Concerning orientation selectivity, numerous models have been proposed.
Some suggest interactions among collinearly aligned RFs
[28,91], others interactions among adjacent RFs
[35]. Mechanisms of iso-orientation
[3,51] or cross-orientation inhibition
[21,80,86], and iso-orientation inhibition with lateral displacement of the RFs
[35,55] are frequently invoked, for reviews see
[19,39,56,122]. In all these models, the sharpening of orientation tuning is mediated by
inhibitory processes that suppress or reduce excitatory responses to stimuli
of non-optimal orientation. Generally these processes imply
functional schemata which demand a high degree of specificity for
connections among orientation columns. Conversely, in the present study, we
assumed that no specific inhibitory connection between cells exist in relation
to their respective physiological properties.
Inhibition, indeed, occurs through structural schemata which
establish non-specific links among columns of both alike and disparate
orientation tuning. In this way, our inhibition schemata cannot be considered
per se neither as cross-orientation inhibition nor as iso-orientation
inhibition, but they exhibit each time different functionalities according to
the local characteristics of the orientation map.
When the angular spread of inhibition 
is increased, this behavior
becomes more evident and the cell in the center of the inhibitory schemata
receives inhibition from neurons tuned to a large set of orientations.
The minor relevance of high specific connections is supported by the
results obtained in the case of ``circular inhibition''
[92,123] when the kernel loses its anisotropy becoming independent of the spatial arrangement of
orientations.
The non-specific character of our inhibition schemata is in accordance
with recent suggestions that broadly tuned interactions
among cortical neurons may provide the structural basis for many of the
inhibitory mechanisms observed in the visual cortex
such as side-inhibition, cross-orientation inhibition, end-inhibition,
spatial frequency inhibition, etc.
[10,11,25,34,67,86,91,125], but see
[21].