Our interaction with dynamic objects requires an accurate synchrony of motor actions with visual events. Such a synchrony must overcome two hurdles, namely delays and variabilities in both visual and motor processing. These two issues are addressed here in experiments that manipulate the gain of making movements synchronous with visual events. Participants were presented with six dots displayed at the vertices of a hexagon. The dots were presented in pairs, the stimulus onset asynchrony (SOA) between the first two pairs being equal to the SOA between the last two pairs (500 msec). Participants were instructed to press a key simultaneously with the presentation of the last pair. If they were accurate within a narrow temporal interval, they received 100 points. Depending on the condition shown graphically at the beginning of the trial, they could also lose 200 points if they were too fast or too slow. To maximize gain, there is an optimal time at which participants should anticipate the onset of the final stimulus based on their visual and motor variabilities. We estimated each participant's variabilities from the condition where there were no penalties and measured their efficiency in conditions where a penalty was introduced. We found significant inefficiencies consistent with risk aversion. The results indicate either that participants underestimate their motor variability or that they do not use an optimal strategy to time motor actions with visual events.
Chaire of Excellence from the French Ministry of Research