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Psychophysical and Physiological Evidence for Viewer-centered Object Representations in the Primate. N.K. Logothetis and J. Pauls. Cerebral Cortex (1995). Background. Input representation. Image. Match ?. Transformations. Recognition. Stored memory representations. - PowerPoint PPT Presentation
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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?