Visual motion processing in the anterior ectosylvian sulcus of the cat.
Scannell, Jack W. Frank Sengpiel, Martin J. Tovae, Philip J. Benson, Colin
Blakemore and Malcolm P. Young.
University Laboratory of Physiology, Parks Road, Oxford, OX1 3PT.
APStracts 3:0042N, 1996.
SUMMARY AND CONCLUSIONS
1) Neurons that are selectively sensitive to the direction of motion of
elongated contours have been found in several cortical areas in many species.
However, in the striate cortex of the cat and monkey, and the extrastriate
area PMLS of the cat, such cells are generally component motion selective,
signalling only the direction of movement orthogonal to the preferred
orientation; a direction that is not necessarily the same as the motion of the
entire pattern or texture of which the cell's preferred contour is part
(Movshon et al. 1985; Gizzi et al. 1990). The primate extrastriate area MT is
the only cortical region currently known to contain a substantial population
of pattern motion selective cells which respond to the shared vector of motion
of mixtures of contours (Movshon et al. 1985; Rodman and Albright 1989; Stoner
and Albright 1992). 2) From analysing published data on the connectivity of
the cat's cortex (Young 1992; Scannell and Young 1993; Scannell et al. 1995)
we predicted that the Anterior Ectosylvian Visual Area (AEV), situated within
the Anterior Ectosylvian Sulcus (AES), might be a higher-order motion
processing area and thus likely to contain pattern motion selective neurons.
This paper presents the results of a study on neuronal responses in AEV. 3)
90% of AEV cells that responded strongly to drifting grating and/or plaid
stimuli were directionally selective (directionality index (DI) > 0.5). For
this group, mean DI = 0.75. Moreover, 55% of these cells were unevequivocally
classified as pattern motion selective and only one neuron was classified as
definitely component motion selective. Thus, high-level pattern motion coding
occurs in the cat extrastriate cortex and is not limited to primate area MT.
4) AEV contains a heterogeneous population of directionally selective cells.
There was no clear relation between the degree of directional selectivity for
plaids or gratings and the degree of selectivity for pattern motion or
component motion. Nevertheless, the 28% of the highly responsive cells were
both more strongly modulated by plaids than gratings and more PM selective
than CM selective. Such cells could correspond to a population of 'selection
units' (Nowlan and Sejnowski 1995) signalling the salience of local motion
information. 5) AEV lacks global retinotopic order but the preferred direction
of motion of neurons (rather than axis of motion, as in MT and PMLS) is mapped
systematically across the cortex. Our data is compatible with AEV being a non-
retinotopic, feature-mapped area in which cells representing similar parts of
'motion space' are brought together on the cortical sheet.
Received 19 October 1995; accepted in final form 7 February 1996.
APS Manuscript Number J702-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 13 March 96