Eyelink toolbox

Eye position was sampled at 1,000 Hz by an infrared eye-monitoring camera system (SR Research). Stimuli were controlled by a computer running Matlab (Mathworks) with Psychtoolbox and Eyelink Toolbox. Visual stimuli were colored rectangles on a computer monitor placed 57 cm from the animal and centered on its eyes. A standard solenoid valve controlled the duration of juice delivery. Solenoid calibration was performed daily.

Participants sat in a head and chin rest positioned 57 cm from an ASUS LCD monitor. The resolution of the monitor was 1920 × 1200 within an area that was 44.8 × 28 cm with no pixel interpolation. Stimulus colors were selected after measuring the luminance of each color channel of the monitor with a spectrophotometer. Fixation was monitored online with an EyeLink 1000 (SR Research) recording at 500 Hz, calibrated once before each testing session and recalibrated as required throughout the experiment (see below). The experiment was programmed with the Psychophysics Toolbox Version 3 (Brainard, 1997 (link); Pelli, 1997 (link)) and Eyelink Toolbox (Cornelissen, Peters, and Palmer, 2002 (link)) in MATLAB (The MathWorks).

Video clips were presented centrally on a 24-inch LCD monitor (LG 24MB65PY-B, physical display size of 516.9 × 323.1 mm, resolution of 1920 × 1200 pixels). Viewing distance amounted to approximately 50 cm, resulting in a visual angle for the videos of 38.03° horizontally × 21.94° vertically. Eye movement data were recorded from the right eye using an EyeLink 1000plus system (SR Research, Ontario, Canada) with a sampling rate of 250 Hz. Head location was fixed using a chin rest and a forehead bar.
Autonomic responses were continuously recorded at a sampling rate of 500 Hz during stimulation using a Biopac MP150 device (Biopac Systems, Inc.). Skin conductance was measured at the thenar and hypothenar eminences of the participant’s non-dominant hand by a constant voltage system (0.5 V) using a bipolar recording with two Hellige Ag/AgCl electrodes (1 cm diameter) filled with 0.05 M NaCl electrolyte. An electrocardiogram (ECG) was recorded using mediware Ag/AgCl electrodes (servoprax, Wesel, Germany) attached to the manubrium sterni and the left lower rib cage. The reference electrode was placed at the right lower rib cage. Stimulus presentation and data collection were controlled using the Psychophysics Toolbox^{42 (link)} on MATLAB R2011b (MathWorks, Natick, MA, USA), and the EyeLink Toolbox^{43 (link)}.

Stimuli were presented on a VIEWPixx monitor (VPixx Technologies Inc., Canada) running in M16 mode (16-bit input resolution, 10–12 bit internal resolution) in a darkened room. The display had a spatial and temporal resolution of 1920 × 1080 and 120 Hz, respectively, and was calibrated to ensure a linear gamma correction. The luminance of white, grey, and black pixels was 105.70, 58.33, and 0.21 cd/m², respectively. Observers viewed the stimulus display binocularly at a viewing distance of 60 cm with their heads stabilised by a chin and forehead rest.
Eye movements (single eye) were recorded with a sampling rate of 1000 Hz with an Eyelink 1000 (SR Research Ltd., Ontario, Canada). Experimental software was written in MATLAB (MathWorks, Natick, MA) using the Psychophysics Toolbox (Kleiner et al., 2007 ) and the Eyelink toolbox (Cornelissen, Peters, & Palmer, 2002 (link)). Observers’ responses were given by key press on a standard keyboard.