Perceived reward certainty in the assessment of delay discounting

Abstract

Reward delays are often associated with reduced probability of reward, although standard assessments of delay discounting do not specify degree of reward certainty. Thus, the extent to which estimates of delay discounting are influenced by uncontrolled variance in perceived reward certainty remains unclear. Here we examine 370 participants who were randomly assigned to complete a delay discounting task when reward certainty was either unspecified (n=184) or specified as 100% (n = 186) in the task trials and task instructions. We examined potential group differences in (a) perceived reward certainty across a range of delays, (b) delay discounting, and (c) associations between perceived reward certainty and delay discounting. Delay significantly reduced perceived reward certainty in both groups, although delay did not significantly interact with group to affect perceived certainty. Despite higher perceived reward certainty in the specified group, no significant group difference in delay discounting was observed. Higher perceived reward certainty was associated with lower delay discounting in both groups. However, we found no evidence that specifying reward certainty influences estimates of delay discounting. Future research should examine whether perceived reward certainty moderates associations between delay discounting and health behavior and whether perceived reward certainty is impacted by interventions that change delay discounting.

Keywords: delay discounting; framing; perceived reward certainty; uncertainty.

FIGURE 1

Flow diagram depicts the numbers of participants who were eligible, started the survey, were randomized to groups, completed the survey, and were included in analyses.

FIGURE 2

Instructions and presentation of choice trials for each specification group. The left side is for the specified group, and the right side is for the unspecified group. The top shows instructions and the bottom shows example trials.

FIGURE 3

Certainty rating by delay for specified and unspecified group. Individual data are presented with blue and red lines. Red triangle points (unspecified) and blue regular points (specified) and dashed lines represent group means. Panel A shows delays ordinally, with equal spacing between delays. Panel B presents delays linearly.

FIGURE 4

Delay discounting by specification group. Individual data are represented by circless, and the group mean is represented by squares. Higher values reflect less discounting. The upper whisker extends from the third quartile to no more than 1.5 times the interquartile range (IQR) above the third quartile. The lower whisker extends from the first quartile to no less than 1.5 IQR below the first quartile.

FIGURE 5

Median perceived reward certainty and delay discounting by specification group. Individual points are in black (triangles for unspecified, circles for specified), with darker points representing more points at that value. Lines represent general linear model predictions by specification group (red dashed line for unspecified, blue solid line for specified).