Neuroplasticity in older adults revealed by temporary occlusion of one eye.

Occluding one eye for several hours alters visual experience. Specifically, occluding one eye shifts the balance of ocular dominance to favour the recently deprived eye, which can be measured using binocular rivalry. This ocular dominance shift demonstrates homeostatic neuroplasticity within the visual system and has been explored in detail in younger adults. Here we measure whether the strength and general features of neuroplasticity revealed by monocular patching are maintained in older adults. Thirty younger (18-35 years) and 30 older adults (60-81 years) participated. Binocular rivalry features were measured before and after 2 h of occlusion. Post-patching, perceptual dominance of the non-patched eye decreased (p < .001) in both age groups. The effect of occlusion on all features of binocular rivalry did not significantly differ between groups. The older visual system maintains the ability to rapidly adjust to changes in perceptual experience induced by eye occlusion. This preservation of neuroplasticity suggests that visual training methods designed to improve visual performance based on eye occlusion should maintain effectiveness into older age.

The effect of aging on the eccentricity dependency of orientation anisotropy of perceptual surround suppression.

The features of perceptual surround suppression vary with eccentricity, such that the suppression strength is increased for horizontally oriented stimuli relative to other orientations near the fovea, but is strongest for radially oriented stimuli more peripherally. Perceptual suppression also varies with age, which has been well-studied for central fixation. However, only limited data are available regarding perceptual suppression in older adults for nonfoveal vision, and none of those studies have taken orientation biases of contrast sensitivity into account. Here, we explored the effects of older age on the eccentricity dependency of orientation biases of perceptual suppression. We found increased perceptual suppression in older adults at both 6° and 15° eccentricities relative to younger adults. A main effect of the horizontal orientation bias was found at 6° and a main effect of the radial orientation bias was found at 15° in both groups. In summary, perceptual surround suppression of contrast is stronger for older adults compared with younger adults at 6° and 15° eccentricities, but retinotopic orientation anisotropies are maintained with age. This study provides new insight into parafoveal visual perception in older adults, which may be particularly important to understand the visual experience of those who depend on nonfoveal vision owing to common age-related eye diseases.

Eccentricity dependence of orientation anisotropy of surround suppression of contrast-detection threshold.

Both neurophysiological and psychophysical data provide evidence for orientation biases in nonfoveal vision-specifically, a tendency for a Cartesian horizontal and vertical bias close to fixation, changing to a radial bias with increasing retinal eccentricity. We explore whether the strength of surround suppression of contrast detection also depends on retinotopic location and relative surround configuration (horizontal, vertical, radial, tangential) in parafoveal vision. Three visual-field locations were tested (0°, 225°, and 270°, angle increasing anticlockwise from 0° horizontal axis) at viewing eccentricities of 6° and 15°. Contrast-detection threshold was estimated with and without a surrounding annulus. At 6° eccentricity, horizontally oriented parallel center-surround (C-S) configurations resulted in greater surround suppression compared to vertically oriented parallel center-surround configurations (p = 0.001). At 15° eccentricity, radially oriented parallel center-surround stimuli conferred greater suppression than tangentially oriented stimuli (p = 0.027). Parallel surrounds resulted in greater suppression than orthogonal surrounds at both eccentricities (p < 0.05). At 6° the horizontal center was more susceptible to suppression than a vertical center (p < 0.001) for both parallel and orthogonal surrounds, while at 15° a radial center was more susceptible to suppression (relative to a tangential center), but only if the surround was parallel (p = 0.005). Our data show that orientation anisotropy of surround suppression alters with eccentricity, reflecting a link between suppression strength and visual-field retinotopy.

The Effect of Aging and Attention on Visual Crowding and Surround Suppression of Perceived Contrast Threshold.

Purpose: The purpose of this study was to study how, in midperipheral vision, aging affects visual processes that interfere with target detection (crowding and surround suppression) and to determine whether the performance on such tasks are related to visuospatial attention as measured by visual search. Methods: We investigated the effect of aging on crowding and suppression in detection of a target in peripheral vision, using different types of flanking stimuli. Both thresholds were also obtained while varying the position of the flanker (placed inside or outside of target, relative to fixation). Crowding thresholds were also estimated with spatial uncertainty (jitter). Additionally, we included a visual search task comprising Gabor stimuli to investigate whether performance is related to top-down attention. Twenty young adults (age, 18-32 years; mean age, 26.1 years; 10 males) and 19 older adults (age, 60-74 years; mean age, 70.3 years; 10 males) participated in the study. Results: Older adults showed more surround suppression than the young (F[1,37] = 4.21; P < 0.05), but crowding was unaffected by age. In the younger group, the position of the flanker influenced the strength of crowding, but not the strength of suppression (F[1,39] = 4.11; P < 0.05). Crowding was not affected by spatial jitter of the stimuli. Neither crowding nor surround suppression was predicted by attentional efficiency measured in the visual search task. There was also no significant correlation between crowding and surround suppression. Conclusions: We show that aging does not affect visual crowding but does increase surround suppression of contrast, suggesting that crowding and surround suppression may be distinct visual phenomena. Furthermore, strengths of crowding and surround suppression did not correlate with each other nor could they be predicted by efficiency of visual search.

A psychophysical technique for estimating the accuracy and precision of retinoscopy.

BACKGROUND: The accuracy and precision of retinoscopy need to be evaluated in an objective and unambiguous manner to judge an individual's performance in this task during training or in research for consistent measurements of refractive error. This study describes and evaluates a psychophysical technique for obtaining simultaneous and unbiased estimates of accuracy and precision in retinoscopy. METHODS: Subjects with zero to 12 years of experience with retinoscopy performed the psychophysical task on a model eye (75 subjects) and on a cyclopleged human eye with spherical refractive error (30 subjects). Subjects made forced choice judgments of 'with' or 'against' for lens powers within ± 0.5 D of expected neutrality (in 0.12 D steps), each placed 20 times before the eye in random order. Accuracy and precision were determined from the mean and standard deviation of the resultant psychometric function. RESULTS: Subjects could be qualitatively divided into those with good and poor accuracy and precision based on the task outcomes. The median and inter-quartile range of accuracy (no experience: 0.16 ± 0.34 D; four or more years of experience: 0.06 ± 0.11 D) and precision (no experience: 0.30 ± 0.39 D; four or more years of experience group: 0.13 ± 0.08 D) improved with task experience (p < 0.001). Median accuracy and precision in the human eye were similar to the model eye (p > 0.8). Accuracy and precision were poorly correlated with each other for both the human eye and model eye (|ρ| ≤ 0.20; p ≥ 0.09 for all). CONCLUSION: The psychophysical retinoscopic task could differentiate subjects based on their accuracy and precision and also capture key elements of improvement in retinoscopic performance with experience. Retinoscopic performance using this task was similar to previous reports using routine clinical retinoscopy. Therefore, the psychophysical technique may be used to evaluate and monitor objectively retinoscopic performance.