Fourier and non-Fourier pattern discrimination compared.
Various studies indicate the existence of non-Fourier visual mechanisms that can extract non-luminance cues (e.g., contrast modulation) as well as a Fourier mechanism that deals with luminance variation only. We compared the pattern discrimination performance of the non-Fourier mechanism with that of the Fourier mechanism by using orientation discrimination and spatial-frequency discrimination tasks. The Fourier patterns used were D6s, the sixth spatial derivative of a Gaussian function multiplied by another Gaussian function in the orthogonal dimension. The corresponding non-Fourier patterns were D6 contrast-modulated cosine gratings. Our results showed a similar trend for the non-Fourier and the Fourier performance at various peak spatial-frequencies or orientations of D6. However, the discrimination threshold of the non-Fourier mechanism was about two-fold higher than that of the Fourier mechanism. The oblique effect was also stronger for non-Fourier patterns. In addition, worse performance for non-Fourier patterns at short stimulus durations (around 33.3 msec) was consistent with the prediction of the two-stage non-Fourier model, which requires more time for the additional rectification and filtering operations.
Lin
L M
LM
Visual Sciences Center, University of Chicago, IL 60637, USA. llin22@midway.uchicago.edu
Wilson
H R
HR
D003463:Cues; D004192:Discrimination, Psychological; D006801:Humans; D008029:Lighting; D008433:Mathematics; D008954:Models, Biological; D010364:Pattern Recognition, Visual / Q000502:physiology*; D012399:Rotation; D012684:Sensory Thresholds / Q000502:physiology; D013997:Time Factors