The brain topography associated with active reversal and suppression of an ambiguous figure

Abstract

Ambiguous figures offer the chance to study endogenous changes in perception in the face of constant stimulus input. We utilised the Necker cube with experimental instructions that maximised either rapid reversal or suppression of the alternating percepts. Our goal was to capture regions crucial to expected, deliberate shifts in perceptual states and compare these to regions associated with suppression of such shifts. Based on evidence for the role of “top-down” factors in ambiguous figure reversals, we expected heightened prefrontal and parietal cortex activation. Data from 15 right-handed adult normals are reported. An ambiguous Necker cube and two versions that stabilised the cube were used as stimulation in a blocked-design fMRI study. We tested for activation differences between the reversal and suppression conditions. Results showed multiple segregated regions of increased activation during reversals that included the left cerebellum and medial frontal regions. The data are discussed as a potential indication that states of strong anticipation and shifts in focal attention can alter perceived salience and generate false perspective information that allows for the illusion of changed object orientation. The data are also consistent with the notion that the process of deliberate ambiguous figure reversal is strongly “top-down” and nonsensory.