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 8° 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 over-estimation 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.