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Single Key Impulsivity Paradigm

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The Single Key Impulsivity Paradigm (SKIP) is a tool for studying the rate and pattern of free operant responses for a reward.  The SKIP is designed to be a modified delay discounting task in which longer delays between responses result in greater rewards for the individual.


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.

SKIP response feedback

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

Trial Definition
Average IRT Mean time between responses
Total Total number of reward directed responses
Shortest Delay Shortest time between responses
Longest Delay Longest time between responses


SKIP Parameters*

Trial Definition
Block Duration allows the experimenter to set the duration of each testing block
Number of Blocks choose how many Blocks will be used across the entire session
Customize IRT Bins set duration of different inter-response time bins for recording responses
Linear Payout calculates payout based on a linear function (can be multiplied times a constant)
Vary Point by % vary the number of points earned by a predetermined percentage (random variance, +/-, within the preset percentage)
Exponential Payout calculates payout based on a exponential function (can be multiplied times a constant)

*While these are the default task settings, many aspects of the SKIP stimulus parameters are readily modifiable using the setup screen.



Single Key Impulsivity Paradigm Setup Screen

SKIP setup



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

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

Laboratory measures of impulsivity.
Dougherty DM, Mathias CW, Marsh DM, and Jagar AA (2005).  
Behavioral Research Methods, 37, 82-90.


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Single Key Impulsivity Paradigm Bibliography

Impulsivity in Multiplayer Online Battle Arena (MOBA) gamers: Preliminary results on experimental and self-report measures

Nuyens, F., Deleuze, J., Maurage, P. Griffiths, M., Kuss, D., and Billieux, J.  (2016).

Journal of Behavioral Addictions, 5, 351-356.     PubMed

Effects of tryptophan depletion and a simulated alcohol binge on impulsivity

Dougherty, D. M., Mullen, J., Hill-Kapturczak, N., Liang, Y., Karns, T. E., Lake, S. L., Mathias, C. M., and Roache, J. D. (2015).

Experimental and Clinical Psychopharmacology, 23, 109-121.       PubMed

Vulnerability for mania - is it linked to problems delaying gratification?

Meyer TD, Newman AL, Jordan G. (2015).

Psychiatry Research, 229, 359-364.      PubMed

Further evidence of the heteroogeneous nature of impulsivity.

Caswell AJ, Bond R, Duka T, Morgan MJ  (2015).

Pesonality and Individual Differences, 76, 68-74.

Reward sensitivity and anger in euthymic bipolar disorder

Duek O, Osher Y, Belmaker RH, Bersudsky Y, Kofman O (2014).

Psychiatry Research, 215, 95-100.      PubMed

Relations among behavioral and questionnaire measures of impulsivity in a sample of suicide attempters

Bagge CL, Littlefield AK, Rosellini AJ, Coffey SF (2013)

Suicide and Life-Threatening Behavior, 43, 460-467.       PubMed

Investigation of impulsivity in a sample of treatment-seeking pathological gamblers: A multidimensional perspective
Billieux J, Lagrange G, Van der Linden M, Lançon C, Adida M, Jeanningros R. (2013).

Psychiatry Research, 198, 291-296.     PubMed

Acute alcohol effects on subtypes of impulsivity and the role of alcohol-outcome expectancies

Caswell AJ, Morgan MJ, Duka T. (2013).

Psychopharmacology, 229, 21-30.     PubMed

Inhibitory Control Contributes to "Motor"- but not "Cognitive"- Impulsivity

Caswell AJ, Morgan MJ, Duka T. (2013).

Experimental Psychology, 60, 324-334.     PubMed

A double-blind trial of the effect of docosahexaenoic acid and vitamin and mineral supplementation on aggression,
impulsivity, and stress

Long S-J, Benton D.  (2013).

Human Psychopharmacology, 28, 238-247.       PubMed

Volunteerism and self-selection bias in human positron emission tomography neuroimaging research

Oswald LM, Wand GS, Zhu S, Selby V (2013).

Brain Imaging and Behavior, 7, 163-176.       PubMed

The relationship between self-report and lab task conceptualizations of impulsivity

Cyders MA, and Coskunpinar A. (2012).

