Each NASA-TLX dimension was presented as a visual analog scale with a title and a bipolar descriptor (very low/very high) at each end. Numerical values were not displayed, but values ranging from 0 to 8 (9 points) were assigned to scale

the position RG7422 in vitro during data analysis. The SAM uses a nine-point scale to rate the perceived valence (i.e. level of happiness) and arousal. Values range between 1 and 9, with higher scores indicating higher valence/arousal. Eye position was acquired binocularly and non-invasively with a fast video-based eye tracker at 500 Hz (desktop configuration of the EyeLink 1000, SR Research, instrument noise 0.01 deg RMS). First, we discarded the eye position data corresponding to the time periods in which participants entered their answers on the keypad. Then, we identified and removed blink periods as portions of the raw data where pupil information was missing. We also removed portions of data where very fast decreases and increases in pupil area occurred (> 50 units/sample, such periods are probably semi-blinks where the pupil is never fully occluded; Troncoso et al., 2008). We added 200 ms before and after each blink/semi-blink to eliminate the initial and final parts where the pupil was still partially selleck chemicals occluded (Troncoso et al.,

2008). We identified saccades with a modified version of the algorithm developed by Engbert and Kliegl (2003; Laubrock et al., 2005; Engbert,

ifenprodil 2006a; Rolfs et al., 2006) with λ = 6 (used to obtain the velocity threshold) and a minimum saccadic duration of 6 ms. To reduce the amount of potential noise, we considered only binocular saccades, that is, saccades with a minimum overlap of one data sample in both eyes (Laubrock et al., 2005; Engbert, 2006a,b; Rolfs et al., 2006). Additionally, we imposed a minimum intersaccadic interval of 20 ms so that potential overshoot corrections might not be categorized as new saccades (Møller et al., 2002). Microsaccades were defined as saccades with magnitude < 2 deg in both eyes (Martinez-Conde et al., 2006, Martinez-Conde et al., 2009; Troncoso et al., 2008; McCamy et al., 2013b). To calculate microsaccade properties, such as magnitude and peak velocity, we averaged the values for the right and left eyes (McCamy et al., 2012; Costela et al., 2013). Figure 2 shows the microsaccadic peak velocity–magnitude relationship (main sequence), and the corresponding microsaccade magnitude and peak velocity distributions. We defined fixations as those time periods during which subjects were not blinking or making saccades larger than 2 deg (Otero-Millan et al., 2008). We assumed a linear relationship between microsaccade magnitude and peak velocity rather than a power law one because the value of r2 was always higher for the linear fits (r2: linear 0.908; power law 0.906).