In this post, I will discuss some binary types of attention and discuss some of the main theories of attention. In relation to cognitive psychology, I will talk about some disorders which can reveal how attention works in a normal brain, and will briefly touch upon the role of memory in attention.
Types of attention
1. Covert / overt attention
Overt attention means directing our sense organs (in particular, eye gaze) to the attended stimuli; covert attention, however, is a mental focus on something different from what we perceive with our sense organs. Example of this can be looking at the pages of a book while thinking of some event which had happened earlier in the day; in this case, your focus on this thought/memory is covert. However, if you were focusing on what you are reading about, such attention could be called overt.
2. Endogenous (goal-directed, top-down) / Exogenous (stimulus-driven, bottom-up) attention
Endogenous attention is a conscious, intentional direction of focus; it is under our control. For example, when we concentrate on exam, we apply goal-directed attention by 'forcing' ourselves to attend to a specific task. On a contrary, exogenous attention is unconscious and is driven by an external stimuli such as loud noise or sudden movement. We attend to these stimuli whether we want or not. This ability enables us to react to dangerous situations before even realising what happened.
3. Serial / parallel processing
The way we process information is closely linked to attention, so I will look at this distinction as well. The idea behind serial processing is that encountering an object we process its features - such as colour, shape, direction and so on - in a series, one thing at a time. Parallel processing is the ability of mind to process multiple signals of differing quality simultaneously, and to compare them to the stored images/memories to understand what it is that we are perceiving.
This distinction provoked an on-going debate among the cognitive psychologists: which type of processing information is really at work when we attend to any particular object?
Feature Integration Theory
Second stage is the focused attention stage which involves serial processing. During this stage, individual features get combined and we become conscious of an object as a whole - one at a time. To combine the features into a recognisable object attention is needed.
There are two types of a visual search task which Treisman used to test the theory: conjunction search and feature search. Feature search (on the left) requires finding an object with only one feature (here: find red shapes), and can be performed pre-attentively; features will 'pop out' and form an illusory pattern. On the contrary, conjunction search (on the right) requires conscious attention; participants need to analyse every object serially to find required object (here: find a red circle).
How can it be that, despite being able to see and process various objects, people with Balint's syndrome fail to see the 'big picture'? And, what can we say about a normal brain, having considered such a disability?
As I said earlier, attention allows us to filter out all the unnecessary information to avoid information overload. Information which is attended to is composed into a salience map: a map which represents a saliency - or, things that stand out - of a corresponding visual field. This is done by bottom-up processing of separate objects/features such as depth, colour etc. The picture below demonstrates a location in our visual field and corresponding saliency map.
But how come we are able to see and understand the 'big picture' if our mind only sees certain things to be salient? Here, top-down mechanisms make their contribution. They compare features that we see with the stored memories and expectations and allow us to see and understanding the meaning of the surroundings without consciously attending to every bit of information contained in it.
Considering this, it seems like the top-down processing mechanism might be impaired in the patients with Balint's syndrome, so that the individual components which they see fail to be compared with the stored knowledge about them and bind into a meaningful picture.
However, some information from the left visual field still gets in; it's just that the patients can not consciously access it. For example, it has been shown that words presented to the patients' left visual field could prime the words in the right visual field, decreasing the response time (Halligan & Marshall (1994); Kolb & Whishaw (1990)). Read more on Semantic Priming in Psychology of Language section.
This finding shows that mislocation to the focus of spatial attention is quite common in healthy people, especially when binding is prevented. The phenomenon appears equivalent to allochiria, thus suggesting a premorbid susceptibility to spatial migration that can be exaggerated by brain damage.