Sensory alternation and vigilance performance: the role of pathway inhibition

Posner's theory of pathway inhibition leads to the expectation that stimulus heterogeneity should attenuate the event rate effect and the decrement function in sustained attention. These predictions were tested through a sensory alternation procedure in which stimulation was shuttled between the auditory and visual modalities. Subjects detected slight reductions in the duration of recurrent flashes of light or bursts of white noise at two event rates (5 and 40 events/min) during a 50-min vigil. Consistent with the model, sensory alternation eliminated the event rate effect. It did not, however, moderate the decrement function. Although pathway inhibition can account for the effects of event rate, other factors are probably responsible for the vigilance decrement.