Through rapid serial visual presentation (RSVP), we asked Ss to identify a partially specified letter (target) and then to detect the presence or absence of a fully specified letter (probe). Whereas targets are accurately identified, probes are poorly detected when they are presented during a 270-ms interval beginning 180 ms after the target. Probes presented immediately after the target or later in the RSVP stream are accurately detected. This temporary reduction in probe detection was not found in conditions in which a brief blank interval followed the target or Ss were not required to identify the target. The data suggest that the presentation of stimuli after the target but before target-identification processes are complete produces interference at a letter-recognition stage. This interference may cause the temporary suppression of visual attention mechanisms observed in the present study.

nisms may be used for space-based attention that are not available for time-based attention. In this study we addressed this issue by comparing the nature of attentional selection in a time-based attention task with previous findings from space-based attention tasks.

To-investigate the temporal allocation of attention, a series of 7 experiments using rapid serial visual presentation (RSVP) was designed to examine the relationship of the attentional demands of various target tasks to the production of the subsequent visual attentional deficit, or "attentional blink" (AB), recently reported by J. E. Raymond, K. L. Shapiro, and K. M. Arnell (1992). The principal finding is that AB occurs only when a target is an object and does not occur when the target is defined by a temporal interval. Target detection difficulty as estimated by d' analysis reveals no relationship between the attentional demands of the target and the production of the AB. A late-selection account of this phenomenon is offered in place of the early-selection account advanced in Raymond et al.'s previous report.

In vision, attentional limitations are reflected in interference or reduced accuracy when two objects must be identified at once in a brief display. In our experiments a brief temporal separation was introduced between the two objects to be identified. We measured how long the object continued to interfere with the second, and hence the time course of the first object's attentional demand. According to conventional serial models, attention is assigned rapidly to one object after another, with a dwell time of only a few dozen milliseconds per item. But we report here that interference lasts for several hundred milliseconds--an order of magnitude more than the prediction of conventional models. We suggest that visual attention is not a high-speed switching mechanism, but a sustained state during which relevant objects become available to influence behaviour. This conclusion is consistent with recent physiological results in the monkey.

Because of attentional limitations, the human visual system can process for awareness and response only a fraction of the input received. Lesion and functional imaging studies have identified frontal, temporal, and parietal areas as playing a major role in the attentional control of visual processing, but very little is known about how these areas interact to form a dynamic attentional network. We hypothesized that the network communicates by means of neural phase synchronization, and we used magnetoencephalography to study transient long-range interarea phase coupling in a well studied attentionally taxing dual-target task (attentional blink). Our results reveal that communication within the fronto-parieto-temporal attentional network proceeds via transient long-range phase synchronization in the beta band. Changes in synchronization reflect changes in the attentional demands of the task and are directly related to behavioral performance. Thus, we show how attentional limitations arise from the way in which the subsystems of the attentional network interact. T he human brain faces an inestimable task of reducing a potentially overloading amount of input into a manageable flow of information that reflects both the current needs of the organism and the external demands placed on it. This task is accomplished via a ubiquitous construct known as ''attention,'' whose mechanism, although well characterized behaviorally, is far from understood at the neurophysiological level. Whereas attempts to identify particular neural structures involved in the operation of attention have met with considerable success (1-5) and have resulted in the identification of frontal, parietal, and temporal regions, far less is known about the interaction among these structures in a way that can account for the task-dependent successes and failures of attention. The goal of the present research was, thus, to unravel the means by which the subsystems making up the human attentional network communicate and to relate the temporal dynamics of their communication to observed attentional limitations in humans.A prime candidate for communication among distributed systems in the human brain is neural synchronization (for review, see ref. 6). Indeed, a number of studies provide converging evidence that long-range interarea communication is related to synchronized oscillatory activity (refs. 7-14; for review, see ref. 15). To determine whether neural synchronization plays a role in attentional control, we placed humans in an attentionally demanding task and used magnetoencephalography (MEG) to track interarea communication by means of neural synchronization.In particular, we presented 10 healthy subjects with two visual target letters embedded in streams of 13 distractor letters, appearing at a rate of seven per second. The targets were separated in time by a single distractor. This condition leads to the ''attentional blink'' (AB), a well studied dual-task phenomenon showing the reduced ability to report the second of two targets when an interval Ͻ5...

After the detection of a target item in a rapid stream of visual stimuli, there is a period of 400-600 ms during which subsequent targets are missed. This impairment has been labelled the 'attentional blink'. It has been suggested that, unlike an eye blink, the additional blink does not reflect a suppression of perceptual processing, but instead reflects a loss of information at a postperceptual stage, such as visual short-term memory. Here we provide electrophysiological evidence that words presented during the attentional blink period are analysed to the point of meaning extraction, even though these extracted meanings cannot be reported 1-2s later. This shows that the attentional blink does indeed reflect a loss of information at a postperceptual stage of processing, and provides a demonstration of the modularity of human brain function.

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Our brain does not process incoming sensory stimuli mechanistically. Instead the current brain state modulates our reaction to a stimulus. This modulation can be investigated by cognitive paradigms such as the attentional blink, which reveal that identical visual target stimuli are correctly reported only on about half the trials. Support for the notion that the fluctuating state of the brain determines stimulus detection comes from electrophysiological investigations of brain oscillations, which have shown that different parameters of ongoing oscillatory alpha activity (~10 Hz) can predict whether a visual stimulus will be perceived or not. The present article reviews recent findings on the role of prestimulus alpha oscillatory activity for visual perception and incorporates these results into a neurocognitive model that is able to account for various findings in temporal attention paradigms, specifically the attentional blink.