Colloquium Vision Science

03. Februar 2015
CITEC, Room 2.015

Thomas Schmidt's research is mainly focused on the role of awareness in visual perception and action, including topics such priming and fast on-line motor control. His research tools are human experimentation with psychophysical methods and mathematical modelling.

Visual stimuli can be classified so rapidly that their analysis may be based on a single sweep of feedforward processing through the visuomotor system. Behavioral criteria for feedforward processing can be evaluated in response priming tasks where speeded pointing or keypress responses are performed towards target stimuli which are preceded by prime stimuli. We apply this method to several classes of complex stimuli. 1) When participants classify natural images into animals or non-animals, the time course of their pointing responses indicates that prime and target signals remain strictly sequential throughout all processing stages, meeting stringent behavioral criteria for feedforward processing (rapid-chase criteria). 2) Such priming effects are boosted by selective visual attention for positions, shapes, and colors, in a way consistent with bottom-up enhancement of visuomotor processing, even when primes cannot be consciously identified. Long-term perceptual learning, e.g., driven by specific phobias, has a similar effect. 3) Many feats of mid-level vision meet the rapid-chase criteria, establishing the theory as a useful tool in identifying visual functions that can be carried out in a feedforward fashion. We argue that "fast" visuomotor measures predominantly driven by feedforward processing should supplement "slow" psychophysical measures predominantly based on visual awareness.