Object recognition in the Object recognition in the inferior temporal cortexinferior temporal cortex

Retinotopy is not useful for object Retinotopy is not useful for object recognition, which is related to shaperecognition, which is related to shape

Object recognition does not appear to Object recognition does not appear to occur in the earlier retinotopic visual occur in the earlier retinotopic visual areasareas

Recording in inferior temporal cortex (IT) Recording in inferior temporal cortex (IT) shows object constancy and little shows object constancy and little retinotopyretinotopy

Inferotemporal CortexInferotemporal Cortex

Lesion studies in Lesion studies in monkeysmonkeys

Kluver-Bucy syndrome: Kluver-Bucy syndrome: temporal lobe lesions with temporal lobe lesions with complex social, sexual and complex social, sexual and eating behavior changes and eating behavior changes and visual impairmentsvisual impairments

With more restricted lesions, With more restricted lesions, inferior temporal gyrus inferior temporal gyrus (inferotemporal cortex) was (inferotemporal cortex) was shown to be critical for visual shown to be critical for visual impairmentsimpairments

Task was matching a choice Task was matching a choice to a target.to a target.

Object recognition not Object recognition not learninglearning

IT lesions cause loss of IT lesions cause loss of previous discriminationsprevious discriminations

Qualitative abnormalities: Qualitative abnormalities: generalize on features, ignore generalize on features, ignore shape, e.g. respond to edge of shape, e.g. respond to edge of circle and edge of triangle not circle and edge of triangle not shape of triangleshape of triangle

Used spatial location to solve Used spatial location to solve some visual problemssome visual problems

What is the nature of the What is the nature of the representation in IT?representation in IT?

Represents intrinsic shape and omits aspects Represents intrinsic shape and omits aspects that depend on specific viewing conditions that depend on specific viewing conditions (object centered recognition)(object centered recognition)

EVIDENCE:EVIDENCE: Monkeys with IT lesions don’t generalize Monkeys with IT lesions don’t generalize

across hemifields as normal ones do (location across hemifields as normal ones do (location is part of cue for them)is part of cue for them)

Vary distance of discs of absolute size and Vary distance of discs of absolute size and they can’t relearn the discrimination (retinal they can’t relearn the discrimination (retinal size cue problem; stuck on local size)size cue problem; stuck on local size)

More evidenceMore evidence IT lesioned monkeys impaired at views of the IT lesioned monkeys impaired at views of the

same stimulus in different orientationssame stimulus in different orientations (discrepant findings like doing P v.T (discrepant findings like doing P v.T

discriminations may be explained by local discriminations may be explained by local features giving a difference cue)features giving a difference cue)

Changes in illumination impair IT lesioned Changes in illumination impair IT lesioned monkeysmonkeys

IT monkeys are not confused by mirror imagesIT monkeys are not confused by mirror images (normal ones are!)(normal ones are!)

Single unit recording Single unit recording evidenceevidence

Large bilateral receptive fieldsLarge bilateral receptive fields Not retinotopically organizedNot retinotopically organized Cluster in groups with similar properties Cluster in groups with similar properties

tuned to stimulus shape (e.g. hand like)tuned to stimulus shape (e.g. hand like) Cell responses modulated by task Cell responses modulated by task

demands, if monkey must respond or demands, if monkey must respond or discrimination is hard, the cell response is discrimination is hard, the cell response is enhanced (not related to motivation)enhanced (not related to motivation)

Representing objects in IRepresenting objects in ITT

Prefer 3-D objectsPrefer 3-D objects Object can be defined by luminosity, texture, Object can be defined by luminosity, texture,

motion, speckle sizemotion, speckle size Some selective for normal, not scrambled, Some selective for normal, not scrambled,

faces: overall structure importantfaces: overall structure important Position, retinal image size, orientation Position, retinal image size, orientation

minimally affect response (even faces rotated minimally affect response (even faces rotated in depth can be ‘recognized’)in depth can be ‘recognized’)