title: Attention modulates neuronal correlates of interhemispheric integration and global motion perception.
abstract: In early retinotopic areas of the human visual system, information from the left and right visual hemifields (VHFs) is processed contralaterally in two hemispheres. Despite this segregation, we have the perceptual experience of a unified, coherent, and uninterrupted single visual field. How exactly the visual system integrates information from the two VHFs and achieves this perceptual experience still remains largely unknown. In this study using fMRI, we explored candidate areas that are involved in interhemispheric integration and the perceptual experience of a unified, global motion across VHFs. Stimuli were two-dimensional, computer-generated objects with parts in both VHFs. The retinal image in the left VHF always remained stationary, but in the experimental condition, it appeared to have local motion because of the perceived global motion of the object. This perceptual effect could be weakened by directing the attention away from the global motion through a demanding fixation task. Results show that lateral occipital areas, including the medial temporal complex, play an important role in the process of perceptual experience of a unified global motion across VHFs. In early areas, including the lateral geniculate nucleus and V1, we observed correlates of this perceptual experience only when attention is not directed away from the object. These findings reveal effects of attention on interhemispheric integration in motion perception and imply that both the bilateral activity of higher-tier visual areas and feedback mechanisms leading to bilateral activity of early areas play roles in the perceptual experience of a unified visual field.
authors.affiliation: Department of Radiology, Medical Physics, University Medical Center Freiburg, Germany.
authors.forename: Burak
authors.initials: B
authors.lastname: Akin
authors.affiliation: Vrije Universiteit Brussel, Brussels, Belgium.
authors.forename: Ceylan
authors.initials: C
authors.lastname: Ozdem
authors.affiliation: Ege University, Izmir, Turkey.
authors.forename: Seda
authors.initials: S
authors.lastname: Eroglu
authors.affiliation: Bozok University, Yozgat, Turkey.
authors.forename: Dudu Taslak
authors.initials: DT
authors.lastname: Keskin
authors.affiliation: Department of Psychology and Key Laboratory of Machine Perception (Ministry of Education), Peking University, Beijing, China Peking-Tsinghua Center for Life Sciences, Beijing, China PKU-IDG/McGovern Institute for Brain Research, Peking University, Beijing, China.
authors.forename: Fang
authors.initials: F
authors.lastname: Fang
authors.affiliation: Department of Psychology & National Magnetic Resonance Research Center, Bilkent University, Ankara, Turkey.
authors.forename: Katja
authors.initials: K
authors.lastname: Doerschner
authors.affiliation: Department of Psychology, University of Minnesota, Minneapolis, MN.
authors.forename: Daniel
authors.initials: D
authors.lastname: Kersten
authors.affiliation: Department of Psychology & National Magnetic Resonance Research Center, Bilkent University, Ankara, Turkey.
authors.forename: Huseyin
authors.initials: H
authors.lastname: Boyaci
mesh_terms: D001288:Attention / Q000502:physiology*; D005133:Eye Movements / Q000502:physiology; D030141:Feedback, Psychological / Q000502:physiology; D005829:Geniculate Bodies / Q000502:physiology; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods; D009038:Motion; D009039:Motion Perception / Q000502:physiology*; D010775:Photic Stimulation / Q000379:methods; D014793:Visual Cortex / Q000502:physiology*; D014794:Visual Fields / Q000502:physiology
keywords: fMRI; global motion perception; interhemispheric integration; perceptual experience of unified visual field; visual brain