Experiential Discounting Task

Background

The Experiential Discounting Task (EDT) is a type of Delay Discounting (DD) task that assesses the degree to which the subjective value of a commodity (e.g. money) decreases as a function of wait time. Brady Reynolds and Ryan Schiffbauer introduced the EDT in 2004 as a more ecologically valid measure of delay discounting that is based on actually experiencing the consequences of delay choices as opposed to simply imagining them as is typically done. In addition, the EDT task combines time delays with probabilities, making the higher reward not only delayed but also more uncertain than the immediate smaller reward.

The goal of the EDT game is to win as much money as one can. Participants choose between a smaller, certain reward available immediately (e.g., 30 cents) or a larger reward after a set delay (e.g., $1 in 7 seconds) and with a lower certainty. Depending on the choices, the smaller amount gets continously increased (after choosing the larger amount) or decreased (after choosing the smaller amount) for the following trial. Using this adjusting algorithm, the program attempts to estimate the indifference points - the point at which the lower value is equally desirable to the higher one - for several temporal delays.

Generally, the EDT task has been shown to be more sensitive to sleep deprivation and substance use than more hypothetical DD tasks, though it is has also been questioned whether the task really measures discounting compared to boredom proneness.

Task Procedure

A participant learns about the general task of the EDT game and works through a short practice to get familiar with the EDT setup. At the start of each new trial, the participant sees two light bulbs that are associated with the larger, delayed and uncertained reward (on the left) and the smaller, immediate and certain one (on the right). Once the START button is pressed, both light bulbs light up, and the participant has to choose the option they prefer. Occasionally, only one light bulb lights up to signal a forced choice trial. If the larger sum is selected via mouse click or touch, a delay period is started. At the end of the delay period, either the little bank icon lights up and the money can be collected or the START button for a next trial reappears without a win. The total amount won is always visible to the participant.

In the example below, the participant first selects the higher amount but does not win. For the second trial, the participant chooses the lower but sure amount which increased from 15cents (first trial) to 17cents (second trial). The bank icon lights up and the participant collects the money. For the subsequent trial, the lower but sure amount is again decreased to 15 cents.

For each of the four tested time delays (0seconds, 7seconds, 14seconds, 28seconds), the program runs at least 16 trials before it starts assessing whether the 'Indifference Point' has been reached. It is assumed that indifference has been reached if the participant selected an equal number of large and small rewards over the last 6 trials suggesting that they hover around their indifference point. If no indifference point can be established, the block continues until the indifference point is found or the block timeout has been reached.

What it Measures

The Experiential Discounting Task (EDT) is a behavioral assessment tool of (choice) impulsivity

Psychological domains

• Inhibitory Control: The ability to withhold a "rash" response for immediate gain in favor of a more valuable future outcome.

Main Performance Metrics

• Indifference Points: Estimated indifference points for various delays

Psychiatric Conditions

Higher discount rates k are linked to the following conditions:

• Addictive Disorders
• Substance Abuse
• Gambling
• Attention Deficit Hyperactivity Disorder (ADHD)
• Bipolar Disorder
• Borderline Personality Disorder (BPD)