Further information on the test/mask model, including alternate fits, is provided in Table S4. This work was supported by the Wellcome Trust through a Principal Research Fellowship to A.J.K. (WT076508AIA) and by Merton College, Oxford through a Domus A three-year studentship to N.C.R. We are grateful to Sandra Tolnai, Jennifer DAPT Bizley, and Kerry Walker for assistance with data collection. We also would like to thank Fernando Nodal, Douglas Hartley, Amal Isaiah, and Bashir Ahmed for

their helpful contributions to the surgical preparations. “
“Visual attention allows observers to focus on a subset of a complex visual scene. Spatial attention, which improves perception of stimuli at attended locations, has been well studied. However, observers can attend to many other attributes of a visual scene (Wolfe et al., 2004), including features (Haenny et al., 1988, Hayden and Gallant, 2009, Khayat et al., 2010, Martinez-Trujillo and Treue, 2004, McAdams and Maunsell, 2000, Motter, 1994 and Treue and Martinez Trujillo, 1999), objects (Blaser et al.,

2000, Houtkamp et al., 2003 and Serences et al., 2004), and periods (Coull and Nobre, Talazoparib 1998, Doherty et al., 2005 and Ghose and Maunsell, 2002). Whether all forms of attention employ common neural mechanisms has been debated extensively (Duncan, 1980 and Maunsell and Treue, 2006). Several psychophysical studies have argued that spatial attention is unique and that nonspatial forms of attention are inextricably tied to spatial location (Kwak and Egeth, 1992 and Nissen and Corkin, 1985). However, other studies argue that spatial and nonspatial forms of attention are qualitatively similar and might be mediated by equivalent mechanisms (Bundesen, 1990, Calpain Duncan, 1980, Keren, 1976, Rossi and Paradiso, 1995 and von Wright, 1970). Neurophysiological studies provide evidence supporting both views. Both spatial attention (Assad, 2003, Maunsell and Treue, 2006, Reynolds and Chelazzi, 2004 and Yantis and Serences, 2003) and feature attention

(Assad, 2003, Hayden and Gallant, 2009, Martinez-Trujillo and Treue, 2004, Maunsell and Treue, 2006, McAdams and Maunsell, 2000, Motter, 1994, Reynolds and Chelazzi, 2004, Treue and Martinez Trujillo, 1999 and Yantis and Serences, 2003) modulate the responses of individual sensory neurons: attending to a stimulus or feature that matches a neuron’s receptive field location or tuning preference typically increases neuronal responses. The similarity in the way different forms of attention affect individual neurons led to the hypothesis that all forms of attention use a similar neuronal mechanism (Martinez-Trujillo and Treue, 2004, Maunsell and Treue, 2006 and Treue and Martinez Trujillo, 1999). However, the retinotopic organization of visual cortex may allow spatial attention to employ a distinct mechanism because the comodulated neurons are typically located near each other.