Research Group: Visual Attention and Perception

Top-down Processes in early vision Olaf Ziebell Issue. Although it is a well-known fact, that neuronal connections exist in both bottom-up and in top-down direction, only the bottom-up pathway is considered in most pictures of the early visual system. Little is known about the role of the strong connections in top-down direction. The most commonly accepted purpose for these connections is control of attention and perceptual learning. But it seems likely that they also have importance beyond that.

In GrKK since 10/96 as Postdoc

Goal: To measure high level influences of attention, expectation, and memory on performance of early visual perception.

Method: Psychophysical measurements of detection rates and reaction times under different conditions. These conditions include preinformation of target or distractor type, as well as the usage of different backgrounds to examine context effects. At the moment stimulus type means stimulus shape, but future experiments will also use other properties like color, motion or orientation.

Another line of experiments will use transcranial magnetic stimulation (TMS) for the investigation of temporal properties of various types of attention.

Problems: Early vision is known for very fast stimulus processing. To measure such processes in near threshold conditions, short, but very precise stimulus presentation is necessary. This can only be accomplished by very low-level computer programming.

Results so far: Some preliminary data suggest the existence of such higher level influences on early vision. But these results do not meet theoretical predictions from current models of attention. Current experiments will have to show, whether this trend can be confirmed.