Abstract

A set of five localized stimuli (ramp, edge, line, dipole, and quadrupole) can be used to measure the contrast sensitivity and phase sensitivity of the visual system. Since each multipole is the derivative of the preceding one, two closely spaced opposite polarity multipoles produce the next higher multipole. We measured thresholds for a pair of opposite polarity multipoles as a function of their separation. We were especially interested in determining the separation at which the two multipoles begin to cancel. Preliminary results show the following transition separations: ramp-edge at 30 min, edge-line at 2 min, line-dipole at 3 min, and dipole-quadrupoie at 1 min. Lateral inhibitory overshoot effects were found near the transition region. Multipole sensitivity can be related to contrast sensitivity by a surprisingly simple formula. The visibility of a dipole is less than what would be expected from the contrast sensitivity function. Our explanation is that at high spatial frequencies the symmetric mechanisms are more sensitive than the antisymmetric ones.

© 1986 Optical Society of America