condition. Slant contrast was most pronounced when the inducer was slanted like a ceiling compared to like a ground. No such difference was found for the reversed slant-contrast. When the cue conflict was minimized slant-contrast was reduced, but only with inducers having ground-like slant. Implications for an existing model explaining the slant effects are discussed.
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| 42. |
- Poom, Leo
(author)
-
Inter-attribute tilt effects and orientation analysis in the visual brain
- 2000
-
In: Vision Research. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0042-6989 .- 1878-5646. ; 40:20, s. 2711-2722
-
Journal article (peer-reviewed)abstract
- A test grating appears to be tilted away from an inducing grating for small angular separations (repulsion), but towards the inducing grating for larger angular separations (attraction). Previous research on luminance gratings suggests that repulsion is c
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| 43. |
- Richter, Hans O., et al.
(author)
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Stabilization of gaze : A relationship between ciliary muscle contraction and trapezius muscle activity
- 2010
-
In: Vision Research. - : Elsevier BV. - 0042-6989 .- 1878-5646. ; 50:23, s. 2559-2569
-
Journal article (peer-reviewed)abstract
- In an experimental study four levels of oculomotor load were induced binocularly. Trapezius muscle activity was measured with bipolar surface electromyography and normalized to a submaximal contraction. Twenty-eight subjects with a mean age of 29 (range 19–42, std 8) viewed a high-contrast fixationt arget for four 5-min periods through: (i) 3.5 dioptre (D) lenses; (ii) 0 D lenses; (iii) individuallya djusted prism D lenses (1–2 D base out); and (iv) +3.5 D lenses. The target was placed close to thei ndividual’s age-appropriate near point of accommodation in conditions (i–iii) and at 3 m in condition( iv). Each subject’s ability to compensate for the added blur was extracted via infrared photorefraction measurements. A bitwise linear regression model was fitted on group level with eye-lens refraction on the x-axis and normalized trapezius muscle EMG (%RVE) on the y -axis. The model had a constant level of trapezius muscle activity – where subjects had not compensated for the incurred defocus by a change in eye-lens accommodation – and a slope, where the subjects had compensated. The slope coefficient was significantly positive in the D (i) and the +D blur conditions (iv). During no blur (ii) and prism blur (iii) there were no signs of relationships. Nor was there any sign of relationship between the convergence response and trapezius muscle EMG in any of the experimental conditions. The results appear directly attributable to an engagement of the eye-lens accommodative system and most likely reflect sensorimotor processing along its reflex arc for the purpose of achieving stabilization of gaze
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| 44. |
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| 45. |
- Rosander, Kerstin, et al.
(author)
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Cortical processing of visual motion in young infants
- 2007
-
In: Vision Research. - : Elsevier BV. - 0042-6989 .- 1878-5646. ; 47:12, s. 1614-1623
-
Journal article (peer-reviewed)abstract
- High-density EEG was used to investigate the cortical processing of a rotatirig visual pattern in 2-, 3-, and 5-month-old infants and in adults. Motion induced ERP in the parietal and the temporal-occipital border regions (OT) was elicited at all ages. The ERP was discernable in the 2-months-olds, significant and unilateral in the 3-month-olds and significantly bilateral in the 5-month-olds and adults. The motion induced ERP in the primary visual area was absent in the 2-month-olds and later than in the OT area for the 3-month-olds indicating that information to OT may be supplied by the VI bypass at these ages. The results are in agreement with behavioural and psychophysical. data in infants.
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| 46. |
- Scholtyssek, Christine, et al.
(author)
-
Brightness discrimination in the harbor seal (Phoca vitulina)
- 2008
-
In: Vision Research. - : Elsevier BV. - 1878-5646 .- 0042-6989. ; 48:1, s. 96-103
-
Journal article (peer-reviewed)abstract
- The brightness discrimination ability of a mate harbor seal was investigated at an ambient illumination of 0.9 lx. The visual stimuli consisted of circular gray discs that were presented on a black background on a TFT monitor. Eight standard intensities were tested against sets of lower comparison intensities. In accordance with Weber's law we observed a constant gain of the just noticeable intensity difference with increasing intensity of the standard stimulus. The calculated Weber fraction is 0.14. This result indicates that the brightness discrimination ability of the harbor seal is comparable to that of humans.
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| 47. |
- Theobald, Jamie, et al.
