THE OBLIQUE EFFECT IN ORIENTATION ACUITY

We have examined the dependence of rotational acuity on the orientatio n bandwidth of a stimulus using two-dimensional, band-pass filtered, s patial noise. Stimuli had a bandwidth of 0.5 octave of spatial frequen cy, centred at 5.0 cyc/deg, and an orientation bandwidth that covered the range from 0.0 to 25.0 deg, Thresholds were obtained on one princi pal (vertical), and one oblique axis (45 deg). It was found that acuit y declined on both axes as bandwidth increased, in a manner that was c ompatible with simple statistical principles with virtually perfect sa mpling of the image. There was some evidence that the intrinsic noise is greater on the oblique axis than on the vertical, and that oblique axes are less densely sampled than the principal axes. These differenc es are small and are insufficient, either on their own or taken togeth er to explain the oblique effect. Copyright (C) 1996 Elsevier Science Ltd