title: Evidence for two distinct mechanisms directing gaze in natural scenes.
abstract: Various models have been proposed to explain the interplay between bottom-up and top-down mechanisms in driving saccades rapidly to one or a few isolated targets. We investigate this relationship using eye-tracking data from subjects viewing natural scenes to test attentional allocation to high-level objects within a mathematical decision-making framework. We show the existence of two distinct types of bottom-up saliency to objects within a visual scene, which disappear within a few fixations, and modification of this saliency by top-down influences. Our analysis reveals a subpopulation of early saccades, which are capable of accurately fixating salient targets after prior fixation within the same image. These data can be described quantitatively in terms of bottom-up saliency, including an explicit face channel, weighted by top-down influences, determining the mean rate of rise of a decision-making model to a threshold that triggers a saccade. These results are compatible with a rapid subcortical pathway generating accurate saccades to salient targets after analysis by cortical mechanisms.
authors.affiliation: Computation and Neural Systems, California Institute of Technology, Pasadena, CA 91125, USA. mhsm3@cam.ac.uk
authors.forename: Michael
authors.initials: M
authors.lastname: Mackay
authors.forename: Moran
authors.initials: M
authors.lastname: Cerf
authors.forename: Christof
authors.initials: C
authors.lastname: Koch
mesh_terms: D001288:Attention / Q000502:physiology; D005145:Face; D005403:Fixation, Ocular / Q000502:physiology*; D005556:Form Perception / Q000502:physiology*; D006801:Humans; D008959:Models, Neurological; D010364:Pattern Recognition, Visual / Q000502:physiology*; D010775:Photic Stimulation / Q000379:methods; D011930:Reaction Time / Q000502:physiology; D012438:Saccades / Q000502:physiology*; D012684:Sensory Thresholds / Q000502:physiology; D014795:Visual Pathways / Q000502:physiology