ptbCorgi
PtbCorgi is a tool suite to facilitate stimulus presentation and project-level management.
PtbCorgi offers several benefits for developing and analyzing experiments. Reproducibility is a core consideration in the design. As a front-end to Psychtoolbox ptbCorgi makes creating and running experimental paradigms simpler. It’s design also lowers the Psychtoolbox learning curve making it simpler for novice individuals to use the power of psychtoolbox to create experiments. This is because ptbCorgi utilizes a modular design that separates core functions and has a GUI for running experiments. As a project-level management and analysis tool ptbCorgi helps organize datasets and running repeated analyses across multiple participants.
Quick Start:
First Run:
ptbCorgiSetup
Then run: ptbCorgi
From the GUI select "choose paradigm", in the "exampleParadigms" directory Pick pdgm_orientation_2afc.m. That will load an example orientation discrimination experiment. You can play an example trial by selecting a condition and choosing "test".
Reproducibility
Reproducibility is a core motivation for ptbCorgi. The stimulus presentation code self-archives the code used to display the stimulus alongside the participant data. This enables recreation of experiments from a single participants data.
Experiment Design & Display
ptbCorgi acts as a front-end GUI and set of convenience scripts for psychtoolbox.
Modular Design
Commonly individuals utilize monolithic scripts for experiment code. These scripts can be daunting for new people to understand. Large scripts also encourage copying large amounts of code for new experiments that may only be minor tweaks on previous experiments. This creates the potential for more bugs/errors to creep in and decreases reusability. Instead of enouraging monolithic experiment scripts ptbCorgi was taken a modular design separating out functionality into separate files.
Key modules:
Experiment Paradigm: (custom files) Defines that parameters for an experimental session.
Trial Display: (custom files) Renders the stimulus for a single trial.
Experimental Session Handling: (ptbCorgi.m) Handles trial ordering and presentation and collection and saving of data.
Psychtoolbox Initialization: (openExperiment.m) Handles initialization of psychtoolbox.
Experiment Paradigm Definition
When most people think of an experiment they think about a collection of conditions defined by different parameters. For example a set of sinusoidal gratings at different orientations and different contrasts. That’s exactly what this file defines. An experimental paradigm is a definition of the parameters of an experiment. It defines a collection of conditions parameters and experiment options (e.g. 2AFC) various experiment wide settings (e.g. viewing distance). At the simplest a user can create a new experiment by changing just the paradigm definition.
Trial Display.
This is the other key part of an experiment. It is the code that actually renders the stimulus is kept separate from the paradigm definition. For each trial the session handling code will execute the trial display function with options chosen from the experiment paradigm definition. This design makes it so that you only have to write the trial rendering code once (say a Gabor in noise) and the rendering code can be reutilized for multiple experiments.
Experimental Session Handling
The code that is the heart of the program handles running an experimental session is separate from the rest of the code. It uses a GUI interface for choosing options for a specific session, and handles different paradigms. The goal is that normal users should never have to modify this code, and have all the control they need to define an experiment from the experiment paradigm file. The session handling code determines trial order, presents trials, collects responses/data, saves the data. An important aspect of the session handling code is that it self-archiving, which enables easy replicability. What this means is that alongside the data all the information needed to reproduce the experiment is stored as well. It stores all the custom matlab code that was executed in running the experiment (except for PTB code and MATLAB core code). It also stores all the output from the matlab window, information about the calibration settings, the system hardware/software, various other pieces of information about the session.
Psychtoolbox initialization
Initializing psychtoolbox is often confusing for new users. There are lot’s of different options and things that can be done. This code handles setting up the display, audio interface (if needed), loading luminance and size calibration, calculating various values that are useful (e.g. conversion factor from pixels to visual angle). Standardizing the initialization helps to ensure experiments are run using appropriate choices, and helps to facilitate usage of device independent units ( visual angles, cm, seconds and NOT pixels and frames). Importantly, ptbCorgi by default does not use the “classic” 0-255 color range, but uses the modern normalized floating point number range 0.0 - 1.0.