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Hong-jin Sun, Tao Li; Differential Detection of Visual Targets Presented in Near and Far Space and its Dependence on the Chromatic Properties of the Targets. Journal of Vision 2012;12(9):911. doi: 10.1167/12.9.911.
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Converging evidence from animal neurophysiology and human clinical studies has suggested that visual information arising from near (peripersonal, within arm’s reach) versus far (extrapersonal, beyond arm’s reach) space may be mediated predominantly by different visual subsystems in the human brain. In our recent study (Li et al, Neuropsychologia, 2011), we tested healthy human observers using either simple detection/localization or identification tasks, in a range of single- and dual-task situations. Healthy human observers showed a behavioural difference in detecting briefly displayed and retinally equivalent visual stimuli in near versus far space. However, identification accuracy under similar conditions showed no such dissociation of near versus far processing. Such differences in sensitivity for detecting visual target presented in near versus far space suggest that distinct neural processes or mechanisms might contribute differentially for near versus far visual information. Because the magnocellular pathway is only sensitive to luminance contrast while the parvocellular pathway is sensitive to both chromatic and luminance contrast, in the present study, we examined the detection performance further by manipulating the luminance and chromatic properties of the target. Healthy human observers were asked to detect a spot briefly presented in a random location at the peripheral visual field in near (0.39m) and far (1.33m) viewing conditions, with matched luminance and visual angle for the visual display in the two conditions. Similar to our previous findings, we found that the visual accuracy was higher in near viewing than far viewing when detecting an achromatic target in either high or low contrast. However, the near/far difference was reversed when the visual target was an isoluminant green spot. These data suggest that retinal information from near versus far space may be preferentially processed by substantially different neural substrates, with active modulation of the relative contributions of involved magnocellular-dorsal and parvocellular-ventral visual pathways.
Meeting abstract presented at VSS 2012
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