Motivation and movement: the effect of monetary incentive on performance speed

From observation of human behavior, we know that speed of movement initiation and execution can be influenced by motivational factors, for example we walk faster when in a hurry (sense of urgency) or write faster during an exam (potential reward of good results). However, there is scant experimental evidence for the motivational modulation of movement in man. Experiments in non-human primates have demonstrated shortening of reaction times in response to reward. However, it is not clear how reward might affect performance of reaction time (RT) tasks in humans, and specifically whether warned and unwarned simple and uncued and precued choice RTs are similarly or differentially affected by reward. The effect of monetary incentive on total time (TT, (RT + MT)) was assessed in 16 healthy participants using four paradigms: warned simple RT (wSRT), unwarned simple RT (uSRT), uncued choice RT (uCRT), and precued choice RT (pCRT). wSRT, uSRT, and pCRT tasks all allow advance preparation and preprogramming of the movement, whereas uCRT does not. We found a significant effect of monetary incentive in shortening TTs in wSRT, uSRT, and pCRT tasks, but no effect on the uCRT task. These results demonstrate that monetary incentive can speed up movement initiation and execution in human participants, but only in tasks where preprogramming of the response is possible. This suggests that in reaction time tasks such as these, monetary incentive is having its effect by enhancing preparation of preprogrammed movement, but has little effect when movements cannot be specified in advance. These "RT and reward" tasks provide a useful paradigm for investigation into the effects of monetary incentive on reaction times in man and to study motivational modulation of movement speed in health and disease.