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 180-450 ms after the first one. Attentional blink was first described in 1992.
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, 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.
The attentional blink is related to, but distinct from the phenomenon of repetition blindness.
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.
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 Inhibition Theory Raymond et al. (1992) suggested that the attentional blink is produced by perceptual uncertainty amongst the target (T1) and following target (T2). They suggest that this confusion happens at some point in the target identification processes. When confusion is eliminated, attentional blink isn’t observed. The researchers also suggested that one way to eliminate confusion is to have items that cannot be named.
The Interference Theory Shapiro et al. (1994) suggested that an interference model may better explain the attentional blink effects than the inhibition model. In this model, the attentional blink is thought to take place because of an out of place item which is selected out of the series because of the interference within the items in the series. Shapiro proposes that the amount of interference increases or decreases with the length of the series.
The Delay of Processing Theory Giesbrecht and Di Lollo (1998) suggests that the attentional blink deficit arises from the wait of target 2 when the person's cognitive processes are busy registering target 1. It is suggested that anything that increases the difficulty of processing the first target will result in a greater attentional blink deficit.
The Attentional Capacity Theory Duncan et al. (1996) suggests that the initial target takes over parts of our attentional capacity to the loss of sight of a target right after the initial target. This theory suggests that the time for which target 1 continues to occupy attentional capacity is related directly to the difficulty of processing target 2.
The Two-Stage Processing Theory Chun & Potter (1995) proposed that quickly processing a series of items requires two back to back stages. The first stage is the initial rapid-detection. Here, the possible targets are noticed. The second stage is the capacity-limited in which items are taken in order to report later. Stage 2 occurs after the acknowledgement of targets in Stage 1. Here, stage 2 must finishing processing target 1, until then, target 2 will not be recognized in stage 2. If there is a situation where the second target comes in the first stage, the highway to stage two is delayed. Attentional blinking occurs when the second target is in stage 1 which causes a delay. The attentional blink mirror a restriction in the process of combining information from an unstable representation to a stable representation (Johnson & Proctor, 2004).
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