Diabetes research advances. Why Jeremy wishes he were a mouse.
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Australia↗
Biomedical subjects
Andrew Metha
Publications and source records attributed to Andrew Metha.
Visual function: the problem with eccentricity.
Age-related macular degeneration (AMD) is the leading cause of blindness in developed countries. With an ageing population, the prevalence of such a condition has resulted in a large proportion of the population relying on peripheral vision to undertake activities of daily living. Peripheral vision is not a scaled-down version of the fovea, simply requiring larger print or increased contrast for detection of objects or reading text. Even when print size is scaled and eye movements are minimised, the peripheral retina cannot perform at the level of the foveal region. Understanding how and why reading performance is limited as a function of eccentricity has important implications for how we approach rehabilitation of patients with central visual loss. This brief review of the extensive literature on reading with peripheral vision and the research aimed at better reading rehabilitation for low vision patients focuses on why many of the problems associated with the reduced reading capability of peripheral vision cannot be completely solved with magnification, reducing eye movements or modifying print.
Blindness↗
Enhanced sensitivity for peripherally-presented collinearly-aligned stimulus elements: contour detection or spatial summation?
BACKGROUND: It has been shown that the detection threshold for a foveally presented Gabor stimulus (Gaussian-windowed sinusoidal grating) is reduced in the presence of two suprathreshold flanking Gabors and that such facilitation is orientation and configuration dependent, with maximal threshold reductions occurring with collinear flanking elements. METHODS: We assessed the effect of varying relative orientation on detection thresholds for chains of three Gabors, with 0.96(o) centre-to-centre spacing, presented at 4.8(o) in the periphery. The central Gabor element in each chain was either collinear with its flanking elements or oriented orthogonally to them. RESULTS: Thresholds for the configuration as a whole were found to be lower using the collinear configuration compared with the orthogonal configuration, consistent with the proposal that orientation-specific long-range intracortical interactions are involved. However, this configuration-dependent threshold difference disappeared when the spatial frequency of the Gabors was doubled from 3.33 cpd to 6.66 cpd. CONCLUSIONS: Configurational dependencies may disappear at higher spatial frequencies because, despite increased spatial summation at detection threshold contrast levels, the intrinsically smaller receptive field sizes of neurons tuned to high spatial frequencies render them incapable of encapsulating more than one of the spatially separated Gabors within their individual receptive fields.
Journal Article↗
Artificial scotoma-induced perceptual distortions are orientation dependent and short lived.
Conditioning human observers with an "artificial scotoma"-a small retinal area deprived of patterned stimulation within a larger area of dynamically textured noise-results in contractions and expansions of perceived space that are thought to reflect receptive-field changes among cells in the primary visual cortex (Kapadia et al., 1994). Here we show that one-dimensional counter-phase flickering grating patterns are also potent stimuli for producing artificial scotomata capable of altering three-element bisection ability analogous to those results reported earlier. Moreover, we found that the magnitude of the induced spatial distortions depends critically on the relative orientations of peri-scotomatous and test-stimulus spatial contrast. In addition, the perceptual distortions are found to be relatively short lived, decaying within 660 ms. The results support the hypothesis that artificial scotoma-induced perceptual distortions are generated by dynamic alteration of connection efficacy within a network linking cortical areas of similar orientation specificity, consistent with established anatomical and physiological results.
Humans↗