The attentional blink: a review of data and theory

Under conditions of rapid serial visual presentation, subjects display a reduced ability to report the second of two targets (Target 2; T2) in a stream of distractors if it appears within 200-500 msec of Target 1 (T1). This effect, known as the attentional blink (AB), has been central in characterizing the limits of humans' ability to consciously perceive stimuli distributed across time. Here, we review theoretical accounts of the AB and examine how they explain key findings in the literature. We conclude that the AB arises from attentional demands of T1 for selection, working memory encoding, episodic registration, and response selection, which prevents this high-level central resource from being applied to T2 at short T1-T2 lags. T1 processing also transiently impairs the redeployment of these attentional resources to subsequent targets and the inhibition of distractors that appear in close temporal proximity to T2. Although these findings are consistent with a multifactorial account of the AB, they can also be largely explained by assuming that the activation of these multiple processes depends on a common capacity-limited attentional process for selecting behaviorally relevant events presented among temporally distributed distractors. Thus, at its core, the attentional blink may ultimately reveal the temporal limits of the deployment of selective attention.

Isolation of a central bottleneck of information processing with time-resolved FMRI

When humans attempt to perform two tasks at once, execution of the first task usually leads to postponement of the second one. This task delay is thought to result from a bottleneck occurring at a central, amodal stage of information processing that precludes two response selection or decision-making operations from being concurrently executed. Using time-resolved functional magnetic resonance imaging (fMRI), here we present a neural basis for such dual-task limitations, e.g. the inability of the posterior lateral prefrontal cortex, and possibly the superior medial frontal cortex, to process two decision-making operations at once. These results suggest that a neural network of frontal lobe areas acts as a central bottleneck of information processing that severely limits our ability to multitask.

The neural correlates of third-party punishment

Legal decision-making in criminal contexts includes two essential functions performed by impartial "third parties:" assessing responsibility and determining an appropriate punishment. To explore the neural underpinnings of these processes, we scanned subjects with fMRI while they determined the appropriate punishment for crimes that varied in perpetrator responsibility and crime severity. Activity within regions linked to affective processing (amygdala, medial prefrontal and posterior cingulate cortex) predicted punishment magnitude for a range of criminal scenarios. By contrast, activity in right dorsolateral prefrontal cortex distinguished between scenarios on the basis of criminal responsibility, suggesting that it plays a key role in third-party punishment. The same prefrontal region has previously been shown to be involved in punishing unfair economic behavior in two-party interactions, raising the possibility that the cognitive processes supporting third-party legal decision-making and second-party economic norm enforcement may be supported by a common neural mechanism in human prefrontal cortex.

Training improves multitasking performance by increasing the speed of information processing in human prefrontal cortex

Our ability to multitask is severely limited: task performance deteriorates when we attempt to undertake two or more tasks simultaneously. Remarkably, extensive training can greatly reduce such multitasking costs. While it is not known how training alters the brain to solve the multitasking problem, it likely involves the prefrontal cortex given this brain region's purported role in limiting multitasking performance. Here, we show that the reduction of multitasking interference with training is not achieved by diverting the flow of information processing away from the prefrontal cortex or by segregating prefrontal cells into independent task-specific neuronal ensembles, but rather by increasing the speed of information processing in this brain region, thereby allowing multiple tasks to be processed in rapid succession. These results not only reveal how training leads to efficient multitasking, they also provide a mechanistic account of multitasking limitations, namely the poor speed of information processing in human prefrontal cortex.

Cognitive load disrupts implicit theory-of-mind processing

Eye movements in Sally-Anne false-belief tasks appear to reflect the ability to implicitly monitor the mental states of other individuals (theory of mind, or ToM). It has recently been proposed that an early-developing, efficient, and automatically operating ToM system subserves this ability. Surprisingly absent from the literature, however, is an empirical test of the influence of domain-general executive processing resources on this implicit ToM system. In the study reported here, a dual-task method was employed to investigate the impact of executive load on eye movements in an implicit Sally-Anne false-belief task. Under no-load conditions, adult participants displayed eye movement behavior consistent with implicit belief processing, whereas evidence for belief processing was absent for participants under cognitive load. These findings indicate that the cognitive system responsible for implicitly tracking beliefs draws at least minimally on executive processing resources. Thus, even the most low-level processing of beliefs appears to reflect a capacity-limited operation.

