| 1. |
- Burstedt, Marie S I, et al.
(författare)
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Retinal function in Bothnia dystrophy. An electrophysiological study.
- 2003
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Ingår i: Vision Research. - 0042-6989 .- 1878-5646. ; 43:24, s. 2559-2571
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Tidskriftsartikel (refereegranskat)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.
(författare)
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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
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Ingår i: Vision Research. - 0042-6989 .- 1878-5646. ; 43:16, s. 1777-1787
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Tidskriftsartikel (refereegranskat)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
(författare)
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Inter-attribute tilt effects and orientation analysis in the visual brain
- 2000
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Ingår i: Vision Research. - : Elsevier. - 0042-6989 .- 1878-5646. ; 40:20, s. 2711-2722
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Tidskriftsartikel (refereegranskat)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
(författare)
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Visual binding of luminance, motion, and disparity edges
- 2002
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Ingår i: Vision Research. - 0042-6989 .- 1878-5646. ; 42:23, s. 2577-2591
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Circadian regulation of phosphodiesterase 6 genes in zebrafish differs between cones and rods : Implications for photopic and scotopic vision
- 2020
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Ingår i: Vision Research. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0042-6989 .- 1878-5646. ; 166, s. 43-51
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Perceptual efficiency and the inversion effect for faces, words and houses
- 2018
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Ingår i: Vision Research. - : Pergamon Press. - 0042-6989 .- 1878-5646. ; 153, s. 91-97
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Tidskriftsartikel (refereegranskat)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.
(författare)
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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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Ingår i: Vision Research. - : Elsevier BV. - 1878-5646 .- 0042-6989. ; 47:10, s. 1394-1409
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Form vision in the insect dorsal ocelli: An anatomical and optical analysis of the Locust Ocelli
- 2007
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Ingår i: Vision Research. - : Elsevier BV. - 1878-5646 .- 0042-6989. ; 47:10, s. 1382-1393
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Tidskriftsartikel (refereegranskat)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.
(författare)
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How task demands influence scanpath similarity in a sequential number-search task
- 2018
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Ingår i: Vision Research. - : Elsevier BV. - 1878-5646 .- 0042-6989. ; , s. 9-23
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Tidskriftsartikel (refereegranskat)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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