The role of Fourier components in discrimination between two types of plaid patterns

Do decision processes have separate access to the individual Fourier components of a complex pattern? Subjects discriminated between plaid patterns formed by multiplying or by summing vertical and horizontal square-wave gratings. Such patterns differ in two ways: (1) product plaids contain distinctive off-axis Fourier components; (2) adjacent luminances are related by equal ratios in the products and by equal differences in the sums. Performance on this task was compared with the separately measured unmasked detection thresholds of the off-axis Fourier components and with performance in control tasks which provided only the 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 components are accessible, but that masking reduces their usefulness.