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Biased Competition Theory
Vision like most sensory information, enters the brain and undergoes cognitive processing. This allows the brain to perceive the external environment, and change behaviour where appropriate. The visual environment is complex and contains many objects, it is rarely static and not only do the objects in the environment move but the perception of these objects changes as the persons spatial location varies. Biased competition theory states that each object in the visual field competes for mental representation and cognitive processing. This theory suggests that the analysis process can be biased by other mental processes such as bottom-up, top-down and working memory systems which prioritise certain features or items for attention and processing. Simply stated the competition for cognitive processing can be biased, often toward the object that is currently attended in the visual field, or toward the object most relevant to behaviour.

Why do we have Biased Competition
The purpose of biased competition is to prioritise task relevant information to make visual search more efficient. A large amount of visual information is taken in at any given moment and there is only a limited capacity available for processing. The visual system therefore needs a way to select relevant and ignore irrelevant information.

A visual search usually has a target (i.e. a coffee cup), which is being searched for (task relevant) in the visual environment, and task irrelevent information is ignored. The biasing from neural mechanisms guides the search to logical spatial locations (i.e. the table) and items that have similar semantic or visual features.

We have biased competition in order to make the visual system more efficient so that cognitive resources can be used selectively for relevant information only.

Neural Mechanisms
There are two major neural pathways that process the visual information between the sensory input and the behavioural response (the ventral stream and the dorsal stream). The two pathways run in parallel, so are both working simultaneously. The ventral stream is important for object recognition and often referred to as the “what” system of the brain, it projects to the inferior temporal cortex. The dorsal stream is important for spatial perception and visuomotor performance and is referred to as the “where” system which projects to the posterior parietal cortex.

As the number of visual objects increases, the information available for each object will decrease due to increased neural workload and decreased cognitive process capacity. This suggests that for an object in the visual field to be cognitively processed there needs to be a way to bias the cognitive resources towards the object. Attention prioritises task relevent objects biasing this process.

Functional magnetic resonance imaging (fMRI []) has shown that bias competition theory can explain the observed attention effects at a neronal level. Attention effects bias the internal weight (strengthens connections) of task relevent features toward the attended object. This is shown by an increase in oxygenated blood to that neuron. Further neurological support comes from neurophysiological studies which have shown that attention results from top-down biasing which in turn influences neuron spiking. In sum, top-down guidance of attention is affected by external inputs which bias neurons in the brain.

Top-down Processes
Top-down guidance of attention refers to when the properties of an object (i.e. Colour, shape) are activated and held in working memory to facilitate the visual search for that object. This controls visual search by guiding attention only to objects that could be the target and avoiding attention on target irrelevant objects. Top-down processes are not a complete representation of the object but are coarse, which is why objects similar in colour, shape or meaning are often attended to in the process of discriminating irrelevant objects.

Neurophysiological studies have showed that the neural mechanisms in top-down processing are also seen in attention and working memory, suggesting top-down processes play an important role in those functions as well. For more on top-down process link to [].

Bottom-up Processes
Bottom-up refers to when a feature stands out in a visual search (the “pop-out” effect). Salient features like bright colours, movement and big objects make the object “pop-out” of the visual search. “Pop-out” features can often attract attention without conscious processing. Objects that stand out are often given priority (bias) in processing. For more link to []

Working Memory
Working memory is often used in conjunction with top-down processes. Working memory retains properties of an object for the purpose of controlling the search for that object. In essence it is a temporary memory of the properties required to control the search (competition bias) such that objects matching or nearly matching these properties will be prioritised in the visual system. It therefore enhances the efficiency of visual search. For more on working memory link to [].