The structure of vigilance.

Vigilance is understood as a primarily behavioral category. Identical stimuli tend to evoke more or less differentiated behavioral responses dependent on a low or high state of vigilance. The rise of vigilance from coma to full attention moves along with increasing differentiation of evoked behavioral responses. With heterogeneous physical, figurative, and verbal stimuli, responses are elicited which can be arranged on an additive (Guttman) scale. Thus, vigilance is suggested to represent a one-dimensional function of the brain.