Lawful relation between perceptual bias and discriminability

Alan Stocker

Abstract: Perception of a stimulus can be characterized by two fundamen- tal psychophysical measures: how well the stimulus can be dis- criminated from similar ones (discrimination threshold) and how strongly the perceived stimulus value deviates on average from the true stimulus value (perceptual bias). We demonstrate that perceptual bias and discriminability, as functions of the stimu- lus value, follow a surprisingly simple mathematical relation. The relation, which is derived from a theory combining optimal encod- ing and decoding, is well supported by a wide range of reported psychophysical data including perceptual changes induced by con- textual modulation. The large empirical support indicates that the proposed relation may represent a psychophysical law in human perception. Our results imply that the computational processes of sensory encoding and perceptual decoding are matched and opti- mized based on identical assumptions about the statistical struc- ture of the sensory environment.