THE ROLE OF FOURIER COMPONENTS IN DISCRIMINATION BETWEEN 2 TYPES OF PLAID PATTERNS

Do decision processes have separate access to the individual Fourier c omponents of a complex pattern? Subjects discriminated between plaid p atterns formed by multiplying or by summing vertical and horizontal sq uare-wave gratings. Such patterns differ in two ways: (1) product plai ds contain distinctive off-axis Fourier components; (2) adjacent lumin ances are related by equal ratios in the products and by equal differe nces in the sums. Performance on this task was compared with the separ ately measured unmasked detection thresholds of the off-axis Fourier c omponents and with performance in control tasks which provided only th e non-Fourier cues. Performance in the plaid discrimination was worse than predicted from the unmasked detection thresholds, but better than predicted from the control tasks. The results argue that Fourier comp onents are accessible, but that masking reduces their usefulness.