An evaluation of the activationist hypothesis of human vigilance.

Abstract

The activationist hypothesis contends that environmental and internal sources of stimulation, working through the reticular formation of the brain, are sources of human alertness. Two experiments were performed to identify stimulus determinants of vigilance decrement in a complex visual monitoring task. The S''s task was to detect a two-digit number as rapidly as possible when it appeared at any one of four stimulus sources. Response latency was the measure of performance. Experiment I sought to manipulate response-produced stimulation arising from the stimulation induced by head and eye movements and immediate memory. Amount of head and eye movements was defined in terms of the spatial separation of sources, and the physiological basis of its stimulation value for alertness was hypothesized to be proprioception and visual collaterals in the reticular formation. Immediate memory was defined as a requirement to remember the four numbers that last appeared at the sources and, when a number appeared, to respond with respect to the last number that had appeared at that source. Immediate memory was hypothesized to provide inputs to the reticular formation from cortical areas. No effects of these variables on vigilance decrement were found. Experiment II asked if the negative results of Exp. I were related to amount rather than variety of stimulation being manipulated. Experiment II introduced variety in head and eye movements by training the pattern of visual observing responses and then changing the pattern on a trial. No effects on vigilance decrement were found. Problems of operationally defining the activationist hypothesis were discussed.