Directional and orientational tuning of feline striate cortical neurones: correlation with neuronal class.

In a subset of 327 simple and complex cells from the striate cortex of cats anaesthetized with N2O/O2/halothane, a range of receptive field properties were compared. These included directional and orientational selectivity, tuning and symmetry; endstopping; receptive field dimensions; length summation; texture sensitivity; ocular dominance; and resting discharge levels. These properties were related to neuronal class (simple or complex) and to the special, intermediate and standard subdivisions of the complex cell category. Special complex cells showed a high incidence of direction selectivity, were less sharply tuned for orientation, more commonly endstopped, more strongly binocular, tended to have higher resting discharge levels and exhibited greater sensitivity to motion of randomly textured patterns than the other classes of neurones. The remaining classes of complex cells, together with simple cells, were more commonly direction-biased or bidirectional, and more selective for orientation than special complex cells. Standard complex cells were marginally more symmetrically tuned for orientation than the other groups. Simple cells represented the most sharply orientation tuned neurones in the cortex; unlike complex cells of all groups they were insensitive to texture motion, generally had lower levels of maintained discharge, and showed least integration of inputs between the two eyes. Assessed by appropriate measures (minimum response fields in special complex cells; length summation in standard complex cells), standard complex cells had significantly larger receptive fields than special complex cells.