Number generation bias after action observation.

Recent studies have demonstrated that conceptual and abstract knowledge could rely on and could be influenced by sensory-motor processing of usual goal-directed actions. In line with this, interactions have been reported between number magnitude and finger grip with, for example, small-magnitude numbers priming grip closure and large-magnitude numbers priming grip aperture. Here, we assessed whether observing a closing or opening grip was able to influence the magnitude of the numbers produced in a random number generation task, and we tested whether this effect was specific to biological hand actions by using non-biological fake hands with the same closure or aperture amplitude. The participants were asked to produce as randomly as possible numbers between 1 and 10 after they observed a change in posture (i.e. grip closing or grip opening) or in colour (i.e. red or blue hand). The results revealed that the participants produced more often small numbers than large ones after observing a grip closing, whereas they produced equally often small and large numbers after observing a grip opening or colour changes. Importantly, this effect was only present for the biological hands but not for the non-biological fake hands. This finding demonstrates that observing a biological grip closing conveys small-magnitude information, which, in turn, influences the mental selection of a numerical response. We discuss our results in the light of the internal random generator process proposed in the domain of numerical cognition and argue that number semantics is stored with a code governed by sensory-motor mechanisms.