Publications (30)166.1 Total impact
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Article: Effects of experimental strabismus on the architecture of macaque monkey striate cortex.
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ABSTRACT: Strabismus, a misalignment of the eyes, results in a loss of binocular visual function in humans. The effects are similar in monkeys, where a loss of binocular convergence onto single cortical neurons is always found. Changes in the anatomical organization of primary visual cortex (V1) may be associated with these physiological deficits, yet few have been reported. We examined the distributions of several anatomical markers in V1 of two experimentally strabismic Macaca nemestrina monkeys. Staining patterns in tangential sections were related to the ocular dominance (OD) column structure as deduced from cytochrome oxidase (CO) staining. CO staining appears roughly normal in the superficial layers, but in layer 4C, one eye's columns were pale. Thin, dark stripes falling near OD column borders are evident in Nissl-stained sections in all layers and in immunoreactivity for calbindin, especially in layers 3 and 4B. The monoclonal antibody SMI32, which labels a neurofilament protein found in pyramidal cells, is reduced in one eye's columns and absent at OD column borders. The pale SMI32 columns are those that are dark with CO in layer 4. Gallyas staining for myelin reveals thin stripes through layers 2-5; the dark stripes fall at OD column centers. All these changes appear to be related to the loss of binocularity in cortical neurons, which has its most profound effects near OD column borders.The Journal of Comparative Neurology 10/2001; 438(3):300-17. · 3.81 Impact Factor -
Article: Neural mechanisms underlying amblyopia.
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ABSTRACT: The nature of the neural basis of amblyopia is a matter of some debate. Recent neurophysiological data show correlates of amblyopia in the spatial properties of neurons in primary visual cortex. These neuronal deficits are probably the initial manifestation of the visual loss, but there are almost certainly additional deficits at higher levels of the visual pathways.Current Opinion in Neurobiology 09/1999; 9(4):480-6. · 7.44 Impact Factor -
Article: Factors limiting contrast sensitivity in experimentally amblyopic macaque monkeys.
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ABSTRACT: Contrast detection is impaired in amblyopes. To understand the contrast processing deficit in amblyopia, we studied the effects of masking noise on contrast threshold in amblyopic macaque monkeys. Amblyopia developed as a result of either experimentally induced strabismus or anisometropia. We used random spatiotemporal broadband noise of varying contrast power to mask the detection of sinusoidal grating patches. We compared masking in the amblyopic and non-amblyopic eyes. From the masking functions, we calculated equivalent noise contrast (the noise power at which detection threshold was elevated by square root of 2) and signal-to-noise ratio (the ratio of threshold contrast to noise contrast at high noise power). The relation between contrast threshold and masking noise level was similar for amblyopic and non-amblyopic eyes. Although in most cases there was some elevation in equivalent noise for amblyopic compared to fellow eyes, signal-to-noise ratio showed greater variation with the extent of amblyopia. These results support the idea that the contrast detection deficit in amblyopia is a cortical deficit.Vision Research 02/1999; 39(25):4152-60. · 2.41 Impact Factor -
Article: Neuronal correlates of amblyopia in the visual cortex of macaque monkeys with experimental strabismus and anisometropia.
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ABSTRACT: Amblyopia is a developmental disorder of pattern vision. After surgical creation of esotropic strabismus in the first weeks of life or after wearing -10 diopter contact lenses in one eye to simulate anisometropia during the first months of life, macaques often develop amblyopia. We studied the response properties of visual cortex neurons in six amblyopic macaques; three monkeys were anisometropic, and three were strabismic. In all monkeys, cortical binocularity was reduced. In anisometropes, the amblyopic eye influenced a relatively small proportion of cortical neurons; in strabismics, the influence of the two eyes was more nearly equal. The severity of amblyopia was related to the relative strength of the input of the amblyopic eye to the cortex only for the more seriously affected amblyopes. Measurements of the spatial frequency tuning and contrast sensitivity of cortical neurons showed few differences between the eyes for the three less severe amblyopes (two strabismic and one anisometropic). In the three more severely affected animals (one strabismic and two anisometropic), the optimal spatial frequency and spatial resolution of cortical neurons driven by the amblyopic eye were substantially and significantly lower than for neurons driven by the nonamblyopic eye. There were no reliable differences in neuronal contrast sensitivity between the eyes. A sample of neurons recorded from cortex representing the peripheral visual field showed no interocular differences, suggesting that the effects of amblyopia were more pronounced in portions of the cortex subserving foveal vision. Qualitatively, abnormalities in both the eye dominance and spatial properties of visual cortex neurons were related on a case-by-case basis to the depth of amblyopia. Quantitative analysis suggests, however, that these abnormalities alone do not explain the full range of visual deficits in amblyopia. Studies of extrastriate cortical areas may uncover further abnormalities that explain these deficits.Journal of Neuroscience 09/1998; 18(16):6411-24. · 7.11 Impact Factor -
Article: Peripheral and central factors limiting the development of contrast sensitivity in macaque monkeys.
