The impact of visual acuity on age-related differences in neural markers of early visual processing

The extent to which age-related differences in neural markers of visual processing are influenced by changes in visual acuity has not been systematically investigated. Studies often indicate that their subjects had normal or corrected-to-normal vision, but the assessment of visual acuity seems to most frequently be based only on self-report. Consistent with prior research, to be included in the current study, subjects had to report normal or corrected-to-normal vision. Additionally, visual acuity was formally tested using a Snellen eye chart. Event-related potentials (ERPs) were studied in young adults (18–32 years old), young–old adults (65–79 years old), and old–old adults (80 + years old) while they performed a visual processing task involving selective attention to color. Age-related differences in the latency and amplitude of ERP markers of early visual processing, the posterior P1 and N1 components, were examined. All results were then re-analyzed after controlling for visual acuity. We found that visual acuity declined as a function of age. Accounting for visual acuity had an impact on whether older and younger adults differed significantly in the size and latency of the posterior P1 and N1 components. After controlling for visual acuity, age-related increases in P1 and N1 latency did not remain significant, and older adults were found to have a larger P1 amplitude than young adults. Our results suggest that until the relationship between age-associated differences in visual acuity and early ERPs is clearly established, investigators should be cautious when interpreting the meaning of their findings. Self-reports about visual acuity may be inaccurate, necessitating formal measures. Additional investigation is needed to help establish guidelines for future research, especially of very old adults

Visual Acuity does not Moderate Effect Sizes of Higher-Level Cognitive Tasks.

Background/study contextDeclining visual capacities in older adults have been posited as a driving force behind adult age differences in higher-order cognitive functions (e.g., the "common cause" hypothesis of Lindenberger & Baltes, 1994, Psychology and Aging, 9, 339-355). McGowan, Patterson, and Jordan (2013, Experimental Aging Research, 39, 70-79) also found that a surprisingly large number of published cognitive aging studies failed to include adequate measures of visual acuity. However, a recent meta-analysis of three studies (La Fleur and Salthouse, 2014, Psychonomic Bulletin & Review, 21, 1202-1208) failed to find evidence that visual acuity moderated or mediated age differences in higher-level cognitive processes. In order to provide a more extensive test of whether visual acuity moderates age differences in higher-level cognitive processes, we conducted a more extensive meta-analysis of topic.MethodsUsing results from 456 studies, we calculated effect sizes for the main effect of age across four cognitive domains (attention, executive function, memory, and perception/language) separately for five levels of visual acuity criteria (no criteria, undisclosed criteria, self-reported acuity, 20/80-20/31, and 20/30 or better).ResultsAs expected, age had a significant effect on each cognitive domain. However, these age effects did not further differ as a function of visual acuity criteria.ConclusionThe current meta-analytic, cross-sectional results suggest that visual acuity is not significantly related to age group differences in higher-level cognitive performance-thereby replicating La Fleur and Salthouse (2014). Further efforts are needed to determine whether other measures of visual functioning (e.g., contrast sensitivity, luminance) affect age differences in cognitive functioning

Visually guided step descent in children with Williams Syndrome

Individuals with Williams syndrome (WS) have impairments in visuospatial tasks and in manual visuomotor control, consistent with parietal and cerebellar abnormalities. Here we examined whether individuals with WS also have difficulties in visually controlling whole-body movements. We investigated visual control of stepping down at a change of level in children with WS (5–16-year-olds), who descended a single step while their movement was kinematically recorded. On each trial step height was set unpredictably, so that visual information was necessary to perceive the step depth and position the legs appropriately before landing. Kinematic measures established that children with WS did not use visual information to slow the leg at an appropriate point during the step. This pattern contrasts with that observed in typically developing 3- and 4-year-old children, implying severe impairment in whole-body visuomotor control in WS. For children with WS, performance was not significantly predicted by low-level visual or balance problems, but improved significantly with verbal age. The results suggest some plasticity and development in WS whole-body control. These data clearly show that visuospatial and visuomotor deficits in WS extend to the locomotor domain. Taken together with evidence for parietal and cerebellar abnormalities in WS, these results also provide new evidence for the role of these circuits in the visual control of whole-body movement

