Activity in Retinotopic Visual Cortex under Focused Spatial Attention Distinguishes Empty from Distracter Locations

Activity in the retinotopic visual cortex is enhanced when the represented visual field region is covertly attended. This observation has been interpreted as a physiological correlate of the spotlight of attention (e.g., Brefczynski and DeYoe, 1999). Moreover, activity in the early visual cortex coding the immediate surround of the attended region is suppressed relatively to passive viewing thereby enhancing the contrast between attended and unattended visual field regions (Müller and Kleinschmidt, 2004). In this study we asked whether activity in the retinotopic visual cortex under focused attention is further modulated by the presence or absence of distracting stimuli. More specifically, we aimed to investigate how neural representations of locations neighboring the attended stimulus would be activated depending on their content. Subjects viewed a rapid serial visual presentation (RSVP) of letters at the center of the screen. In two quadrants of the visual field additional clusters of distracting letters were presented permanently, the remaining two quadrants remained empty. A block design was used in which subjects either had to respond to a target stimulus in the RSVP or simply fixated the RSVP without any further task. Distracter locations and empty locations were switched in successive blocks. BOLD responses were recorded with a 3 T Siemens Trio scanner. After retinotopic mapping we assessed the activity in visual cortex representations of locations depending on whether they coded an empty quadrant or one that contained distracter stimuli. Activity of visual areas depended on the allocation of attention and differed between areas coding distracter and empty locations. These data provide a physiological correlate for the behavioral effects of distracting information on visual discrimination performance. References: Brefczynski JA, DeYoe EA. A physiological correlate of the 'spotlight' of visual attention. Nat Neurosci 1999; 2: 370–374. Müller NG, Kleinschmidt A. The attentional 'spotlight's' penumbra: center-surround modulation in striate cortex. Neuroreport 2004; 15: 977–980.