Been around the block: How efficacy and reward shape cognitive effort allocation over time

Background Modern accounts of cognitive effort posit that it is actively controlled based on a cost-benefit analysis, integrating (subjective) costs and possible rewards, which is furthermore moderated by efficacy (i.e., whether there is a clear relationship between successful task performance and reward). Although there is evidence that reward and efficacy interact, this relationship may not be stable over time, given that reward attenuates time-on-task effects while efficacy’s relationship with time-on-task is still unclear. Methods Thirty participants performed a Stroop task with a block design, with block-wise manipulation of efficacy (possible rewards were either contingent upon correct task performance or determined without regard to task performance) and reward (high or low). Behavioral measures (response time and accuracy), pupil data (tonic and phasic pupil size), and blink measures (rate and duration) were recorded and analyzed using a mixed-effects modelling approach, with each block split into two halves to assess time-on-task effects. Results The behavioral data showed strong effects for efficacy, a pattern that was also largely mirrored in phasic pupil size, suggesting substantial effort allocation. In contrast, we found no clear impact of time-on-task or reward on behavioral data or phasic pupil size. However, tonic pupil size and blink metrics (rate and duration) did reflect time-on-task effects, with reward and efficacy attenuating these in some cases. Taken together, the present results suggest a strong and stable control mode for high-efficacy/high-reward blocks, with low-efficacy/low-reward blocks leading to disengagement, whereas the mixed block types seemed to be tackled with suboptimal levels of cognitive effort while still showing signs of increasing fatigue. Conclusions Thereby, this study contributes corroborating evidence in favor of the account that information regarding efficacy is robustly integrated into the cost-benefit analysis underlying the allocation of cognitive control resources, and highlights the complex dynamics of cognitive effort over time.