The influence of stimulus shape on orientation acuity

Orientation acuity was estimated for vertical and oblique bar stimuli. Discrimination thresholds were affected by changes in the length and width of the targets, falling as bar length was increased and, conversely, rising as the bars were made wider. These changes are complimentary, in that overall discrimination performance can be predicted by a single measure of the orientation "entropy" of the target, namely the height-to-width ratio. The data provide support for a model of orientation coding where discrimination performance is not simply a reflection of the signal-to-noise ratio in single cells in the striate cortex