The slowing of visual processing by hypoxia.

An additive factors method (AFM) experiment was undertaken to determine whether the preprocessing and identification stages of information processing are implicated in the slowing of reaction time (RT) by hypoxia. The subjects (n = 14) responded at two levels of light intensity to pairs of lines that differed in length while breathing a low oxygen mixture that produced arterial oxyhaemoglobin saturations ranging between 64%-66%. The results showed a relatively large interaction between light intensity and hypoxia that was interpreted as evidence for slowing of the preprocessing stage. Differences in line length were plotted in terms of Crossman's confusion function and relatively small interactions with both hypoxia and light intensity were found, reflecting increases in slope. The light intensity x confusion level interaction was interpreted as evidence that AFM assumptions may not have been met completely in this experiment. This leads to the possibility that hypoxia slowed the identification stage indirectly rather than directly, although the latter hypothesis cannot be ruled out entirely at present. It is argued that visual slowing probably plays an important role in the disruption of perceptual-motor tasks by hypoxia.