Which Can Explain The Pip-And-Pop Effect During A Visual Search: Multisensory Integration Or The Oddball Effect?

In a dynamic search task, participants were instructed to search for a visual target among various distractors. An auditory stimulus presented in synchrony with a color change of the visual target can improve the efficiency of the search, which is known as the pip-and-pop effect. Some researchers have suggested that the underlying mechanism of this effect is multisensory integration, while others have thought it is due to an oddball stimulation that attracts attention. Utilizing the eye movement technique, we conducted 3 experiments to investigate the pip-and-pop effect and its causes. In Experiment 1, we used a static search paradigm and controlled for the presence or absence of sound cues when the visual target was presented. It turned out that sound had no effect on a static search; that is, no pip-and-pop effect was found. In Experiment 2, we used a dynamic search paradigm in which the participants were instructed to search for vertical or horizontal line segments among various directional distractor segments and as the color of individual segments changed randomly during the stimulus presentation, with and without the sound cue. We found that the pip-and-pop effect was present. The irrelevant sound reduced the mean fixation number and expanded the mean saccade amplitude. In Experiment 3, we also used a dynamic search paradigm and controlled the frequency of synchronization between the sound and the target color change. There were 3 types of sound conditions: No-sound, 1-sound, and 2-sound. The results suggest that as the frequency of synchronization between the sound and the target color change increases (2-sound condition), the pip-and-pop effect also increases. Therefore, we propose that the pip-and-pop effect is more likely to result from the attention attracted by oddball stimuli than from the multisensory integration of synchronized auditory-visual stimuli.