Attentional blink (AB) is a phenomenon observed in rapid serial visual presentation (RSVP). When presented with a sequence of visual stimuli in rapid succession at the same spatial location on a screen, a participant will often fail to detect a second salient target occurring in succession if it is presented between 150-450 ms after the first one.It is easier to process a single target that is presented briefly, than to process a target that is presented in a stream of stimuli. Attentional blink was first described in 1992.
Research and theories
The precise adaptive significance behind the attentional blink is unknown, but it is thought to be a product of a two-stage visual processing system attempting to allocate episodic context to targets. In this two-stage system, all stimuli are processed to some extent by an initial parallel stage, and only salient ones are selected for in-depth processing, in order to make optimum use of limited resources at a late serial stage.
One curious aspect of attentional blink is that it usually includes "lag 1 sparing", meaning that targets presented very close together in time (at "lag 1" or consecutively in the RSVP stream) are not affected by the attentional blink, even though items presented at slightly greater lags are significantly impaired. There is as yet no conclusive explanation for the phenomenon of lag 1 sparing, although it is thought to be related to the first parallel stage of the two-stage system of stimulus selection and processing.
According to the LC-NE hypothesis, when a salient, or meaningful stimulus is presented, in the neurons in the locus coeruleus release norepinephrine a neurotransmitter that benefits the detection of the stimulus. The effect of this release lasts for 100 ms after the salient stimulus is presented and benefits the second target when presented immediately after the first one, accounting for lag 1 sparing. Eventually the neurons in the locus coeruleus enter a refractory period, due to the auto-inhibitory effect of norepinephrine. According to the hypothesis, targets presented during this refractory period cannot trigger a release of norepinephrine, resulting in the attentional blink. The episodic distinctiveness hypothesis of the ST2 model suggests that the attentional blink reflects a limitation of the visual system attempting to allocate unique episodic contexts to the ephemeral target stimuli presented in RSVP. The attentional blink can be moderated by changes in visual similarity between targets and distractor stimuli, but it can also be affected by conceptual similarities, suggesting that stimuli are processed to quite a deep level preconsciously, with much of the resulting information discarded before it reaches consciousness. Depending on the stimuli and the target rate, there are two errors made when identifying the target. the first error is pre-target intrusion, which is naming the stimulus that occurred before the target as the target. The second error is post-target intrusion, which is naming a stimulus that occurred after the target as the target.
Target 1 Based Theory
This theory suggests that there are many reasons why attentional blink occurs whether it be resource depletion, delayed selection or working memory consolidation. All of which has to do with the process of target 1. There are two stages in this theory, at the first stage the target is identified. At this stage the target is subjected to decay and being overwritten if there are more stimuli after it. At the second stage, serial processing begins, which means that the targets can be processed one at a time. This occurs because of limited capacity in the brain. Wyble et al.'s model of episodic simultaneous type serial token (ESTST), also has two process. The first process is identifying information about the stimulus abstractly. In order to recall the stimulus correctly, the identity information is bounded by a token and therefore encoded in to working memory. In order for the information to be bound to a token additional attentional effort is needed. For this to happen an extra 200 milliseconds is needed. The first target in a multiple task rapid serial visual presentation (RSVP) is a temporary but relatively long lasting deficit in the identification of stimuli presented after the first target.
Distractor Based Theory
This theory is about the disruptive distractors between target 1 and target 2 are the reason for attentional blink. This theory suggests that when target 1 is identified it opens a gate for processing. If there are no stimuli after target one the gate remains open. However, if there are stimuli after the first target the gate will close because of a overload of processing. If the second target is presented when the gate is close then the brain is not able to process it. There has been varies maniuplations to the attentional blink paradigm. These manipulations include the target category (letters, digits, colors etc.), the number of targets (1 vs 2 vs 3), the relationship between the target and the non-target(distractor), and also the duration of the stimuli in the RSVP stream. The attentional blink is related to, but distinct from the phenomenon of repetition blindness.
The human brain is not completely mature at birth and instead develops overtime into adulthood. Neuroimaging studies have found some neural correlates involved in the AB. These studies have shown that the frontal network is implicated for the capacity-limited function of the AB. Successful target consolidation appears to be a role of the frontal areas, rather than the temporo-parietal. Successful report of a target is connected to the frontal cortex. In the dual-target detection process, the frontal cortex is critical, which is also supported by patient studies using RSVP tasks. Frontal lobe patients show lower T2 detection rates across all serial positions and a later point of recovery in the AB which is specific to frontal lobe patients. Temporal lobe patients show a typical AB deficit for T2 detection peaking at 300 ms. The cortical activation during attentional blink is not only limited to the frontal lobe, evidence suggests that attentional blink is also associated with temporal, right parietal and frontal cortices. The organization and storage functions of the working memory are used during the consolidation of target items in the visual STM.
