Purchase this article with an account.
Justin Ales, Lawrence Appelbaum, Anthony Norcia; Neural signatures of shape discrimination decisions at threshold. Journal of Vision 2010;10(7):106. doi: 10.1167/10.7.106.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
The lateral occipital cortex (LOC) is known to selectively activate to intact objects versus scrambled controls, to be selective for figure-ground relationship, and to exhibit at least some degree of invariance for size and position. Because of these features, it is considered to be a crucial part of the object recognition pathway. Here we determined if the LOC is involved in shape discriminations. High-density EEG was recorded while subjects performed a threshold-level shape discrimination task on figures segmented by either phase or orientation cues. Our paradigm allowed us to separate responses due to the figural cue from the responses corresponding to the discrimination of shape. The appearance or disappearance of a figure region in the stimuli generated robust visual evoked potentials localized throughout retinotopic cortex. Contrasting responses from trials containing a shape change (hits) with trials in which no change occurred (correct rejects) revealed activity preceding the subject's response in the LOC that was selective for presence of the target shape change. Task-dependent activity that was time-locked to the subjects' response was found in frontal cortex. Activity in the LOC was determined to be related to shape discrimination for several reasons: Shape-selective responses were silenced when subjects viewed identical stimuli but their attention was directed away from the shapes to a demanding letter discrimination task; shape-selectivity was present across all cues used to define the figure; shape-selective responses were present under conditions where stimulus-locked activity was absent. These results indicate that decision-related activity is present in the LOC when subjects are engaged in threshold-level shape discriminations.
This PDF is available to Subscribers Only