Probabilistic Reward Task

Script Author: Katja Borchert, Ph.D. (katjab@millisecond.com), Millisecond

Created: January 22, 2015

Last Modified: January 02, 2025 by K. Borchert (katjab@millisecond.com), Millisecond

Script Copyright © Millisecond Software, LLC

Background

This script implements a Probabilistic Reward Task, a simple categorization task using a differential reinforcement schedule of monetary reward. It can be used as a measure of reward responsiveness (hedonic capacity).

The setup of this script allows for absolute sizing of the stimuli. By default, the stimuli are NOT absolutely sized (the script uses the largest 4:3 portion of the current screen for data presentation). However, you can change the sizing parameter settings under section Defaults to turn on absolute sizing.

The implemented procedure is based on:

Pizzagalli, D.A., Jahn, A.L, & O'Shea, J.P. (2005). Toward an Objective Characterization of an Anhedonic Phenotype: A Signal-Detection Approach. Biol Psychiatry, 57(4), 319–327.

Duration

15 minutes

Description

Participants are asked to categorize faces into "short" and "long" mouths. Correct responses are intermittedly rewarded with an asymmetric reinforcement schedule for short and long mouths. For half the participants short mouths get reinforced about 60% of the times ("frequent reward") whereas long mouths get reinforced only about 20% of the times ("infrequent reward"); for the other half of the participants the reverse is true.

Responsekeys are counterbalanced within groups. Assignment to the 4 experimental condition (2 reinforcement schedules x 2 response keys assignments) is done by groupnumber.

Procedure

2 reward frequency schedules x 2 response key assignments: Assignment to the 4 experimental groups is done by groupnumber

group 1 (odd groupnumbers)-> short mouth faces are frequently rewarded if response is correct (potentially 30 out of 50 trials);
long mouth faces are infrequently rewarded if correct (potentially 10 out of 50 trials)

group 2 (even groupnumbers)-> long mouth faces are frequently rewarded if response is correct (potentially 30 out of 50 trials);
short mouth faces are infrequently rewarded if correct (potentially 10 out of 50 trials)

within those groups, response key assignments are counterbalanced


1. Practice Block:
• a short demonstration of 2 trials
• 2 trials, 1 of short mouth faces and 1 of long mouth faces (same durations as test trials)

2. Test Blocks:
• 3 Blocks, each block runs 100 trials (50 short mouth trials, 50 long mouth trials)
• order of short and long mouth trials is randomly determined with the constraint that
no more than 3 consecutive runs of the same trial type
• frequently rewarded mouth trials: 30 (30/50->60%); infrequently rewarded mouth trials: 10 (10/50->20%)
-> per block there are 40 potential reward trials
-> the reinforcement schedules for each trial type are randomized (see section Editable Lists for more info)
-> if a trial has been randomly determined to be a rewarded trial but the response is incorrect, the next
correct trial of the same trial type is rewarded instead
• there is a forced 30s (default) rest period inbetween each test block; the task continues automatically

Trial Sequence:
fixation (500ms)->No Mouth Face->(500ms)->Mouth Face(100ms)->No Mouth Face until response
(response latency is taken and measured from onset of Mouth Face)

Stimuli

Face Stimuli are not original to Pizzagalli et al (2005). They can be edited under section Editable Stimuli.
(The default short mouth is about 88% of the long mouth).
Sizes of stimuli on screen are proportional to the monitor/canvas size;
Absolute Sizing can be turned on under section Defaults.

Instructions

Instructions are not original to Pizzagalli et al (2005). They can be edited under section Editable Instructions.

Summary Data

File Name: probabilisticrewardtask_summary*.iqdat

Data Fields

Raw Data

File Name: probabilisticrewardtask_raw*.iqdat

Data Fields

Parameters

The procedure can be adjusted by setting the following parameters.