klab
"What I cannot create, I do not understand." – R. Feynman
Lee H. de-Wit, Jonas Kubilius, Hans P. Op de Beeck, Johan Wagemans

A reversal of part-whole Gestalts in a patient with visual form agnosia

AVA , Leuven (Belgium) , 2012-12-18 pdf Program

For many visual phenomena the ‘whole’ is not just different from the sum of its ‘parts’, but these parts seem to become lost or inaccessible. Neuroimaging (Kubilius, Wagemans, & Op de Beeck, 2011) suggests that this increased behavioral sensitivity to ‘wholes’ over ‘parts’ reflects the way in which visual input is integrated as it progresses from V1 to LOC. More specifically while early visual areas may contain more information about parts (edges), higher areas contain more information about wholes (shapes). Typical behavior is consistent with a ‘read-out’ of information from these higher areas. But how is information read-out from the visual hierarchy when these higher stages of visual processing are damaged? Here we report results from one such well-documented case, patient DF, who, in contrast to the normal controls, demonstrated better access to parts than to wholes in the configural superiority effect used by Kubilius et al. We further show that such behavior is consistent with simulations of the early layers of HMAX, a popular model of the ventral visual stream. Our results highlights that compelling Gestalts can break down with selective lesions to the ventral stream, particularly to the area LO. Moreover, the combination of neuroimaging, modeling, and patient neuropsychology potentially provides a useful tool for investigating not only how visual input is processed, but also to test how information is read-out from the hierarchy of visual areas.