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ABSTRACT: The aim of this study was to evaluate the contribution of peripheral and central factors to the development of visual sensitivity. We used the approach of (Pelli, 1981, 1990) to evaluate the hypothesis that intrinsic noise is high in infants compared with adults, and therefore sets an important limit on contrast sensitivity in infants. We measured contrast thresholds in the presence of various levels of dynamic spatiotemporal broadband noise in infant monkeys, and evaluated the developmental changes in contrast threshold and intrinsic noise. Our data show that intrinsic noise is high in infants and falls with contrast threshold during development. However, contrast thresholds in high-contrast noise also fall during development, although by a smaller amount. Therefore, while changes in intrinsic noise set an important limit on the development of contrast sensitivity across spatial frequencies, changes in non-additive sources of noise also contribute, particularly at high spatial frequencies. We interpret these results in terms of Pelli's hypothesis about the sources of additive and non-additive noise affecting visual detection. In these terms, additive noise reflects peripheral factors and non-additive noise reflects central ones. Our results suggest that changes in peripheral sources of noise represent an important limit for the development of visual sensitivity.Vision Research 02/1998; 38(1):61-70. · 2.41 Impact Factor -
Article: Effects of early-onset artificial strabismus on pursuit eye movements and on neuronal responses in area MT of macaque monkeys.
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ABSTRACT: In humans, esotropia of early onset is associated with a profound asymmetry in smooth pursuit eye movements. When viewing is monocular, targets are tracked well only when they are moving nasally with respect to the viewing eye. To determine whether this pursuit abnormality reflects an anomaly in cortical visual motion processing, we recorded eye movements and cortical neural responses in nonamblyopic monkeys made strabismic by surgery at the age of 10-60 d. Eye movement recordings revealed the same asymmetry in the monkeys' pursuit eye movements as in humans with early-onset esotropia. With monocular viewing, pursuit was much stronger for nasalward motion than for temporalward motion, especially for targets presented in the nasal visual field. However, for targets presented during ongoing pursuit, temporalward and nasalward image motion was equally effective in modulating eye movement. Single-unit recordings made from the same monkeys, under anesthesia, revealed that MT neurons were rarely driven binocularly, but otherwise had normal response properties. Most were directionally selective, and their direction preferences were uniformly distributed. Our neurophysiological and oculomotor measurements both suggest that the pursuit defect in these monkeys is not due to altered cortical visual motion processing. Rather, the asymmetry in pursuit may be a consequence of imbalances in the two eyes' inputs to the "downstream" areas responsible for the initiation of pursuit.Journal of Neuroscience 11/1996; 16(20):6537-53. · 7.11 Impact Factor -
Article: Amblyopia: a developmental disorder of the central visual pathways.
Cold Spring Harbor Symposia on Quantitative Biology 02/1996; 61:39-48. -
Article: Development of contrast sensitivity across the visual field in macaque monkeys (Macaca nemestrina).
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ABSTRACT: Interpretation of measurements of visual performance in infants must be based on knowledge of the locus of highest sensitivity in the infant retina. While we know that adult contrast sensitivity and spatial resolution is highest at the fovea, recent anatomical data show that the infant fovea is relatively immature. We have studied that variation of contrast sensitivity across the visual field during development in infant monkeys in order to investigate the behavioral consequences of this immaturity. The results show that, unlike adults, the sensitivity of the infant foveal region is similar to that of the near periphery. Central contrast sensitivity and spatial resolution improve substantially relative to the periphery over the first 20-40 postnatal weeks. Thus, contrast sensitivity in the periphery is relatively mature in infants with respect to more central regions of the visual field. The maturation pattern seen behaviorally is consistent with physiological and anatomical maturation patterns in macaque monkey.Vision Research 02/1996; 36(2):239-47. · 2.41 Impact Factor -
Article: Spatial frequency channels in experimentally strabismic monkeys revealed by oblique masking.
