Pavlovian-Instrumental Transfer (PIT) Task

A MATLAB/PsychToolbox implementation of a Pavlovian-Instrumental Transfer task. Participants complete instrumental training (approach or withdrawal) and Pavlovian conditioning before performing PIT trials in which Pavlovian background stimuli are presented alongside instrumental stimuli.

Based on

Huys, Q.J.M., et al. (2011).

Geurts, D.E.M., et al. (2022).

Original task code by Q.J.M. Huys. Modified and extended by Elizabeth Endecott.

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Requirements

• MATLAB (R2019b or later recommended)
• Psychtoolbox-3

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Setup

1. Clone or download the repository
2. Open MATLAB and navigate to the task folder
3. Ensure the following folder structure exists:

task/
├── data/
│   └── backup/
├── shrooms/
│   ├── 1/          (12 mushroom images: shroom_1.jpg ... shroom_12.jpg)
│   └── 2/          (12 mushroom images: shroom_1.jpg ... shroom_12.jpg)
└── stimuli/
    ├── 1/          (5 fractal images: fractal1.jpg ... fractal5.jpg)
    └── 2/          (5 fractal images: fractal1.jpg ... fractal5.jpg)

4. Edit modifyme.m to set your experimental parameters (see below)
5. Run runexp in the MATLAB command window to start the experiment

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Configuration

modifyme.m is the only file that may need editing between sessions. Key settings:

Parameter	Description
name	Project name, used in saved filename
english / dutch	Set language (1 = active, 0 = inactive)
cb_method	Counterbalancing method (see below)
dosave	Set to 1 to save data (always 1 during experiments)
doinstr	Set to 0 to skip instructions during debugging
payment	Set to 0 for patients not receiving payment
txtsize	Text size in pixels (40 for 1024x768, up to 65 for larger screens)

Counterbalancing Methods (cb_method)

Option	Description
1	Running log file (recommended). Tracks assignments in data/counterbalance_log.mat and assigns whichever condition has fewer participants. Works with any subject numbering.
2	Modulo. Even subject numbers start with approach, odd with withdrawal. Guarantees alternation but not randomization.
3	Random. No guarantee of balance across participants.

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Experiment Structure

Initial VAS ratings
│
├── Block 1
│   ├── Instrumental training (approach or withdrawal)
│   ├── Pavlovian training
│   └── PIT session
│
├── Break (2 minutes)
│
├── Block 2 (opposite condition)
│   ├── Instrumental training
│   ├── Pavlovian training (short)
│   └── PIT session
│
├── Final VAS ratings
│
└── Debriefing (Day 2 only)

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Files

Main files

File	Description
runexp.m	Master file. Run this to start the experiment. Calls all other scripts.
modifyme.m	The only file that may need editing between sessions.

Task scripts

File	Description
preps.m	Sets up all stimulus sequences and counterbalancing before the experiment starts.
setup.m	Opens the PsychToolbox display window and preloads all stimulus images.
pittraining.m	Runs a single instrumental training trial with feedback.
pavlov.m	Runs a single Pavlovian conditioning trial.
pavquery.m	Runs a single Pavlovian comparison (query) trial, interleaved with Pavlovian training.
pit.m	Runs a single PIT trial (no feedback).

Instruction files

File	Description
pitinstr_approach.m	Instructions for the approach instrumental training block.
pitinstr_avoid.m	Instructions for the withdrawal instrumental training block.
pitinstr_start.m	Instructions shown at the start of each PIT session.
pavinstr.m	Full instructions for the first Pavlovian training block.
pavinstr_short.m	Abbreviated refresher instructions for the second Pavlovian block.

Questionnaire files

File	Description
VASpics.m	VAS ratings of Pavlovian fractal stimuli (run pre and post conditioning).
debrief.m	Post-experiment debriefing questions (Day 2 only).

Helper files

File	Description
centermouseclick.m	Displays a central orange square and waits for the participant to click it to initiate each trial.
checkabort.m	Checks for Escape key press and aborts the experiment gracefully.
displaytext.m	Displays centered text on screen. Used throughout for instructions and feedback.
givebreak.m	Displays a countdown break screen between blocks.
mygetclicks.m	Waits for a mouse button press and release.

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Data

Data is saved as .mat files in data/ with a backup copy in data/backup/. Files are named:

[name]_[type]_[subjn]_[day]_[datetime].mat

For example: GADA_C_1001_1_250115_1430.mat

If the experiment crashes, a .crashed.mat file is saved. If aborted via Escape, a .aborted.mat file is saved.

Key Variables

Trial indices

Variable	Description
nt	Instrumental trial number
np	Pavlovian trial number
npit	PIT trial number

Reaction times

Variable	Description
treact	Instrumental trial RTs
pavreact	Pavlovian query trial RTs
pitreact	PIT trial RTs

Instrumental training

Variable	Description
ainst	Correct response per trial (1=Go, 2=NoGo)
mprest	Mushroom stimulus presented per trial
lrt	Stimulus position (1=left, 3=right)
crtfb	Whether accurate (1) or erroneous (0) feedback was given
crt	Correctness of participant's choice (1=correct, 0=incorrect)
cht	Participant's choice (0=NoGo, 1=left, 3=right, NaN=invalid)
r	Reward outcome (1=reward, -1=punishment)

Pavlovian training

Variable	Description
pavpres	Pavlovian stimulus presented per trial
posp	Stimulus position (1=left, 3=right)
cppres	Stimulus pair presented at each query trial
chq	Participant's choice at query trials
crm	Whether correct (higher value) stimulus was chosen

PIT

Variable	Description
ains	Correct response per trial (1=Go, 2=NoGo)
mpres	Mushroom stimulus presented per trial
mpresp	Pavlovian background stimulus per trial
lr	Stimulus position (1=left, 3=right)
ch	Participant's choice (0=NoGo, 1=left, 3=right, NaN=invalid)
cr	Correctness of participant's choice (1=correct, 0=incorrect)

VAS and debriefing

Variable	Description
OVaspic	VAS ratings matrix (session x stimulus), stored as proportion of scale (0=left, 1=right)
ODebr	Debriefing ratings matrix (session x question), stored as proportion of scale

Notes

• To check whether a participant started with the approach block, see Z.approachstart in the saved data (1 = started with approach).
• If Z.approachstart = 1, the first 60 instrumental trials and first 100 PIT trials are approach.
• Stimulus position (lr/lrt/posp) uses values 1 and 3 based on the drm coordinate array in setup.m.

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Sound

Sound is disabled by default. To re-enable it, uncomment the PsychPortAudio sections in setup.m, pavlov.m, and pit.m simultaneously. See the header in setup.m for full instructions.

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Abort

To abort the experiment mid-session, press the Escape key. The experiment will close gracefully and save a .aborted.mat file with all data collected up to that point.