(author)
-
Visual summation in night-flying sweat bees: A theoretical study
- 2006
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In: Vision Research. - : Elsevier BV. - 1878-5646 .- 0042-6989. ; 46:14, s. 2298-2309
-
Journal article (peer-reviewed)abstract
- Bees are predominantly diurnal; only a few groups fly at night. An evolutionary limitation that bees must overcome to inhabit dim environments is their eye type: bees possess apposition compound eyes, which are poorly suited to vision in dim light. Here, we theoretically examine how nocturnal bees Megalopta genalis fly at light levels usually reserved for insects bearing more sensitive superposition eyes. We find that neural summation should greatly increase M. genalis's visual reliability. Predicted spatial summation closely matches the morphology of laminal neurons believed to mediate such summation. Improved reliability costs acuity, but dark adapted bees already suffer optical blurring, and summation further degrades vision only slightly. (c) 2006 Elsevier Ltd. All rights reserved.
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| 48. |
- Torbaghan, Solmaz Shariat, et al.
(author)
-
Inhibition of return in a visual foraging task in non-human subjects
- 2012
-
In: Vision Research. - : Elsevier BV. - 0042-6989 .- 1878-5646. ; 74, s. 2-9
-
Journal article (peer-reviewed)abstract
- Inhibition of return is thought to help guide visual search by inhibiting the orienting of attention to previously attended locations. We have previously shown that, in a foraging visual search task, the neural responses to objects in parietal cortex are reduced after they have been examined. Here we ask whether the animals' reaction times (RTs) in the same task show a psychophysical correlate of inhibition of return: a slowing of reaction time in response to a probe placed at a previously fixated location. We trained three animals to perform an RT version of the visual foraging task. In the foraging task, subjects visually searched through an array of five identical distractors and five identical potential targets; one of which had a reward linked to it. In the RT variant of the task, subjects had to rapidly respond to a probe if it appeared. We found that RTs were slower for probes presented at locations that contained previously fixated objects, faster to potential targets and between the two for behaviorally irrelevant distractors that had not been fixated. These data show behavioral inhibitory tagging of previously fixated objects and suggest that the suppression of activity seen previously in the same task in parietal cortex could be a neural correlate of this mechanism.
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| 49. |
- Venkataraman, Abinaya Priya, et al.
(author)
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Blur adaptation : Contrast sensitivity changes and stimulus extent
- 2015
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In: Vision Research. - : Elsevier. - 0042-6989 .- 1878-5646. ; 110:PA, s. 100-106
-
Journal article (peer-reviewed)abstract
- A prolonged exposure to foveal defocus is well known to affect the visual functions in the fovea. However, the effects of peripheral blur adaptation on foveal vision, or vice versa, are still unclear. In this study, we therefore examined the changes in contrast sensitivity function from baseline, following blur adaptation to small as well as laterally extended stimuli in four subjects. The small field stimulus (7.5° visual field) was a 30. min video of forest scenery projected on a screen and the large field stimulus consisted of 7-tiles of the 7.5° stimulus stacked horizontally. Both stimuli were used for adaptation with optical blur (+2.00. D trial lens) as well as for clear control conditions. After small field blur adaptation foveal contrast sensitivity improved in the mid spatial frequency region. However, these changes neither spread to the periphery nor occurred for the large field blur adaptation. To conclude, visual performance after adaptation is dependent on the lateral extent of the adaptation stimulus.
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| 50. |
- Venkataraman, Abinaya Priya, et al.
(author)
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Peripheral resolution and contrast sensitivity : Effects of stimulus drift
- 2017
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In: Vision Research. - : Pergamon Press. - 0042-6989 .- 1878-5646. ; 133, s. 145-149
-
Journal article (peer-reviewed)abstract
- Optimal temporal modulation of the stimulus can improve foveal contrast sensitivity. This studyevaluates the characteristics oftheperipheral spatiotemporal contrast sensitivity function in normal-sighted subjects.The purpose is to identify a temporal modulation that can potentially improve the remaining peripheral visual function in subjects with central visual field loss. High contrast resolution cut-off for grating stimuli with four temporal frequencies (0, 5, 10 and 15 Hz drift) was first evaluated in the 10° nasal visual field.Resolution contrast sensitivity for all temporal frequencies was then measured at four spatial frequencies between 0.5 cycles per degree (cpd) and the measured stationary cut-off. All measurements were performed with eccentric optical correction. Similar to foveal vision, peripheral contrast sensitivity is highest for a combination of low spatial frequency and 5 to 10 Hz drift. At higher spatial frequencies, there was a decrease in contrast sensitivity with 15 Hz drift.Despitethis decrease, the resolution cut-off did not vary largely between the different temporal frequencies tested. Additional measurements of contrast sensitivity at 0.5 cpd and resolution cut-off for stationary (0 Hz) and 7.5 Hz stimuli performed at 10, 15, 20 and 25° in the nasal visual field also showed the same characteristics across eccentricities.
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