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Modulation of Visual Stimulus Discrimination by Sustained Focal Attention: An MEG Study

¹From the MEG Centre, and the ²Institute of Medical Psychology and Behavioural Neurobiology, University of Tübingen, Tübingen, Germany; the ⁵Department of Pathophysiology of Vision and Neuroophthalmology, University Eye Hospital, Tübingen, Germany; the ³Max-Planck Research School and Graduate School of Neural and Behavioural Sciences, and the ⁴Max-Planck-Institute for Biological Cybernetics, Tübingen, Germany; and ⁶The Smith-Kettlewell Eye Research Institute, San Francisco, California.

PURPOSE. Visual attention, normally focused on the center of the visual field, can be shifted to a location in the periphery. This process facilitates the recognition of objects in the attended region. The present experiment was designed to investigate the time course of sustained attention that is known to augment stimulus perception in normal subjects.

METHODS. Cortical activity of the human brain related to shifts of the attentional focus was examined with magnetoencephalography. Subjects had to identify a stimulus presented on a screen at one of two locations in the periphery of their visual fields. Sustained attention was either deployed toward the target by a preceding cue or not.

RESULTS. Results confirmed a reaction time advantage on recognizing objects in the part of the visual field where attention had been deployed. A stronger magnetic brain response was detected for noncued targets at a latency of 260 to 380 ms after target onset. Source localization revealed a neuronal generator of the attention-related component in the parietal cortex.

CONCLUSIONS. Sustained attention facilitates target detection. The component that is localized in the parieto-occipital cortex in the noncued condition is thought to reflect a transient shift of attention toward the target location.