Object recognition in the inferior temporal cortex

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Presentation transcript:

Object recognition in the inferior temporal cortex Retinotopy is not useful for object recognition, which is related to shape Object recognition does not appear to occur in the earlier retinotopic visual areas Recording in inferior temporal cortex (IT) shows object constancy and little retinotopy

Inferotemporal Cortex

Lesion studies in monkeys Kluver-Bucy syndrome: temporal lobe lesions with complex social, sexual and eating behavior changes and visual impairments With more restricted lesions, inferior temporal gyrus (inferotemporal cortex) was shown to be critical for visual impairments Task was matching a choice to a target.

Object recognition not learning IT lesions cause loss of previous discriminations Qualitative abnormalities: generalize on features, ignore shape, e.g. respond to edge of circle and edge of triangle not shape of triangle Used spatial location to solve some visual problems

What is the nature of the representation in IT? Represents intrinsic shape and omits aspects that depend on specific viewing conditions (object centered recognition) EVIDENCE: Monkeys with IT lesions don’t generalize across hemifields as normal ones do (location is part of cue for them) Vary distance of discs of absolute size and they can’t relearn the discrimination (retinal size cue problem; stuck on local size)

More evidence IT lesioned monkeys impaired at views of the same stimulus in different orientations (discrepant findings like doing P v.T discriminations may be explained by local features giving a difference cue) Changes in illumination impair IT lesioned monkeys IT monkeys are not confused by mirror images (normal ones are!)

Single unit recording evidence Large bilateral receptive fields Not retinotopically organized Cluster in groups with similar properties tuned to stimulus shape (e.g. hand like) Cell responses modulated by task demands, if monkey must respond or discrimination is hard, the cell response is enhanced (not related to motivation)

Representing objects in IT Prefer 3-D objects Object can be defined by luminosity, texture, motion, speckle size Some selective for normal, not scrambled, faces: overall structure important Position, retinal image size, orientation minimally affect response (even faces rotated in depth can be ‘recognized’)