James Elliott

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.

A week-long meditation retreat decouples behavioral measures of the alerting and executive attention networks

Previous studies have examined the influence of meditation on three functionally different components of attention: executive control, alerting, and orienting. These studies have consistently found that meditation training improves both executive attention and alerting, but there has not been a consistent and clear effect of meditation training on orienting. In addition, while previous studies have shown that the functional coupling of the alerting and executive networks increases the processing of task irrelevant stimuli, it is unknown if participating in a meditation retreat can decouple these components of attention and lead to improved performance. The current study investigated the influence of a week-long intensive meditation retreat on three components of attention by randomly assigning participants to either pre- or postretreat testing groups. A modified attention network test (ANT) was used. Executive attention was measured as the difference in response time (RT) between congruent and incongruent task irrelevant flankers (conflict effect). Reflexive and volitional orienting were measured by manipulating cue validity and stimulus onset asynchrony (SOA). The coupling of executive attention and alerting was measured by examining flanker interference as a function of the SOA of an alerting cue. The meditation retreat improved task based indices of executive attention, but not reflexive or volitional orienting. There was clear behavioral evidence of coupling between executive attention and alerting in the preretreat group, as the conflict effect peaked when an alerting cue was presented 300 ms before the target. Importantly, there was no increase in the conflict effect for the postretreat group. This is consistent with the notion that the retreat decoupled the executive and alerting networks. These results suggest that previously reported improvements in the executive and alerting networks after meditation training might be mediated by the same underlying mechanism.

Multimodal target detection using single trial evoked EEG responses in single and dual-tasks

The detection of event-related potentials in the electroencephalogram signal is a common way for creating a brain-computer interface (BCI). Successful detection of evoked responses can be enhanced by the user selectively attending to specific stimuli presented in the BCI task. Because BCI users need a system that performs well in a variety of contexts, even ones that may impair selective attention, it is critical to understand how single trial detection is affected by attention. We tested 16 participants using a rapid serial visual/auditory presentation paradigm under three conditions, one in which they detected the presence of a visual target, one in which they detected the presence of an auditory target, and one in which they detected both visual and auditory targets. The behavioral performance indicates that the visual task was more difficult than the auditory task. Consistent with the higher behavioral difficulty of the visual task, single trial performance showed no difference between single and dual-task for the visual target detection (mean=0.76). However, the area under the curve for the auditory target detection was significantly lower than the dual-task (mean=0.81 for single task, 0.75 for dual-task). The results support the conclusion that single-trial target detection is impaired when attention is divided between multiple tasks.

Multiple measures of visual attention predict novice motor skill performance when attention is focused externally.

Multiple lines of evidence indicate that the control of attention and motor skill performance are related. Athletes of various skill levels differ in terms of their control over the focus of attention and directing athletes to adopt an internal or external focus of attention modulates performance. However, it is unclear (a) whether the relationship between skill level and attentional control arises from preexisting individual differences in attention or from practice of the motor skill and (b) whether the effect of adopting an internal or external focus of attention on motor performance is influenced by individual differences in attention. To address these issues, individuals were measured on three distinct attention functions - orienting, alerting, and executive - prior to engaging in a novel golf-putting task performed with either external or internal focus instructions. The results indicated that, on average, attentional functioning and putting performance were related but that the strong relationships with orienting and executive attention were only present in the group given external focus instructions. These findings suggest that individual differences in attentional abilities are predictive of novel skill performance under an external focus of attention and they shed light on the mechanisms underlying the effects of focus instructions during motor performance.

Neurocognitive and Somatic Components of Temperature Increases during g-Tummo Meditation: Legend and Reality

Stories of g-tummo meditators mysteriously able to dry wet sheets wrapped around their naked bodies during a frigid Himalayan ceremony have intrigued scholars and laypersons alike for a century. Study 1 was conducted in remote monasteries of eastern Tibet with expert meditators performing g-tummo practices while their axillary temperature and electroencephalographic (EEG) activity were measured. Study 2 was conducted with Western participants (a non-meditator control group) instructed to use the somatic component of the g-tummo practice (vase breathing) without utilization of meditative visualization. Reliable increases in axillary temperature from normal to slight or moderate fever zone (up to 38.3°C) were observed among meditators only during the Forceful Breath type of g-tummo meditation accompanied by increases in alpha, beta, and gamma power. The magnitude of the temperature increases significantly correlated with the increases in alpha power during Forceful Breath meditation. The findings indicate that there are two factors affecting temperature increase. The first is the somatic component which causes thermogenesis, while the second is the neurocognitive component (meditative visualization) that aids in sustaining temperature increases for longer periods. Without meditative visualization, both meditators and non-meditators were capable of using the Forceful Breath vase breathing only for a limited time, resulting in limited temperature increases in the range of normal body temperature. Overall, the results suggest that specific aspects of the g-tummo technique might help non-meditators learn how to regulate their body temperature, which has implications for improving health and regulating cognitive performance.

