Dynamic properties of orientation discrimination assessed by using classification images

doi:10.1073/pnas.0507259103

Dynamic properties of orientation discrimination assessed by using classification images

Institute of Ophthalmology, University College London, Bath Street, London EC1V 9EL, United Kingdom

Edited by George Sperling, University of California, Irvine, CA, and approved January 31, 2006 (received for review August 19, 2005)

Abstract

Recent physiological studies indicate that the tuning properties of neurons under acute preparation in primary visual cortex can change over time. We used a psychophysical reverse correlation paradigm to examine the potential repercussions of this neuronal property for human observers' ability to discriminate the orientation of targets over time. Observers were required to identify the orientation of a Gabor target presented within dynamic white noise. Frames from the noise movies were pooled to compute dynamic classification images (CIs) associated with the observers' discrimination performance, which then were fit with a weighted difference-of-Gabor function. Best-fitting templates were temporally bandpass, tuned to more oblique orientations than the stimulus but, crucially, did not change over time. The results suggest that the template for orientation discrimination is selected within the first 50 ms of stimulus onset and that, unlike the response of single cells, there is no measurable dynamic component to either orientation or spatial frequency tuning of human orientation discrimination.

Footnotes

*To whom correspondence should be addressed. E-mail: i.mareschal{at}ucl.ac.uk
Author contributions: I.M., S.C.D., and P.J.B. designed research, performed research, analyzed data, and wrote the paper.
Conflict of interest statement: No conflicts declared.
This paper was submitted directly (Track II) to the PNAS office.
↵ † Xing, J. & Ahumada, A. J. (2002) J. Vision 2, 343a (abstr.).
↵ ‡ Chen, K. Y., Eckstein, M. & Shimozaki, S. S. (2003) J. Vision 3, abstr. 182.
↵ § Benucci, A., Frazor, R. & Carandini, M. (2005) J. Vision 5, abstr. 84.
Abbreviations:

CI,

classification image;

SF,

spatial frequency;

c/deg,

cycles per degree