Top-down facilitation of visual recognition

doi:10.1073/pnas.0507062103

Top-down facilitation of visual recognition

^*Martinos Center at Massachusetts General Hospital, Harvard Medical School, Charlestown, MA 02129; and ^¶Program in Biophysics and ^‡Department of Psychology, Harvard University, Cambridge, MA 02138

Edited by Riitta Hari, Helsinki University of Technology, Espoo, Finland (received for review August 17, 2005)

Abstract

Cortical analysis related to visual object recognition is traditionally thought to propagate serially along a bottom-up hierarchy of ventral areas. Recent proposals gradually promote the role of top-down processing in recognition, but how such facilitation is triggered remains a puzzle. We tested a specific model, proposing that low spatial frequencies facilitate visual object recognition by initiating top-down processes projected from orbitofrontal to visual cortex. The present study combined magnetoencephalography, which has superior temporal resolution, functional magnetic resonance imaging, and a behavioral task that yields successful recognition with stimulus repetitions. Object recognition elicited differential activity that developed in the left orbitofrontal cortex 50 ms earlier than it did in recognition-related areas in the temporal cortex. This early orbitofrontal activity was directly modulated by the presence of low spatial frequencies in the image. Taken together, the dynamics we revealed provide strong support for the proposal of how top-down facilitation of object recognition is initiated, and our observations are used to derive predictions for future research.

Footnotes

↵ † To whom correspondence should be addressed at: Martinos Center at Massachusetts General Hospital, Harvard Medical School, 149 Thirteenth Street, Charlestown, MA 02129. E-mail: bar{at}nmr.mgh.harvard.edu.
↵ § K.S.K. and A.S.G. contributed equally to this work.
Author contributions: M.B. designed research; M.B., K.S.K., A.S.G., J.B., and A.M.S. performed research; A.M.D., M.S.H., D.L.S., B.R.R., and E.H. contributed new reagents/analytic tools; M.B., A.S.G., A.M.S., and K.M. analyzed data; and M.B. wrote the paper.
Conflict of interest statement: No conflicts declared.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations: HSF, high spatial frequency; LSF, low spatial frequency; OFC orbitofrontal cortex; MEG, magnetoencephalography; fMRI, functional MRI; ROI, region of interest; RT, reaction time.