S Tweten | PubMed Health

PubMed1991

Using metamers to explore motion perception.

We examined conditions under which two quite different types of random-dot cinematograms were perceptually matched. In one stimulus type, directions of motion were defined by a uniform distribution; in the other, directions were drawn from a discrete set of just a few, widely separated directions. Cinematograms whose range of uniformly distributed directions lay between 180 and 270 deg could be matched by cinematograms containing just 6-10 discrete directions. The number of discrete directions required for a match was a nonmonotonic function of the range of directions present in the other cinematogram. The results are consistent with a line-element model in which the outputs of 12 direction-selective mechanisms, each with a half-amplitude half-bandwidth of 30 deg, are combined nonlinearly to produce the percept of motion.

Humans↗

PubMed1990

A comparison of three clinical methods of spatial contrast-sensitivity testing in normal subjects.

Three methods clinically used for measuring spatial contrast sensitivity were performed monocularly in normal subjects to compare their sensitivity and applicability. The methods tested were (1) the Von Békésy tracking procedure, (2) the Method of Increasing Contrast, both carried out on a Nicolet CS-2000 automated Vision Tester, and (3) the Vistech Contrast Test System, a photographic test chart. The results show that the threshold sensitivities of the Von Békésy tracking procedure and the Method of Increasing Contrast were not significantly different. For sensitivity to middle and high spatial frequency, the Vistech test chart was found to approximate the Method of Increasing Contrast. With automated testing, a slower rate of contrast progression and a larger visual angle produced lower thresholds of detection of the contrast-sensitivity function. Using a slow rate of contrast progression, both the Vistech test chart and the Method of Increasing Contrast were rapidly conducted, easy to administer, and gave good approximations of the spatial contrast-sensitivity function.

Adult↗