Effort in Oculomotor Control: Role of Instructions and Reward on Spatio-temporal Eye Movement Dynamics

Effort is an important construct in several psychological disciplines, yet there is little consensus on how it manifests in behavior. Here, we focus on effort in terms of performance improvements beyond speed-accuracy tradeoffs and argue that oculomotor kinematics are conducive to a more fine-grained understanding of effortful behavior. Specifically, we investigated the efficiency and persistence of mere task instructions to induce transient effort. In a saccadic selection task, participants were instructed to look at targets as quickly and accurately as possible (standard instructions) or to mobilize all resources and respond even faster and more accurately ('to give 110%', effort instructions). We compared results to standard speeded performance (baseline block) and to a potential upper performance limit linking effort to performance-contingent rewards (reward block). Performance improved beyond speed-accuracy tradeoffs when reward was present. Effort instructions reduced saccade latencies, increased amplitudes and changed the saccade main sequence relationship. Yet, these effects were more strongly pronounced and more persistent over time when effort was additionally rewarded. Altogether, the present findings underscore the possibility to intentionally activate cognitive resources for regulating oculomotor performance. Yet, its effectiveness and maintenance over time are more successful when behavior is rendered purposeful by the presence of reward.