Behavioral indicators of feedforward processing: Visual awareness, attention, and performance

Our department is working on basic research on visual perception, visual awareness and visual attention. In addition, we are dealing with topics like the perception of phobic stimuli, spatial cognition, visual memory, and visuomotor control.

Our main topic of interest is the difference between conscious and unconscious perception. In our experiments, participants are asked to respond to certain stimuli ("targets") by pressing a button or moving a device. These responses are influenced by other stimuli, called primes, which are presented just previously to the targets.

For example, you might be asked to indicate whether a target dot is red or green by pressing a corresponding key as quickly as possible. Then, a red or green prime presented a few dozen milliseconds before can already trigger a motor response. This priming effect is independent of the visibility of the prime; it is essentially the same for conscious and unconscious prime stimuli.

These "response-priming effects" probably occur because prime and target are processed in the visuomotor system in a strictly sequential way, both trying to take control of the same motor response. Such visuomotor processes could rely on the first waves of activation triggered by prime and target stimuli. 

In contrast, becoming aware of the prime seems to rely on complicated processes, leading to intracortical feedback loops and needing more time. In support of this explanation, it can be shown that the earliest observable motor response depends only on characteristics of the prime, but is independent of all characteristics of the actual target. In addition, priming effects are independent of prime visibility.

Currently, we are interested in using priming effects as a "window" into the world of pre-conscious visual processing stages. 

For example, we ask whether visual feats like color or lightness constancy, perceptual grouping, and figure-ground segmentation are already present in pre-conscious processing stages, and whether they require time-demanding recurrent processing or occur with the first feedforward sweep activation. We also investigate the role of stimulus strength of prime and target stimuli, for instance, by checking whether motor activation and priming are stronger in spider-phobics when processing a phobic prime or target picture.

If you want to find out more, check out our please visit our Wikipedia page on "Response Priming" (click "here" for English version).

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