The effects of hypoxia on auditory reaction time and P300 latency

A predominant feature of hypoxia is that it slows information processing. Evidence is accumulating that early visual mechanisms are an important locus of this slowing. Audition is believed to be insensitive to hypoxia, implying relatively less slowing with auditory stimuli. Subjects breathed air or a low oxygen mixture (65% arterial oxyhemoglobin saturation) while RT (reaction time) and the EEG were collected to oddball binaural tone pips at 500 Hz, 1000 Hz, and 4000 Hz. Hypoxia slowed RT and the event-related brain potential P300 in a correlated manner and by an identical amount that was generally independent of frequency. On the assumption that P300 indexes the time to evaluate a stimulus and RT indexes this time plus the time to select and execute a response, stimulus evaluation is implicated as a major locus of slowing in this experiment. The amount of slowing was comparable to that found previously with RT and P300 to visual stimuli. It may be that audition is more sensitive to hypoxia than is currently believed, at least where the speed of processing is concerned.