be awarded a second marshmallow, both of which can then be eaten. Despite its simplicity and ease of administration, evidence from longitudinal studies suggests that the number of seconds preschoolers wait to obtain the second marshmallow is predictive of higher SAT scores, better social and emotional coping in adolescence, higher educational achievement, and less cocaine/crack use. Delay discounting Like the marshmallow test, delay discounting is also a delay of gratification paradigm. It is designed around the principle that the subjective value of a reinforcer decreases, or is 'discounted,' as the delay to reinforcement 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 decline more steeply as a function of delay compared to the normal population (i.e. greater preference for immediate reward). 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 (SSRT) test. 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 test 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. The participant is instructed to respond as fast as possible to the 'go' signal while maintaining the highest possible inhibition accuracy (on no-go trials). During the task, the time at which the 'stop' signal is presented (the stop signal delay or SSD) is dynamically adjusted to match the time after the 'go' signal at which the participant is just able/unable to inhibit their 'go' response. If the participant fails to inhibit their 'go' response, the 'stop' signal is moved slightly closer to the original 'go' signal, and if the participant successfully inhibits their