A comparison of visual and auditory reaction time and P300 latency thresholds to acute hypoxia.

To investigate the influence of stimulus modality on the slowing produced by hypoxia, thresholds were estimated using reaction time (RT) and the event-related brain potential P300. Six trained subjects responded to oddball light flashes or tone pips while breathing low-oxygen mixtures that were manipulated to produce arterial blood oxygen saturations (SaO2) ranging from 77-86%. Both RT and P300 were slowed in a dose-dependent manner. The threshold for slowing was independent of stimulus modality for both measures, and estimated to be in the range 81-82% SaO2. P300 amplitude dissociated from the response time measures by exhibiting an inverted-U dose-response function. We draw three conclusions from these results: a) the failure to observe a higher visual threshold for the response time measures is inconsistent with the traditional belief that audition is relatively insensitive to hypoxia; b) the equal sensitivity of P300 latency and RT to hypoxia implicates stimulus evaluation processes in slowing; and c) P300 amplitude may reflect the activity of physiological compensatory mechanisms to hypoxia.