Does reward modulate actions or bias attention?

Editor's Note: These short reviews of a recent paper in the Journal, written exclusively by graduate students or postdoctoral fellows, are intended to mimic the journal clubs that exist in your own departments or institutions. For more information on the format and purpose of the Journal Club, please see The neural mechanisms underlying decision making have often been probed by asking subjects to choose between movements (e.g., making a saccade to a left or right target) (Sugrue et al., 2005). In studying decisions, the influence of so-called " top-down " factors such as reward magnitude, reward probability, and motivation are of fundamental interest and importance. Unfortunately, these parameters are much more difficult to quantify and modulate empirically than are " bottom-up " factors such as contrast and luminance. In their recent article in The Journal of Neuroscience, Milstein and Dor-ris (2007) studied the effect of expected value (the product of reward magnitude and probability) on saccadic control. This work builds on the saccadic decision literature , the vast majority of which is based on investigations on nonhuman primate brains (Schall, 2001; Ikeda, 2003). Milstein and Dorris (2007) instructed human participants to fixate a central spot and then make a saccadic eye movement to a red target which appeared after a 400 ms blank screen (Fig. 1) [Milstein and Dorris (2007), their Fig. 1 magnitude of the reward was dependent on the side of the target and varied across blocks of trials. The probability of the target appearing on the left or right was fixed for each block but also varied independently across blocks. The aim was to investigate whether saccadic preparation toward a particular target was influenced by the expected value of that location. Saccadic reaction time (SRT) was measured as a conventional index of preparation. In addition, the authors used a relatively novel probe to interrogate saccadic preparation before target presentation, by presenting a distractor halfway through the warning period, after 200 ms (Fig. 1 A) (30% of trials). These were green, rather than red, but were otherwise identical to real targets and served to trigger erroneous saccades termed " oculomotor capture. " The underlying assumption was that a certain amount of saccadic preparedness must already have been reached if distractors were able to bring the planning circuitry to saccade threshold (Theeuwes, 1999). No reward was given on trials in which oculomotor capture occurred, so there was an incentive …