title: The effect of spatial attention on contrast response functions in human visual cortex.
abstract: Previous electrophysiology data suggests that the modulation of neuronal firing by spatial attention depends on stimulus contrast, which has been described using either a multiplicative gain or a contrast-gain model. Here we measured the effect of spatial attention on contrast responses in humans using functional MRI. To our surprise, we found that the modulation of blood oxygenation level-dependent (BOLD) responses by spatial attention does not greatly depend on stimulus contrast in visual cortical areas tested [V1, V2, V3, and MT+ (middle temporal area)]. An additive model, rather than a multiplicative or contrast-gain model best describes the attentional modulations in V1. This inconsistency with previous single-unit electrophysiological data has implications for the population-based neuronal source of the BOLD signal.
authors.affiliation: The Salk Institute, La Jolla, California 92037, USA.
authors.forename: Giedrius T
authors.initials: GT
authors.lastname: Buracas
authors.forename: Geoffrey M
authors.initials: GM
authors.lastname: Boynton
mesh_terms: D000328:Adult; D001288:Attention / Q000502:physiology*; D001931:Brain Mapping; D002560:Cerebrovascular Circulation / Q000502:physiology; D015350:Contrast Sensitivity / Q000502:physiology*; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005260:Female; D005403:Fixation, Ocular / Q000502:physiology*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D010812:Physical Stimulation / Q000379:methods; D013028:Space Perception / Q000502:physiology*; D014793:Visual Cortex / Q000098:blood supply / Q000502:physiology*