Jocelyn L. Sy

Electrophysiological evidence for both perceptual and postperceptual selection during the attentional blink

When two masked targets are presented in rapid succession, correct identification of the first target (T1) leads to a dramatic impairment in identification of the second target (T2). Several studies of this so-called attentional blink (AB) phenomenon have provided behavioral and physiological evidence that T2 is processed to the semantic level, despite the profound impairment in T2 report. These findings have been interpreted as an example of perception without awareness and have been explained by models that assume that T2 is processed extensively even though it does not gain access into consciousness. The present study reports two experiments that test this assumption. In Experiment 1, the perceptual load of the T1 task was manipulated and T2 was a word that was either related or unrelated to a context word presented at the beginning of each trial. The event-related potential (ERP) technique was used to isolate the context-sensitive N400 component evoked by the T2 word. The ERP data revealed that there was a complete suppression of the N400 during the AB when the perceptual load was high, but not when perceptual load was low. Experiment 2 replicated the high-load condition of Experiment 1 while ruling out two alternative explanations for the reduction of the N400 during the AB. The results of both experiments demonstrate that word meanings are not always accessed during the AB and are consistent with studies that suggest that attention can act to select information at multiple stages of processing depending on concurrent task demands.

Personal names do not always survive the attentional blink: Behavioral evidence for a flexible locus of selection.

Models of the attentional blink phenomenon (AB) typically assume that unattended information is processed to the post-perceptual level prior to selection for access to consciousness. The present experiments test this assumption by manipulating the perceptual load of the first target task (T1) and whether the second target (T2) was the participants own name or someone elses name. In three experiments, increasing T1-load increased the severity of the AB for personal names. The results suggest that selection during the AB is not fixed at the post-perceptual stage, but rather the stage at which selection occurs during the AB is flexible.

A new perspective on the perceptual selectivity of attention under load

The human attention system helps us cope with a complex environment by supporting the selective processing of information relevant to our current goals. Understanding the perceptual, cognitive, and neural mechanisms that mediate selective attention is a core issue in cognitive neuroscience. One prominent model of selective attention, known as load theory, offers an account of how task demands determine when information is selected and an account of the efficiency of the selection process. However, load theory has several critical weaknesses that suggest that it is time for a new perspective. Here we review the strengths and weaknesses of load theory and offer an alternative biologically plausible computational account that is based on the neural theory of visual attention. We argue that this new perspective provides a detailed computational account of how bottom‐up and top‐down information is integrated to provide efficient attentional selection and allocation of perceptual processing resources.

Radial bias is not necessary for orientation decoding.

Multivariate pattern analysis can be used to decode the orientation of a viewed grating from fMRI signals in early visual areas. Although some studies have reported identifying multiple sources of the orientation information that make decoding possible, a recent study argued that orientation decoding is only possible because of a single source: a coarse-scale retinotopically organized preference for radial orientations. Here we aim to resolve these discrepant findings. We show that there were subtle, but critical, experimental design choices that led to the erroneous conclusion that a radial bias is the only source of orientation information in fMRI signals. In particular, we show that the reliance on a fast temporal-encoding paradigm for spatial mapping can be problematic, as effects of space and time become conflated and lead to distorted estimates of a voxels orientation or retinotopic preference. When we implement minor changes to the temporal paradigm or to the visual stimulus itself, by slowing the periodic rotation of the stimulus or by smoothing its contrast-energy profile, we find significant evidence of orientation information that does not originate from radial bias. In an additional block-paradigm experiment where space and time were not conflated, we apply a formal model comparison approach and find that many voxels exhibit more complex tuning properties than predicted by radial bias alone or in combination with other known coarse-scale biases. Our findings support the conclusion that radial bias is not necessary for orientation decoding. In addition, our study highlights potential limitations of using temporal phase-encoded fMRI designs for characterizing voxel tuning properties.

Post-perceptual processing during the attentional blink is modulated by inter-trial task expectancies.

The selective processing of goal-relevant information depends on an attention system that can flexibly adapt to changing task demands and expectations. Evidence from visual search tasks indicates that the perceptual selectivity of attention increases when the bottom-up demands of the task increase and when the expectations about task demands engendered by trial history are violated. Evidence from studies of the attentional blink (AB), which measures the temporal dynamics of attention, also indicates that perceptual selectivity during the AB is increased if the bottom-up task demands are increased. The present work tested whether expectations about task demands engendered by trial history also modulate perceptual selectivity during the AB. Two experiments tested the extent to which inter-trial switches in task demands reduced post-perceptual processing of targets presented during the AB. Experiment 1 indexed post-perceptual processing using the event-related potential (ERP) technique to isolate the context sensitive N400 ERP component evoked by words presented during the AB. Experiment 2 indexed post-perceptual processing using behavioral performance to determine the extent to which personal names survive the AB. The results of both experiments revealed that both electrophysiological (Exp. 1) and behavioral (Exp. 2) indices of post-perceptual processing were attenuated when consecutive trials differed in terms of their perceptual demands. The results are consistent with the notion that the selectivity of attention during the AB is modulated not only by within-trial task demands, but also can be flexibly determined by trial-by-trial expectations.

