Spatiotemporal Dynamics of Attention-Induced Distortions and Illusions

Abstract

Selective attention induces perceptual distortions, ranging from repulsion of objects located near the attended area (Suzuki and Cavanagh, 1994 Investigative Ophthalmology and Visual Science 35 2081) to magnification of inattended objects (Tsal and Shalev, 1996 Journal of Experimental Psychology: Human Perception and Performance 22 233 – 243). Two hypothetical mechanisms have been postulated: a shift of receptive field positions away from the locus of attention (receptive-field shift hypothesis) or the enlargement of perceived space around the attended location (spatial-enlargement hypothesis). The aim of the present study was to distinguish between these two hypotheses, by investigating the spatial and temporal properties of attention-induced distortions.

Perceptual judgments on Vernier alignment, line tilt, line length, and size of outlined figures were used to measure attention-induced changes in perception. Attention was induced exogenously (by blinking a specific set of dots around the test stimuli) or endogenously (by instructing the subject to selectively attend the dots). After inducing attention, the test stimuli were briefly flashed. A staircase method was used to measure the attentional effect. The experiment was performed with 3 Korean and 3 German subjects.

A vertical line was perceived as repelled from the locus of attention, and a line segment appeared longer when attention was given to its vicinity. In addition, several well-known illusions (eg the Ponzo and the Gibson illusions) were produced by having the subjects merely attend a set of inducing dots. The effects decreased as the distance between the locus of attention or the time between the onset of attention and the stimulus presentation increased. The results imply that the space-enlargement hypothesis provides a better explanation for the attention-induced changes in perception than the receptive-field-shift hypothesis.