Manipulation of Arousal by Caffeine Reduces Metacontrast Masking Mostly When Target and Mask Shapes Are Incongruent

Abstract

Metacontrast masking is a popular method used to control target accessibility for explicit perception. It is thus a valuable tool in research on preconscious processing, consciousness mechanisms, and visual sensory interactions. However, the dependence of metacontrast effects on nonspecific factors determining subjects’ general arousal level has not been studied. We manipulated arousal by caffeine versus placebo treatment and found, instead of the expected uniform improvement in target perception with caffeine, an intricate interaction between target-to-mask temporal delay, congruence between target and mask shapes, and arousal condition. Caffeine improved target perception mostly when a longer SOA was used in combination with shape-wise incongruent target-mask pairings. Possible reasons for this effect are discussed.