Multistable phenomena: Changing views in perception

Traditional explanations of multistable visual phenomena (e.g. ambiguous fi gures, perceptual rivalry) suggest that the basis for spontaneous reversals in perception lies in antagonistic connectivity within the visual system. In this review, we suggest an alternative, albeit speculative. explanation for visual multistability - that spontaneous alternations reflect responses to active, programmed events initiated by brain areas that integrate senso ry and non-sensory information to coordinate a diversity of behaviors. Much evidence suggests that perceptual reversals are themselves more closely re lated to the expression of a behavior than to passive sensory responses: (1 ) they are initiated spontaneously, often voluntarily, and are influenced b y subjective variables such as attention and mood; (2) the alternation proc ess is greatly facilitated with practice and compromised by lesions in non- visual cortical areas; (3) the alternation process has temporal dynamics si milar to those of spontaneously initiated behaviors; (4) functional imaging reveals that brain areas associated with a variety of cognitive behaviors are specifically activated when vision becomes unstable. In this scheme, re organizations of activity throughout the visual cortex, concurrent with per ceptual reversals, are initiated by higher, largely non-sensory brain cente rs. Such direct intervention In the processing of the sensory input by brai n structures associated with planning and motor programming might serve an important role in perceptual organization, particularly in aspects related to selective attention.