A simple experiment: data collection code
In this page you can find a simple but complete experiment aiming at provigind you a programming paradigm and example/starting point for developing your experiments for the MEG lab. The experimental paradigm is very basic and consist in pressing the red/blue button on the response box if the stimulus, after a cue, was a tone/gabor. Eyes are tracked by means of the Eye Tracker. Photodiode based techniques are used to assure 1 msec hig precision real synchronization.
The code is very simple and its aim is to illustrate how to use MEG lab devices for a visual experiment, involving stimuli presentation, response collection, eye-tacking and triggers (with photodiode correction). The not MEG-related code is intended to be only a suggestion, since here the focus is not the experimental paradigm itself, but how commands related to MEG devices integrate into it. The aim is that the reader can understand & re-use code snippets from here in experiment programming.
Matlab & PsychToolbox knoweledge is assumed. If not the case, we suggest to follow a good tutorial before.
The experiment consists of a cue followed by a stimulus and has the following instructions:
- press the red button if stimulus is a beep, press the blue button if stimulus is a gabor ;
- keep the gaze at fixation
The script is structured as follows:
- A few "INIT" sections:
- General experiment-level parameters initializations
- Datapixx (blue boxes) initialization
- Psychtoolbox initialization
- Eyelink initialization
- Eyelink calibration
- INSTRUCTIONS to the subject
- A "TRIAL LOOP", cycling trough trials and containing:
- A "INIT TRIAL" section, in which all trial-dependent parameters are initialized
- A session in which "EYELINK RECORDING" starts
- A "PRESENTATION LOOP", allowing for fine control of the trial at each single screen refresh (frame)
- A "CLOSINGS" session, in which devices are gracefully closed and data are locally saved
Here you can download the MATLAB code. Don't esitate to contact the MEG core staff for any question.