Andrew B. Watson Estimation of local spatial scale

The concept of local scale asserts that for a given class of psychophysical measurements, performance at any two visual field locations is equated by magnifying the targets by the local scale associated with each location. Local scale has been hypothesized to be equal to cortical magnification or alternatively to the linear density of receptors or ganglion cells. Here, we show that it is possible to estimate local scale without prior knowledge about the scale or its physiological basis. THE CONCEPT OF LOCAL SCALE Visual spatial sensitivity varies across the visual field in an orderly way, generally declining with distance from the point of fixation.1-4 This variation has complicated our understanding of spatial vision, since whatever we discover to be so at one point in the visual field may not be so at another. For those who wish to model spatial sensitivity, this variation has introduced an additional dimension along which all parameters of the model might conceivably vary. However, a concept has been introduced by Koenderink et al. 4 and Rovam