Single Key Impulsivity Paradigm

Single Key Impulsivity Paradigm

In the paradigm, participants are free to respond as often as desired to obtain a reward and the size of the reward is related to the delay between consecutive responses. Most of the previous variations of reward-directed paradigms are forced-choice tasks where participants must choose between sooner-smaller and later-larger rewards. Because the participant is free to choose the length of the delay between responses for reward, the SKIP permits the research to draw conclusions based on the overall rate and pattern of those responses. This can be useful for researchers interested in exploring responses related to impulsive behavior and the modifiability of these response patterns with payment.

Many of this paradigm's parameters are adjustable to manipulate payment for the participant's free operant responses. Although the settings vary, in general, the longer the participant waits between consecutive responses, the more each response earns. For example, a setting that has been used in previous research has been 1¢ paid for every 2 seconds between consecutive responses. Using this example, a 30-second delay between responses would result in a payment of 15¢. The computer monitor displays two point counters (see illustration below). The counter at the top of the screen displays the total points accumulated during the session, and the counter at the bottom of the screen displays the number of points earned by the most recent response. This latter point counter displays the number of points for 3 seconds after each response (or until the next response, if it occurs within 3 seconds). This latter point counter is intended to give participants feedback about the delay contingency without explicit instructions. Participants can infer that responses emitted at a faster rate earn smaller rewards than responses emitted at a slower rate based on the payment for each response.

The SKIP allows the experimenter to select either Linear or Exponential Payout options. In the Linear Payout option, there is a constant relationship between the length of delay between responses and payment of earnings and/or losses. In the Exponential Payout option the amount of earnings and/or losses increases exponentially as the length of the delay between responses increases.

An additional feature of the SKIP task is the inclusion of payment options. The three types of payment options are earnings (Reward), losses (Penalty), and Combined earnings/losses. These types of payment options are included to allow the researcher to explore the influence of reinforcement or punishment on the participant's delay choices. Certain participants may be more influenced by one type of payment over others.

SKIP Variable Types

SKIP Parameters*

Single Key Impulsivity Paradigm Setup Screen

Analyses of the Single Key Impulsivity Paradigm

• What variable is used to test impulsivity?

  Impulsivity can be measured in several ways with the SKIP. To get an overall evaluation of impulsive responding across the entire session, either the total number of responses or the average response time (i.e. Average IRT) are used. These values typically have a skewed distribution when collecting data across multiple participants or sessions, so transformation may be necessary (log or square root are both common).
  Alternatively, the Longest Delay reflects the greatest duration between two responses and is interpreted as a measure of the greatest impulse control exhibited during the session.

• Evaluation of performance interpretability requires thoughtful examination of responses to the non-impulsive stimuli.

  As long as the participants completes the task, responded at least once, and appeared to exert effort, then performance is interpretable. Because participants are instructed of the task length, it is imperative that participants do not have access to watch, clock, or other timing devices during testing.

Single Key Impulsivity Paradigm Citation

When citing this instrument in a publication, please use the following reference:

Laboratory behavioral measures of impulsivity.

Dougherty, D. M., Mathias, C. W., Marsh, D. M., and Jagar, A. (2005).

Behavior Research Methods, 37, 82-90.

Single Key Impulsivity Paradigm Bibliography