N.K. Logothetis and J. Pauls

N.K. Logothetis and J. Pauls

Cerebral Cortex (1995)

Psychophysical and Physiological Evidence for Viewer-centered Object Representations in the Primate

Background

Theories of object representations

Face selective cells

3D models (Marr, Biederman)

View dependent 2D templates (Basri & Ullman, Poggio)

Found in STS

Mostly view dependent

Image Input representation

Match ?

Stored memory representations

RecognitionTransformations

MethodsTrained 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

RecordingsRecorded from 773 neurons in AMTS

Findings—psychophysicalRecognition performance fell off sharply when object rotated more than 30-40o beyond training view

Both for wire and amoeboid objects

Findings—psychophysicalInterpolation 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—psychophysicalViewpoint invariance for ‘basic’ objects among different class distractors

Findings—physiologicalView specific, object specific cells (71 of 773)

Cell responses to target viewsCell responses to distractor views

Findings—physiologicalView 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?