Young children have a extreme attentional blink, this may be the result of the gradual development of the pre-frontal cortex. Developmental differences have previously been described in spatial attention tasks using visual search paradigms. Increased reaction times and slopes of reaction times over display size have been reported for younger participants relative to adults together with improvements in processing speed with increasing age. The reaction time between children and adults increased when the number of stimuli increased.
This deficit suggests an limitation of our central nervous system to deal with rapidly changing stimuli, highlighting the serial aspect of attentional function. An increased attentional blink suggests a less efficient processing mechanism in adolescents who are high in impulse behavior, when they are presented with rapid input. Moreover, more high impulsivity adolescents have an attentional blink temporally displaced toward later time lags, compared to other adolescents. This finding perhaps is not surprising given that impulsivity is a core behavioral deficit in children with ADHD.To account for these findings, we have proposed an attention-gating model, in which a gate controls the flow of information from a perceptual buffer to a level where the cognitive processing required for target detection and identification takes place. Since processing capacity is limited, attention gating facilitates perceptual and cognitive processing by allowing only an adequate amount of information to access this level at a given time. An attentional blink occurs also when the temporal mechanism of gating is altered. As in the ADHD children, high impulsivity subjects of the current study appear to have a slower dynamics of gating, with more stimuli flowing in the second stage of processing. As a result, those subjects without adequate resources to process the extra ‘‘bits’’ of information would demonstrate a deeper and wider blink. On the other hand, those with more resources would be able to process the additional information and demonstrate not just lag-1, but also lag-2 or perhaps even lag-3, sparing. As a result, they would demonstrate a blink with a relatively normal magnitude but temporally displaced toward later time lags. Therefore, when compared to those with low impulsivity, high-impulsivity subjects as a group showcase a profile of attentional blink displaced toward a later time.
An important factor which influences the AB is the role of emotions. Research has shown that when the second target (T2) in RSVP is an emotionally relevant stimulus it is more likely to be perceived during the attentional blink. The attentional blink is not only modulated by emotional relevance of (T2) but also by the emotional relevance of (T1). In short: when (T1) is emotionally relevant the AB is lengthened, when (T2) is emotionally relevant then the AB is reduced. This research suggests that emotion mediates attention.
There have also been studies using images as emotional stimuli. Emotionally negative pictures preceding the target by 2 items were found to induce greater deficits in processing the target stimuli than neutral pictures did. Thus, it seems that emotional information can elicit attentional biases which temporarily prevent awareness of actively sought out stimuli. Attentional blink increases when the target one word is positive or negative. When looking at threatening images such as a machete as the second target, it is better identified at lag 2 and lag 3 and the attentional blink is not there. Neutral targets like a tree are better identified when it is at lag 8 or more. If the second target is pleasant like a baby then it was better identified at lag 2, lag3, and lag 8. Attentional blink is not only effected by the target (positive or negative), but also by the person emotional state of mind. When a person is stressed, certain hormones are released that effect learning, attention, and memory. When a person's emotional (stress) level is aroused then the ability to predict the second target is slightly better.
Aging causes overall attentional blink performance to worsen, both on early and late lags. It has been shown that age negatively correlates with performance on the AB task and that the magnitude of the AB increases with age. Aging participants have a longer attentional blink due to a reduced ability to sustain attention. Studies have shown meditation is accompanied by increased activation in cortical regions involved in the control of attention. These cortical regions are also those regions known to be involved in target processing during the attentional blink.
A study conducted by Heleen Slagter, Richard Davidson and colleagues, suggests that meditation, particularly vipassana, may reduce the duration of attentional blink. In an experiment, 17 people received three months of intensive training in meditation. Those 17 along with 23 meditation novices performed an attention task in which they successively picked out two numbers embedded in a series of letters. The novices exhibited attentional blink and missed the second number. In contrast, all the trained meditators consistently picked out both numbers. This indicated meditation practice can improve focus. The finding that frequent meditators perform better in an RSVP task might not be due to improved focus. To the contrary, a number of articles illustrated that a diffuse state of attention, not focus, leads to a better performance in an RSVP task. For example Olivers and Niewuenhuis (2005) show that non-task related music in the background or doing free association during an RSVP task leads to attenuation of the attentional blink. They argue that this is done by producing diffuse attentional state.
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- Biello, David (October 2007) Searching for God in the Brain Scientific American
- Scientific American video blog
- The Laboratory for Attention, Brain, and Behavior, led by Dr. Barry Giesbrecht, has published a number of studies addressing the attentional blink.
- Theory and instructions for attentional blink
- Computational Models of the Attentional Blink