Functional imaging studies during viewing of visual threat stimuli, show faster detection of threat-related cues and activation of the visual cortex, but the functional visual processes underlying these phenomena have not been determined.

Eighteen healthy subjects were pre-selected on the basis of their trait anxiety, in order to form a low- and a high-trait anxiety group. Pattern VEPs were elicited in a baseline and a verbal threat condition with two stimulus contrast magnitudes.

Compared to baseline, threat accelerated contrast perception in the low- but not the high-trait anxiety group, as evidenced by significant reductions in P100-latency. This reduction in the low anxiety group was greater with increasing stimulus contrast magnitude, consistent with a multiplicative gain control mechanism.

The efficiency of the P100-latency reduction mechanism depends on trait anxiety, in a manner reminiscent of the inverted U-shape curve which relates anxiety to motor/behavioral performance responses. These results are compelling because they extend the effects of anxiety from response systems to perceptual processes. Data based on the effects of threat on visual search studies should be reappraised to include an effect of threat on contrast perception.