Federico Paolo, Mirabella Giovanni
Department of Biotechnological and Applied Clinical Sciences, University of L'Aquila, Via Vetoio, 67100, L'Aquila, Italy.
Exp Brain Res. 2014 Apr;232(4):1293-307. doi: 10.1007/s00221-014-3846-8. Epub 2014 Jan 31.
It is solidly established that unequal stimulus frequencies lead to faster responses to the more likely stimulus; however, the effect of this probability bias on response inhibition is still debated. To tackle this issue, we administered two versions of the stop-signal task to 18 right-handed healthy subjects. In one version, we manipulated the frequency of right and left targets appearance when subjects were required to produce speeded responses (no-stop trials) with the right arm, whereas stop signals occurred with equal frequencies after right or left targets (no-stop signal bias). In the other version, we manipulated the frequency of appearance of stop signals after right or left targets, whereas no-stop trials toward right or left targets had the same frequency (stop-signal bias). Surprisingly, we found a very modest, if any, increase in response readiness toward the more frequent stimulus. However, the no-stop signal bias had an effect on the speed of inhibitory control, as subjects were always faster to suppress a movement toward the side where targets were less likely to occur. Differently, the stop-signal bias had a much more powerful effect. In fact, subjects were faster to withhold movements toward the side where targets were more frequent, while they exhibited longer reaction times for reaches toward the more likely targets. Overall, these results suggest that action preparation and action inhibition are independent competing processes, but subjects tend to place automatically greater importance on the stop task.
业已确凿证实，刺激频率不均会导致对更可能出现的刺激产生更快的反应；然而，这种概率偏差对反应抑制的影响仍存在争议。为解决这一问题，我们对18名右利手健康受试者进行了两个版本的停止信号任务。在一个版本中，当要求受试者用右臂做出快速反应（无停止试验）时，我们操纵左右目标出现的频率，而停止信号在左右目标之后出现的频率相等（无停止信号偏差）。在另一个版本中，我们操纵左右目标之后停止信号出现的频率，而对左右目标的无停止试验频率相同（停止信号偏差）。令人惊讶的是，我们发现，对于更频繁出现的刺激，反应准备程度即使有增加也非常轻微。然而，无停止信号偏差对抑制控制的速度有影响，因为受试者总是能更快地抑制向目标出现可能性较小一侧的动作。不同的是，停止信号偏差的影响要大得多。事实上，受试者能更快地抑制向目标更频繁出现一侧的动作，而对于向更可能出现的目标伸手，他们的反应时间更长。总体而言，这些结果表明动作准备和动作抑制是相互独立的竞争过程，但受试者往往会自动更重视停止任务。
