Previous research has suggested that oral respiration may disturb cognitive function and health. The present study investigated whether oral respiration negatively affects visual attentional processing during a visual search task. Participants performed a visual search task in the following three breathing conditions: wearing a nasal plug, wearing surgical tape over their mouths, or no modification (oral vs. nasal vs. control). The participants searched for a target stimulus within different set sizes of distractors in three search conditions (orientation vs colour vs conjunction). Experiment 1 did not show any effect due to respiration. Experiment 2 rigorously manipulated the search efficiency and found that participants required more time to find a poorly discriminable target during oral breathing compared with other breathing styles, which was due to the heightened intercept under this condition. Because the intercept is an index of pre-search sensory processing or motor response in visual search, such cognitive processing was likely disrupted by oral respiration. These results suggest that oral respiration and attentional processing during inefficient visual search share a common cognitive resource.
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