Attentional selection for locations

Jens-Max Hopf et al

In: The Neuroscience of Attention,  Ed. George R. Mangun

Oxford University Press

Summary/Review of the above chapter

The spatial aspect of the focus of attention is influenced by voluntary or goal-directed requirements. Perceptual processing is seen to be facilitated at attended relative to unattended locations. Inputs from unattended locations tend to be suppressed. EEG research has shown that evoked event-related potentials (ERPs) were larger in sensory areas, such as both the primary and extrastriate visual cortex, for attended than for ignored stimuli. The activity of the primary cortex can appear later than the activity of the extrastriate cortex85266_large, suggesting feedback from the extrastriate and frontal areas to the primary visual cortex. However, recent research suggests that there can also be initial modulation of the V1 primary cortex and also of the lateral geniculate nucleus of the thalamus. This looks to occur even before there are top-down influences on the primary area. Spatial attention is related to blood oxygen-level dependent (BOLD) enhancements in the visual cortex areas retinoscopically matching the attended locations. Perceptual processing in areas close to, but not at the centre of attention, is reduced relative to more distant areas, indicating a zone of attenuation around the zone of enhancement. This is also viewed as being the result of a top-down driven narrowing of the focus of attention. The focus of attention is suggested to be capable of being contracted or extended, but not of being divided between two separate locations.

Where there is a visual search for an object, for which there is no particular attended location, a modulation known as N2pc increases in relation to the amount of distracters from the target that attention is being directed towards. The receptive field of neurons is reduced so as to restrict them to the region of the attended input. This restriction is seen as being a top-down process.

Attention to features rather than locations is achieved by enhancing responses in the appropriately specialised areas of the visual cortex, although this processing is seen to be closely linked to the process for attention to locations. So attention to colour enhances activity in areas of V4 related to colour, and attention to motion enhances activity in motion-related areas. This enhancement can occur merely as a result of the anticipation of detecting a relevant feature. Overall, the relationship between attention to location, features and objects is seen as flexible rather than rigid.

 

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