Uncalibrated distortions vs undersampling.

In a recent paper of ours [Hess & Field (1993). Vision Research, 33, 2663-2670], we claim that there was a predictable relationship between position errors and contrast errors for an undersampled system. In this paper we re-state our main points. We feel that the response to that paper by Levi and Klein in the accompanying article does not require us to produce changes in our original position. We believe that the data support the notion that the principal causes of the positional errors in the normal periphery and the in the amblyopic visual system are due to uncalibrated distortions in the local signs of visual neurons. We believe that undersampling plays a major role in producing positional errors only in the far periphery at, or very near, the acuity limit. We maintain that our initial studies provide strong evidence that undersampling is insufficient as an explanation for the positional errors in the periphery of normals (Hess & Field, 1993) or the central field of amblyopes [Hess & Field (1994). Vision Research, 34, 3397-3406.