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Ilona Bloem, Taryn Janati, Sam Ling; Attentional modulation interacts with orientation anisotropies in contrast sensitivity.. Journal of Vision 2015;15(12):220. doi: https://doi.org/10.1167/15.12.220.
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The magnitude of attentional modulation in the LGN has recently been shown to depend on stimulus orientation, whereby oblique orientations yield larger attentional effects than cardinal orientations – a pattern of effects that is absent in visual cortex (Ling, Pratte & Tong, 2013). Here, we examined what impact, if any, this orientation-based anisotropy in subcortical attentional modulation may have on behavior. To do so, we first established the effect of stimulus contrast on the strength of the orientation sensitivity, by mapping the contrast psychometric functions for oblique and cardinal orientations. Participants performed a fine orientation discrimination task on a grating (4°; 7 cpd) varying in contrast from trial-to-trial, oriented either cardinally (0° or 90°) or obliquely (45° or 135°) at fixation. Results revealed a robust oblique effect, consistent with a multiplicative attenuation of contrast responses for oblique orientations. Next, we evaluated how orientation interacts with attention by measuring the same psychometric functions while varying the attentional load. The low attentional load condition consisted solely of a fine orientation discrimination task at fixation, while the high attentional load condition consisted of participants performing the same orientation discrimination task, concurrent with a demanding RSVP task at fixation. Results suggest that attentional load affects the sensitivity for cardinal and oblique orientations differently. Specifically, while attentional load only marginally affects the contrast response function for cardinal orientations, both the response gain and sensitivity decrease when attentional load increases for obliques. In sum, the magnitude of the effect of attention on the contrast response function seems to depend on the orientation of the stimulus. This is consistent with previous neuroimaging findings, showing that attention seems to strengthen the orientation-selective responses for oblique orientations to a larger degree than responses for cardinals within LGN, suggesting that early attentional modulation may have a substantial impact on behavior.
Meeting abstract presented at VSS 2015
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