Effects of arousal on biased competition in attention and short-term memory

A recent theory proposes that arousal amplifies the competition between stimulus representations, strengthening already strong representations and weakening already weak representations in perception and memory. Here, we report a stringent test of this arousal-biased competition theory in the context of visual attention and short-term memory. We examined whether pre-trial arousal enhances the bottom-up attentional bias toward physically salient versus less salient stimuli in a multi-letter identification task. Arousal was manipulated by presenting an arousing versus a neutral picture (Experiment 1) or sound (Experiment 2) at the start of each trial. Bayesian statistics revealed strong evidence for the null hypothesis in both experiments: Arousal did not modulate the effects of physical salience on letter identification. The experiments were repeated with EEG measurements and subjective stimulus ratings, which confirmed that the stimuli successfully manipulated physiological and subjective arousal. These results pose a challenge for the arousal-biased competition theory.