Binocular attributes of length summation and end stopping in cat striate cortex

Length selectivity for each eye was compared as response increment-decrement to optimal sine-wave grating patches, in strongly binocular, striate cortical neurons in adult cats. Neurons were characterized as simple, or as standard, intermediate or special complex, on criteria that included length summation. Length summation was characterized for stimulus length, incremented symmetrically about the receptive field, up to optimal response levels. Many neurons additionally showed end stopping: response decrement to supra-optimal lengths. Optimal length and/or end stopping for each eye differed in most neurons, although the distributions of optimal length or percentage end stopping for each eye were comparable for the overall sample and for each neuronal subclass. However, paired comparisons of length and end-stopping data for each neuron revealed a marked tendency for receptive fields to be relatively smaller on average, but more strongly end stopped, for contralateral input. On the Wilcoxon signed rank test, these differences were statistically significant for standard complex neurons. There was also a tendency for differences in end stopping to be greater and more widely scattered for neurons with near-horizontal than near-vertical orientation preferences. Although the functional value of skew in the distributions of interocular differences in optimal length and end stopping remains conjectural, the scatter and balanced distribution of these differences in length specificity across the neuronal population may provide a basis for encoding visual perspective cues.