Individual differences in sensory eye dominance reflected in the dynamics of binocular rivalry

HighlightsA large subset of observers experience imbalance between their two eyes.The stronger eye is dominant longer and more frequently during binocular rivalry.Large eye imbalance also predicts frequent return transitions to the dominant eye.Sighting and sensory eye dominance are unrelated. ABSTRACT Normal binocular vision emerges from the combination of neural signals arising within separate monocular pathways. It is natural to wonder whether both eyes contribute equally to the unified cyclopean impression we ordinarily experience. Binocular rivalry, which occurs when the inputs to the two eyes are markedly different, affords a useful means for quantifying the balance of influence exerted by the eyes (called sensory eye dominance, SED) and for relating that degree of balance to other aspects of binocular visual function. However, the precise ways in which binocular rivalry dynamics change when the eyes are unbalanced remain uncharted. Relying on widespread individual variability in the relative predominance of the two eyes as demonstrated in previous studies, we found that an observer’s overall tendency to see one eye more than the other was driven both by differences in the relative duration and frequency of instances of that eye’s perceptual dominance. Specifically, larger imbalances between the eyes were associated with longer and more frequent periods of exclusive dominance for the stronger eye. Increases in occurrences of dominant eye percepts were mediated in part by a tendency to experience “return transitions” to the predominant eye – that is, observers often experienced sequential exclusive percepts of the dominant eye’s image with an intervening mixed percept. Together, these results indicate that the often‐observed imbalances between the eyes during binocular rivalry reflect true differences in sensory processing, a finding that has implications for our understanding of the mechanisms underlying binocular vision in general.

Impact of target probability on single-trial EEG target detection in a difficult rapid serial visual presentation task

In non-invasive brain-computer interface (BCI), the analysis of event-related potentials (ERP) has typically focused on averaged trials, a current trend is to analyze single-trial evoked response individually with new approaches in pattern recognition and signal processing. Such single trial detection requires a robust response that can be detected in a variety task conditions. Here, we investigated the influence of target probability, a key factor known to influence the amplitude of the evoked response, on single trial target classification in a difficult rapid serial visual presentation (RSVP) task. Our classification approach for detecting target vs. non target responses, considers spatial filters obtained through the maximization of the signal to signal-plus-noise ratio, and then uses the resulting information as inputs to a Bayesian discriminant analysis. The method is evaluated across eight healthy subjects, on four probability conditions (P=0.05, 0.10, 0.25, 0.50). We show that the target probability has a statistically significant effect on both the behavioral performance and the target detection. The best mean area under the ROC curve is achieved with P=0.10, AUC=0.82. These results suggest that optimal performance of ERP detection in RSVP tasks is critically dependent on target probability.

Accurate expectancies diminish perceptual distraction during visual search

The load theory of visual attention proposes that efficient selective perceptual processing of task-relevant information during search is determined automatically by the perceptual demands of the display. If the perceptual demands required to process task-relevant information are not enough to consume all available capacity, then the remaining capacity automatically and exhaustively “spills-over” to task-irrelevant information. The spill-over of perceptual processing capacity increases the likelihood that task-irrelevant information will impair performance. In two visual search experiments, we tested the automaticity of the allocation of perceptual processing resources by measuring the extent to which the processing of task-irrelevant distracting stimuli was modulated by both perceptual load and top-down expectations using behavior, functional magnetic resonance imaging, and electrophysiology. Expectations were generated using a trial-by-trial cue that provided information about the likely load of the upcoming visual search task. When the cues were valid, behavioral interference was eliminated and the influence of load on frontoparietal and visual cortical responses was attenuated relative to when the cues were invalid. In conditions in which task-irrelevant information interfered with performance and modulated visual activity, individual differences in mean blood oxygenation level dependent responses measured from the left intraparietal sulcus were negatively correlated with individual differences in the severity of distraction. These results are consistent with the interpretation that a top-down biasing mechanism interacts with perceptual load to support filtering of task-irrelevant information.

Persistent Biases in Binocular Rivalry Dynamics within the Visual Field

Binocular rivalry is an important tool for measuring sensory eye dominance—the relative strength of sensory processing in an individual’s left and right eye. By dichoptically presenting images that lack corresponding visual features, one can induce perceptual alternations and measure the relative visibility of each eye’s image. Previous results indicate that observers demonstrate reliable preferences for several image features, and that these biases vary within the visual field. However, evidence about the persistence of these biases is mixed, with some suggesting they affect only the onset (i.e., first second) of rivalry, and others suggesting lasting effects during prolonged viewing. We directly investigated individuals’ rivalry biases for eye and color within the visual field and interestingly found results that mirrored the somewhat contradictory pattern in the literature. Each observer demonstrated idiosyncratic patterns of biases for both color and eye within the visual field, but consistent, prolonged biases only for the eye of presentation (sensory eye dominance, SED). Furthermore, the strength of eye biases predicted one’s performance on a stereoacuity task. This finding supports the idea that binocular rivalry and other binocular visual functions may rely on shared mechanisms, and emphasizes the importance of SED as a measure of binocular vision.

Target–target similarity and the attentional blink: Task-relevance matters!

Studies of the attentional blink (AB) indicate that similarity modulates the magnitude of the impairment in reporting the second of two masked targets. The present experiments tested whether similarity-based modulations of the AB are determined by all object dimensions or by task-relevant dimensions only. Similarity between target faces was manipulated on two dimensions, only one of which was task relevant. The results indicated that similarity on the task-relevant dimension modulated the AB, whereas similarity on task-irrelevant dimension did not. These results suggest that selection during the AB can occur on the level of task-relevant dimensions.