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Top-down control over visual-contrast sensitivity


de la Rosa,  S
Department Human Perception, Cognition and Action, Max Planck Institute for Biological Cybernetics, Max Planck Society;

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de la Rosa, S., Schneider, B., & Gordon, M. (2007). Top-down control over visual-contrast sensitivity. Poster presented at 30th European Conference on Visual Perception, Arezzo, Italy.

Cite as: http://hdl.handle.net/11858/00-001M-0000-0013-CC7B-F
The visual system is able to adjust its contrast sensitivity to the ambient contrast level. Others have shown that this adjustment is driven by stimulus parameters in a bottom - up fashion and higher order processes by means of attention. We present evidence that contrast sensitivity is under true top - down control. We paired an absolute identification paradigm with a cueing paradigm to measure identification accuracy for four low-contrast stimuli that were intermixed with an occasional high-contrast stimulus. Foreknowledge of the presentation of the high-contrast stimulus was manipulated by presenting valid and invalid cues. In experiment 1 we found that identification and discriminability of low-contrast stimuli was impaired only when the occurrence of the high-contrast stimulus was unpredictable but not when it was predictable. Only a top - down gain-control mechanism whose functions were to maximize discriminability while protecting the system from overload was consistent with the results. Experiment 2 p rovided further support for the idea that an important function of gain control is to protect visual mechanisms from overload.