Multistability in perception: binding sensory modalities, an overview

Abstract

This special issue presents research concerning multistable perception in different sensory modalities. Multistability occurs when a single physical stimulus produces alternations between different subjective percepts. Multistability was first described for vision, where it occurs, for example, when different stimuli are presented to the two eyes or for certain ambiguous figures. It has since been described for other sensory modalities, including audition, touch and olfaction. The key features of multistability are: (i) stimuli have more than one plausible perceptual organization; (ii) these organizations are not compatible with each other. We argue here that most if not all cases of multistability are based on competition in selecting and binding stimulus information. Binding refers to the process whereby the different attributes of objects in the environment, as represented in the sensory array, are bound together within our perceptual systems, to provide a coherent interpretation of the world around us. We argue that multistability can be used as a method for studying binding processes within and across sensory modalities. We emphasize this theme while presenting an outline of the papers in this issue. We end with some thoughts about open directions and avenues for further research.

Figure 1.

Illustration of binocular rivalry. Different images are presented to the left and right eyes (‘Stimulus’). The subject experiences switches from perception of one image (face) to the other (house) (‘Percept’). Note that ‘mixed percepts’ (composed of parts of both images) are also experienced (‘piecemeal rivalry’). The phenomenology of binocular rivalry can be experienced with monocular rivalry (see demonstration under the Wikipedia entry).

Figure 2.

Illustration of ambiguous images. The figure in (a) may be perceived as a cube with either the lower left face or the upper-right face in front. The figure in (b) may be perceived as either a vase or two faces in silhouette. The subject experiences switches from perception of one interpretation to perception of the other.

Figure 3.

Illustration of moving plaids. Two series of oblique lines (gratings) with orthogonal directions of movements are superimposed (‘Stimulus’). The subject may perceive the image (‘Percept’) as two gratings moving in opposite directions, or as a single cross-hatched object moving upwards (indicated by the arrow). The percept alternates between the two interpretations.

Figure 4.

Illustration of the verbal transformation effect. A word is presented repeatedly (‘Stimulus’, here ‘life life life’). After some time, the percept may change (‘Percept’), reflecting a different perceptual organization of the sound segments (e.g. ‘fly fly fly … ’), and then may alternate between the two organizations (or other organizations may occur).

Figure 5.

Schematic spectrogram of stimuli used to study auditory streaming. A succession of tones with two different frequencies, A and B, is presented (‘Stimulus’). The subject may perceive either a single stream with a ‘gallop’ rhythm (ABA–ABA–ABA … , illustrated by the green lines connecting A and B in ‘Percept’) or as two regular streams (A–A–A and B—B—B, illustrated by the blue line connecting the A tones and the red line connecting the B tones). The percept can alternate between the two interpretations.

Figure 6.

Illustration of motion quartets (visual and tactile). When a subject is presented with two successive visual images (‘Visual loop’) with two black dots moving from one configuration (on one diagonal) to another (on the inverse diagonal), the subject may perceive either a horizontal or a vertical displacement of the two black dots, and switch from one percept to the other (‘Percept’). The same bistability illusion may be obtained with tactile stimuli (‘Tactile loop’), using motion touch zones on the thumb.

Figure 7.

Illustration of binaral rivalry (olfactory). When a subject is presented with two different odours (‘Stimulus’), one in each nostril, perception may switch from one odour to the other (‘Percept’).

Figure 8.

Stimuli producing visual interocular grouping. Different parts of two images are presented to the left and the right eyes (‘Stimulus’). The subject perceptually reconstructs the original images and experiences switches from perception of one figure to perception of the other (‘Percept’).