Motivational influences on response inhibition

Response inhibition ability is commonly assessed using the stop-signal paradigm, which provides a sensitive and reliable measure of inhibitory ability: stop-signal reaction time (SSRT). SSRT is based on a simple 'race' model, which asserts that on a given stop-signal trial, a "go-process," involving target identification, motor planning, and response initiation, races against a "stop-process," involving stop-signal target identification and motor planning processes. SSRT is assumed to reflect a trait ability that is independent of contextual influences, such as strategic or motivational bias. However, in the stop-signal task, there is a basic tradeoff between responding quickly on "go" trials and correctly withholding a response on "stop" trials. It is unknown whether motivational orientation toward speed or accuracy can influence SSRT. If SSRT varies with strategic control, then estimates of stop latency confirming inhibitory control deficits in clinical populations may reflect different motivational or strategic concerns rather than differences in inhibitory efficacy. Additionally, our interpretations about neural correlates of performance on such tasks are compromised because we cannot distinguish between information related to motivational bias and that related to inhibitory control processes. In this case, alternative procedures and/or measures of inhibitory ability are necessary and related brain correlates should be re-examined. This doctoral thesis addresses this overarching issue by (1) demonstrating motivational influences on behavioral and brain measures of response inhibition ability; (2) offering a novel variant of the stop-signal task and a revised SSRT model that accounts for variations in motivational bias and provides estimates of stop latency and variability; and (3) presenting a working theoretical model to explain the observed phenomena.