Recent research using change-detection tasks has shown that a directed-forgetting cue, indicating that a subset of the information stored in memory can be forgotten, significantly benefits the other information stored in visual working memory. How do these directed-forgetting cues aid the memory representations that are retained? We addressed this question in the present study by using a recall paradigm to measure the nature of the retained memory representations. Our results demonstrate that a directed-forgetting cue leads to higher fidelity representations of the remaining items and a lower probability of dropping these representations from memory. Next, we show that this is possible because the to-be-forgotten item is expelled from visual working memory following the cue allowing maintenance mechanisms to be focused on only the items that remain in visual working memory. Thus, the present findings show that cues to forget benefit the remaining information in visual working memory by fundamentally improving their quality relative to conditions in which just as many items are encoded but no cue is provided.

Most models assume that response time (RT) comprises the time required for successive processing stages, but they disagree about whether information is transmitted continuously or discretely between stages. We tested these alternative hypotheses by measuring when movement-related activity began in the frontal eye field (FEF) of macaque monkeys performing visual search. Previous work showed that RT was longer when visual neurons in FEF took longer to select the target, a finding consistent with prolonged perceptual processing during less efficient search. We now report that the buildup of saccadic movement-related activity in FEF is delayed in inefficient visual search. Variability in the delay of movement-related activity accounted for the difference in RT between search conditions and for the variability of RT within conditions. These findings provide neurophysiological support for the hypothesis that information is transmitted discretely between perceptual and response stages of processing during visual search.

A half-century's worth of research has established the existence of numerous event-related potential components measuring different cognitive operations in humans including the selection of stimuli by covert attention mechanisms. Surprisingly, it is unknown whether nonhuman primates exhibit homologous electrophysiological signatures of selective visual processing while viewing complex scenes. We used an electrophysiological technique with macaque monkeys analogous to procedures for recording scalp event-related potentials from humans and found that monkeys exhibit short-latency visual components sensitive to sensory processing demands and lateralizations related to shifting of covert attention similar to the human N2pc component. These findings begin to bridge the gap between the disparate literatures by using electrophysiological measurements to study the deployment of visual attention in the brains of humans and nonhuman primates.macaque ͉ monkey ͉ visual search ͉ electroencephalogram ͉ local field potentials E ver since Caton's experiments with animals (1) inspired Berger's (2) discovery of the electroencephalogram (EEG) in humans, the literatures on animal and human electrophysiology have developed largely independently. This chasm is principally because of methodological differences. Invasive single-unit recording in animals have yielded a rich literature describing the functional characteristics of individual neurons (3-6). In contrast, decades of noninvasive EEG and eventrelated potential (ERP) research with humans have revealed many aspects of large ensemble activity during different cognitive processes (7)(8)(9)(10)(11)(12)(13)(14). This has resulted in gaps in our understanding of how the brains of humans and nonhuman primates process information during cognitively demanding tasks. For example, it is unknown whether macaque monkeys exhibit electrophysiological indices of covert visual attention homologous to those described in human subjects. The need for studies directly comparing electrophysiological measures of dynamic information processing between species has been identified as a major weakness in our understanding of brain function (15). In this study, we sought to bridge this gap by recording ERPs from monkeys performing a difficult visual search task to obtain data directly comparable with studies of human subjects. This work builds on pioneering studies that have sought to establish nonhuman primate homologues of a number of human ERP components indexing other cognitive processes. For example, research has established homologues of the human P3 component (16)(17)(18)(19), early sensory potentials (also known as visual evoked potentials or VEPs, e.g.,, and the mismatch and selection negativities in cross modal and auditory oddball tasks (24-28). Additionally, a number of other studies have explored the neural substrates of the electrical activity in the brain that gives rise to the observed EEG and averaged ERPs, typically by using cross-modal tasks (24,25,(29)(30)(31).This study addresses a cr...

It has been intensely debated whether visual stimuli are processed to the point of semantic analysis in the absence of awareness. In the present study, we measured the extent to which the meaning of a stimulus was registered using the N400 component of human event-related potentials (ERPs), a highly sensitive index of the semantic mismatch between a stimulus and the context in which it is presented. Observers judged the semantic relatedness of a context and target word while ERPs were recorded under continuous flash suppression (Experiment 1 and 2) and binocular rivalry (Experiment 3). Finally, we parametrically manipulated the visibility of the target word by increasing the contrast between the target word and the suppressive stimulus presented to the other eye (Experiment 4). We found that the amplitude of the N400 was attenuated with increasing suppression depth and was absent whenever the observers could not discriminate the meaning of suppressed words. We discuss these findings in the context of single-process models of consciousness which can account for a large body of empirical evidence obtained from visual masking, attentional manipulations and, now, interocular suppression paradigms.