Psychophysical investigations of global form perception: coding, selection, and dynamics.

A major goal of Professor Suzuki’s research has been to understand the cortical mechanisms that enable people to perceive coherent global forms from retinal illumination patterns that are often ambiguous as to what meaningful forms and configurations are present. Strategically, he has broken down the problem of global form perception into several (non-exhaustive) component processes: (1) encoding of global geometric features, (2) voluntary (attentive) and involuntary (driven by pattern salience modulated by context and experience) selections of global forms into awareness, and (3) maintenance of the multistability of visual awareness (effectively balancing exploration of multiple potential scene interpretations with persistence of a single interpretation). He has used psychophysical paradigms, recently combined with computational modeling, that allow for parametric comparisons of his behavioral results with known physiological properties of visual neurons. Specific experimental techniques used are, (a) brief shape-aftereffect paradigms (for probing population coding and attentional selection of global form features), (b) multistable binocular rivalry (for understanding how the course of spontaneous shifts in visual awareness across different global forms and scene interpretations are influenced by the organization of form coding, prior experience, and cognitive factors such as attention and intention), (c) rapid flicker paradigms (for understanding potential roles of temporal coding in segregating and preserving multistable representations), (d) stochastic resonance paradigms (for investigating the mechanisms that control the dynamics of spontaneous shifts in visual awareness), and (e) visual search paradigms including priming and adaptation manipulations (for understanding experiential factors that adaptively modulate pattern salience and influence automatic pattern selection). These lines of research will provide insights into the ultimate questions of (1) how neural activity throughout the ventral visual stream (the “what” pathway: V1, V2, V4, and IT) generates a seemingly coherent and unitary visual awareness while responding concurrently to different components and aspects of retinal stimulation, and (2) how visual awareness is maintained in a meta-stable state so that it shifts from one coherent scene interpretation to another (driven spontaneously or by attention) at a rate optimized for efficient analyses of the visual environment.