Phasic alertness reverses the beneficial effects of accessory stimuli on choice reaction

Humans respond faster to visual target stimuli when these are accompanied by auditory accessory stimuli. This accessory stimulus effect occurs even though accessory stimuli do not predict which response has to be made. Similar performance benefits occur when auditory stimuli serve as so-called alerting cues by preceding rather than accompanying the visual targets. This latter effect is attributed to phasic alertness, a short-lived increase of the brain's readiness for responding to external information. Phasic alertness and accessory stimulation each have been studied extensively, but it is unclear how the two work in concert. Therefore, the present study investigated how auditory alerting modulates the effects of subsequent accessory stimuli accompanying the targets of a visual choice reaction task. Results showed that accessory stimuli helped performance in the absence of alerting cues but impaired performance when alerting cues had been presented beforehand (Experiment 1). This reversed accessory stimulus effect did not seem due to expectations regarding the combination of accessory stimuli and alerting cues (Experiment 2). Together, the present findings reveal that phasic alertness changes the effects of accessory stimulation in a qualitative fashion: Alerting turns the otherwise helping accessory stimulus into a saboteur of performance.