Impaired avoidance learning after closed-head injury: dissociation between two tasks due to classical conditioning.

Like controls, a Closed-Head Injury (CHI) group learned quickly to press a button during a 3-s warning stimulus in order to avoid a noxious buzzer. In a similar task, however, the CHI group had greater difficulty achieving the learning criterion compared to controls when required to prevent an innocuous visual display (i.e., a circle). The difficulty levels of these two avoidance tasks were identical. The major differences concerned the temporal contiguity of the warning cue with the stimulus to be avoided and the intrinsic aversiveness of the buzzer compared to the appearance of a circle on a computer screen. We hypothesize that, although both tasks were operant in essential character, the buzzer may have produced a degree of classical conditioning. These results suggest that CHI survivors may have some difficulty forming connections between arbitrary stimuli when performance depends almost entirely upon conscious, effortful processing. When a stimulus is sufficiently noxious to be capable of producing an affective or autonomic response, however, automatic processes may aid in the formation of associations.