Attention is the process by which certain information is selected for further processing and other information is discarded. Attention is needed to avoid sensory overload. The brain does not have the capacity to fully process all the information it receives and nor would it would be efficient for it to do so.
Inattentional blindness: a failure to be aware of a visual stimulus because attention is directed away from it.
Change blindness: a failure to notice the appearance/disappearance of objects between two alternating images.
SPATIAL AND NON-SPATIAL ATTENTIONAL PROCESS
In terms of visual attention one of the most pervasive metaphors is to think about attention in terms of a spotlight. The spotlight may highlight a particular location in space. E.g. if that location contains a Salient object: any aspect of a stimulus that, for whatever reason, stands out from the rest. Moving the focus of attention is termed orienting and is conventionally divided into:
- Covert orienting: moving attention without moving the eyes or head
- Overt orienting: moving the eyes or head along with the focus of attention
It is important not to take the spotlight metaphor too literally. There is evidence to suggest that attention can be split between two nonadjacent locations without incorporating the middle locations.
According Posner attention operates on spatial basis. It can be explaining by assuming that the spotlight initially shifts to the cued location, but if the target does not appear, attention shifts to another location called disengagement.There is a processing cost in terms of reaction time associated with going back to the previously attended location, called inhibition of return.
Inhibition of return: a slowing of reaction time associated with going back to a previously attended location.
Exogenous orienting: Attention that is externally guided by a stimulus.
Endogenous orienting: Attention is guided by the goals of the perceiver.
Another commonly used paradigm that uses endogenous attention is called visual search: a task of detecting the presence of absence of a specified target object in an array of other distracting objects.
Visual search is a good example of a mix of bottom-up processing (perceptual identification of objects and features) and top-down processing (holding in mind the target and endogenously driven orienting of attention)
Examples of non-spatial attention mechanism include object-based attention and time-based/temporal attentional processes. with regards to object based attention, if two objects are transparently superimposed in the same spatial location,then participants can still selectively attend to one or the other.
Attentional blink: An inability to report a target stimulus if it appears soon after another target stimulus.
THE ROLE OF THE FRONTOPARIETAL NETWORK IN ATTENTION
This section considers the role of the parietal lobes in attention. In general, various frontal and parietal regions tend to be co-activated in tasks requiring attention. However, there are differences in specialization within this network with frontal regions being more implicated in task selection and motor selection, and parietal regions acting as a hub that pulls together bottom-up (sensory) signals with top-down (goal-based) signals.
The "where" pathway, salience maps and orienting of attention
From early visual processing in the occipital cortex, two important pathways can be distinguished that are specialised for different types of information.
- A ventral route (what pathway) leading into the temporal lobes is concerned with identifying objects.
- A dorsal route (where pathway) leading into the parietal lobes is specialised for locating objects in space.
Saccades: a fast ballistic movement of the eyes.
Lesioning LIP in one hemisphere leads to slower visual search in the contralateral visual field even in the absence of saccades.
Frontal eye field: part of the frontal lobes responsible for voluntary movement of the eyes.
Stage right
Why do actors make a hidden entrance from stage right?
The right parietal lobes of humans are generally considered to have a more dominant role in spatial attention than its left hemisphere equivalent. One consequence of this is that right-hemisphere lesions have severe consequences for spatial attention, particularly for the left space (as in the condition of “neglect”). Another consequence of right-hemisphere spatial dominance is that, in a nonlesioned brain, there is over-attention to the left side of space (termed pseudo-neglect).
Hemispheric differences in parietal lobe contributions to attention
The right parietal lobe shows a maximal responsiveness to stimuli on the far left side, a moderate responsiveness to the middle and a weaker response to the far right side. The left parietal lobe shows the reverse profile.
Hemispatial neglect: a failure to attend to stimuli on the opposite side of space to a brain lesion.
Pseudo-neglect: in a non-lesioned brain there is over-attention to the left side of space.
Mevorach and colleagues have proposed that the left and right lobes have different roles in non-spatial attention: specifically, the right hemisphere is considered important for attending to a salient stimulus, and the left hemisphere is important for suppressing a non-salient stimulus or "ignoring the elephant in the room"
The relationship between attention, perception and awareness
Attention is a mechanism for the selection of information. Awareness is an outcome that is, in many theories, linked to that mechanism. Perception is the information that is selected from and, ultimately, forms the content of awareness.
Phenomenal consciousness: the raw feeling of a sensation, the content of awareness
Access consciousness: the ability to report on the content of awareness
THEORIES OF ATTENTION
Feature integration theory
Feature integration theory (FIT) is a model of how attention selects perceptual objects and binds the different features of those objects.
According to FIT, perceptual features such as color and shape are coded in parallel and prior to attention. If an object does not share features with other objects in the array it appears to pop out.
Illusory conjunctions: a situation in which visual features of two different objects are incorrectly perceived as being associated with a single object.
FIT is an example of what has been termed and early selection model of attention. Recall that the main reason for having attentional mechanisms is to select some information for further processing, at the expense of other information. According to early selection theories, information is selected according to perceptual attributes (e.g. color or pitch).This can be contrasted with late selection theories that assume that all incoming information is processed up to a level of meaning (semantics) before being selected for further processing. One of the most frequently cited examples of late selection is the negative priming effect: if an ignored object suddenly becomes the attended object, then participants are slower at processing it.
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| Negative priming effect: participants must name the red objects and ignore the blue one, if an ignored object becomes an attended object on the subsequent trial, then there is a cost of processing. |
Biased competition theory
The biased competition theory of Desimone and Duncan explicitly rejects a spotlight metaphor of attention. Instead "attention is an emergent property of many neural mechanisms working to resolve competition for perceptual processing and control of behaviour.
The model explains certain neuropsychological findings. Damage to the parietal lobe not only produces neglect; it may also lead to a symptom called extinction: in the context of attention, unawareness of a stimulus in the presence of competing stimuli.
The premotor theory of attention
The premotor theory of attention assumed that the orienting of attention is nothing more than preparation of motor actions, as such it is primarily a theory of spatial attention.
Seeing one object at a time
Patient's with Balint's syndrome typically have damage to both the left and the right parietal lobes and have severe spatial disturbances. Patients with Balint's syndrome may notice only one object at a time; this is termed simultanagnosia. Within the biased competition theory it could be regarded as an extreme form of perceptual competition due to a limited spatial selection capacity. Within feature integration theory, it can be construed as an inability to bind features to locations and, hence, to each other.
NEGLECT AS A DISORDER OF SPATIAL ATTENTION AND AWARENESS
Patients with neglect (also called hemispatial neglect, visuo-spatial neglect or visual neglect) fail to attend to stimuli on the opposite side of space to their lesion—normally a right-sided lesion resulting in inattention to the left side of space.
Characteristics of neglect
Line bisection: as task involving judging the central point of a line.
Cancellation task: a variant of the visual search paradigm in which the patient must search for targets in an array, normally striking them through as they are found.