Second-order feature extraction in the visual cortex: selective and invariant sensitivity of neurons to the shape and orientation of cruciform and corner figures
N A Lazareva, I A Shevelev, G A Sharaev, R V Novikova, A S Tikhomirov (Department of Sensory Physiology, Institute of Higher Nervous Activity and Neurophysiology, Moscow 117865, Russia;
In area 17 of the cat visual cortex nearly all units have a definite
selectivity to orientation of a single light bar flashing in the receptive
field or moving across it. An effective system for image processing needs
also units with selectivity to lines crossing at different angles. Many
neurons (56/174) that we studied in the cat striate cortex significantly (by 3.2 times on average) increased their responses
to cross-like or corner figures flashing in the receptive field as compared
with the single light bar of preferred orientation. We found
71.4% of these neurons to be selective to the configuration and orientation
of these figures with all possible types of invariance of the
neuron's selectivity to form and/or orientation: neurons with selectivity to form of the
figures and invariance to their orientation and, vice versa, units invariant
to configuration but selective to orientation. Some cells (18/56)
were invariant both to form and orientation of the cross-like
or corner figure but sensitive to the appearance of any such figure in
the receptive field. Characteristics of tuning to the shape of the figure
(an angle between its lines) were about the same for a cross and a corner.
We found a direct relation between the orientation-tuning width and selectivity for bars, crosses, and corners. Most cells sensitive to crosses (35/46) responded to the figure with angles of 45° or
90° between the lines. The remainder (11/46) responded
to crosses with angles of 68°. We suggest that the studied units
are suited for the selection of crosses or corners
and play an important role in feature extraction and processing in the
striate cortex.
[The study was supported by the Russian Foundation for Basic Research.]
© 1998 Pion Ltd