Talk:What and where pathways
From Scholarpedia
Reviewer A
Altogether this is a nice little review of the subject. Here are some weak points in need of revision.
1. “What type of stimulus representation is impaired after IT lesions? A great deal of research has been devoted to this question. Generally, such experiments measure whether monkeys can discriminate different stimuli, before and after experimental lesions in IT cortex – and from any such differences, object-processing mechanisms are inferred. A current summary might be that the IT cortex represents aspects of the intrinsic shape of the stimulus that are useful for recognition (e.g., the salient features in a face and their relative positions), generalizing across idiosyncratic aspects of stimulus appearance that depend on specific viewing conditions.” This is misleading, indeed wrong, since it seems to apply to both humans and monkeys Many types of stimulus representations have been impaired after IT lesions in monkeys including discrimination of objects, patterns, colors and size. The only criterion is that the discrimination task is relatively difficult as measured by the performance of normals matched in experience. There is no evidence that “intrinsic “ shape is crucial. Indeed the ‘face’ example is particularly misleading as there is no evidence at all for a specific impairment in face discrimination after IT lesions in monkeys.
2. The OA, OB, OC terminology introduced by von Economo was useful in its day. However the modern delineation of these areas into V1, V2, V3 V4, and MT etc makes these earlier designations of interest only to the historian and very confusing for the reader of a general brief review such as this one. Fig 2 a should be dropped
3. VP is now well established as the ventral part of V3 and should be called that in the figure.
4. There should be some indication that the “two stream” idea is an over simplification and that the “dorsal” stream is divided into a dorsal one (many parietal areas) involved in space and one running down STS involved in movement/. Indeed early parts of the ventral stream have pattern and color components
5. Fig. 3 is not schematic: it is totally imaginary and speculative. There is good evidence for clustering of properties in IT and maybe some for vertical organization but there is no evidence for the columns shown in the figure, except maybe for the face ones.
6. An ordinary reader will be confused about the relation of LOC in humans and V4 and IT in monkeys. This should e clarified even if only to say explicitly that it is unclear.
7. There is no good evidence for IT cells sensitive to any objects except for faces and face components and hands (or body parts) and not for “other biological stimuli.”
8. ..‘evoked potential studies in humans with implanted electrodes have also shed light on the mechanisms by which the primate brain represents objects.” This needs expansion or at least a reference.
Charlie Gross
