INTEGRATION OF FORM AND MOTION IN THE ANTERIOR SUPERIOR TEMPORAL POLYSENSORY AREA (STPa) OF THE MACAQUE MONKEY. Oram, M. W. and D. I. Perrett. School of Psychology, University of St. Andrews, Fife, KY16 9JU, U.K.
APStracts 2:0375N, 1995.
SUMMARY AND CONCLUSIONS
1. Processing of visual information in primates is believed to occur in at least 2 separate cortical pathways, commonly labelled the "Form" and "Motion" pathways. This division lies in marked contrast to our everyday visual experience in which we have a unified percept of both the form and motion of objects, implying integration of both types of information. We report here on a neuronal population in the anterior part of the superior temporal polysensory area (STPa) sensitive to both form (heads and bodies) and selective for motion direction. 2. A total of 161 cells were found sensitive to body form and motion. The majority of cells (125/161, 78%) responded to only one combination of view and direction (termed unimodal cells, e.g. left profile view moving left, not right profile moving left or left profile moving right). We show that the response of some of these cells is selective for both the motion and the form of a single object not simply the juxtaposition of appropriate form and motion signals. 3. A smaller number of cells (9/161, 6%) responded selectively to two, opposite, combinations of view and direction (e.g. left profile moving left and right profile moving right but no other view and direction combinations). A few cells (4/161, 2%) showed "object- centred" selectivity to view and direction combinations, responding to all directions of motion where the body moves in a direction compatible with the direction it faces, for example, responding to left profile going left, right profile going right, face view moving towards, back view moving away but not other view and direction combinations. 4. The majority of the neurones (106/138, 77%) selective for specific body view and direction combinations responded best to compatible motion (e.g. left profile moving left), and one quarter (23%) showed selectivity for incompatible motion (e.g. right profile moving left). 5. The relative strengths of motion and form inputs to cells in STPa conjointly sensitive to information about form and motion were assessed. The majority of the responses (95%) were characterised as showing non-linear summation of form and motion inputs. 6. The capacity to discriminate different directions and different forms was compared across three populations of STPa cells, namely those sensitive to (a) form only, (b) motion only and those sensitive to (c) both form and motion. The selectivity of the latter class could be predicted from combinations of the other 2 classes. 7. The response latencies of cells selective for form and motion are on average coincident with cells selective for direction of motion (but not stimulus form). Both these cell populations have response latencies on average 20 ms earlier than cells selective for static form. 8. Calculation of the average of Early response latency cells (cells whose response latency was under the sample mean) suggests that direction information is present in cell responses some 35 ms before form information becomes evident. Direction information and form information become evident within 5 ms of each other in the average Late response latency cells (those cells whose response latency was greater than the sample mean). Inputs relating to movement show an initial response period which does not discriminate direction. The quality of initial direction discrimination appeared to be independent of response latency. The initial discrimination of form was related to response latency in that cells with longer response latencies showed greater initial discrimination of form in their responses. We argue that these findings are consistent with form inputs arriving to area STPa approximately 20 ms after motion inputs into area STPa. 

Received 1 November 1995; accepted in final form 7 December 1995.
APS Manuscript Number J690-4.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 23 December 95