Performance in Temporal Discounting Tasks by People with Intellectual Disabilities Reveals Difficulties in Decision-Making and Impulse Control

The subjective value of rewards declines as a function of the delay to receive them (temporal discounting). Three temporal discounting tasks that assessed preferences between small amounts of money (10 pence) over short delays (60 s), moderate amounts of money (10) pound over moderate delays (2 weeks), and large amounts of money(1000) pound overlong delays (12 months) were presented to people with intellectual disabilities (Full-Scale IQ < 70) and to a comparison group (ns = 20 for each group). Measures of IQ, financial knowledge, memory, and executive functioning were also obtained. Only a third of the service users were able to perform the temporal discounting tasks consistently, and they tended to respond impulsively. The proportion of participants responding consistently increased following training. Both the initial performance and the effect of training were related to executive functioning but not IQ