Visual acuity measured with luminance-modulated and contrast-modulated noise letter stimuli in young adults and adults above 50 years old

The human visual system is sensitive in detecting objects that have different luminance level from their background, known as first-order or luminance-modulated (LM) stimuli. We are also able to detect objects that have the same mean luminance as their background, only differing in contrast (or other attributes). Such objects are known as second-order or contrast-modulated (CM), stimuli. CM stimuli are thought to be processed in higher visual areas compared to LM stimuli, and may be more susceptible to ageing. We compared visual acuities (VA) of five healthy older adults (54.0±1.83 years old) and five healthy younger adults (25.4±1.29 years old) with LM and CM letters under monocular and binocular viewing. For monocular viewing, age had no effect on VA [F(1, 8)= 2.50, p> 0.05]. However, there was a significant main effect of age on VA under binocular viewing [F(1, 8)= 5.67, p< 0.05]. Binocular VA with CM letters in younger adults was approximately two lines better than that in older adults. For LM, binocular summation ratios were similar for older (1.16±0.21) and younger (1.15±0.06) adults. For CM, younger adults had higher binocular summation ratio (1.39±0.08) compared to older adults (1.12±0.09). Binocular viewing improved VA with LM letters for both groups similarly. However, in older adults, binocular viewing did not improve VA with CM letters as much as in younger adults. This could reflect a decline of higher visual areas due to ageing process, most likely higher than V1, which may be missed if measured with luminance-based stimuli alone

Aging and vision

AbstractGiven the increasing size of the older adult population in many countries, there is a pressing need to identify the nature of aging-related vision impairments, their underlying mechanisms, and how they impact older adults’ performance of everyday visual tasks. The results of this research can then be used to develop and evaluate interventions to slow or reverse aging-related declines in vision, thereby improving quality of life. Here we summarize salient developments in research on aging and vision over the past 25years, focusing on spatial contrast sensitivity, vision under low luminance, temporal sensitivity and motion perception, and visual processing speed

Visuomotor Adaptation During Asymmetric Walking

Necessary for effective ambulation, head stability affords optimal conditions for the perception of visual information during dynamic tasks. This maintenance of head-in-space equilibrium is achieved, in part, by the attenuation of the high frequency impact shock resulting from ground contact. While a great deal of experimentation has been done on the matter during steady state locomotion, little is known about how head stability or dynamic visual acuity is maintained during asymmetric walking. In this study, fifteen participants were instructed to walk on a split-belt treadmill for ten minutes while verbally reporting the orientation of a randomized Landolt-C optotype that was projected at heel strike. Participants were exposed to the baseline, adaptation, and washout conditions, as characterized by belt speed ratios of 1:1, 1:3, and 1:1, respectively. Step length asymmetry, shock attenuation, high (impact) and low (active) frequency head signal power, and dynamic visual acuity scores were averaged across the first and last fifty strides of each condition. Over the course of the first fifty strides, step length asymmetry was significantly greater during adaptation than during baseline (p d =2.442). Additionally, high frequency head signal power was significantly greater during adaptation than during baseline (p d =1.227), indicating a reduction in head stability. Shock attenuation was significantly lower during adaptation than during baseline (p d =-0.679), and a medium effect size suggests that dynamic visual acuity was lower during adaptation than during baseline as well (p =0.052; d =0.653). When comparing the baseline and adaptation conditions across the last fifty strides, however, many of these decrements were greatly reduced. The results of this study indicate that the locomotor asymmetry imposed by the split-belt treadmill during the early adaptation condition is responsible for moderate decrements to shock attenuation, head stability, and dynamic visual acuity. Moreover, the relative reduction in magnitude of these decrements across the last fifty strides underscores the adaptive nature of the locomotor and visuomotor systems

Neuroimaging in Leber Hereditary Optic Neuropathy: State-of-the-art and future prospects

