Covert orienting of attention controls vigilance decrement at low event rate.

Factors controlling sustained visual orienting were investigated by combining the paradigms of covert orienting and vigilance. Analysis suggests a close relationship between orienting of attention and vigilance which is dependent on the event rate during the vigilance task. At a low event rate both facilitatory and inhibitory effects of orienting are found. Vigilance decrement is related to the accumulation of inhibition over time, supporting Posner, et als 1984 theory. Invalid cues reduce the decrement. At a high event rate, however, neither facilitation nor inhibition effects are reliable, and vigilance decrement is related to limitations of the allocation of attentional capacity, supporting Parasuraman's multifactorial theory. The results suggest that facilitation and inhibition caused by orienting are important opposing mechanisms in visual attention, allowing the nervous system to control the distribution of attention both over visual space and over time.