No abstract

Observers can voluntarily select which items are encoded into working memory, and the efficiency of this process strongly predicts memory capacity. Nevertheless, the present work suggests that voluntary intentions do not exclusively determine what is encoded into this online workspace. Observers indicated whether any items from a briefly stored sample display had changed. Unbeknownst to observers, these changes were most likely to occur in a specific quadrant of the display (the dominant quadrant). Across 84 subjects and 5 groups of observers, change detection accuracy was significantly higher for items in the dominant quadrant, suggesting that memory encoding was biased towards the dominant quadrant. Only 9 of the 84 subjects were able to correctly specify the dominant quadrant when asked whether any location was more likely to contain the changed item, but more sensitive forced-choice procedures did reveal above-chance discrimination of the dominant quadrant. Nevertheless, because forced choice performance was unrelated to the size of the bias and no observer reported a biased encoding strategy, the bias was unlikely to depend on voluntary encoding strategies. The encoding bias was not due to a reduction in the response threshold for indicating changes in the dominant quadrant (Experiment 2). Finally, separate measures of the number and resolution of the representations in memory suggested that encoding was biased in a discrete slot-based fashion (Experiment 3). That is, although items in the dominant quadrant were more likely to be encoded into memory, mnemonic resolution for the favored items was not affected.

Various studies have demonstrated enhanced visual processing when information is presented across both visual hemifields rather than in a single hemifield (the bilateral advantage). For example, reported that observers were able to track twice as many moving visual stimuli when the tracked items were presented bilaterally rather than unilaterally, suggesting that independent resources enable tracking in the two visual fields. Motivated by similarities in the apparent capacity and neural substrates that mediate tracking and visual working memory (WM), the present work examined whether or not a bilateral advantage also arises during storage in visual WM. Using a recall procedure to assess working memory for orientation information, we found a reliable bilateral advantage; recall error was smaller with bilateral sample displays than with unilateral displays. To demonstrate that the bilateral advantage influenced storage per se rather than just encoding efficiency, we replicated the observed bilateral advantage using sequentially presented stimuli. Finally, to further characterize how bilateral presentations enhanced storage in working memory, we measured both the number and the resolution of the stored items and found that bilateral presentations lead to an increased probability of storage, rather than enhanced mnemonic resolution. Thus, the bilateral advantage extends beyond the initial selection and encoding of visual information to influence online maintenance in visual working memory.The organization of the visual system is primarily contralateral such that information from the left visual hemifield is initially processed in the right hemisphere while information from the right visual hemifield is processed in the left hemisphere. Although information from these separate pathways is eventually integrated via the connecting fibers of the corpus callosum, various studies have reported enhanced performance when items are distributed across both hemifields such that both the right and left hemispheres receive the initial input, compared to when a single hemisphere processes the same amount of information. This effect has been termed the bilateral advantage. Alvarez and Cavanagh (2005) provided one of the most compelling demonstrations of a bilateral advantage using a task that required observers to simultaneously track multiple targets that were presented in either unilateral or bilateral displays. This study revealed an approximate doubling of tracking capacity when the targets were spread across both hemifields compared to when the same number of targets occupied a single hemifield, suggesting independent attentional capacities in the right and left cerebral hemispheres. The Alvarez and Cavanagh (2005) findings dovetail with several other studies that also showed a clear bilateral advantage during encoding-limited tasks that required pattern matching (Muller, Malinowski, Gruber and Hillyard, 2003;Reuter-Lorenz, Stanczak and Miller, 1999;Sereno and Kosslyn, 1991) or rapid target discrimination (Awh and Pas...

Although cognitive control and reinforcement learning have been researched extensively over the last few decades, only recently have studies investigated their interrelationship. An important unanswered question concerns how the control system decides what task to execute and how vigorously to carry out the task once selected. Based on a recent theory of control formulated according to principles of hierarchical reinforcement learning, we asked whether rewards can affect top-down control over task performance at the level of task representation. Participants were rewarded for correctly performing only one of two tasks in a standard task-switching experiment. Reaction times and error rates were lower for the reinforced task compared to the non-reinforced task. Moreover, the switch cost in error rates for the non-reinforced task was significantly larger compared to the reinforced task, especially for trials in which the imperative stimulus afforded different responses for the two tasks, resulting in a "non-paradoxical" asymmetric switch cost. These findings suggest that reinforcement at the task level resulted in greater application of top-down control rather than in stronger stimulus-response pathways for the rewarded task.

Successful execution of goal-directed behaviors often requires the deployment of cognitive control, which is thought to require cognitive effort. Recent theories have proposed that anterior cingulate cortex (ACC) regulates control levels by weighing the reward-related benefits of control against its effort-related costs. However, given that the sensations of cognitive effort and reward valuation are available only to introspection, this hypothesis is difficult to investigate empirically. We have proposed that two electrophysiological indices of ACC function, frontal midline theta and the reward positivity (RewP), provide objective measures of these functions. To explore this issue, we recorded the electroencephalogram (EEG) from participants engaged in an extended, cognitively-demanding task. Participants performed a time estimation task for 2 h in which they received reward and error feedback according to their task performance. We observed that the amplitude of the RewP, a feedback-locked component of the event related brain potential associated with reward processing, decreased with time-on-task. Conversely, frontal midline theta power, which consists of 4-8 Hz EEG oscillations associated with cognitive effort, increased with time-on-task. We also explored how these phenomena changed over time by conducting within-participant multi-level modeling analyses. Our results suggest that extended execution of a cognitively-demanding task is characterized by an early phase in which high control levels foster rapid improvements in task performance, and a later phase in which high control levels were necessary to maintain stable task performance, perhaps counteracting waning reward valuation.