John S. Werner

Aging and human macular pigment density: Appended with translations from the work of Max Schultze and Ewald Hering

The optical density of human macular pigment was measured for 50 observers ranging in age from 10 to 90 years. The psychophysical method required adjusting the radiance of a 1 degree, monochromatic light (400-550 nm) to minimize flicker (15 Hz) when presented in counterphase with a 460 nm standard. This test stimulus was presented superimposed on a broad-band, short-wave background. Macular pigment density was determined by comparing sensitivity under these conditions for the fovea, where macular pigment is maximal, and 5 degrees temporally. This difference spectrum, measured for 12 observers, matched Wyszecki and Stiless standard density spectrum for macular pigment. To study variation in macular pigment density for a larger group of observers, measurements were made at only selected spectral points (460, 500 and 550 nm). The mean optical density at 460 nm for the complete sample of 50 subjects was 0.39. Substantial individual differences in density were found (ca. 0.10-0.80), but this variation was not systematically related to age.

DEVELOPMENT OF SCOTOPIC SENSITIVITY AND THE ABSORPTION SPECTRUM OF THE HUMAN OCULAR MEDIA.

Scotopic spectral sensitivity was measured for nine observers (aged 4.5 months to 66 years) from 400 to 650 nm (10-nm steps) by using a 42 degree naturally viewed stimulus. The dependent measure was the visually evoked cortical-potential amplitude that was phase locked to an 8-Hz flickering stimulus. Sensitivity was similar for all observers at middle and long wavelengths, but at short wavelengths there was a decrease in sensitivity with increasing age. The density of the preretinal ocular media was estimated by subtracting the log scotopic spectral-sensitivity function of each observer from the human rhodopsin-absorbance spectrum when the two sets of curves were pinned at long wavelengths. The density of the infant ocular media was lower than that for adults. To quantify the sequence of ocular-media development, scotopic sensitivity was determined for an additional 42 observers (aged 1 month to 70 years) at two spectral points: 553 nm, where the optic-media density is low, and 405-430 nm, where the density is high. From these data, optic-media density at 400 nm was calculated. Despite substantial individual differences within each age, a clear aging function emerged. Preretinal optic-media density increased monotonically from birth throughout adulthood. Thus optical density at 400 nm differs by about a factor of 22 between the average 1-month-old infant and the average 70-year-old adult.

Light, vision, and aging.

Recent research on aging of chromatic and spatial vision processes is reviewed. Changes in these visual processes with advancing age are largely continuous. Age-related declines in visual performance may be explained in terms of reductions in the illuminance of the visual stimulus due to changes in the ocular media and losses of efficiency at a neural level. Thus, some prominent characteristics of the senescent visual system are similar to those of the younger visual system operating at a lower ambient light level. One important determinant of retinal aging may be the light history of the individual, i.e., cumulative exposure to high-energy photons from solar radiation may accelerate retinal aging. If these abstractions from the literature are valid, then it will become more important to control the light environment throughout the life span.

Long-range interactions in visual perception

Classical receptive-field concepts have been used to explain local perceptual effects such as border contrast and Mach bands, but are not sufficient to explain global perceptual effects. Examples are the perception of illusory contours, area contrast, color constancy, depth planes, coherent motion and texture contrast. These diverse effects require neurophysiological mechanisms within the visual pathways with long-range interactions. Candidate mechanisms are suggested, including converging feedforward projection to account for the emergence of new response properties at higher levels, recruitment of lateral connections to compensate for loss of afference and explain filling-in, and re-entrant projections from higher levels using synchronization of neuronal responses to account for binding.

Loci of spectral unique hues throughout the life span

Spectral unique hues (blue, green, and yellow) were determined for 50 observers ranging in age from 13 to 74 years. Each unique hue was measured at three luminance levels (0.5-log-unit steps). There were no significant changes in the spectral locations of red-green equilibrium hues (unique blue and yellow) as a function of luminance level or age. In contrast, significant shifts in unique green loci occurred as a function of both age and luminance. Unique green loci shifted toward shorter wavelengths with age. These results are consistent with the hypothesis that with advancing age there is a parallel decline in the input of all three cone types to the red-green chromatic channel and either a selective decline in short-wave-sensitive cone input to the yellow-blue chromatic channel or a change in the way in which cone signals are combined within the yellow-blue channel.

Effect of chromatic adaptation on the achromatic locus : The role of contrast, luminance, and background color

Two superposed annular test lights of complementary spectral composition were presented as 60-90 incremental test flashes on 480 steady backgrounds. Two observers adjusted the ratio of the two test lights to maintain an achromatic appearance under conditions of adaptation that varied with respect to background luminance, chromaticity and stimulus contrast. The shift in chromaticity of the achromatic point was in the direction of the chromaticity of the background, while the magnitude of the shift increased as an increasing function of background luminance and as a decreasing function of contrast. These data confirm and extend a model of chromatic adaptation that has the following properties: (1) non-additivity of transient test and steady background fields, in the sense that the background, although physically adding to the test flash, only affects its hue by way of altering the gain of cone pathways; (2) Vos-Walraven cone spectral sensitivities; and (3) adaptation sites in the cone pathways having the same action spectra as Stiles pi 5, pi 4 and (modified) pi 1 mechanisms, and which generate receptor-specific attenuation factors (von Kries Coefficients) according to Stiles generalized threshold vs intensity function, zeta (x).