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ABSTRACT: Although the spatial vision deficits of human strabismic amblyopes have been well documented, surprisingly little is known about the mechanisms underlying their visual performance. In an effort to reveal the structure underlying the spatial vision deficits associated with strabismic amblyopia, we measured the performance of monkeys (Macaca nemestrina) with experimental strabismus in a contrast detection task with oblique masks. The masks were two adjacent identical oblique sine-wave gratings modulated in space by a Gaussian envelope. The target stimulus was a vertically oriented Gabor patch that appeared superimposed on the center of either the left or the right mask. The animals were trained by operant methods to indicate the location of the target. We measured detection thresholds in each eye independently for a large number of test and mask spatial frequencies. For each test spatial frequency, detection thresholds were elevated in the presence of the mask. The threshold evaluations showed a peak for a particular spatial frequency that was typically similar to the test spatial frequency. This pattern of results is consistent with the idea that the tests are detected by a discrete number of channels tuned to a narrow range of spatial frequencies. The data from the deviated eyes did not appear qualitatively different from those of the fellow eyes, and could be accounted by the same number of channels in both eyes. Quantitative estimates of the channels' characteristics revealed that the channels derived from the deviated eyes' data were similar to those yielded by the fellow eyes, but showed a reduction in their sensitivity to contrast.Vision Research 11/1995; 35(19):2737-42. · 2.41 Impact Factor -
Article: Does experimentally-induced amblyopia cause hyperopia in monkeys?
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ABSTRACT: We assessed refractive errors in 19 monkeys (Macaca nemestrina) raised with experimentally produced strabismus or unilateral defocus. These procedures resulted in hyperopic anisometropia in 10 monkeys. All 10 of the hyperopic animals were amblyopic; the amblyopic eye was always the more hyperopic eye. The degree of anisometropia was correlated with the degree of amblyopia. Hyperopic anisometropia did not develop in non-amblyopic animals. There was an association between early onset of visual abnormality and later development of hyperopic anisometropia. Since the refractive changes were correlated with changes in axial length and vitreous chamber depth, we suggest that amblyopia may cause alterations in eye growth and late-onset hyperopia.Vision Research 06/1995; 35(9):1289-97. · 2.41 Impact Factor -
Article: Suprathreshold contrast sensitivity in experimentally strabismic monkeys.
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ABSTRACT: Human strabismic amblyopes show deficits in spatial vision that can be revealed in a variety of visual tasks. In particular, they show a reduced sensitivity to contrast for a wide range of spatial frequencies. The ability of strabismic amblyopes to process contrast information at levels well above detection threshold is less well understood and somewhat controversial. In the course of investigating the neural basis of strabismic amblyopia we studied contrast processing both at and above detection threshold in experimentally strabismic monkeys (Macaca nemestrina). First we trained them to perform a contrast detection task and measured their contrast sensitivity for a wide range of spatial frequencies. Then we trained them to discriminate between two gratings that were identical except for their contrast. We show that these monkeys exhibit deficits in both tasks. The deficits in the contrast discrimination task cannot be solely attributed to their deficit at threshold.Vision Research 07/1994; 34(12):1575-83. · 2.41 Impact Factor -
Article: Contrast sensitivity and vernier acuity in amblyopic monkeys.
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ABSTRACT: Human psychophysical studies suggest that strabismic and anisometropic amblyopes may have characteristically different patterns of visual loss. In particular, anisometropic amblyopes often show deficits on spatial localization tasks that scale with their spatial resolution losses, whereas strabismic amblyopes can show localization deficits that are large relative to their losses in spatial resolution. We have compared the performance of non-human primates with experimentally-induced anisometropic and strabismic amblyopia on contrast detection and vernier acuity tasks. The performance of both groups of animals was fundamentally similar: both strabismic and anisometropic monkeys showed deficits in spatial localization that were large relative to their resolution losses, although the animals with the most disproportionate losses were strabismic. We investigated the extent to which contrast sensitivity losses accounted for the vernier acuity deficits. The results showed that, in most cases of either strabismic or anisometropic amblyopia, when the vernier stimuli for each eye were equated in terms of effective contrast, the extent of the vernier acuity deficit was reduced to approximately the extent of the spatial resolution deficit. In two cases, both of strabismic amblyopia, we found that equating the stimuli in this way was not sufficient to make the deficits equal, a pattern that has been described for human strabismic amblyopes.Vision Research 12/1993; 33(16):2301-11. · 2.41 Impact Factor -
Article: Differential development of two visual functions in primates.