The efficacy of transcranial direct current stimulation to prefrontal areas is related to underlying cortical morphology

Applying a weak electrical current to the cortex can have effects on a range of behaviours. Techniques such as transcranial direct current stimulation (tDCS) have been widely used in both research and clinical settings. However, there is significant variability across individuals in terms of their responsiveness to stimulation, which poses practical challenges to the application of tDCS, but also provides a unique opportunity to study the link between the brain and behaviour. Here, we assessed the role of individual differences in cortical morphology - specifically in prefrontal cortical regions of interest - for determining the influence of tDCS on decision-making performance. Specifically, we employed magnetic resonance imaging (MRI) and a previously replicated paradigm in which we modulated learning in a simple decision-making task by applying tDCS to the left prefrontal cortex in human subjects of both sexes. Cortical thickness of the left (but not right) prefrontal cortex accounted for almost 35% of the variance in stimulation efficacy across subjects. This is the first demonstration that variations in cortical architecture are associated with reliable differences in the effects of tDCS on cognition. Our findings have important implications for predicting the likely efficacy of different non-invasive brain stimulation treatments on a case by case basis.

Distractor inhibition predicts individual differences in the attentional blink

BACKGROUND

The attentional blink (AB) refers to humans' impaired ability to detect the second of two targets (T2) in a rapid serial visual presentation (RSVP) stream of distractors if it appears within 200-600 ms of the first target (T1). Here we examined whether humans' ability to inhibit distractors in the RSVP stream is a key determinant of individual differences in T1 performance and AB magnitude.

METHODOLOGY/PRINCIPAL FINDINGS

We presented subjects with RSVP streams (93.3 ms/item) of letters containing white distractors, a red T1 and a green T2. Subjects' ability to suppress distractors was assessed by determining the extent to which their second target performance was primed by a preceding distractor that shared the same identity as T2. Individual subjects' magnitude of T2 priming from this distractor was found to be negatively correlated with their T1 accuracy and positively related to their AB magnitude. In particular, subjects with attenuated ABs showed negative priming (i.e., worse T2 performance when the priming distractor appeared in the RSVP stream compared to when it was absent), whereas those with large ABs displayed positive priming (i.e., better T2 performance when the priming distractor appeared in the RSVP stream compared to when it was absent). Thus, a subject's ability to suppress distractors, as assessed by T2 priming magnitude, predicted both their T1 performance and AB magnitude.

CONCLUSIONS/SIGNIFICANCE

These results confirm that distractor suppression plays a key role in RSVP target selection and support the hypothesis that the AB results, at least in part, from a failure of distractor inhibition.

Current evidence for automatic Theory of Mind processing in adults

Theory of Mind (ToM) is thought to play a key role in social information processing as it refers to the ability of individuals to represent the mental states of others (e.g., intentions, desires, beliefs). A provocative hypothesis has been put forward which espouses the existence of two ToM systems: one that is implicit and involves the automatic analysis of the belief states of others and another that is not automatic and is involved in explicitly reasoning about others' mental states. Recently, Phillips et al. (2015) have suggested that there is limited evidence for automatic ToM processing, after identifying a confound in a previous high-profile paper supporting the existence of this cognitive operation in infants and adults (Kovács, Téglás, & Endress, 2010). Here, we take a broader view of the literature and find, contrary to the conclusions of Phillips et al., that there is a substantial body of literature which demonstrates that adult humans are able to engage in unconscious and unintentional, and thus automatic, analyses of others' mental states. However, whether this ability is best described under a one, two or multiple systems ToM account remains to be determined.

