title: Collinear facilitation is independent of receptive-field expansion at low contrast.
abstract: Modulation of single-cell responses by compound stimuli (target plus flankers) extending outside the cell's receptive field (RF) may represent an early neural mechanism for encoding objects in visual space, enhancing their perceptual saliency. The spatial extent of contextual modulation is wide. The size of the RF is known to be dynamically variable. It has been suggested that RF expansion when target contrast decreases is the real cause of effects attributed to modulation by flankers. This is not the case. We directly compared, in the same cells, the extent of RF size changes when stimulus contrast decreased with that revealed by systematically changing the target-and-collinear-flankers separation. We found that RF expansion at low contrast was not universal, and that the spatial extent of RF expansion, when it existed, was smaller than that of collinear flanker modulation. We conclude that the two processes in striate cortex work independently from each other.
authors.affiliation: The Smith-Kettlewell Eye Research Institute, 2318 Fillmore Street, San Francisco, CA 94115, USA. takuji@ski.org.
authors.forename: Takuji
authors.initials: T
authors.lastname: Kasamatsu
authors.forename: Rich
authors.initials: R
authors.lastname: Miller
authors.forename: Zhao
authors.initials: Z
authors.lastname: Zhu
authors.forename: Michael
authors.initials: M
authors.lastname: Chang
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Ishida
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000818:Animals; D002415:Cats; D015350:Contrast Sensitivity / Q000502:physiology; D004594:Electrophysiology; D008027:Light; D010364:Pattern Recognition, Visual / Q000502:physiology; D010775:Photic Stimulation; D011984:Sensory Receptor Cells / Q000502:physiology*; D012815:Signal Processing, Computer-Assisted; D014793:Visual Cortex / Q000033:anatomy & histology / Q000502:physiology*; D014794:Visual Fields / Q000502:physiology*; D014795:Visual Pathways / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology*