Psychophysical and Physiological Evidence for Viewer-centered Object Representations in the Primate N.K. Logothetis and J. Pauls Cerebral Cortex (1995)

Background Theories of object representations Face selective cells Input representation Image Match ? Transformations Recognition Stored memory representations Theories of object representations 3D models (Marr, Biederman) View dependent 2D templates (Basri & Ullman, Poggio) Face selective cells Found in STS Mostly view dependent

Methods Trained three juvenile rhesus macaques on an object recognition task Performed psychophysical tests after training Recorded from the upper bank of the anterior medial temporal sulcus (AMTS) Stimuli: Computer generated ‘wire like’ and ‘amoeboid’ objects

Training Began with training monkeys to recognize a single view of an object presented sequentially among distractor objects Slowly increased rotations up to + or – 90o before training with a new object Feedback with juice reward

Testing

Recordings Recorded from 773 neurons in AMTS

Findings—psychophysical Recognition performance fell off sharply when object rotated more than 30-40o beyond training view Both for wire and amoeboid objects

Findings—psychophysical Interpolation with wire objects Monkeys could interpolate between two training views up to 120o apart Three to five views allowed monkey to generalize to entire ‘great circle’

Findings—psychophysical ‘Pseudo-mirror symmetrical’ wire objects Some of the wire objects have mirror symmetrical 0o and 180o views due to lack of self-occlusion

Findings—psychophysical Viewpoint invariance for ‘basic’ objects among different class distractors

Findings—physiological View specific, object specific cells (71 of 773) Cell responses to distractor views Cell responses to target views

Findings—physiological View invariant, object specific cells (8 of 773)

Findings—physiological

Findings—physiological Multiple cells tuned to different views of the same object

Author’s conclusions: Object recognition depends on training view A small number of stored views can be used to achieve invariance with wire like objects Neurons in IT found that respond selectively to learned objects, mostly to specific views Problems: Highly unnatural stimuli View selective neurons used for recognition or after recognition? Interpolation with self occluded (solid) objects?