Eye Tracking

Eye movements were recorded with an EyeLink 1000 system (SR Research Ltd., Ottawa, Canada) at 1000 Hz, calibrated using a 9-point grid at the start of each session and after each break. A fixation cross preceding each scene served as a drift-correction target; the next scene appeared only after successful correction. Gaze position data were aligned to the MEG recording via triggers sent at trial onset.

Precision

• Mean 9-point calibration error: 0.268 degrees (95% CI [0.227, 0.306])

• Pre-scene drift correction magnitude: median 0.440 degrees (IQR 0.270-0.670 degrees), with 92.9% of corrections below 1.0 degree (95% CI [89.4, 96.3])

Event Detection

Saccades and fixations were detected using a velocity-based algorithm (Engbert & Mergenthaler, 2006): for each session, samples exceeding five standard deviations of the sample-wise velocity were classified as saccades, and all remaining non-blink samples were classified as fixations. Fixations shorter than 50 ms or longer than 1000 ms, and the last fixation of each trial, were excluded from analysis.

Gaze Event Counts

Across all participants and sessions, scene viewing produced 203,356 fixations (mean 40,671 per subject, 95% CI [37,966, 44,548]), 213,810 saccades (mean 42,762 per subject, 95% CI [39,684, 46,777]), and 9,954 blinks (mean 1,991 per subject, 95% CI [1,173, 2,841]). The captioning task (see Semantic Captioning Task) produced an additional 61,624 fixations, 56,047 saccades, and 18,097 blinks.

Fixation durations (n = 199,289, top 2% outliers removed) had a median of 254.4 ms (95% CI [230.8, 273.6]; IQR 196.0-345.6 ms). Saccade durations (n = 209,541) had a median of 25.2 ms (95% CI [23.4, 28.0]; IQR 14.2-35.0 ms) – both consistent with established values for free viewing of natural scenes.

Loading Eye-Tracking Data

pyAVS loads and enriches eye-tracking events via pyavs.load_eye_events() and pyavs.load_and_enrich_eye_events(), which apply the corrections described in Known Issues (e.g. multi-saccade cleanup, trigger-delay correction). See AVSComposer Guide for the recommended combined MEG + eye-tracking workflow.