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Behavioral Paradigms
A wide variety of behavioral tests have been devised for the assessment of impulsivity in both clinical and experimental settings. While no single test is a perfect predictor or a sufficient replacement for an actual clinical diagnosis, when used in conjunction with parent/teacher reports, behavioral surveys, and other diagnostic criteria, the utility of behavioral paradigms lies in their ability to narrow in on specific, discrete aspects of the impulsivity umbrella. Quantifying specific deficits is of use to the clinician and the experimenter, both of whom are generally concerned with obtaining objectively measurable treatment effects.

Marshmallow Test
One widely recognizable tests for impulsivity is the delay of gratification paradigm commonly known as the ‘marshmallow test’ (Mischel et al., 1972). Developed in the 1960s to assess ‘willpower’ and self-control in preschoolers, the marshmallow test consists of placing a single marshmallow in front of a child and informing them that they will be left alone in the room for some duration. The child is told that if marshmallow remains uneaten when the experimenter returns, they will be awarded a second marshmallow, both of which can then be eaten.

Despite its simplicity and ease of administration, evidence from longitudinal studies suggested that the number of seconds preschoolers waited to obtain the second marshmallow (i.e., delay of gratification) was predictive of higher SAT scores, better social and emotional coping in adolescence, higher educational achievement, and less cocaine/crack use (Mishel et al., 1988; Shoda et al, 1990; Ayduk et al., 2000).

Delay Discounting
Like the marshmallow test, delay discounting is also a delay of gratification paradigm (Mazur, 1987). It is designed around the principle that the subjective value of a reinforcer decreases, or is ‘discounted,’ as the delay until that reinforcer is received increases. Subjects are given varying choices between smaller, immediate rewards and larger, delayed rewards. By manipulating reward magnitude and/or reward delay over multiple trials, ‘indifference’ points can be estimated whereby choosing the small, immediate reward, or the large, delayed reward are about equally likely. Subjects are labeled impulsive when their indifference points reflect an increase in preference for the small, immediate rewards compared to the normal population. Unlike the marshmallow test, delay discounting does not require verbal instruction and can be implemented on non-human animals.

Go/no-go and stop-signal reaction time tasks
Two common tests of response inhibition used in humans are the go/no-go task, and a slight variant known as the stop signal reaction time test (SSRT). During a go/no-task, the participant is trained over multiple trials to make a particular response (e.g., a key-press) when presented with a ‘go’ signal. On some trials, a ‘stop’ signal is presented just prior to, or simultaneously with the ‘go’ signal, and the subject must inhibit the impending response. The SSRT is similar, except that the ‘stop’ signal is presented after the ‘go’ signal. This small modification increases the difficulty of inhibiting the ‘go’ response, because the participant has typically already initiated the ‘go’ response by the time the ‘stop’ signal is presented (Winstanley et al, 2006).

Balloon Analogue Risk Task
The balloon analogue risk task (BART) was designed to assess risk-taking behavior (Lejuez, 2002). Subjects are presented with a computer depiction of a balloon that can be incrementally inflated by pressing a response key. As the balloon inflates, the subject accumulates rewards with each new key-press. The balloon is programmed with a constant probability of popping. If the balloon pops, all rewards for that balloon are lost, or the subject may choose to stop inflating and ‘bank’ the reward for that balloon at any time. Therefore, more key-presses equate to greater reward, but also greater probability of popping and negating rewards for that trial. Presumably, those with an affinity for ‘risk-taking’ are more likely pop the balloon, earning less reward overall than the typical population.


 * Other common impulsivity tasks include the Continuous performance task (CPT), 5-choice serial reaction time task (5-CSRTT), Iowa gambling task (IGT), Stroop task, and Matching familiar figures task.