Psychophysics toolbox version 3

Stimuli were generated using MATLAB 8.5 (The MathWorks) and Psychophysics Toolbox, version 3 (Brainard, 1997 (link); Pelli, 1997 (link)). A DLP projector (PROPixx; VPixx Technologies) showed the stimuli at a refresh rate of 120 Hz centered onto a translucent screen (25 horizontal × 16 vertical degrees of visual angle [DVA]). The screen was located in front of the participant (viewing distance, 125 cm) within the dimly lit, magnetically shielded MEG room. Stimulus timing was controlled with a data and video processing peripheral (DATAPixx; VPixx Technologies) and monitored via a photograph diode placed at the upper left corner of the projection screen. The delay between trigger and stimulation onset was corrected with this method.

The functional study was conducted in a single session. The participants performed the same task three times, once for each digit (thumb (D1), index (D2), and little (D5)) of the right hand. The task consisted of flexing one finger from an extended position periodically following a visual cue. The visual cue was projected on a screen at the end of the scanner’s bore, which the participants viewed using a mirror. The visual cue was generated in ‘Matlab’ (The MathWorks, Natick, United States) using the ‘Psychophysics Toolbox Version 3’ (Brainard 1997 (link); Kleiner et al. 2007 ). The task paradigm consisted of 30 s of baseline with one-minute blocks: 30 s paced flexing-extension at 1 Hz and 30 s rest, repeated ten times, resulting in 10 min and 30 s of acquisition for each digit (defined as one run). For this task, flexion of D5 usually resulted in co-movement of D4 and the distal phalanx of D3. Nevertheless, we refer to this movement as ‘D5’. All participants underwent approximately 32 min of functional data recording, encompassing three 10-min runs, one for each digit. A functional localizer was used prior to the three-digit acquisition runs to ensure the left primary sensorimotor areas coverage. The stimulus paradigm consisted of fingertapping with 30 s of baseline, then alternating between 12 s of movement, and 24 s of rest, using a 3D EPI gradient echo sequence.

Stimuli were presented on a 19-inch CRT monitor (1024 x 768 pixels) at 100 Hz. Participants were seated with their head resting on a chin and forehead rest in order to reduce head movements. The eyes were horizontally and vertically aligned with the center of the screen at a distance of 62 cm. Eye movements were recorded with the EyeLink 1000 system (detection algorithm: pupil and corneal reflex; 1000 Hz sampling; saccade detection was based on a 30 deg/s velocity and 9500 deg/s² acceleration thresholds). Participant responses in the orientation perception task were recorded on a standard keyboard. A five point-calibration on the horizontal and vertical axes was run at the beginning of each experimental block. The programs for stimulus presentation and data collection were written in MATLAB (MathWorks) using the Psychophysics Toolbox Version 3 [47 (link)], [48 (link)], and Eyelink Toolbox extensions [49 (link)].

The psychomotor vigilance task (PVT) is a simple but mentally demanding reaction time test, which is often used in research on sustained attention and fatigue [17 (link)]. In the present study, a 30 min version of PVT was administered (Figure 1). During the test, subjects were required to monitor three adjacent boxes representing a millisecond counter. Once the counter occurred in the center of a computer monitor, they needed to respond by pressing the space bar as quickly as possible. Subjects were given a maximum of 1 s to stop the counter and received their reaction time (RT) after the counter was presented. The interval of counters was 2-10 s (mean = 6 s), and the task included 300 trials in total. The stimulus presentation was programmed with the Psychophysics Toolbox Version 3 (http://psychtoolbox.org) for MATLAB (The MathWorks, Inc., Natick, MA, US).