Irene Petrizzo, Giovanni Anobile, David Burr, Roberto Arrighi
Motor adaptation distorts space
European Workshop on Cognitive Neuropsychology EWCN 2020
Introduction : It has been recently demonstrated that adapting to self-produced motion induces a compression of both perceived numerosity and duration. These results suggest the existence of visuomotor mechanisms that encode numerosity and duration of external as well as internal events. However, according to the ATOM theory, the perception of time and numerosity might also be linked to the processing of spatial information, with all these dimensions tapping a common neural mechanism. To test this hypothesis, we assessed whether motor adaptation also affects the perception of visual stimuli distance, and compared these results to visual adaptation (to high density texture), which is known to distort spatial separation.
Methods : We measured the effects of visual and motor adaptation on the perceived separation of dots. Participants were presented with two vertically aligned dot pairs, separated by about 4° (with random variation of 0.3°), and centered 9.55° either side of fixation. They indicated in 2AFC which pair appeared separated by the shorter distance. In the adaptation trials, the stimuli were preceded by a 5-sec presentation of dense visual texture (visual adaptation), or by the participant rapidly tapping in mid-air with their dominant hand (motor adaptation) for 6 secs (in separate sessions). The effect of adaptation was measured by the shift of the point of subjective equality (PSE) before and after adaptation.
Results : Our data show that adaptation to self-produced fast hand movement induces a significant compression of the perceived spatial separation of the stimuli presented around the tapping location. The magnitude of motor adaptation aftereffects was robust, around 3%, a little smaller than that achieved by visual adaptation (around 10%). Importantly, distortions of perceived distance occurred only for stimuli presented around the adapted location, showing that the effect of both motor and visual adaptation is spatially selective.
Discussion : We report here that the estimated distance of two visual stimuli was compressed by repetitive motor action, similarly to adaptation to dense visual patterns. The spatial selectivity of the aftereffects suggests they do not derive from a decisional bias, but points to spatially selective mechanisms combining motor and visual information. To conclude, our results extend previous reports about the interaction of the perceptual and motor systems in the processing of time and numerosity to the processing of visual space. This is in line with the core idea of the ATOM theory of a shared representation for time, numerosity and space that optimizes the combination of perceptual information with motor planning and execution.
References : Walsh V Trends in cogn sci 7.11 (2003) 483-488 Hisakata R et al Curr Bio 26.14 (2016) 1911-1915 Anobile G et al J of Exp Psychology: General in press
Keywords : Perception & imagery; normal population; group study; adults; not relevant; behavioural, behavioural.