2.3. Apparatus for Lip Response Collection

All participants were required to hold a wood stick with their lips devoted to collect the motor responses, as reported in our previous works [13,41,42]. At the end of the stick there was a 15 g weight, with the aim to stabilize the apparatus and make the return to the starting point easier (Figure 2). The proper motor response consisted in lifting the stick from a starting point until the end position was met, after which no more lifting was possible. At the instant when the end position was reached, a circuit was closed providing a +5 V square-wave output. The output signal was transmitted to a PC via the serial port by the Matlab software. After each trial, response time (RespT) was displayed on the screen to give online feedback to the participants.

Schematic illustration of the experimental setup.