docs/data_dictionary.md

# PolyCAT Data Dictionary

This document describes every field in the shared data files.

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## `data/metadata/participants.csv`

One row per recorded participant.

| Field | Type | Units | Description |
|-------|------|-------|-------------|
| `participant_id` | string | — | Participant identifier (e.g., `P01`) |
| `age` | int | years | Age at time of recording |
| `gender` | string | — | Self-reported gender (`Male` / `Female`) |
| `dominant_eye` | string | — | Dominant eye (`left` / `right`) |
| `hardware_sampling_rate_hz` | int | Hz | EyeLink hardware sampling rate (1000 Hz for all participants). Effective per-eye rate depends on recording mode: 1000 Hz for monocular sessions, 500 Hz for binocular sessions. See `recording_mode` in `sessions.csv` for per-session details. |
| `has_part_a` | bool | — | Whether Part A data exists |
| `has_part_b` | bool | — | Whether Part B data exists |
| `n_trials_total` | int | — | Total trials across both parts |
| `n_image_trials` | int | — | Number of image (non-empty) trials |
| `n_empty_trials` | int | — | Number of empty-aperture trials |
| `included_in_release` | bool | — | True if participant is included in the released dataset |
| `exclusion_reason` | string | — | Reason for exclusion (empty if included) |

---

## `data/metadata/sessions.csv`

One row per session folder in the raw data.

| Field | Type | Units | Description |
|-------|------|-------|-------------|
| `participant_id` | string | — | Participant identifier |
| `part` | string | — | Experiment part (`A` or `B`) |
| `session_id` | string | — | Session folder name (e.g., `session_20260118_100426`) |
| `session_label` | string | — | `primary`, `split_primary`, or `extra` |
| `session_timestamp` | ISO 8601 | — | Parsed from session folder name |
| `n_trials` | int | — | Number of data rows in that session's `trials.csv` |
| `included_in_release` | bool | — | True if session contributes to the released dataset |
| `exclusion_reason` | string | — | Reason for exclusion (empty if included) |
| `recording_mode` | string | — | Eye recording mode: `binocular` (both eyes, 500 Hz effective per eye), `monocular_R` (right eye only, 1000 Hz), or `no_gaze_file` (excluded sessions) |

---

## `data/metadata/trials.csv`

One row per trial across all included participants and parts. This is the **source-of-truth trial table**.

| Field | Type | Units | Description |
|-------|------|-------|-------------|
| `participant_id` | string | — | Participant identifier |
| `part` | string | — | `A` or `B` |
| `session_id` | string | — | Session folder this trial came from |
| `trial_uid` | string | — | Unique trial ID: `{pid}_{part}_b{block:02d}_t{trial:02d}` |
| `mini_block` | int | — | Block number (1–9) |
| `trial_in_block` | int | — | Trial number within block (1–39) |
| `trial_type` | string | — | `image` or `empty` |
| `image_id` | string | — | CAT2000 image identifier (e.g., `A_Random_169`) |
| `image_path` | string | — | Relative path to source image |
| `category` | string | — | CAT2000 category (Fractal, Object, OutdoorNatural, Random, Satelite, Sketch) |
| `polygon_id` | string | — | Polygon identifier (e.g., `polygon_25`) |
| `polygon_case` | string | — | Polygon group (`reference`, `convexity_varied`, or `irregular`) |
| `polygon_json_path` | string | — | Relative path to polygon JSON definition |
| `aperture_scale_factor` | int | — | Polygon scaling factor applied during experiment |
| `cue_pos_id` | string | — | Fixation cue grid position (e.g., `grid_11`) |
| `cue_x_px`, `cue_y_px` | float | pixels | Cue position in screen coordinates |
| `cue_x_deg`, `cue_y_deg` | float | degrees | Cue position in degrees from screen center |
| `stimulus_duration_s` | float | seconds | Stimulus presentation time (4.0) |
| `iti_s` | float | seconds | Inter-trial interval (0.5) |
| `center_screen_x_px`, `center_screen_y_px` | float | pixels | Screen center (1920, 1080) |
| `center_screen_x_deg`, `center_screen_y_deg` | float | degrees | Screen center in degrees (0, 0) |
| `fixation_achieved` | bool | — | Whether drift-check fixation was achieved |
| `fixation_attempts` | int | — | Number of drift-check attempts |
| `fixation_total_time_s` | float | seconds | Total time spent on drift check |
| `ts_trial_start` ... `ts_trial_end` | float | seconds | Key event timestamps (experiment clock) |
| `aborted` | bool | — | Whether the trial was aborted |

---

## `data/fixations/fixations_all.csv`

One row per fixation event. Fixations detected by EyeLink's built-in algorithm (velocity threshold 30 deg/s, acceleration 8000 deg/s²).

