EVIDENCE THAT THE SLOWING CAUSED BY ACUTE-HYPOXIA IS MODALITY DEPENDENT

Background: AFM (Additive Factors Method) experiments conducted with v isual stimuli suggest that the slowing produced by acute hypoxia is lo cated at the earliest preprocessing stage of information processing an d that later stages are unaffected (the bottleneck hypothesis). Method s: To determine the contribution of degraded visual functioning to slo wing, we bypassed this modality and measured reaction time in an AFM p aradigm to auditory (Experiment 1) and kinesthetic (Experiment 2) stim uli. In both experiments hypoxia was induced with low oxygen mixtures and arterial blood oxygen saturation (SaO(2)) was controlled at 65%. T ask difficulty was manipulated in Experiment 1 with tones that differe d in intensity and in Experiment 2 with lifted cylinders that differed in weight. Results: The results for Experiment 1 showed an interactio n between task difficulty and hypoxia, indicating slowing of the prepr ocessing stage. Slowing was not found in Experiment 2. The absence of slowing in Experiment 2 is surprising and indicates that slowing may b e confined to vision and audition and may not involve later, more cent ral, stages. We discuss the need to measure cerebral oxygenation in or der to understand the sharp differences between the the bottleneck hyp othesis, developed by controlling SaO(2), and the more traditional beh avioral model which postulates multiple cognitive deficits.