Respiratory phases are associated with the performance on various cognitive tasks. This paper reviews behavioral and psychophysiological studies that compared the effects of inhalation and exhalation phases on perception and cognition. First, previous findings are summarized, based on psychological functions such as simple motor reaction, attention, and memory. Second, four methodical difficulties inherent in conducting such studies are discussed: choice of respiratory route (i.e., nasal vs. oral), manner of breathing (i.e., spontaneous vs. controlled), instruction on how to breathe, and manipulation of the timing of stimulus presentation. Finally, several research questions are raised to understand the relationship between respiratory phases and psychological functions.
