Biased competition theory advocates the idea that each object in the visual field competes for cortical representation and cognitive processing.Desimone, R., & Duncan, J. (1995). Neural Mechanism of Selective Visual Attention. Annual Review of Neuroscience, 18, 193-222. This theory suggests that the process of visual processing can be biased by other mental processes such as bottom-up and top-down systems which prioritize certain features of an object or whole items for attention and further processing. Biased competition theory is, simply stated, the competition of objects for processing. This competition can be biased, often toward the object that is currently attended in the visual field, or alternatively toward the object most relevant to behavior.
History Research into the subject of attentional mechanisms in regard to visual perception was undertaken as an attempt to better understand the functional principles and potential constraints surrounding visual perception Rolls, E. T. (2008). Memory, attention and decision-making: A unified computational neuro-science approach; Oxford University Press, Oxford. Visual search tasks are commonly used by experimenters to aid the exploration of visual perception.
The classical view of visual attention suggests that there are two basic principles: the pre-attentive stage and the attentive stage.Rolls, E. T. (2008). Memory, attention and decision-making: A unified computational neuro-science approach; Oxford University Press, Oxford. In the pre-attentive stage, an individual has an unlimited capacity for perception which is capable of processing information from the entire visual field concurrently. During the attentive stage, the processing of visual information corresponding to local spatial areas takes place.Rolls, E. T. (2008). Memory, attention and decision-making: A unified computational neuro-science approach; Oxford University Press, Oxford. This classical view of visual attention suggests that there is no competition within the visual field. Within this theory an individual is assumed to be capable of processing all information provided concurrently. Until recently it was still thought that individuals had a pre-attentive stage. This is no longer the case, research has now suggested that the pre-attentive stage is now limited in its capacity.Rolls, E. T. (2008). Memory, attention and decision-making: A unified computational neuro-science approach; Oxford University Press, Oxford.
The attentive stage of being able to process important information has now transformed into what is known as selectivity. The classical view of attention has built the ground work for the recent emergence of two new principles to benefit the understanding of visual attention. The first of these relates to the limited capacity of information processing. This suggests that at any given time, only a small amount of information can actually be retained and used to control behaviour. The principle of selectivity incorporates the notion that a person has the ability to filter out unwanted information. Koch and Ullman Koch C, & Ullman S (1985) Shifts in selective visual attention: towards the underlying neural circuitry. Human Neurobiology 4:219-227. proposed that attentive selection could be implemented by competitive "winner-takes-all" networks.
Robert Desimone and John DuncanDesimone, R., & Duncan, J. (1995). Neural Mechanism of Selective Visual Attention. Annual Review of Neuroscience, 18, 193-222. expanded on this idea. They proposed that at some point between the visual input of objects and the response to objects in the visual field there is some competition occurring; competition for representation, analysis, and behavior. This suggests that attention to stimuli makes more demands on processing capacity than unattended stimuli.Desimone, R., & Duncan, J. (1995). Neural Mechanism of Selective Visual Attention. Annual Review of Neuroscience, 18, 193-222. This idea of competition led researchers to develop a new theory of attention, which they termed the “biased competition theory".Desimone, R., & Duncan, J. (1995). Neural Mechanism of Selective Visual Attention. Annual Review of Neuroscience, 18, 193-222. The theory attempts to provide an explanation of the processes leading visual attention and their effects on the brain's neural systems.Rolls, E. T. (2008). Memory, attention and decision-making: A unified computational neuro-science approach; Oxford University Press, Oxford.
Function Biased competition serves to prioritize task relevant information to make visual search more efficient.Desimone, R., & Duncan, J. (1995). Neural Mechanism of Selective Visual Attention. Annual Review of Neuroscience, 18, 193-222. A large amount of visual information is taken in at any given moment and there is a limited capacity available for processing. The visual system therefore needs a way to select relevant information and ignore irrelevant stimuli. A visual search usually has a target (e.g. a coffee cup), which is being searched for (task relevant) in the visual environment, and task irrelevant information is ignored. The biasing from neural mechanisms guides the search to logical spatial locations (e.g. the table) and items that have similar semantic or visual features to the item that is being searched for. It has been suggested that more than 30 cortical areas in the visual system are used for the processing of visual stimuli, and that there is competition from objects in the visual field that takes place in multiple areas of this extensive network.Desimone R, Ungerleider LG. (1989). Neural mechanisms of visual processing in monkeys. In Handbook of Neuropsychology, Vol. 2, ed. F Boller, J Grafman, pp. 267-99. New York: Elsevier.
