Carbon monoxide exposure and auditory duration discrimination

Two young adults performed an auditory duration discrimination task while sitting in an open office (i.e., without sensory isolation). The percentage of errors rose when carboxyhemoglobin (HbCO) readings of 3.2% or 4.7% were produced by a rebreathing method; there was a parallel but statistically insignificant trend at 2.0% HbCO. Analysis of the data by psychophysical measures, however, showed no significant changes of difference threshold, criterion value, or point of subjective equality. After the tape was rearranged to meet criteria of a constant interval, a balanced order of presentation, and psychological rather than physical equality of tone length, eight young adults performed the task better in an isolation booth than in an open office, scores in both situations being unaffected by increases of HbCO to greater than 8%. Further trials with five young adults compared responses before and after administration of 80 ml of CO (HbCO 4.92%); again, no effect of carbon monoxide was seen relative to control experiments. The error score of nonsmoking young adults can be increased by a level of HbCO as low as 3.2%. The likelihood of such a response, however, is markedly influenced by task difficulty, environment, and the arousal of the subjects. Furthermore, the nature of the functional disturbance remains uncertain; psychophysical measures show no significant impairment of auditory duration discrimination.