Towards a general theory of the visual acuities for shape and spatial arrangement.

A wide range of pattern acuity measurements are presented, and detailed comparisons are made between different acuities for different stimuli and tasks. The most striking finding is that only a small number of cues and mechanisms are involved, and there are thus considerable inhomogeneities in spatial perception, even under focused attention and foveal viewing. A theory for pattern acuity is elaborated, bringing the pattern acuity phenomena into a more general scheme for the visual perception of spatial pattern. Four distinct mechanisms are required to account for all the data. Two of these analyse the shape of small segments of contour using high grade position and slope information; the other two relate the positions of these segments also using position and slope information, but of lower grade.