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ABSTRACT: Psychophysical data suggest that spatial resolution and spatial position sensitivity may be limited by different neural mechanisms. We investigated this hypothesis from a developmental perspective by studying the development of these two kinds of visual performance in two groups of infant macaque monkeys (Macaca nemestrina), one normal and one given an experimental strabismus. The results show that these two visual functions develop at different rates in normal monkeys and are disrupted differentially by abnormal early visual experience. However the relationship between the two measures is the same in strabismic and normally reared monkeys; the performance of strabismic monkeys resembles that of younger normal monkeys.Proceedings of the National Academy of Sciences 12/1989; 86(22):8998-9001. · 9.68 Impact Factor -
Article: Analysis of the development of spatial contrast sensitivity in monkey and human infants.
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ABSTRACT: The development of spatial contrast sensitivity in human and monkey infants reveals changes in the properties of underlying contrast-detection mechanisms in the visual system. A reanalysis of published data shows that the development of the spatial contrast sensitivity function can be described satisfactorily by the simultaneous vertical and horizontal scaling of a template function whose shape on a log-log axis does not change during development. Because individuals differ in the point to which contrast sensitivity has developed at any particular time, the use of group-averaged data as a basis for estimating the course of the developmental process has two undesirable results. First, it provides estimates of spatial contrast sensitivity during development that do not reflect any individual's sensitivity. Second, it incorrectly suggests that the shape of the spatial contrast sensitivity function changes during development.Journal of the Optical Society of America. A, Optics and image science 01/1989; 5(12):2166-72. -
Article: Operant measurements of contrast sensitivity in infant macaque monkeys during normal development.
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ABSTRACT: The development of contrast sensitivity was measured longitudinally in seven Macaca nemestrina monkeys. Operant conditioning methods were used to train and then test infant monkeys from the ages of 1 to 12 months. Several changes were observed in the contrast sensitivity function, including an overall increase in sensitivity to contrast, a shift in the peak of the function toward higher spatial frequencies, and an increase in the cutoff spatial frequency. The time-courses for the changes in the contrast sensitivity function were characterized by rapid development during the first 10-20 weeks, followed by a gradual asymptotic development to adult levels over the remainder of the year. Sensitivity to contrast was found to develop with different time-courses for different spatial frequencies; sensitivity to low spatial frequencies reached adult levels much earlier than sensitivity to high spatial frequencies.Vision Research 02/1988; 28(3):387-96. · 2.41 Impact Factor -
Article: Effects of early unilateral blur on the macaque's visual system. II. Anatomical observations.
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ABSTRACT: We studied the effects of early unilateral blur on the anatomical organization of the visual pathways in 8 macaque monkeys. Blur was induced in one eye, beginning 2-14 d after birth, by 0.5% atropine twice a day. Atropinization was stopped at 6-8 months of age, and the animals were studied for anatomy 3-24 months later. The retina and all other eye tissues showed normal histology. In the dorsal lateral geniculate nucleus (LGN), cells in parvocellular layers receiving input from the atropine-treated eye were 9-32% smaller and were more lightly stained than those in layers innervated by the untreated eye. These changes were generally larger in the LGN ipsilateral to the treated eye. LGN cell size changes were absent or much smaller in the magnocellular layers. In the striate cortex, the distribution of the oxidative enzyme cytochrome oxidase (CO) was markedly altered in layer 4C beta. Layer 4C beta is uniformly stained in normal animals, but showed a distinct pattern of alternating high and low CO bands in the atropine-treated animals; the bands of higher CO activity were narrower than the bands of lower activity and had a 857-1050 micron repeat. Fainter banding was seen in layers 4A, 4C alpha, and 6, but the density of the rows of dark CO-stained dots in layer 3 was unaffected. Double-labeling revealed that the narrow dark CO bands were associated with the centers of the ocular dominance columns devoted to the atropine-treated eye. The distribution of 14C-2-deoxyglucose uptake in visual cortex produced by 4.5-9 c/deg spatial frequency stimulation was strongly biased toward the untreated eye. The treated eye could, however, elicit reasonably strong uptake when stimulated with patterns containing lower spatial frequencies. These results suggest that unilateral neonatal blur preferentially affects the parvocellular layers of the LGN and layer 4C beta of striate cortex, which are the portions of the central visual system associated with the processing of information concerning fine spatial detail. These anatomical changes are consistent with the high spatial frequency loss of vision demonstrated behaviorally and electrophysiologically in the atropine eye-driven visual system of these same animals.Journal of Neuroscience 06/1987; 7(5):1327-39. · 7.11 Impact Factor -
Article: Effects of early unilateral blur on the macaque's visual system. I. Behavioral observations.
