Directional and orientational tuning in the striate cortex of the cat for contrast and textured stimuli

Abstract

1. Striate cortical neurones respond selectively to the orientation of moving contrast bars. The mechanism for that selectivity has alternatively been attributed to the
geniculo-cortleal synapse or Inhibitory intracortical circuitry. Functionally, that selectivity has suggested a role for the single cell in contour analysis in a hierarchical process of feature extraction.
2. Comparison of tuning of complex cells for moving contrast bars and texture-fields has established the mediation of orientation and direction selectivities by separate mechanisms. An unresolved question is the contributions of orientation and direction to the complex cell's response.
3. Tuning for stationary and moving contrast bars, moving spots and fields of visual noise was evaluated. Tuning for a texture- bar moving across a field of visual noise of similar texture and equal mean luminance was compared with tuning for a moving contrast bar and a field of visual noise.
4. Tuning for a stationary contrast bar had poor predictive value for tuning for moving stimuli; timing for a stationary bar was sharper and more symmetrical than for the same bar in motion and preferred direction for a spot was not orthogonal to preferred orientation. Preferred direction for texture motion could be predicted from preferred direction for a spot. Cells bimodal In tuning for a moving texture-field were unimodal in tuning for a spot. These findings are reviewed in the context of models for the role of intrscortical inhibition.
5. Comparison of tuning for a moving texture-bar with a moving contrast bar and texture-field demonstrated that, in the absence of luminance cues, complex cells are sensitive only to texture motion. A role for direction-selective units in the representation of form is suggested.