Neural population dynamics of human working memory.

The activity of neurons in macaque prefrontal cortex (PFC) persists during working memory (WM) delays, providing a mechanism for memory. Although theory, including formal network models, assumes that WM codes are stable over time, PFC neurons exhibit dynamics inconsistent with these assumptions. Recently, multivariate reanalyses revealed the coexistence of both stable and dynamic WM codes in macaque PFC.

Joint representation of working memory and uncertainty in human cortex.

Neural representations of visual working memory (VWM) are noisy, and thus, decisions based on VWM are inevitably subject to uncertainty. However, the mechanisms by which the brain simultaneously represents the content and uncertainty of memory remain largely unknown. Here, inspired by the theory of probabilistic population codes, we test the hypothesis that the human brain represents an item maintained in VWM as a probability distribution over stimulus feature space, thereby capturing both its content and uncertainty.

To look or not to look: dissociating presaccadic and covert spatial attention.

Attention is a central neural process that enables selective and efficient processing of visual information. Individuals can attend to specific visual information either overtly, by making an eye movement to an object of interest, or covertly, without moving their eyes. We review behavioral, neuropsychological, neurophysiological, and computational evidence of presaccadic attentional modulations that occur while preparing saccadic eye movements, and highlight their differences from those of covert spatial endogenous (voluntary) and exogenous (involuntary) attention.

Different computations underlie overt presaccadic and covert spatial attention.

Perception and action are tightly coupled: visual responses at the saccade target are enhanced right before saccade onset. This phenomenon, presaccadic attention, is a form of overt attention-deployment of visual attention with concurrent eye movements. Presaccadic attention is well-documented, but its underlying computational process remains unknown.

How exogenous spatial attention affects visual representation.

Orienting covert spatial attention to a target location enhances visual sensitivity and benefits performance in many visual tasks. How these attention-related improvements in performance affect the underlying visual representation of low-level visual features is not fully understood. Here we focus on characterizing how exogenous spatial attention affects the feature representations of orientation and spatial frequency.

Presaccadic attention improves or impairs performance by enhancing sensitivity to higher spatial frequencies.

Right before we move our eyes, visual performance and neural responses for the saccade target are enhanced. This effect, presaccadic attention, is considered to prioritize the saccade target and to enhance behavioral performance for the saccade target. Recent evidence has shown that presaccadic attention modulates the processing of feature information.

Attention model of binocular rivalry.

When the corresponding retinal locations in the two eyes are presented with incompatible images, a stable percept gives way to perceptual alternations in which the two images compete for perceptual dominance. As perceptual experience evolves dynamically under constant external inputs, binocular rivalry has been used for studying intrinsic cortical computations and for understanding how the brain regulates competing inputs. Converging behavioral and EEG results have shown that binocular rivalry and attention are intertwined: binocular rivalry ceases when attention is diverted away from the rivalry stimuli.

Proactive Control: Neural Oscillatory Correlates of Conflict Anticipation and Response Slowing.

Proactive control allows us to anticipate environmental changes and adjust behavioral strategy. In the laboratory, investigators have used a number of different behavioral paradigms, including the stop-signal task (SST), to examine the neural processes of proactive control. Previous functional MRI studies of the SST have demonstrated regional responses to conflict anticipation-the likelihood of a stop signal or P(stop) as estimated by a Bayesian model-and reaction time (RT) slowing and how these responses are interrelated.

Saccade Preparation Reshapes Sensory Tuning.

Human observers make large rapid eye movements-saccades-to bring behaviorally relevant information into the fovea, where spatial resolution is high. In some visual tasks [1-4], performance at the location of a saccade target improves before the eyes move. Although these findings provide evidence that extra-retinal signals evoked by saccades can enhance visual perception, it remains unknown whether and how presaccadic modulations change the processing of feature information and thus modulate visual representations.

Deconstructing Interocular Suppression: Attention and Divisive Normalization.

In interocular suppression, a suprathreshold monocular target can be rendered invisible by a salient competitor stimulus presented in the other eye. Despite decades of research on interocular suppression and related phenomena (e.g.

Perigenual anterior cingulate event-related potential precedes stop signal errors.

Momentary lapses in attention disrupt goal-directed behavior. Attentional lapse has been associated with increased "default-mode" network (DMN) activity. In our previous fMRI study of a stop signal task (SST), greater activation of the perigenual anterior cingulate cortex (pgACC) - an important node of the DMN - predicts stop signal errors.

Event-related potentials for post-error and post-conflict slowing.

In a reaction time task, people typically slow down following an error or conflict, each called post-error slowing (PES) and post-conflict slowing (PCS). Despite many studies of the cognitive mechanisms, the neural responses of PES and PCS continue to be debated. In this study, we combined high-density array EEG and a stop-signal task to examine event-related potentials of PES and PCS in sixteen young adult participants.

Backward position shift in apparent motion.

We investigated the perceived position of visual targets in apparent motion. A disc moved horizontally through three positions from -10° to +10° in the far periphery (20° above fixation), generating a compelling impression of apparent motion. In the first experiment, observers compared the position of the middle of the three discs to a subsequently presented reference.

Surround modulation of global form perception.

We demonstrate a novel surround modulation of global form perception by using Glass patterns in a center-surround configuration. Glass patterns contain randomly distributed dot pairs, or dipoles, whose orientations are determined by a geometric transform. By integrating across dipoles, an observer can perceive a global structure in the image.