Senescent changes in scotopic contrast sensitivity

Scotopic contrast sensitivity functions (CSFs) were measured for 50 observers between the ages of 20 and 88 years. Using a maximum-likelihood, 2-alternative, temporal forced-choice threshold-estimation algorithm, scotopic CSFs were measured at 7 spatial frequencies ranging from 0.2 to 3.0 cpd, with mean retinal illuminance equated for observers at -0.85 log scotopic Trolands. For each stimulus condition, eight cycles of a horizontal sinusoidal grating were presented within +/- 1 S.D. of a 2-D Gaussian-spatial envelope and within a 1-s Gaussian-temporal envelope. Stimuli were centered on the nasal retina along the horizontal meridian 6 degrees from the fovea. Scotopic CSFs were found to be low-pass. Statistically significant age-related declines in contrast sensitivities were found for spatial frequencies at or below 1.2 cpd. There was also a statistically significant decrease in the high frequency cut-off with age (P < 0.01). An explanation of these results in terms of optical factors is rejected, while the results are consistent with age-related changes in the magnocellular pathway.

Sensitivity of human foveal color mechanisms throughout the life span

Spectral sensitivities of mechanisms dominated by short-, middle-, or long-wavelength-sensitive cones were measured for 76 observers ranging in age from 10 to 84 years. The short-wavelength mechanism was isolated with a yellow adapting background and five test wavelengths between 420 and 550 nm modulated at 2 Hz. Sensitivity declined with age, but the slopes of the functions varied as a function of wavelength. When the data were corrected for light losses in the ocular media, the slopes were similar for lambda less than or equal to 500 nm and still significantly correlated with age. At 440 nm, the sensitivity of the short-wavelength mechanism, specified at the retinal level, declined at a rate of 0.08 log unit per decade. Sensitivity at 550 nm under these conditions was dependent on middle- and/or long-wavelength-sensitive cones and was not correlated significantly with age. To study isolated middle- and long-wavelength mechanisms, sensitivities were measured at six wavelengths between 500 and 650 nm, using a 20-Hz test stimulus and appropriate chromatic adapting backgrounds. The sensitivities at all wavelengths were correlated negatively with age. When specified at the retinal level, the sensitivity at 560 nm declined at a rate of 0.11 log unit per decade for both middle- and long-wavelength mechanisms. These data support the view that the sensitivities of all three cone types and/or at least one of their postreceptoral pathways declines from 10 to 84 years of age.

Development of visual memory in infants.

Publisher Summary Preverbal infants encode and retain some information about their visual world from the first hours of life. Even neonates demonstrate recognition memory. This chapter reviews and interprets infant visual recognition memory literature in terms of the particular methodologies used in each study. This literature is related to work on memory of older children and adults, highlighting many consistencies that appear in the memory systems of infants and more mature subjects. Although clear conclusions about specific aspects of infant recognition memory are not possible at this time, some generalizations have emerged. These may perhaps best be summarized by a set of hypotheses. As with all hypotheses, they remain to be scrutinized by further empirical evidence.

Individual differences in contrast sensitivity functions: Longitudinal study of 4-, 6- and 8-month-old human infants

Contrast sensitivity functions (CSFs) of 25 infants were measured longitudinally at 4, 6 and 8 months of age using a preferential-looking method and the method of constant stimuli. Sine-wave gratings varied from 0.27 to 4.32 c/deg, contained eight unattenuated cycles (with edges tapered to uniform gray), and rose to the desired contrast in 2 sec. (1) The average CSF was described on log-log coordinates by a band-pass function. With development it increased in overall sensitivity to contrast, shifted its peak toward slightly higher spatial frequencies, and increased its high frequency cutoff. (2) Log sensitivity at the CSF peak was slightly higher for female than male infants at 6 months, consistent with the hypothesis that vernier acuity (which also may differ between the sexes at this age) is partly mediated by analyzers tuned to low frequencies. (3) Within age groups the individual differences were such that log sensitivities for neighboring spatial frequencies generally correlated more highly than distant frequencies. With development the correlations among distant frequencies below 1.0 c/deg increased. Monte Carlo simulations of a model that shifts spatial analyzers to higher frequencies with age reproduced these results but simulations of adultlike, unshifting analyzers did not. (4) Measures taken 2 months apart tended to correlate more highly than those taken 4 months apart, though some individual differences in the CSF peak remained stable over 4 months.