Spatial scaling of end-stopped perceptive fields: differences in neural bases of end-zones, flanks and centers.

Length and width spatial interactions associated with a small test line centered on a rectangular background were measured at 0, 5 and 10 deg retinal eccentricities. Results indicated an elongated central region of summation with antagonistic flanks and end-zones comparable to earlier results [Yu, C. & Essock, E. A. (1996). Vision Research 36, 2883-2896]. The extent of the end-zones, flanks and centers (length and width) exhibited significantly different spatial scaling, which was steepest for the end-zones (E2 = 0.45 deg), less steep for the flanks (E2 = 0.77 deg) and least steep for the centers (E2 = 2.05 deg). Perceptive fields measured with concentric circular stimuli showed center and surround scaling equivalent to center and flank scaling, respectively, in line target experiments. These results suggest that: (1) psychophysical end-stopping and flank-inhibition reflect different underlying cortical neural processes; and (2) the spatial interactions apparent on the conventional Westheimer paradigm are partly governed by cortical factors.