Eleven participants [five males, six females; average age: 32 years (SD ± 6.01); six native English speakers, five non-native English speakers (two Arabic, one

Spanish, one Swedish and one German native speakers); 10 naive, one author (E.S.)] participated in a single experimental session. Author data were not considered in the subjective measurements analyses (see Questionnaires section). All participants were college-educated: five had PhDs and six had MSc degrees. All subjects had normal or AZD9668 chemical structure corrected-to-normal vision. The Barrow Neurological Institute’s Institutional Review Board approved the study (protocol number 10BN142). Experiments conformed with The Code of Ethics of the World Medical Association (Declaration of Helsinki), printed in the British Medical

Journal (18 July 1964; WMA, 1964). Written informed consent was obtained from each participant. Subjects were paid $40 for their participation. In a dark room, participants rested their forehead and chin on the EyeLink 1000 head/chin support, ~57 cm away from a linearized video monitor (Barco Reference Calibrator V, 75 Hz refresh rate). There were two experimental conditions (an Easy mental arithmetic VX 809 task, and a Difficult mental arithmetic task) and one Control condition (fixation only). The experiment consisted of one session with six blocks. Each block included three trials (one trial per condition; each trial was 180 s long). Thus, each subject ran six blocks * three trials * 3 min per trial, for a total of 54 min of recorded data. The first trial in each block was always the Control task, and the last two trials corresponded to the Easy and Difficult mental arithmetic tasks. Trial sequence

STK38 was balanced within each participant and randomized across participants (see Fig. 1B for one example). Participants took short breaks (~2–5 min) after each block. The entire session lasted ~1.45 h. An instruction screen indicating the task to perform preceded each trial. Participants were instructed to look at the center of a black circular target with a diameter of 0.05 degrees of visual angle (deg) presented at the center of the monitor’s screen, on a 50% gray background, in each task (Fig. 1A). A beep sounded whenever the participants’ gaze wandered beyond 3 deg from the fixation target, to remind them to keep looking at it. During the Control task, participants performed no mental arithmetic (i.e. they fixated the central target solely). During the Easy task, participants were instructed to count forwards mentally, as fast and accurately as possible, in steps of two starting at a random three-digit even number (same random numbers for each subject).