Davida Y. Teller

Relation of increment thresholds to brightness and luminance.

Under ordinary conditions, both the brightness and the increment threshold of an illuminated disk vary directly with its luminance. However, when the disk is surrounded by an annulus more intense than the disk, the brightness of the disk decreases while its luminance remains unchanged.This set of experiments was performed to determine whether, when brightness is varied independently of luminance, the increment threshold depends upon the luminance or upon the brightness of the disk, or upon both factors. We measured the increment threshold for a flash added to the center of a large illuminated disk when the disk was surrounded by a contiguous annulus whose luminance could be varied. Measurements were also taken of the increment threshold as a function of time after the onset of the annulus. Correcting for light scattered in the eye, we found the increment threshold under all conditions to be independent of the luminance of the annulus (and thus independent of the brightness of the region), and dependent only upon the retinal illuminance of the region to which the test flash was added. It is concluded that brightness and the increment threshold cannot depend upon the same properties of the visual system.

Visual acuity and visual responsiveness in dark-reared monkeys (Macaca nemestrina).

Abstract Infant pigtail macaques were reared in darkness during the first 3 or 6 months after birth. Following dark rearing, the animals were relatively unresponsive on a series of informal visual tests (placing, startle, etc.). Testing with a forced-choice preferential looking task showed acuities between 2.5 and 7.5 c/deg ( 20240 and 2080 Snellen) in all dark reared monkeys compared with 15 c/deg ( 2040 Snellen) in control animals. These results suggest that in macaque infants dark rearing is more harmful to visual responsiveness than to visual acuity per se .

Oblique effects in normally reared monkeys (Macaca nemestrina): Meridional variations in contrast sensitivity measured with operant techniques

Abstract The present paper describes a newly completed operant methodology for the assessment of spatial vision in pigtail macaque ( Macaco nemestrina ) monkeys. Automated techniques for the generation, calibration, and presentation of sinusoidal grating stimuli, and for control of the operant experiment, are described in detail. Contrast sensitivity functions have been obtained in four animals for gratings in vertical, oblique, and horizontal orientations. The data demonstrate that the monkey visual system, like that of humans, shows variations of contrast sensitivity with grating orientation at high spatial frequencies. One monkey showed a classical oblique effect, i.e. similar sensitivity for vertical and horizontal and a lower sensitivity for oblique gratings. The other three monkeys showed contrast sensitivity differences between horizontal and vertical gratings. The similarity of monkey and human contrast sensitivity variations and the implications of these results for use of the macaque monkey as an animal model for human vision are discussed.

Local adaptation in stabilized vision

Abstract The increment threshold for a small stimulus superimposed upon adapting spots of various diameters was measured under scotopic conditions in the peripheral retina. Confirming Westheimer (1965) , it was found that adapting spots of about 1° diameter raise the threshold more than either larger or smaller spots. This experiment was repeated using a stabilized-image technique to avoid movements of the adapting field over the retina. The reduction of threshold with increase of the adapting spot diameter above 1° was found to be more pronounced with stabilization than without. Hence, Westheimers phenomenon cannot be explained by eye movements and temporal excitability changes, and must be attributed to physiological interactions within the visual system.

Sensitization by annular surrounds: sensitizaton and masking

Abstract Westheimer (1965) has shown that the rod threshold at the center of a 45′ disk of light is as much as a log unit higher than it is upon disks of larger diameters. In the present paper we explore the influence of such spatial interactions on the rapid changes in the threshold which occur in early light and dark adaptation (masking). That is early light and cark adaptation curves were traced with a 5′ test spot centered upon adapting disks of various diameters from 12 min to 3 deg of arc. Standard early light and dark adaptation curves were found on the larger sizes of disks, with a clear maximum in the threshold occuring near or slightly after the instant of onset of the disk, and (under some conditions) a secondary maximum at or near the instant of offset of the disk. For the smaller range of disks, however, both the rise and the fall of the threshold were monotonic, with no maxima near disk onset or offset. These data suggest that the threshold maximum of early light adaptation results from the interaction of center and surround processes of neural units.

Structure-function relationships in human red/green color vision

The relationship between molecular structure of the visual pigment genes and red-green color vision was studied in 126 normal and 63 color-defective males. We found that the great majority of defects in red-green color vision are associated with the formation of 5′R-G hybrid genes (protan series), deletion of the G gene (deutan series), or the formation of 5′R-G hybrid genes (deutan series). Within these two series, however, dichromacy and trichromacy cannot always be predicted from the molecular patterns, particularly among protans. Amino acid residues in exon 5 largely determine whether a hybrid gene will be more R-like or more G-like in phenotype. We observed numerous genetic polymorphisms in the R and G pigment genes of both normal and color-defective subjects. These polymorphisms may account for some, but not all, of the observed variations in color vision phenotypes. A common Ser/Ala polymorphism at position 180 of the R pigment gene was found to be highly correlated with the bimodal distribution of Raleigh matches we observed among 50 color-normal Caucasian males.