Leber Hereditary Optic Neuropathy (LHON) is an inherited mitochondrial retinal disease that causes the degeneration of retinal ganglion cells and leads to drastic loss of visual function. In the last decades, there has been a growing interest in using Magnetic Resonance Imaging (MRI) to better understand mechanisms of LHON beyond the retina. This is partially due to the emergence of gene-therapies for retinal diseases, and the accompanying expanded need for reliably quantifying and monitoring visual processing and treatment efficiency in patient populations. This paper aims to draw a current picture of key findings in this field so far, the challenges of using neuroimaging methods in patients with LHON, and important open questions that MRI can help address about LHON disease mechanisms and prognoses, including how downstream visual brain regions are affected by the disease and treatment and why, and how scope for neural plasticity in these pathways may limit or facilitate recovery

Spatial attention in cognitive healthy ageing

In young adults, spatial attention typically manifests in a processing advantage for the left side of space (“pseudoneglect”)(Bowers & Heilman, 1980), whereas older adults tend to display no strongly lateralised bias, or a preference towards the right side of space (Benwell, Thut, Grant, & Harvey, 2014; Schmitz & Peigneux, 2011). However in addition, in recent studies, pseudoneglect has also been found to be maintained into old age (Brooks, Darling, Malvaso, & Della Sala, 2016; Brooks, Sala, & Darling, 2014; Friedrich, Hunter, & Elias, 2018). This suggests that the traditional view of an attenuated spatial asymmetry bias with increasing age may be too simplistic and that the spatial biases observed could be sensitive to a range of influences besides age. In addition, the traditionally observed shifts in spatial asymmetry in older adults have been attributed to neuroanatomical changes in the right hemisphere (with age), however as yet, there is limited evidence linking neurophysiological results to such behavioural shifts. To this end, for older adults, spatial attention research lacks systematic investigation of intra- and inter-task consistency. In the first of the four experiments of this thesis, I built on an earlier study which investigated young adults (Learmonth, Gallagher, Gibson, Thut, & Harvey, 2015, see 2018), and addressed this issue by investigating the magnitude and direction of spatial asymmetry in older adults aged between 60 to 86 years in five commonly used spatial tasks (line bisection, landmark, grey and grating scales and lateralised visual detection). I also compared the obtained spatial biases to a driving task. Results confirmed a stable retest reliability of all spatial tasks across two testing days in older adults. The line bisection and greyscales tasks elicited significant left spatial biases, in accordance with pseudoneglect, while the other tasks showed no significant biases to either side of space. Interestingly, in the driving task a right bias emerged for older adult and was stable across testing sessions. Yet, it failed to correlate with the other spatial measures. In comparison to the young adults’ sample from Learmonth et al. (2015, 2018), only the landmark task was age sensitive. However, none of the task showed significant inter task correlations. This replicates the findings of Learmonth et al. (2015, 2018) for an older age group. So in view of my findings of no significant inter-task correlations, as well as the inconsistent directions of the observed spatial biases for the older adults, I present supporting evidence that pseudoneglect is a multi-component phenomenon and highly task sensitive. Each task may reflect a distinct neural mechanism, likely to be impacted differently by age or other non- spatial modulators. In fact, the influence of other non -spatial modulators on spatial attention was the central topic of the other three experiments presented in Chapters 3 and 4. I employed a dual task paradigm (Chapters 3 and 4) and electroencephalography (EEG) (Chapter 4 only) to investigate behaviourally as well as neurophysiologically if an increase in attentional load has a reducing effect on spatial asymmetry and whether this would be more pronounced with old age. Interestingly, for the last experiment including EEG (Chapter 4) in particular, results showed that although older adults perform similarly well to young adults on a behavioural level, changes are visible on a neuronal level. Specifically, I found that older adults showed an age related reduction in the right hemisphere, for right lateralized targets at the early stages of stimuli processing, indexed by the N1 component, which was absent in young adults. Moreover, the results suggest that older adults used additional neuronal recruitment in the later stages of stimuli processing (P3), to compensate for increased task difficulty and increased resource allocation, likely improving the behavioural results of the older adults so that they were similar to young adults. The work presented in this thesis thus suggest that ageing per se does not result in an attenuated spatial asymmetry (that would be seen as equal to a decline in spatial attention ability). Instead I would argue that, independently of age, a set of underlying non spatial factors (such as load for example) influence the magnitude and direction of spatial asymmetry. In addition, additional neuronal recruitment and intrinsic mechanisms are used in older adults to compensate for possible deficits and this results in maintained performance in this age group