Age-related effects of temporal contingencies on response speed and memory: an operant analysis

Single-subject methods were used to study influences of extended training and temporal contingencies. Five younger (18 to 21 years) and five older (65 to 74 years) healthy men responded to a series of matching-to-sample discriminations with sample-choice intervals of 0, 5, 10, and 15 s. During baseline sessions, there was no time limit placed on the response to the choice stimuli. Subsequently, correct responses were reinforced only if they occurred within a specified limit. Men of both ages responded faster to the choice stimuli as increasingly stringent limits were imposed, and speeds exceeded those under the baseline condition when the men had been instructed to be accurate and prompt. When the limits subsequently were removed, response speeds decreased somewhat but still were above earlier baseline performances. Under both baseline and time limit conditions, responding was slower when the choice stimuli were delayed, indicating that the procedure tapped short-term memory processes as well as psychomotor speed. Responding also was slower when the stimulus pool involved eight rather than two stimuli. Although performances of the older men improved substantially during the course of training, the younger men improved to the same extent so that age differences were not appreciably reduced.