Spatial filters and the localization of luminance changes in human vision

Relative location acuities similar to vernier acuity were measured for a variety of different luminance profiles and contrasts. The results are interpreted in terms of the extraction of zero-bounded centroids in the responses of a limited range of bandpass spatial filters, with centre frequencies between 3.5 and 30 c/deg. The process by which the outputs of the filters are combined is examined, and MIRAGE, a specific proposal, tested and found to be supported. Analysis of the results obtained at lower contrasts suggests that the major source of noise lies not in the amplification of the filters, but is due to the location of the centroids being distorted by spurious noise zero-crossings. The pattern of noise intrusion is readily explained in terms of MIRAGE.