Detecting Unattended Stimuli Depends on the Phase of Prestimulus Neural Oscillations

Neural oscillations appear important for perception and attention processes because stimulus detection is dependent upon the phase of 7-11 Hz oscillations before stimulus onset. Previous work has examined stimulus detection at attended locations, but it is unknown whether unattended locations are also subject to phasic modulation by ongoing oscillatory activity, as would be predicted by theories proposing a role for neural oscillations in organizing general neural processing. Here, we recorded brain activity with EEG while human participants of both sexes detected brief visual targets preceded by a spatial cue and determined whether performance for cued (attended) and uncued (unattended) targets was influenced by oscillatory phase across a range of frequencies. Detection of both attended and unattended targets depended upon an ∼5 Hz theta rhythm and an ∼11-15 Hz alpha rhythm. Critically, detection of unattended stimuli was more strongly modulated by the phase of theta oscillations than was detection of attended stimuli, suggesting that attentional allocation involves a disengagement from ongoing theta sampling. There was no attention-related difference in the strength of alpha phase dependence, consistent with a perceptual rather than attentional role of oscillatory phase in this frequency range. These results demonstrate the importance of neural oscillations in modulating visual processing at both attended and unattended locations and clarify one way in which attention may produce its effects: through disengagement from low-frequency sampling at attended locations.SIGNIFICANCE STATEMENT Past work on the interaction between oscillatory phase and neural processing has shown the involvement of posterior ∼7-11 Hz oscillations in visual processing. Most studies, however, have presented stimuli at attended locations, making it difficult to disentangle frequencies related to attention from those related to perception. Here, we compared the oscillatory frequencies involved in the detection of attended and unattended stimuli and found that ∼11-15 Hz oscillations were related to perception independently of attention, whereas ∼5 Hz oscillations were more prominent for the detection of unattended stimuli. This work demonstrates the importance of neural oscillations for mediating stimulus processing at both attended and unattended locations and clarifies the different oscillatory frequencies involved in attention and perception.

Delayed Reentrant Processing Impairs Visual Awareness

In object-substitution masking (OSM), a sparse, common-onset mask impairs perception of a target when the mask’s offset is later than the target’s offset and spatial attention is dispersed. OSM is thought to reflect the interaction of feed-forward and reentrant processes in the brain: Upon stimulus presentation, a low-resolution representation of the target and mask progresses from sensory to anterior brain regions, triggering reentrant processing to confirm stimulus identity. It is hypothesized that dispersing spatial attention prolongs the required reentrant iterations, increasing the likelihood that only the lingering mask stimulus will remain physically present and thus substitute for the target in consciousness. However, empirically, it remains unclear whether substitution stems from delayed feed-forward or reentrant processing. Here, we demonstrate that delayed reentrant processing causes OSM, by showing that a task tapping high-level brain regions involved in reentrant processing leads to a spatially attended target being replaced by the mask. Our results confirm a key role for reentrant processing in conscious perception.

Disrupting prefrontal cortex prevents performance gains from sensory-motor training

Humans show large and reliable performance impairments when required to make more than one simple decision simultaneously. Such multitasking costs are thought to largely reflect capacity limits in response selection (Welford, 1952; Pashler, 1984, 1994), the information processing stage at which sensory input is mapped to a motor response. Neuroimaging has implicated the left posterior lateral prefrontal cortex (pLPFC) as a key neural substrate of response selection (Dux et al., 2006, 2009; Ivanoff et al., 2009). For example, activity in left pLPFC tracks improvements in response selection efficiency typically observed following training (Dux et al., 2009). To date, however, there has been no causal evidence that pLPFC contributes directly to sensory-motor training effects, or the operations through which training occurs. Moreover, the left hemisphere lateralization of this operation remains controversial (Jiang and Kanwisher, 2003; Sigman and Dehaene, 2008; Verbruggen et al., 2010). We used anodal (excitatory), cathodal (inhibitory), and sham transcranial direct current stimulation (tDCS) to left and right pLPFC and measured participants' performance on high and low response selection load tasks after different amounts of training. Both anodal and cathodal stimulation of the left pLPFC disrupted training effects for the high load condition relative to sham. No disruption was found for the low load and right pLPFC stimulation conditions. The findings implicate the left pLPFC in both response selection and training effects. They also suggest that training improves response selection efficiency by fine-tuning activity in pLPFC relating to sensory-motor translations.