| Field | Type | Units | Description |
|-------|------|-------|-------------|
| `participant_id` | string | — | Participant identifier |
| `part` | string | — | `A` or `B` |
| `session_id` | string | — | Session folder |
| `trial_uid` | string | — | Unique trial ID |
| `fixation_index` | int | — | Fixation order within trial and eye (1-indexed) |
| `eye` | string | — | `L` (left) or `R` (right) |
| `image_id` | string | — | CAT2000 image identifier |
| `category` | string | — | CAT2000 category |
| `polygon_id` | string | — | Polygon identifier |
| `start_time_ms` | float | ms | Fixation start relative to stimulus onset |
| `end_time_ms` | float | ms | Fixation end relative to stimulus onset |
| `duration_ms` | float | ms | Fixation duration |
| `x_px`, `y_px` | float | pixels | Average fixation position (screen coordinates, top-left origin) |
| `x_deg`, `y_deg` | float | degrees | Fixation position relative to screen center |
| `pupil_size` | float | area | Mean pupil size (EyeLink arbitrary units) |

---

## `data/gaze/*.tsv`

Sample-level gaze data. One TSV file per session. Tab-separated.

| Field | Type | Units | Description |
|-------|------|-------|-------------|
| `participant_id` | string | — | Participant identifier |
| `part` | string | — | `A` or `B` |
| `session_id` | string | — | Session folder |
| `trial_uid_raw` | string | — | Raw trial UID from EDF (e.g., `B_MB01_T001`) |
| `timestamp_rel_ms` | float | ms | Time relative to stimulus onset |
| `eye` | string | — | `L` or `R` |
| `x_px`, `y_px` | float | pixels | Gaze position (screen coordinates) |
| `pupil_size` | float | area | Pupil size (EyeLink units) |
| `validity` | int | — | 0 = valid gaze, 1 = missing/out-of-range |

---

## `data/metadata/quality_metrics.csv`

One row per participant. Aggregated quality statistics.

| Field | Type | Units | Description |
|-------|------|-------|-------------|
| `participant_id` | string | — | Participant identifier |
| `total_trials` | int | — | Total trials for this participant |
| `valid_trials` | int | — | Trials with tracking ratio >= 0.8 |
| `excluded_trials` | int | — | Trials below tracking threshold |
| `tracking_ratio_mean` | float | — | Mean tracking ratio (0–1) |
| `tracking_ratio_std` | float | — | Std of per-trial tracking ratio |
| `calibration_error_deg_mean` | float | degrees | Mean validation error (if available) |
| `fixations_per_trial_mean` | float | — | Mean fixation count per trial |
| `fixations_per_trial_std` | float | — | Std of fixation count per trial |
| `fixation_duration_mean_ms` | float | ms | Mean fixation duration |
| `fixation_duration_std_ms` | float | ms | Std of fixation duration |
| `data_loss_percent` | float | % | Percentage of trials with no fixations |

---

## `data/manifests/polygon_geometry.csv`

One row per polygon shape (27 total). Canonical center coordinates.

| Field | Type | Units | Description |
|-------|------|-------|-------------|
| `polygon_id` | string | — | Polygon identifier |
| `polygon_case` | string | — | Polygon condition type |
| `json_filename` | string | — | Filename of polygon JSON definition |

---

## `data/manifests/stimulus_manifest.csv`

One row per trial slot (702 total: 351 per part). Defines the fixed stimulus-polygon-cue assignment shared by all participants.

| Field | Type | Units | Description |
|-------|------|-------|-------------|
| `aperture_scale_factor` | int | — | Polygon scaling factor |
| `category` | string | — | CAT2000 category |
| `cue_pos_id` | string | — | Fixation cue grid position |
| `cue_x_px`, `cue_y_px` | float | pixels | Cue position |
| `image_id` | string | — | Image identifier |
| `image_path` | string | — | Path to image file |
| `mini_block` | int | — | Block number (1–9) |
| `part` | string | — | `A` or `B` |
| `polygon_case`, `polygon_id` | string | — | Polygon condition and ID |
| `polygon_json_path` | string | — | Path to polygon JSON |
| `stimulus_duration_s` | float | seconds | Presentation duration |
| `trial_in_block` | int | — | Trial position within block |
| `trial_type` | string | — | `image` or `empty` |
| `trial_uid` | string | — | Trial identifier |

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## Coordinate Systems

**Screen coordinates:** Origin at top-left corner of the 3840x2160 display. X increases rightward, Y increases downward.

**Degree coordinates:** Origin at screen center (1920, 1080 px). Computed using the display geometry:
- 27" diagonal, 3840x2160 resolution, 70 cm viewing distance
- Pixels-per-degree: ~78.5 (computed from `ppd = distance_cm * tan(1 deg) / cm_per_px`; see `docs/acquisition_protocol.md` for full derivation)

**Time reference:**
- `timestamp_rel_ms` and `start_time_ms` / `end_time_ms`: relative to stimulus onset (ms)
- `ts_*` fields in trials.csv: experiment clock (seconds from session start)

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## Known Data Issues

| Issue | Scope | Details |
|-------|-------|---------|
| P05 missing trials | Part B only | P05 completed only 317 of 351 Part B trials (34 missing from block 9) due to a session interruption. Total: 668 trials instead of 702. |
| Aborted trials | 48 trials across 9 participants | Trials that were aborted before stimulus presentation. Marked with `aborted=True`; all timestamp and stimulus fields are NaN. Participants affected: P05 (7), P07 (1), P10 (2), P13 (9), P18 (9), P20 (2), P24 (13), P25 (1), P28 (4). |