Ronald G. Boothe

Cones block signals from rods

Abstract Incremental thresholds were measured against four kinds of background light that had identical effects on rods: blue or red light entering the pupil near its edge or near its center. The match of scotopic luminance for each subject was based on his own absolute rod threshold for the two colors. Data from dark adaptation curves and the Stiles-Crawford effect show that only the rod system could detect the test flash. Yet, the threshold was either 0.3 or 0.5 log units higher against the red background than against the scotopically matched blue background, depending upon whether the red background light entered the pupil near its edge or near its center, respectively. The rods were shown to be indifferent to the loci at which the background light entered the pupil. The incremental threshold rose by more than a log unit when the test flash was presented at the same time as the change of locus at which the red background light entered the pupil. It follows that excitation of cones can prevent detection of a test flash by the rod system.

Morphology of the retina and dorsal lateral geniculate nucleus in dark-reared monkeys (Macaca nemestrina)

Abstract Nine infant monkeys were reared in continuous darkness from 2 weeks to 1, 3 and 6 months of age. One monkey was dark-reared from 3 to 7 months after birth. Light microscopic morphological studies of retina and dorsal lateral geniculate nucleus (dLGN) were done on animals sacrificed immediately after emerging from darkness and others that were tested behaviorally before sacrifice. Neither retina nor dLGN showed any obvious changes in cell number, size or staining characteristics when compared to light-reared, age-matched controls. Autoradiographic tracing of labeled retinal ganglion cell synaptic terminals indicated a normal distribution for dark-reared animals.

Binocular interaction in the dark

Abstract Replication of the Lansford-Baker phenomenon confirmed that light adaptation of one eye in a particular way can subsequently lower thresholds during dark adaptation of the other eye. Pressureblinding the non-test eye when dark adapted lowered thresholds in the test eye by the same amount, but pressure-blinding the non-test eye when light adapted had no noticeable effect on the test eye. It follows that a dark adapted eye sends signals to the brain that interfere with detection of signals elicited from the test eye by weak stimuli. The evidence favours interpretation in terms of binocular rivalry rather than ordinary discrimination of signal from noise.

Trichromacy in normally reared and light deprived infant monkeys (Macaca nemestrina)

Abstract Infant macaque monkeys ( Macaca nemestrina )were separated from their mothers a few days after birth and individually housed in a specially designed testing cage. Each was taught to discriminate white light from each of several narrow-band wavelengths of light selected from across the visible spectrum. During the first 2 months after birth, each of the infants learned to discriminate all wavelengths tested from white light, regardless of relative luminance. An infant which had been raised in continuous darkness from 2 weeks until 3 months after birth was similarly tested. This dark-reared infant also successfully learned to discriminate all wavelengths tested from white light. It is concluded that infant pigtail monkeys have trichromatic color vision by the age of 2 months, and that their trichromacy remains present following a period ofdark rearing during the first 3 months after birth.

Accommodative range in amblyopic monkeys (Macaca nemestrina)

Three naturally strabismic and two chronic bilaterally atropinized monkeys were tested for spatial contrast sensitivity and range of accommodation. All eyes that showed deficits in contrast sensitivity also showed deficits in accommodation. The strabismic monkeys all showed interocular differences in their CSFs and in their accommodative ranges. The atropine monkeys had no interocular differences on either measure. However, one had depressed contrast sensitivity relative to normal and also showed a reduced accommodative range. A statistically significant correlation was found between the high frequency cutoffs of the CSFs and accommodative ranges. These deficits in accommodative range that accompany contrast sensitivity losses in the monkey are similar to the deficits in accommodative range that accompany amblyopia in humans.

Visual acuity development in infant monkeys (Macaca nemestrina) having known gestational ages

Abstract In a previous report, Teller et al. (1978) measured the postnatal development of visual acuity in infant macaque monkeys with a forced-choice preferential looking (FPL) method. They reported a general trend toward better resolution with age, but found considerable variability among individual infants of the same age. We have repeated these measurements, in the same species using the same methods, in infant monkeys with known gestational ages. We find that when acuity development is plotted as a function of post-term age, the time course is similar to the previous study, but the variability is reduced.

Optical and neural factors limiting acuity development: evidence obtained from a monkey model.

Infants have much poorer acuity than adults. Recent experiments with infant monkeys indicate that this poor acuity cannot be explained on the basis of optics (quality of the retinal image) or sampling frequency (inter-receptor spacing). On the other hand, the poor acuity is not just a reflection of immature cognitive or motor development. Rather, the development of adult acuity levels appears to depend on maturation of neural elements in the early stages of the visual system.

Meridional variations in acuity and CSFS in monkeys (Macaca nemestrina) reared with externally applied astigmatism

Infant macaque monkeys have been raised under such conditions that all visual experience was obtained while looking through a cylindrical lens. When tested at older ages, these monkeys were found to have meridional differences in acuity and contrast sensitivity. The direction of the differences were predictable on the basis of the defocus produced by the rearing condition. The data support the theory, previously suggested on the basis of clinical and correlational studies, that astigmatism is a major cause factor in the occurrence of meridional amblyopia.

10 – Experience and Development in the Visual System: Anatomical Studies

Publisher Summary In the geniculostriate pathway, as in several other developing neural systems, more neurons are born and migrate into position than are present in the adult. This chapter discusses the development of the geniculostriate pathways in the mammalian visual system and the ways by which this development can be modified by postnatal visual deprivation. These geniculostriate pathways include the connections between retinal ganglion cells and the dorsal lateral geniculate nucleus (LGN), and between the LGN and striate cortex. Development is a continuous process. The chapter discusses it in terms of five discrete stages—(1) generation of neurons, (2) cell migration, (3) formation of pathways between nuclei, (4) cell death, and (5) formation and pruning of connections. It provides a brief overview of the five stages that take place during normal visual system development. It discusses the ways in which development can be modified by postnatal visual deprivation, emphasizing studies of monocular deprivation. The chapter also discusses the evidence that monocular deprivation effects are because of a combination of binocularly competitive and noncompetitive mechanisms.