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laBran
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PolyCAT

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eye-tracking
saliency
visual-attention
gaze
fixations
polygonal-aperture
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PolyCAT / docs /file_formats.md
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PolyCAT File Formats

Gaze TSV (data/gaze/*.tsv)

Tab-separated sample-level gaze data. One file per session, named {participant_id}_part{part}_{session_id}.tsv.

  • Sampling rate: 500 Hz per eye (binocular recording; hardware rate 1000 Hz split between eyes)
  • Scope: Only samples during stimulus presentation (4.0 s per trial) are included
  • Eyes: One row per sample per eye (binocular sessions produce 2 rows per timestamp)

Validity codes

Code Meaning
0 Valid gaze sample (within screen bounds 0-3840 x 0-2160)
1 Missing or out-of-range (blink, track loss, or coordinates outside screen)

Fixations CSV (data/fixations/fixations_all.csv)

Comma-separated fixation events. Fixations detected by EyeLink's built-in algorithm with:

  • Saccade velocity threshold: 30 deg/s
  • Saccade acceleration threshold: 8000 deg/s^2

Only fixations starting during stimulus presentation are included. Fixation end_time_ms is clamped to stimulus offset.

Per-participant files

Individual files at data/fixations/per_participant/{participant_id}_fixations.csv with the same schema.

Saliency Maps

NumPy format (data/saliency_maps/by_polygon/{polygon_id}/{image_id}_fixmap.npy)

  • 2D float32 array at stimulus resolution (3840 x 2160)
  • Gaussian kernel sigma = 1.0 degrees visual angle (~78.5 pixels)
  • Values outside polygon aperture set to 0
  • Normalized to sum to 1 (probability distribution)
  • Only generated for polygon-image combinations with >= 3 observers

PNG format (data/saliency_maps/by_polygon/{polygon_id}/{image_id}_fixmap.png)

  • Grayscale visualization of the saliency map
  • 8-bit, linearly scaled from 0 (min) to 255 (max)

Scanpaths (data/scanpaths/{participant_id}/{trial_uid}.csv)

One CSV per trial, containing the ordered fixation sequence.

Columns: fixation_index, start_time_ms, end_time_ms, x_px, y_px, duration_ms

MATLAB Export (data/fixations/fixations.mat)

CAT2000-compatible MATLAB struct:

fixations.x       % double vector: x positions (pixels)
fixations.y       % double vector: y positions (pixels)
fixations.dur     % double vector: durations (ms)
fixations.subj    % cell array: participant IDs
fixations.img     % cell array: image IDs
fixations.polygon % cell array: polygon IDs (PolyCAT extension)

Coordinate System

Screen pixels: 3840 x 2160, origin top-left. x_px increases rightward, y_px increases downward.

Degrees: Relative to screen center (1920, 1080 px).

Conversion formula:

x_deg = (x_px - 1920) / ppd
y_deg = (y_px - 1080) / ppd

Where ppd (pixels per degree) is computed from:

  • Screen diagonal: 27 inches = 68.58 cm
  • Resolution: 3840 x 2160 px
  • Screen width: 59.77 cm, height: 33.62 cm (from diagonal + 16:9 aspect ratio)
  • Viewing distance: 70 cm
  • Pixel pitch = screen_width / horizontal_pixels = 59.77 cm / 3840 ≈ 0.01557 cm/px
  • 1° at 70 cm = 70 × tan(1°) ≈ 1.2228 cm
  • ppd = 1.2228 / 0.01557 ≈ 78.5 px/deg

Time Reference

Context Reference point Units
timestamp_rel_ms (gaze TSV) Stimulus onset for that trial milliseconds
start_time_ms / end_time_ms (fixations) Stimulus onset for that trial milliseconds
ts_* fields (trials.csv) Session start (experiment clock) seconds