The influence of tDCS intensity on decision-making training and transfer outcomes

Transcranial direct current stimulation (tDCS) has been shown to improve single- and dual-task performance in healthy participants and enhance transferable training gains following multiple sessions of combined stimulation and task practice. However, it has yet to be determined what the optimal stimulation dose is for facilitating such outcomes. We aimed to test the effects of different tDCS intensities, with a commonly used electrode montage, on performance outcomes in a multisession single/dual-task training and transfer protocol. In a preregistered study, 123 participants, who were pseudorandomized across four groups, each completed six sessions (pre- and posttraining sessions and four combined tDCS and training sessions) and received 20 min of prefrontal anodal tDCS at 0.7, 1.0, or 2.0 mA or 15-s sham stimulation. Response time and accuracy were assessed in trained and untrained tasks. The 1.0-mA group showed substantial improvements in single-task reaction time and dual-task accuracy, with additional evidence for improvements in dual-task reaction times, relative to sham performance. This group also showed near transfer to the single-task component of an untrained multitasking paradigm. The 0.7- and 2.0-mA intensities varied in which performance measures they improved on the trained task, but in sum, the effects were less robust than for the 1.0-mA group, and there was no evidence for the transfer of performance. Our study highlights that training performance gains are augmented by tDCS, but their magnitude and nature are not uniform across stimulation intensity.NEW & NOTEWORTHY Using techniques such as transcranial direct current stimulation to modulate cognitive performance is an alluring endeavor. However, the optimal parameters to augment performance are unknown. Here, in a preregistered study with a large sample (123 subjects), three different stimulation dosages (0.7, 1.0, and 2.0 mA) were applied during multitasking training. Different cognitive training performance outcomes occurred across the dosage conditions, with only one of the doses (1.0 mA) leading to training transfer.

Orientation-invariant object recognition: evidence from repetition blindness

The question of whether object recognition is orientation-invariant or orientation-dependent was investigated using a repetition blindness (RB) paradigm. In RB, the second occurrence of a repeated stimulus is less likely to be reported, compared to the occurrence of a different stimulus, if it occurs within a short time of the first presentation. This failure is usually interpreted as a difficulty in assigning two separate episodic tokens to the same visual type. Thus, RB can provide useful information about which representations are treated as the same by the visual system. Two experiments tested whether RB occurs for repeated objects that were either in identical orientations, or differed by 30, 60, 90, or 180 degrees . Significant RB was found for all orientation differences, consistent with the existence of orientation-invariant object representations. However, under some circumstances, RB was reduced or even eliminated when the repeated object was rotated by 180 degrees , suggesting easier individuation of the repeated objects in this case. A third experiment confirmed that the upside-down orientation is processed more easily than other rotated orientations. The results indicate that, although object identity can be determined independently of orientation, orientation plays an important role in establishing distinct episodic representations of a repeated object, thus enabling one to report them as separate events.

Anodal tDCS applied during multitasking training leads to transferable performance gains

Cognitive training can lead to performance improvements that are specific to the tasks trained. Recent research has suggested that transcranial direct current stimulation (tDCS) applied during training of a simple response-selection paradigm can broaden performance benefits to an untrained task. Here we assessed the impact of combined tDCS and training on multitasking, stimulus-response mapping specificity, response-inhibition, and spatial attention performance in a cohort of healthy adults. Participants trained over four days with concurrent tDCS - anodal, cathodal, or sham - applied to the left prefrontal cortex. Immediately prior to, 1 day after, and 2 weeks after training, performance was assessed on the trained multitasking paradigm, an untrained multitasking paradigm, a go/no-go inhibition task, and a visual search task. Training combined with anodal tDCS, compared with training plus cathodal or sham stimulation, enhanced performance for the untrained multitasking paradigm and visual search tasks. By contrast, there were no training benefits for the go/no-go task. Our findings demonstrate that anodal tDCS combined with multitasking training can extend to untrained multitasking paradigms as well as spatial attention, but with no extension to the domain of response inhibition.

The Attentional Blink Impairs Detection and Delays Encoding of Visual Information: Evidence from Human Electrophysiology

This article explores the time course of the functional interplay between detection and encoding stages of information processing in the brain and the role they play in conscious visual perception. We employed a multitarget rapid serial visual presentation (RSVP) approach and examined the electrophysiological P3 component elicited by a target terminating an RSVP sequence. Target-locked P3 activity was detected both at frontal and parietal recording sites and an independent component analysis confirmed the presence of two distinct P3 components. The posterior P3b varied with intertarget lag, with diminished amplitude and postponed latency at short relative to long lags—an electroencephalographic signature of the attentional blink (AB). Under analogous conditions, the anterior P3a was also reduced in amplitude but did not vary in latency. Collectively, the results provide an electrophysiological record of the interaction between frontal and posterior components linked to detection (P3a) and encoding (P3b) of visual information. Our findings suggest that, although the AB delays target encoding into working memory, it does not slow down detection of a target but instead reduces the efficacy of this process. A functional characterization of P3a in attentive tasks is discussed with reference to current models of the AB phenomenon.

