What is the subjective cost of cognitive effort? Load, trait, and aging effects revealed by economic preference

Abstract

It has long been assumed that people treat cognitive effort as costly, but also that such effort costs may vary greatly across individuals. Individual differences in subjective effort could present a major and pervasive confound in behavioral and neuroscience assessments, by conflating cognitive ability with cognitive motivation. Self-report cognitive effort scales have been developed, but objective measures are lacking. In this study, we use the behavioral economic approach of revealed preferences to quantify subjective effort. Specifically, we adapted a well-established discounting paradigm to measure the extent to which cognitive effort causes participants to discount monetary rewards. The resulting metrics are sensitive to both within-individual factors, including objective load and reward amount, and between-individual factors, including age and trait cognitive engagement. We further validate cognitive effort discounting by benchmarking it against well-established measures of delay discounting. The results highlight the promise and utility of behavioral economic tools for assessing trait and state influences on cognitive motivation.

Figure 1. Cognitive effort discounting (COG-ED) paradigm.

Task structure including N-back practice, effort discounting, and N-back re-do.

Figure 2. Subjective value of rewards for task engagement across multiple levels of the N-back for OA and YA.

Subjective value decreases linearly with load (N). OA discount more than YA at all levels (N = 2–4). SE are shown. n_YA = 25 participants * 6 levels = 150 and n_OA = 25 participant * 4 levels = 100. Data also included for illustrative purposes in .

Figure 3. Area under the cognitive effort discounting curve predicts Need for Cognition.

Need for Cognition as predicted by Area Under the Curve of subjective value for levels N = 2–4 of the N-back. n = 50 participants.

Figure 4. Area under the cognitive effort discounting curve predicts delay discounting.

Area under the curves: for effort, averaged across $1 and $5 offers, levels N = 2–4; for delay, averaged across $1,000 and $25,000 offers, delays from one week to ten years. n = 33 participants.