Stroop Task Experiment

A configurable Stroop task implementation in MATLAB using Psychtoolbox, designed for cognitive research with TTL pulse support for MEA/EEG/sEEG recording.

Overview

This Stroop task presents participants with color words (Red, Green, Blue, etc.) displayed in congruent, incongruent, or neutral colors. The experiment is designed to collect electrophysiological response across different conflict conditions to study cognitive control and interference. Reaction time can also be infered through the audio recording, but is not the focus.

Requirements

Software

• MATLAB (R2019b or later recommended)
• Psychtoolbox-3
• Image Processing Toolbox (for icon resizing)

Hardware

• Computer with display
• Audio recording capability
• Optional: XID device for TTL pulses (experiment runs without it)

Project Structure

Stroop Task/
├── README.md               # This file
├── .gitignore             # Git ignore rules (excludes output/)
├── scripts/
│   ├── stroopTask.m       # Main experiment function
│   ├── instructions.m     # Instructions and practice trials
│   └── archive/          # Legacy/backup scripts
├── icons/
│   ├── colour_icon.png   # Cue icon 1
│   └── text_icon.png     # Cue icon 2
└── output/               # Experiment data (auto-generated)
    └── YYYY-MM-DD/       # Date-specific folders
        ├── low/          # Low conflict data
        ├── equal/        # Equal conflict data
        └── high/         # High conflict data

Usage

Trial Proportions

Condition	Congruent	Incongruent	Neutral
Low (1)	80%	0%	20%
Equal (2)	50%	30%	20%
High (3)	30%	50%	20%

Basic Usage

% Add project to MATLAB path
addpath(genpath('path/to/Stroop Task'))

% Run different conflict conditions
stroopTask(1);     % Low conflict (80% congruent)
stroopTask(2);   % Equal conflict (50% congruent)  
stroopTask(3);    % High conflict (30% congruent)

Experiment Flow

Each trial consists of:

1. Fixation cross (1s) - TTL code: 66
2. Cue icon (1s) - TTL code: 99
3. Stimulus word (2s) - TTL code: 255
4. Response collection during stimulus presentation
5. End marker - TTL code: 254

Response Keys

• Escape: Exit experiment early

Output Data

File Naming

Stroop_t<TYPE>_<LABEL>_<TIMESTAMP>.mat

Example: Stroop_t1_low_08-10-2025_14-32-10.mat

Data Structure

out = struct(
    'stroop_type',   1,                    % Condition type (1,2,3)
    'label',        'Low conflict',        % Human-readable label
    'label_short',  'low',                % Short label for files
    'pct',          [80, 0, 20],          % [congruent, incongruent, neutral] %
    'counts',       struct(...),          % Actual trial counts
    'respMat',      [3 x nTrials],        % [wordIdx; colorIdx; cue]
    'audio_data',   [...],                % Recorded audio
    'ExpStartTime', datetime(...)         % Experiment timestamp
);

Response Matrix (out.respMat)

• Row 1: Word index (1-8 for colors, 9 for "XXXX")
• Row 2: Color index (1-8 for RGB colors)
• Row 3: Cue condition (1 or 2, corresponding to icon files)

TTL Pulse Codes

Event	Code	Description
Fixation onset	66	Cross appears
Cue onset	255	Icon appears
Stimulus onset	255	Word appears
Response window end	99	Trial complete
Block end	254	Experiment finished

Contact

Author: Jakub Kowalczyk
Institution: Newcastle University
Email: j.kowalczyk2@newcastle.ac.uk Last Updated: October 2025