On the role of working memory in spatial contextual cueing

The human visual system receives more information than can be consciously processed. To overcome this capacity limit, we employ attentional mechanisms to prioritize task-relevant (target) information over less relevant (distractor) information. Regularities in the environment can facilitate the allocation of attention, as demonstrated by the spatial contextual cueing paradigm. When observers are exposed repeatedly to a scene and invariant distractor information, learning from earlier exposures enhances the search for the target. Here, we investigated whether spatial contextual cueing draws on spatial working memory resources and, if so, at what level of processing working memory load has its effect. Participants performed 2 tasks concurrently: a visual search task, in which the spatial configuration of some search arrays occasionally repeated, and a spatial working memory task. Increases in working memory load significantly impaired contextual learning. These findings indicate that spatial contextual cueing utilizes working memory resources.

The meaning of the mask matters: evidence of conceptual interference in the attentional blink

The rapid serial visual presentation (RSVP) experiment reported here investigated the role of conceptual interference in the attentional blink (AB). Subjects were presented with RSVP streams that contained five stimuli: Target 1, a distractor, Target 2, a second distractor, and a symbol mask. Target 1 was a green letter, Target 2 was a red letter, and the distractors were either white letters or white digits. The stimuli were presented in a font typically seen on the face of a digital watch. Thus, "S" and "O" were identical to "5" and "0," respectively. This allowed us to present streams that were conceptually different even though featurally identical: The two letter targets were followed by distractors that were recognized either as "5" and "0" or as "S" and "O." The AB was substantially attenuated when subjects were told the distractors were digits rather than letters. This result indicates that conceptual interference plays a role in the AB.

Evidence against benefits from cognitive training and transcranial direct current stimulation in healthy older adults

Cognitive training and brain stimulation show promise for ameliorating age-related neurocognitive decline. However, evidence for this is controversial. In a Registered Report, we investigated the effects of these interventions, where 133 older adults were allocated to four groups (left prefrontal cortex anodal transcranial direct current stimulation (tDCS) with decision-making training, and three control groups) and trained over 5 days. They completed a task/questionnaire battery pre- and post-training, and at 1- and 3-month follow-ups. COMT and BDNF Val/Met polymorphisms were also assessed. Contrary to work in younger adults, there was evidence against tDCS-induced training enhancement on the decision-making task. Moreover, there was evidence against transfer of training gains to untrained tasks or everyday function measures at any post-intervention time points. As indicated by exploratory work, individual differences may have influenced outcomes. But, overall, the current decision-making training and tDCS protocol appears unlikely to lead to benefits for older adults.

Do implicit and explicit belief processing share neural substrates?

Humans rely on their ability to infer another person's mental state to understand and predict others' behavior ("theory of mind," ToM). Multiple lines of research suggest that not only are humans able to consciously process another person's belief state, but also are able to do so implicitly. Here we explored how general implicit belief states are represented in the brain, compared to those substrates involved in explicit ToM processes. Previous work on this topic has yielded conflicting results, and thus, the extent to which the implicit and explicit ToM systems draw on common neural bases is unclear. Participants were presented with "Sally-Anne" type movies in which a protagonist was falsely led to believe a ball was in one location, only for a puppet to later move it to another location in their absence (false-belief condition). In other movies, the protagonist had their back turned the entire time the puppet moved the ball between the two locations, meaning that they had no opportunity to develop any pre-existing beliefs about the scenario (no-belief condition). Using a group of independently localized explicit ToM brain regions, we found greater activity for false-belief trials, relative to no-belief trials, in the right temporoparietal junction, right superior temporal sulcus, precuneus, and left middle prefrontal gyrus. These findings extend upon previous work on the neural bases of implicit ToM by showing substantial overlap between this system and the explicit ToM system, suggesting that both abilities might recruit a common set of mentalizing processes/functional brain regions. Hum Brain Mapp 38:4760-4772, 2017. © 2017 Wiley Periodicals, Inc.