The Biased Competition Model Desimone suggested that the Biased Competition Model comprised five main tenets:4. Desimone, R. (1998). Visual attention mediated by biased competition in extrastriate visual cortex. ‘’Phil. Trans. R. Soc. Lond. B, 353’’, 1245-1255. Objects presented simultaneously in the visual field compete for cell responses in the visual cortex. When two stimuli are presented at the same time they will activate their neuronal representations. The responses will be determined by these two stimuli interacting in a competitive manner. Two stimuli that activate cells in the same area of the cortex will provide the strongest competitive interactions. Competitive interactions have the ability to be biased in preference of one stimulus due to many different neural mechanisms. This is called feedback bias. These may include Top-down feedback (for example, one stimulus may hold more situational relevance) or Bottom-up influences (for example, one stimulus is more novel than another). Feedback biasing is not purely the result of spatial location. Biasing during processing can be due to a stimuli possessing specific, relevant feature. Such features may include color, texture, and shape. A main source of Top-down biasing derives from the structures in the brain involved with working memory, more specifically, from the prefrontal cortex.
Neural mechanisms There are two major neural pathways that process the information in the visual field; the ventral stream and the dorsal stream. The two pathways run in parallel and 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.Ungerleider, L. G., & Haxby, J. V. (1994). ‘What’ and ‘where’ in the human brain. Current Opinion in Neurobiology, 4, 157-165. The dorsal stream is important for spatial perception and performance and is referred to as the “where” system Ungerleider, L. G., & Haxby, J. V. (1994). ‘What’ and ‘where’ in the human brain. Current Opinion in Neurobiology, 4, 157-165. which projects to the posterior parietal cortex.Desimone, R., & Duncan, J. (1995). Neural Mechanism of Selective Visual Attention. Annual Review of Neuroscience, 18, 193-222. According to the biased competition theory, an individual's visual system has limited capacity to process information about multiple objects at any given time. For example, if an individual was presented with two stimuli (objects) and was asked to identify attributes of each object at the same time, the individual's performance would be worse in comparison to if the objects were presented separately. This suggests multiple objects presented simultaneously in the visual field will compete for neural representation due to limited processing resources.
Single cell recording studies conducted by Kastner and Ungerleider examined the neural mechanisms behind the biased competition theory.Kastner, S., L, G., Ungerleider. (2001). The neural basis of biased competition in human visual cortex. Neuropsychologia. 39, 1263-1276. In their experiment the size of the receptive field's (RF) of neurons within the visual cortex were examined. A single visual stimulus was presented alone in a neuron's RF, followed with another stimulus presented simultaneously within the same RF.Kastner, S., L, G., Ungerleider. (2001). The neural basis of biased competition in human visual cortex. Neuropsychologia. 39, 1263-1276. The single ‘effective’ stimuli produced a low firing rate, whereas the two stimuli presented together produced a high firing rate. The response to the paired stimuli was reduced. This suggests that when two stimuli are presented together within a neuron's RF, the stimuli are processed in a mutually suppressive manner, rather than being processed independently.Kastner, S., L, G., Ungerleider. (2001). The neural basis of biased competition in human visual cortex. Neuropsychologia. 39, 1263-1276. This suppression process, according to Kastner and Ungerleider, occurs when two stimuli are presented together because they compete for neural representation, due to limited cognitive processing capacity.Kastner, S., L, G., Ungerleider. (2001). The neural basis of biased competition in human visual cortex. Neuropsychologia. 39, 1263-1276.
The RF experiment suggests that as the number of objects increase, the information available for each object will decrease due to increased neural workload (suppression), and decreased cognitive capacity.Kastner, S., L, G., Ungerleider. (2001). The neural basis of biased competition in human visual cortex. Neuropsychologia. 39, 1263-1276. In order for an object in the visual field or RF be efficiently processed, there needs to be a way to bias these neurological resources towards the object. Attention prioritizes task relevant objects, biasing this process. For example, this bias can be towards an object which is currently attended to in the visual field or RF, or towards the object that is most relevant to one's behavior.
Functional magnetic resonance imaging (fMRI) has shown that biased competition theory can explain the observed attention effects at a neuronal level. Attention effects bias the internal weight (strengthens connections) of task relevant features toward the attended object. This was shown by Reddy, Kanwisher, and van Rullen who found an increase in oxygenated blood to a specific neuron following a locational cue.Reddy, L., Kanwisher, N.G, & VanRullen, R. (2009). Attention and biased competition in multiple voxel object representations. Proceedings of the National Academy of Sciences, 106, 50, 21447-21452. Further neurological support comes from neurophysiological studies which have shown that attention results from Top-down biasing, which in turn influences neuronal spiking.Deco, G., & Rolls, E.T. (2005). Neurodynamics of biased competition and cooperation for attention: A model with Spiking Neurons. Journal of Neurophysiology, 94, 295-313. In sum, external inputs affect the Top-down guidance of attention, which bias specific neurons in the brain.
Empirical evidence for Biased Competition Theory