FOURIER AND NON-FOURIER PATTERN-DISCRIMINATION COMPARED

Various studies indicate the existence of non-Fourier visual mechanism s that can extract non-luminance cues (e.g., contrast modulation) as w ell as a Fourier mechanism that deals with luminance variation only, W e compared the pattern discrimination performance of the non-Fourier m echanism with that of the Fourier mechanism by using orientation discr imination and spatial-frequency discrimination tasks. The Fourier patt erns used were D6s, the sixth spatial derivative of a Gaussian functio n multiplied by another Gaussian function in the orthogonal dimension. The corresponding non-Fourier patterns were D6 contrast;modulated cos ine gratings, Our results showed a similar trend for the non-Fourier a nd the Fourier performance at various peak spatial-frequencies or orie ntations of D6. However, the discrimination threshold of the non-Fouri er mechanism was about two-fold higher than that of the Fourier mechan ism. The oblique effect was also stronger for non-Fourier patterns, In addition, worse performance for non-Fourier patterns at short stimulu s durations (around 33.3 msec) was consistent with the prediction of t he two;stage non-Fourier model, which requires more time for the addit ional rectification and filtering operations. Copyright (C) 1996 Elsev ier Science Ltd.