Visuospatial Asymmetries Arise from Differences in the Onset Time of Perceptual Evidence Accumulation.

Healthy subjects tend to exhibit a bias of visual attention whereby left hemifield stimuli are processedmore quickly and accurately than stimuli appearing in the right hemifield. It has long been held that this phenomenon arises fromthe dominant role of the right cerebral hemisphere in regulating attention.However,methods that would enablemore precise understanding of themechanisms underpinning visuospatial bias have remained elusive.We sought to finely trace the temporal evolution of spatial biases by leveraging a novel bilateral dot motion detection paradigm. In combination with electroencephalography, this paradigm enables researchers to isolate discrete neural signals reflecting the key neural processes needed formaking these detection decisions. These include signals for spatial attention, early target selection, evidence accumulation, and motor preparation. Using this method, we established that three key neural markers accounted for unique between-subject variation in visuospatial bias: hemispheric asymmetry in posterior α power measured before target onset,which is related to the distribution of preparatory attention across the visual field; asymmetry in the peak latency of the early N2c target-selection signal; and, finally, asymmetry in the onset time of the subsequent neural evidence-accumulation process with earlier onsets for left hemifield targets.Our development of a single paradigm to dissociate distinct processing components that track the temporal evolution of spatial biases not only advances our understanding of the neuralmechanisms underpinning normal visuospatial attention bias, butmay also in the future aid differential diagnoses in disorders of spatial attention. [ABSTRACT FROM AUTHOR]