Modeling judgments of linear extent

Subjects were asked to make judgments of linear extent, specifically, to assess and reproduce the span between dots, with distances that ranged from 0.5 to 8degrees of visual angle. The errors of judgment were modeled by regressing against linear and Fourier components, yielding a model for each of the 25 subjects who participated in the five experiments and for each session in which the subjects were tested. Most of the models manifested a complex profile of underestimates and overestimates of span as a function of the span being judged. Successive cycles of under- and overestimation of spans appeared as quasiperiodic oscillations in some of the models. We hypothesize that spatial position is encoded by neuron receptive fields that are organized as a mosaic, and these judgment errors may reflect defects in or competitive interaction among these receptive fields.