Regional sensitivity for shape discrimination.

In a task where subjects had to detect smooth deviations from circularity, we assessed whether performance varied with eccentricity. Our stimuli were circular 4th derivatives of Gaussian contours (CD4s) whose radii were sinusoidally modulated. We used D4s of different peak spatial frequencies and overall diameters. Although performance declined with eccentricity for all radial frequencies tested, once scaling was taken into account, sensitivity was similar at all eccentricities. This was the basis of the scale-invariance also exhibited by this task. Thus, shape discrimination does not appear to be a specialized function limited to central vision.