Journal of Research in Personality, 46, 121-124.

Adults with a family history of alcohol related problems are more impulsive on measures of response initiation and response inhibition.

Acheson, A., Richard, D. M., Mathias, C. W., and Dougherty, D. M. (2011).

Drug and Alcohol Dependence, 117, 198-203.     PubMed

Criminal conviction, impulsivity, and course of illness in bipolar disorder

Swann, A.C., Lijffijt, M., Lane, S.D., Kjome, K.L., Steinberg, J. L., and Moeller, F. G. (2011).
Bipolar Disorders, 13, 173-181.     PubMed     PubMed Central

A meta-analysis of the convergent validity of self-control measures
Duckworth, A. L., and Kern, M. L. (2011).
Journal of Research in Personality, 45, 259-268.     PubMed     PubMed Central

Impulsivity and risk-taking in co-occurring psychotic disorders and substance abuse.

Duva, S. M., Silverstein, S. M., and Spiga, R.  (2011).

Psychiatry Research, 186, 351-355.     PubMed

Effects of acute tryptophan depletion on three types of behavioral impulsivity.

Dougherty, D. M., Richard, D. M., James, L. M., and Mathias, C. W. (2010).

International Journal of Tryptophan Research, 3, 99-111.

Fifty years of the Barratt Impulsiveness Scale: An update and review.
Stanford, M. S., Mathias, C. W., Dougherty, D. M., Lake, S. L., Anderson, N. E., and Patton, J. H. (2009).
Personality and Individual Differences, 47, 385-395.

Severity of bipolar disorder is associated with impairment of response inhibition.

Swann, A. C., Lijffijt, M., Lane, S. D., and Moeller, F. G.  (2009).

Journal of Affective Disorders, 116, 30-36. PubMed     PubMed Central

Trait impulsivity and response inhibition in antisocial personality disorder.

Swann, A. C., Lijffijt, M., Lane, S. D., Steinberg, J. L., and Moeller, F. G.  (2009).

Journal of Psychiatric Research, 43, 1057-1063. PubMed     PubMed Central

Behavioral assessment of impulsivity in pathological gamblers with and without substance use disorder histories versus health controls.

Ledgerwood, D. M., Alessi, S. M., Phoenix, N., and Petry, N. M.  (2009).

Drug and Alcohol Dependence, 105, 89-96. PubMed

Multidimensional assessments of impulsivity in subjects with a history of suicide attempts.

Wu C.-S., Liao, S.-C., Lin, K.-M., Tseng, M. M.-C., Wu, E. C-H., and Liu, S-K.  (2009)

Comprehensive Psychiatry, 315-321. PubMed

A test of alcohol dose effects on multiple behavioral measures of impulsivity.
Dougherty, D. M., Marsh-Richard, D. M., Hatzis, E. S., Nouvion, S. O., and Mathias, C. W. (2008).   
Drug and Alcohol Dependence, 96, 111-120. PubMed     PubMed Central

Laboratory measures of impulsivity.
Dougherty, D. M., Mathias, C. W., Marsh, D. M., and Jagar, A. A. (2005).   
Behavior Research Methods, 37, 82-90.  PubMed

Behavioral impulsivity paradigms: A comparison of hospitalized adolescents with Disruptive Behavior Disorders.
Dougherty, D. M., Bjork, J. M., Harper, R. A., Marsh, D. M., Moeller, F. G., Mathias, C. W., and Swann, A. C. (2003).   
Journal of Psychology and Psychiatry, 44, 1145-1157.  PubMed

Comparison of women with high and low trait impulsivity using behavioral measures of response-disinhibition and reward-choice. 
Marsh, D. M., Dougherty, D. M., Mathias, C. W., Moeller, F. G., and Hicks, L. R. (2002). 
Personality and Individual Differences, 33,1291-1310.

Laboratory measures of impulsivity: A comparison of women with or without childhood aggression.
Mathias, C. W., Dougherty, D.M., Marsh, D.M., Moeller, F.G., Hicks, L.R., Dasher, K., and Bar-Eli, L. (2002).   
The Psychological Record, 52, 289-303.


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