Complementary Hand Responses Occur in Both Peri- and Extrapersonal Space

Human beings have a strong tendency to imitate. Evidence from motor priming paradigms suggests that people automatically tend to imitate observed actions such as hand gestures by performing mirror-congruent movements (e.g., lifting one’s right finger upon observing a left finger movement; from a mirror perspective). Many observed actions however, do not require mirror-congruent responses but afford complementary (fitting) responses instead (e.g., handing over a cup; shaking hands). Crucially, whereas mirror-congruent responses don't require physical interaction with another person, complementary actions often do. Given that most experiments studying motor priming have used stimuli devoid of contextual information, this space or interaction-dependency of complementary responses has not yet been assessed. To address this issue, we let participants perform a task in which they had to mirror or complement a hand gesture (fist or open hand) performed by an actor depicted either within or outside of reach. In three studies, we observed faster reaction times and less response errors for complementary relative to mirrored hand movements in response to open hand gestures (i.e., ‘hand-shaking’) irrespective of the perceived interpersonal distance of the actor. This complementary effect could not be accounted for by a low-level spatial cueing effect. These results demonstrate that humans have a strong and automatic tendency to respond by performing complementary actions. In addition, our findings underline the limitations of manipulations of space in modulating effects of motor priming and the perception of affordances.人类具有强烈的模仿倾向。来自运动启动范式（motor priming paradigms）的研究证据表明，人们会自动倾向于通过做出镜像一致动作来模仿观察到的手部手势——例如从镜像视角观察到左侧手指活动时，抬起自己的右侧手指。然而，许多观察到的动作并不需要做出镜像一致的回应，而是需要互补适配的回应，例如递出杯子、握手等场景。至关重要的是，镜像一致的回应无需与他人发生肢体互动，而互补动作则通常需要此类互动。鉴于绝大多数运动启动相关实验均使用了缺失背景信息的刺激材料，互补回应的空间或互动依赖性尚未得到系统评估。为解决这一问题，我们让被试完成一项任务：根据画面中演员做出的手部手势（握拳或张开手掌），做出镜像或互补动作，且演员的位置分为可及范围内与可及范围外两种。在三项实验中，我们发现，当观察到张开手掌的手势（即‘握手’动作）时，被试做出互补手部动作的反应时显著短于镜像动作，且响应错误率更低，这一结果不受演员感知到的人际距离影响。该互补效应无法通过低水平空间线索效应解释。上述结果证明，人类具有强烈且自动化的互补动作回应倾向。此外，我们的研究结果也表明，通过空间操纵来调节运动启动效应与可供性（affordances）感知的思路存在局限性。