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ABSTRACT: We raised 8 macaque monkeys with chronic atropinization of one eye throughout the first 6-10 months after birth. This rearing procedure produces retinal image blur, with the most pronounced contrast attenuation occurring at high spatial frequencies. Measurements of contrast sensitivity were made using behavioral methods in 6 monkeys and evoked potential methods in 2 monkeys. The results showed that this rearing procedure produced long-term deficits in the contrast sensitivity and spatial resolution of the atropinized eye, which were not due to residual losses in accommodative capacity. There was considerable interanimal variation in the magnitude of the effects on visual performance. Similar losses in visual performance are seen in some forms of human amblyopia. Rearing monkeys with chronic instillation of atropine therefore provides a nonhuman primate model for studying the underlying neural mechanisms of anisometropic amblyopia.Journal of Neuroscience 06/1987; 7(5):1318-26. · 7.11 Impact Factor -
Article: Effects of early unilateral blur on the macaque's visual system. III. Physiological observations.
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ABSTRACT: We studied the properties of visual cortical and lateral geniculate neurons in 5 macaque monkeys raised with the vision of one eye blurred by daily instillation of atropine. This rearing reduced the degree of binocular interaction in striate cortical neurons and caused a modest shift in eye dominance away from the atropine-treated eye. It also led to a difference in the spatial properties of neurons driven by the 2 eyes: neurons driven by the treated eye tended to have lower optimal spatial frequencies, poorer spatial resolution, and lower contrast sensitivity than neurons driven by the untreated eye. Some of the few binocularly driven neurons had receptive fields with sharply different spatial properties in the 2 eyes, with the treated eye's receptive field always having poorer spatial resolution. In striate cortex, the effects on neuronal spatial properties were less marked in layer 4 than in more superficial or deeper layers; there was no difference in the spatial properties of lateral geniculate neurons driven by the 2 eyes. A small sample of extrastriate cortical neurons from a single animal showed effects similar to those seen in striate cortex. The striate cortical changes varied consistently from animal to animal: The less affected animals had no discernible eye dominance shift and relatively small differences in spatial properties between the eyes; the more affected animals had substantial eye dominance shifts and larger interocular spatial differences. These variations were also reflected in, and consistent with, behavioral and anatomical measurements performed in the same monkeys.Journal of Neuroscience 06/1987; 7(5):1340-51. · 7.11 Impact Factor -
Article: Accommodative range in amblyopic monkeys (Macaca nemestrina).
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ABSTRACT: 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.Vision Research 02/1984; 24(12):1829-34. · 2.41 Impact Factor -
Article: Accomodative defocus does not limit development of acuity in infant Macaca nemestrina monkeys.
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ABSTRACT: In an experiment with ten macaque monkeys (Macaca nemestrina), a combination of photorefraction and corneal reflex photography was used to measure simultaneously the plane of focus and direction of gaze while they were presented with fixation targets. The monkeys ranged in age from 2 days to 10 weeks. Some of the infants that were less than 1 month old failed to change accommodation to targets at any distance, whereas others showed limited accommodative abilities. The magnitude of the accommodative response of infants older than 4 weeks appeared to be adultlike. Infant monkey's visual acuity improves dramatically after 4 weeks. These results, which show that the improvement in spatial resolution cannot be accounted for by increased accommodative accuracy, parallel those obtained from human infants where accommodative competence is attained by about 4 months of age.Science 04/1982; 215(4538):1409-11. · 31.20 Impact Factor
Top co-authors
Top Journals
Institutions
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1994–2001
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Howard Hughes Medical Institute
Chevy Chase, MD, USA
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1989–1999
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New York University USA
- • Center for Neural Science (CNS)
- • Department of Psychology
New York City, NY, USA
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1988
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Emory University
Atlanta, GA, USA
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1984
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University of Washington Seattle
Seattle, WA, USA
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