The influences of visibility and anomalous integration process on the perception of global spatial form versus motion in human amblyopia

Department of Optometry and Visual Science, Applied Vision Research Centre, The Henry Wellcome Laboratories for Vision Sciences, City University, London EC1V OHB 22, UK.
Vision Research (Impact Factor: 1.82). 03/2005; 45(4):449-60. DOI: 10.1016/j.visres.2004.08.026
Source: PubMed


Do amblyopes demonstrate general irregularities in processes of global image integration? Or are these anomalies stimulus specific? To address these questions we employed directly analogous global-orientation and global-motion stimuli using a method that allows us to factor out any influence of the low-level visibility loss [Simmers, A. J., Ledgeway, T., Hess, R. F., & McGraw, P. V. (2003). Deficits to global motion processing in human amblyopia. Vision Research 43, pp. 729-738]. The combination of orientation and motion coherence thresholds reported here provides comparable psychophysical measures of global processing by spatial-sensitive and motion-sensitive mechanisms in the amblyopic visual system. The results show deficits in both global-orientation and global-motion processing in amblyopia, which appear independent of any low-level visibility loss, but with the most severe deficit affecting the extraction of global motion. This provides evidence for the existence of a dominant temporal processing deficit in amblyopia.

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    • "Thresholds for discriminating global motion direction follow a similar trend for both stimulus types with coherence thresholds asymptoting to stable levels as the contrast of the stimuli increases and becoming independent of contrast. These results show that integration of global motion at suprathreshold contrasts is possible for both achromatic and chromatic stimuli, as shown previously for achromatic [3] [32] [33] and chromatic stimuli [3]. Based on these results, all experiments are performed at the 8Â threshold condition to acquire coherence thresholds, at which the motion coherence level is contrast-independent. "
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    ABSTRACT: Background: Psychophysical evidence suggests that the perception of the motion and color of moving stimuli are determined separately in the human brain. Here we aim to determine the role of visual cortical areas hMT+ and V1/V2 in each task by measuring the effect of rTMS of each area using an off-line continuous theta-burst stimulation (cTBS) protocol. Methods: In the motion task, the direction of moving dots was identified using a global motion stimulus that avoids tracking, and in the detection task for the same stimulus, the presence of the dots was detected regardless of motion. Performance was measured using forced-choice methods in 8 subjects, both before and at 4 time-intervals in the 1-hour after brain stimulation. All experiments were done using achromatic and isoluminant, red-green chromatic stimuli. Results: Performance on global motion for both achromatic and chromatic stimuli was significantly impaired following cTBS of visual area hMT+, with a maximum effect occurring 11 min after stimulation. In comparison, there was no effect of cTBS on the motion task for areas V1/V2 or the vertex (control). cTBS did not affect the detection task in either area. Conclusions: Our experiments validate the use of cTBS as an advantageous off-line rTMS protocol for studying visual areas. The results indicate a causal link between neural activity in area hMT+ and perception of motion of isoluminant chromatic stimuli. We conclude that area hMT+ is part of a common pathway processing the global motion of chromatic and achromatic stimuli, but is not involved in their detection.
    Brain Stimulation 11/2014; 8(2). DOI:10.1016/j.brs.2014.11.001 · 4.40 Impact Factor
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    • "In cats, the dorsal pathway seems less affected than the ventral pathway (Schröder et al., 2002). Psychophysical studies suggest that both perception of global motion and translation of vision into movement are affected in amblyopic subjects (Simmers et al., 2003, 2005), implying deficits in the dorsal visual pathway leading to the posterior parietal cortex. A study, with attentive visual tracking of moving targets (Secen et al., 2011) "
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    ABSTRACT: Amblyopia is a cerebral visual impairment considered to derive from abnormal visual experience (e.g., strabismus, anisometropia). Amblyopia, first considered as a monocular disorder, is now often seen as a primarily binocular disorder resulting in more and more studies examining the binocular deficits in the patients. The neural mechanisms of amblyopia are not completely understood even though they have been investigated with electrophysiological recordings in animal models and more recently with neuroimaging techniques in humans. In this review, we summarize the current knowledge about the brain regions that underlie the visual deficits associated with amblyopia with a focus on binocular vision using functional magnetic resonance imaging. The first studies focused on abnormal responses in the primary and secondary visual areas whereas recent evidence shows that there are also deficits at higher levels of the visual pathways within the parieto-occipital and temporal cortices. These higher level areas are part of the cortical network involved in 3D vision from binocular cues. Therefore, reduced responses in these areas could be related to the impaired binocular vision in amblyopic patients. Promising new binocular treatments might at least partially correct the activation in these areas. Future neuroimaging experiments could help to characterize the brain response changes associated with these treatments and help devise them.
    Frontiers in Integrative Neuroscience 08/2014; 8:62. DOI:10.3389/fnint.2014.00062
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    • "For global motion, there is compelling evidence for a specific deficit in addition to those inherited from abnormal local processing . For global form, the evidence is less convincing (for example, Simmers et al., 2003, 2005; Husk and Hess, 2013). This is particularly interesting in light of the evidence described above which suggests that local temporal processing is less affected by amblyopia than local spatial processing. "
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    ABSTRACT: Amblyopia is a neurodevelopmental disorder of the visual system that is associated with disrupted binocular vision during early childhood. There is evidence that the effects of amblyopia extend beyond the primary visual cortex to regions of the dorsal and ventral extra-striate visual cortex involved in visual integration. Here, we review the current literature on global processing deficits in observers with either strabismic, anisometropic, or deprivation amblyopia. A range of global processing tasks have been used to investigate the extent of the cortical deficit in amblyopia including: global motion perception, global form perception, face perception, and biological motion. These tasks appear to be differentially affected by amblyopia. In general, observers with unilateral amblyopia appear to show deficits for local spatial processing and global tasks that require the segregation of signal from noise. In bilateral cases, the global processing deficits are exaggerated, and appear to extend to specialized perceptual systems such as those involved in face processing.
    Frontiers in Psychology 06/2014; 5:583. DOI:10.3389/fpsyg.2014.00583 · 2.80 Impact Factor
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