Professor Nikolay Petkov 
Head of Computer Science Department, Groningen University, The Netherlands  

Title: Bringing information science and neurobiology together:
Computational Models of Grating and Bar Cells

Abstract:
Bringing information science and neurobiology together: Computational
Models of Grating and Bar Cells

Computational models of periodic- and aperiodic-pattern selective cells,
also called grating and bar cells, respectively, are proposed. Grating
cells are found in areas V1 and V2 of the visual cortex of monkeys and
respond strongly to bar gratings of a given orientation and periodicity
but very weakly or not at all to single bars. This non-linear behaviour,
which is quite different from the spatial frequency filtering behaviour
exhibited by the other types of orientation selective neurons such as
the simple cells, is incorporated in the proposed computational model by
using an AND-type non-linearity to combine the responses of simple cells
with symmetric receptive field profiles and opposite polarities. 
The functional behaviour of bar cells, which are found in the same areas
of the visual cortex as grating cells, is less well explored and
documented in the literature. In general, these cells respond to single
bars and their responses decrease when further bars are added to form a
periodic pattern.

These properties of bar cells have been  implemented in a computational
model in which the responses of bar cells are computed as thresholded
differences of the responses of corresponding simple (or complex) cells
and grating cells. Bar and grating cells seem to play complementary
roles in resolving the ambiguity with which the responses of simple and
complex cells represent oriented visual stimuli, in that bar cells are
selective only for form information as present in contours and grating
cells only respond to oriented texture information. The proposed model
is capable of explaining the results of neurophysiological experiments
as well as the psychological observation that the perception of texture
and the perception of form are complementary processes.

Short bio-data about Professor Petkov:

Nikolay Petkov is professor of computer science, holding a chair of
parallel computing at the University of Groningen in the Netherlands. He
is also director of research of the Institute of Mathematics and
Computing Science, head of the Department of Computer Science and head
of the Centre for High Performance Computing of the same university.
He got his D.Sc. (Dr.sc.techn.) degree in Computer Engineering
(Informationstechnik) from Dresden University of Technology. Prior to
joining the Computing Science Department of the University of Groningen,
he held research positions at the University of Wuppertal, the
University of Erlangen-N\"urnberg, the Academy of Sciences of GDR
in Berlin, the Academy of Sciences of Slovacia in Bratislava and Dresden
University of Technology.

Nikolay Petkov is the author of the books {\em Systolische Algorithmen
und Arrays} (Berlin: Akademie-Verlag, 1989) and {\em Systolic Parallel
Processing} (Amsterdam: North-Holland, Elsevier Sci. Publ., 1993) and
of further 70 scientific papers; he also holds several patents. He is
member of the editorial boards of the journals {\em Parallel Computing}
(North-Holland), {\em Parallel Algorithms and Applications}
(Gordon and Breach) and {\em Real-Time Imaging} (Academic Press) and of
a number of Dutch and international professional bodies.  In 1989 he has
been awarded an Alexander von Humboldt scholarship of the
Federal Republic of Germany.

When:  12 noon, Friday 28 August

Where:   Commerce CO 2.07