Sojung Youn¹ (), Jenna Glotfelty¹, Ming-Ray Liao¹, Brian Anderson¹; ¹Texas A&M University

Caffeine is commonly used to improve alertness, and has been shown to impact memory and tasks involving the attention network. However, the influence of caffeine on visual search, attentional capture, and learning-dependent attentional biases is not known. Here, we studied the effects of caffeine on visual search and attentional learning in university-aged participants across two experiments. For both experiments, following caffeine abstention, participants were randomly assigned to receive dissolvable caffeine strips (200mg) or placebo breath strips. Experiment 1 involved a visual search task where participants were asked to identify the rotated direction of the target letter “T” among multicolored “L” distractors. The target could be rendered in a frequent or an infrequent color, and the search trials varied in set size (5 to 50 items). Overall, participants were faster to report the frequent colored target. The two experiment groups exhibited comparable search slopes and frequent color benefits, while the caffeine group exhibited a smaller intercept, indicative of faster target identification and responding. In Experiment 2, participants completed an additional singleton task in which they searched for a shape singleton target. A uniquely-colored distractor was presented on a subset of trials, which could be rendered in a frequent or infrequent color. Similar to the first experiment, participants overall benefited from learning the statistical regularities, but caffeine did not modulate this benefit. Neither did caffeine influence the magnitude of attentional capture or overall response speed. Collectively, it appears that caffeine has little influence on statistically learned attentional biases or the efficiency of distractor filtering. Our data are consistent with an effect of caffeine on the process of target identification, with Experiment 2 suggesting that this benefit is not reducible to faster motor responses.