Cognitive regulation of saccadic velocity by reward prospect

Abstract

It is known that expectation of reward speeds up saccades. Past studies have also shown the presence of a saccadic velocity bias in the orbit, resulting from a biomechanical regulation over varying eccentricities. Nevertheless, whether and how reward expectation interacts with the biomechanical regulation of saccadic velocities over varying eccentricities remains unknown. We addressed this question by conducting a visually guided double-step saccade task. The role of reward expectation was tested in monkeys performing two consecutive horizontal saccades, one associated with reward prospect and the other not. To adequately assess saccadic velocity and avoid adaptation, we systematically varied initial eye positions, saccadic directions and amplitudes. Our results confirmed the existence of a velocity bias in the orbit, i.e., saccadic peak velocity decreased linearly as the initial eye position deviated in the direction of the saccade. The slope of this bias increased as saccadic amplitudes increased. Nevertheless, reward prospect facilitated velocity to a greater extent for saccades away from than for saccades toward the orbital centre, rendering an overall reduction in the velocity bias. The rate (slope) and magnitude (intercept) of reward modulation over this velocity bias were linearly correlated with amplitudes, similar to the amplitude-modulated velocity bias without reward prospect, which presumably resulted from a biomechanical regulation. Small-amplitude (≤ 5°) saccades received little modulation. These findings together suggest that reward expectation modulated saccadic velocity not as an additive signal but as a facilitating mechanism that interacted with the biomechanical regulation.

Motivational state, reward value, and Pavlovian cues differentially affect skilled forelimb grasping in rats

“…These findings provide strong evidence for an effect of reward value on motor skill performance. Similar performance effects of reward have been shown in saccade velocity and wrist movement reaction times (Takikawa et al 2002;Xu-Wilson et al 2009;Opris et al 2011;Chen et al 2013). Accuracy of the movement, measured in success rate, also showed a significant effect of reward value, but aversive quinine-flavored pellets were accurately grasped by the end of training as well, indicating that grasps for quinine-flavored pellets were not invigorated but were still performed accurately.…”

“…Studies in rodents further supported this concept and showed that net expected rewards, rather than immediate reward history, determine performance vigor (Wang et al 2013). However, when the value of the upcoming reward was known beforehand, faster saccades were performed in high reward value trials compared with low reward value or no reward trials (Takikawa et al 2002;Xu-Wilson et al 2009;Shadmehr et al 2010;Chen et al 2013). Similar results were observed in an experiment studying reaction times of wrist movements (Opris et al 2011).…”

Role of expected reward in frontal eye field during natural scene search

“…Specifically, we tested for differences in latency and velocity of saccades, since previous studies have shown that expected reward can decrease the latency and increase the velocity of saccades (Kawagoe et al 1998;Haith et al 2012;Beierholm et al 2013;Choi et al 2014).…”

“…Therefore, to ask whether saccade velocity varies with reward expectancy, we needed a velocity measure that accounts for the fact that velocity varies as a function of amplitude. We use "vigor" (Choi et al 2014), which describes how much the velocity of a saccade is above or below the expected velocity (for all saccades) given the saccade amplitude (see METHODS for calculation of vigor; Fig. 2, F and G).…”

“…This results in movements with greater vigor (higher velocity), lower latency, and greater accuracy (Chen et al 2013;Choi et al 2014;Reppert et al 2015). In other words, the movement itself reflects the expectation of reward.…”