Nadja Jankovic¹, Rachel Yapp¹, Aaron Richardson¹, Vincent Di Lollo¹, Thomas M. Spalek¹; ¹Simon Fraser University

In a visual search task that involves the detection of an oddball amongst distractors (e.g., one red diamond among three green diamonds), responses (RTs) are faster when the search display is preceded by a brief, task-irrelevant stimulus (e.g., white screen flash) on half the trials (“alerting” effect). In a parallel procedure in audition, one of two tones precedes the search display on every trial. Longer RTs are observed if the preceding tone is infrequent (20%) rather than frequent (80%). This is known as the “deviance distraction” effect. We tested the idea that the violation of an expectation determines whether alerting or distraction effects are obtained. In a first experiment, the task-irrelevant stimulus was a brief white flash on only 20% of the trials. On the remaining 80% the screen remained mid-grey until the search display. Two options are considered. If the white flash violates the expectation established by the 80% grey screens, a deviance distraction effect (i.e., longer RTs) should occur. In contrast, if expectation does not play a role, an alerting effect (i.e., shorter RTs) should occur. We found no RT differences supporting the hypothesis that distraction and alerting effects canceled each other. In a second experiment the invariant grey screen was replaced by a brief black flash on 80% of the trials. From Experiment 1 we expected alerting and distraction effects to cancel each other on white-flash trials but alerting to occur on black-flash trials. No RT differences occurred between white- and black-flash trials, however both RTs were faster than those found in Experiment 1, suggesting alerting effects – but no deviance distraction effects – in both conditions in Experiment 2. This pattern of results prompts a systematic investigation of how probability of preceding task-irrelevant stimuli affects performance on the search task.

Acknowledgements: Natural Sciences and Engineering Research Council of Canada