Perceptual load modulates the processing of distractors presented at task-irrelevant locations during the attentional blink

The distribution of attention in both space and time is critical for processing our dynamic environment. Studies of spatial attention suggest that the distribution of attention is decreased when the perceptual load of a task increases, resulting in decreased processing of task-irrelevant distractors. Studies of the attentional blink (AB) suggest that the temporal distribution of attention also influences distractor processing, such that distractor processing increases during the AB relative to outside the AB (Jiang & Chun, 2001). Two experiments are reported in which the extent to which the difficulty of the first target task (T1) modulates the processing of task-irrelevant distractors during the AB was tested. To investigate this issue, both the first and second target tasks (T1 and T2) required identifying a central stimulus that was flanked by low-load or high-load distractors. Consistent with previous studies of the AB, there was evidence of more distractor processing during the AB than outside the AB. Critically, however, the interference caused by distractors presented simultaneously with T2 during the AB was reduced when T1 perceptual load was high relative to when it was low. These results suggest that increasing T1 perceptual load decreases distractor processing during the AB and that perceptual processes influence both the temporal and spatial distribution of attention.

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.

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.

Acute exercise modulates feature-selective responses in human cortex

An organisms current behavioral state influences ongoing brain activity. Nonhuman mammalian and invertebrate brains exhibit large increases in the gain of feature-selective neural responses in sensory cortex during locomotion, suggesting that the visual system becomes more sensitive when actively exploring the environment. This raises the possibility that human vision is also more sensitive during active movement. To investigate this possibility, we used an inverted encoding model technique to estimate feature-selective neural response profiles from EEG data acquired from participants performing an orientation discrimination task. Participants (n = 18) fixated at the center of a flickering (15 Hz) circular grating presented at one of nine different orientations and monitored for a brief shift in orientation that occurred on every trial. Participants completed the task while seated on a stationary exercise bike at rest and during low- and high-intensity cycling. We found evidence for inverted-U effects; such that the peak of the reconstructed feature-selective tuning profiles was highest during low-intensity exercise compared with those estimated during rest and high-intensity exercise. When modeled, these effects were driven by changes in the gain of the tuning curve and in the profile bandwidth during low-intensity exercise relative to rest. Thus, despite profound differences in visual pathways across species, these data show that sensitivity in human visual cortex is also enhanced during locomotive behavior. Our results reveal the nature of exercise-induced gain on feature-selective coding in human sensory cortex and provide valuable evidence linking the neural mechanisms of behavior state across species.

Distractor suppression when attention fails: behavioral evidence for a flexible selective attention mechanism.

Despite consistent evidence showing that attention is a multifaceted mechanism that can operate at multiple levels of processing depending on the structure and demands of the task, investigations of the attentional blink phenomenon have consistently shown that the impairment in reporting the second of two targets typically occurs at a late, or post-perceptual, stage of processing. This suggests that the attentional blink phenomenon may represent the operation of a unique attentional mechanism that is not as flexible as other attentional mechanisms. To test whether the attentional blink is a fixed or flexible phenomenon, we manipulated first target task demands (i.e., difficulty) and measured the influence this had on processing a subsequently presented distractor and the second target. If the attentional blink represents a mechanism that is fixed and consistently fails at a single stage of processing, then manipulations of task difficulty should not affect distractor processing. However, if the attentional blink represents a more multifaceted and flexible mechanism, then task difficulty should modulate distractor processing. The results revealed that distractor processing during the AB was attenuated under high task difficulty. In addition, unlike previous studies, we failed to find a correlation between distractor processing and the severity of the attentional blink. Using a simulation, we demonstrate that the previously reported correlations may have been spurious and due to using variables that were not independent. Overall, the present results support the conclusion that the selectivity of attention during the AB is flexible and depends on the structure and demands of the task.