| # PolyCAT Acquisition Protocol
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| ## Equipment
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| | Component | Specification |
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| |-----------|--------------|
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| | Eye tracker | EyeLink 1000+ (SR Research) |
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| | Mounting | Head-mounted (desktop mount) |
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| | Recording mode | Binocular |
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| | Sampling rate | 500 Hz per eye (1000 Hz hardware, split binocular) |
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| | Display | 27" 4K LCD monitor |
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| | Resolution | 3840 x 2160 pixels |
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| | Refresh rate | 144 Hz |
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| | Viewing distance | 70 cm |
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| | Background luminance | Gray (0.3 normalized) |
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| ## Display Geometry
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| The pixels-per-degree (PPD) value is computed from the physical display properties:
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| ```
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| Screen diagonal = 27" = 68.58 cm
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| Aspect ratio = 16:9
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| Screen width = 68.58 * (16/sqrt(16^2 + 9^2)) = 59.77 cm
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| Screen height = 68.58 * (9/sqrt(16^2 + 9^2)) = 33.62 cm
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| Pixel pitch = 59.77 / 3840 = 0.01557 cm/px
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| PPD = viewing_distance * tan(1 deg) / pixel_pitch
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| = 70 * tan(1 deg) / 0.01557
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| = 70 * 0.017455 / 0.01557
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| ≈ 78.5 px/deg
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| ```
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| Note: This gives the conversion for uniform pixel density. Since pixels are square on modern displays, horizontal and vertical PPD are equal.
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| ## Calibration
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| - **Calibration type:** HV13 (13-point horizontal-vertical)
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| - **Validation:** Performed before each block
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| - **Drift check:** Before each trial (fixation on cue position)
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| - **Drift retry limit:** 1 attempt, max 10 seconds
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| - **Re-calibration:** Triggered if drift check fails
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| ## Saccade Detection Parameters
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| The EyeLink built-in saccade detection was configured with:
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| | Parameter | Value |
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| |-----------|-------|
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| | Velocity threshold | 30 deg/s |
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| | Acceleration threshold | 8000 deg/s^2 |
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| Fixations are defined as periods between saccades (EyeLink cognitive configuration).
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| ## Experiment Design
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| ### Structure
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| Each participant completed 2 parts (A and B), typically on separate days.
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| Each part consists of:
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| - 9 mini-blocks of 39 trials each = 351 trials
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| - 36 image trials + 3 empty trials per block
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| - 1 memory probe after each block
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| ### Trial Sequence
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| 1. **Drift check** — Participant fixates on a cue at one of 9 grid positions (3x3 grid at 960/1920/2880 x 540/1080/1620 px). Max 10 s, 1 retry.
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| 2. **Stimulus presentation** — Image displayed through polygon aperture for 4.0 seconds.
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| 3. **Inter-trial interval** — Blank screen for 0.5 seconds.
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| ### Stimuli
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| - **Images:** 600 images from the CAT2000 dataset across 6 categories:
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| - Fractal, Object, OutdoorNatural, Random, Satelite, Sketch
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| - 100 images per category (102 available, 100 used per part assignment)
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| - **Polygon apertures:** 27 shapes with systematically varied geometric properties
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| - See `data/manifests/polygon_geometry.csv` for center coordinates
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| - See `data/stimuli/polygons/*.json` for vertex definitions
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| - **Aperture scale factor:** 1987 (applied uniformly)
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| ### Memory Task
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| After each block, a memory probe image was shown for 3 seconds:
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| - Participants judged whether the image was "old" (seen in that block) or "new"
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| - Response time and accuracy recorded
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| - Purpose: ensure attentive viewing
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| ### Fixation Cue Positions
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| A 3x3 grid of possible fixation cue locations:
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| | Grid ID | X (px) | Y (px) |
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| |---------|--------|--------|
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| | grid_11 | 960 | 540 |
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| | grid_12 | 1920 | 540 |
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| | grid_13 | 2880 | 540 |
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| | grid_21 | 960 | 1080 |
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| | grid_22 | 1920 | 1080 |
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| | grid_23 | 2880 | 1080 |
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| | grid_31 | 960 | 1620 |
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| | grid_32 | 1920 | 1620 |
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| | grid_33 | 2880 | 1620 |
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| ## Data Collection Timeline
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| Data was collected between January 15, 2026 and February 25, 2026. Most participants completed Part A and Part B on separate days.
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| ## Split Sessions
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| Some participants required multiple session folders to complete a single part (due to experiment restarts or technical issues). In these cases:
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| - Trials are concatenated across sessions using `trial_uid` as the unique key
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| - For overlapping trials (recorded in multiple sessions), the later session's data takes precedence
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| - The `sessions.csv` metadata file labels these as `split_primary`
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