Biased competition theory advocates the idea that each object in the visual field competes for cortical representation and cognitive processing.
[3] 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.
[9] The theory attempts to provide an explanation of the processes leading visual attention and their effects on the brain's neural systems.
[10] Biased competition serves to prioritize task relevant information to make visual search more efficient.
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.
[15] The dorsal stream is important for spatial perception and performance and is referred to as the “where” system [16] which projects to the posterior parietal cortex.
[17] According to the biased competition theory, an individual's visual system has limited capacity to process information about multiple objects at any given time.
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.
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.
[23] Further neurological support comes from neurophysiological studies which have shown that attention results from Top-down biasing, which in turn influences neuronal spiking.
[24] In sum, external inputs affect the Top-down guidance of attention, which bias specific neurons in the brain.
There is evidence that observers have Top-down control over the locations that will benefit from biased competition in spatial selection visual tasks.
Evidence supports that observers can make voluntary decision about which locations are selected[36] or features that capture the attention in a stimulus-driven manner.
Increased activity in the visual cortex was also observed; this was the result of Top-down biasing due to the favoring of the attended location.
Ferrera and Lisberger [44] provided evidence for competitive interactions in the selection of targets for smooth pursuit eye movements.