Larger effect of aging on the perception of higher-order stimuli

Visual motion detection thresholds can be reliably measured during walking and standing

Introduction

In upright standing and walking, the motion of the body relative to the environment is estimated from a combination of visual, vestibular, and somatosensory cues. Associations between vestibular or somatosensory impairments and balance problems are well established, but less is known whether visual motion detection thresholds affect upright balance control. Typically, visual motion threshold values are measured while sitting, with the head fixated to eliminate self-motion. In this study we investigated whether visual motion detection thresholds: (1) can be reliably measured during standing and walking in the presence of natural self-motion; and (2) differ during standing and walking.

Methods

Twenty-nine subjects stood on and walked on a self-paced, instrumented treadmill inside a virtual visual environment projected on a large dome. Participants performed a two-alternative forced choice experiment in which they discriminated between a counterclockwise ("left") and clockwise ("right") rotation of a visual scene. A 6-down 1-up adaptive staircase algorithm was implemented to change the amplitude of the rotation. A psychometric fit to the participants' binary responses provided an estimate for the detection threshold.

Results

We found strong correlations between the repeated measurements in both the walking (R = 0.84, p < 0.001) and the standing condition (R = 0.73, p < 0.001) as well as good agreement between the repeated measures with Bland-Altman plots. Average thresholds during walking (mean = 1.04°, SD = 0.43°) were significantly higher than during standing (mean = 0.73°, SD = 0.47°).

Conclusion

Visual motion detection thresholds can be reliably measured during both walking and standing, and thresholds are higher during walking.

Zebrafish optomotor response to second-order motion illustrates that age-related changes in motion detection depend on the activated motion system

Various aspects of visual functioning, including motion perception, change with age. Yet, there is a lack of comprehensive understanding of age-related alterations at different stages of motion processing and in each motion system. To understand the effects of aging on second-order motion processing, we investigated optomotor responses (OMR) in younger and older wild-type (AB-strain) and acetylcholinesterase (achesb55/+) mutant zebrafish. The mutant fish with decreased levels of acetylcholinesterase have been shown to have delayed age-related cognitive decline. Compared to previous results on first-order motion, we found distinct changes in OMR to second-order motion. The polarity of OMR was dependent on age, such that second-order stimulation led to mainly negative OMR in the younger group while older zebrafish had positive responses. Hence, these findings revealed an overall aging effect on the detection of second-order motion. Moreover, neither the genotype of zebrafish nor the spatial frequency of motion significantly changed the response magnitude. Our findings support the view that age-related changes in motion detection depend on the activated motion system.

The relationship between central and mid-peripheral motion perception and the hazard perception test in younger and older adults

INTRODUCTION

Vision standards for driving are typically based on visual acuity, despite evidence that it is a poor predictor of driving safety and performance. However, visual motion perception is potentially relevant for driving, as the vehicle and surroundings are in motion. This study explored whether tests of central and mid-peripheral motion perception better predict performance on a hazard perception test (HPT), which is related to driving performance and crash risk, than visual acuity. Additionally, we explored whether age influences these associations, as healthy ageing impairs performance on some motion sensitivity tests.

METHODS

Sixty-five visually healthy drivers (35 younger, mean age: 25.5; SD 4.3 years; 30 older adults, mean age: 71.0; SD 5.4 years) underwent a computer-based HPT, plus four different motion sensitivity tests both centrally and at 15° eccentricity. Motion tests included minimum displacement to identify motion direction (Dmin ), contrast detection threshold for a drifting Gabor (motion contrast), coherence threshold for a translational global motion stimulus and direction discrimination for a biological motion stimulus in the presence of noise.

RESULTS

Overall, HPT reaction times were not significantly different between age groups (p = 0.40) nor were maximum HPT reaction times (p = 0.34). HPT response time was associated with motion contrast and Dmin centrally (r = 0.30, p = 0.02 and r = 0.28, p = 0.02, respectively) and with Dmin peripherally (r = 0.34, p = 0.005); these associations were not affected by age group. There was no significant association between binocular visual acuity and HPT response times (r = 0.02, p = 0.29).

CONCLUSIONS

Some measures of motion sensitivity in central and mid-peripheral vision were associated with HPT response times, whereas binocular visual acuity was not. Peripheral testing did not show an advantage over central testing for visually healthy older drivers. Our findings add to the growing body of evidence that the ability to detect small motion changes may have potential to identify unsafe road users.

Aging effects on contrast sensitivity in visual pathways: A pilot study on flicker adaptation

Contrast sensitivity is reduced in older adults and is often measured at an overall perceptual level. Recent human psychophysical studies have provided paradigms to measure contrast sensitivity independently in the magnocellular (MC) and parvocellular (PC) visual pathways and have reported desensitization in the MC pathway after flicker adaptation. The current study investigates the influence of aging on contrast sensitivity and on the desensitization effect in the two visual pathways. The steady- and pulsed-pedestal paradigms were used to measure contrast sensitivity under two adaptation conditions in 45 observers. In the non-flicker adaptation condition, observers adapted to a pedestal array of four 1°×1° squares presented with a steady luminance; in the flicker adaptation condition, observers adapted to a square-wave modulated luminance flicker of 7.5 Hz and 50% contrast. Results showed significant age-related contrast sensitivity reductions in the MC and PC pathways, with a significantly larger decrease of contrast sensitivity for individuals older than 50 years of age in the MC pathway but not in the PC pathway. These results are consistent with the hypothesis that sensitivity reduction observed at the overall perceptual level likely comes from both the MC and PC visual pathways, with a more dramatic reduction resulting from the MC pathway for adults >50 years of age. In addition, a similar desensitization effect from flicker adaptation was observed in the MC pathway for all ages, which suggests that aging may not affect the process of visual adaptation to rapid luminance flicker.

Treatment of age-related visual impairment with a mitochondrial-acting peptide

Age-related visual decline and disease due to neural dysfunction are major sources of disability that have resisted effective treatment. In light of evidence that visual impairment and mitochondrial dysfunction advance with age, we characterized age-related decline of spatial visual function in mice and investigated whether treatment of aged mice with the mitochondrion-penetrating peptide elamipretide that has been reported to improve mitochondrial function, would improve it. Impaired photopic acuity measured by using a virtual optokinetic system emerged near 18 months and declined to ∼40% below normal by 34 months. Daily application of the synthetic peptide elamipretide, which has high selectivity for mitochondrial membranes that contain cardiolipin and promotes efficient electron transfer, was able to mitigate visual decline from 18 months onwards. Daily application from 24 months onwards, i.e. when acuity had reduced by ∼16%, reversed visual decline and normalized function within 2 months. Recovered function persisted for at least 3 months after treatment was withdrawn and a single treatment at 24 months delayed subsequent visual decline. Elamipretide applied daily from 32 months onwards took longer to take effect, but substantial improvement was found within 2 months. The effects of age and elamipretide treatment on contrast sensitivity were similar to those on acuity, systemic and eye drop applications of elamipretide had comparable effects, scotopic spatial visual function was largely unaffected by age or treatment, and altered function was independent of variation in optical clarity. These data indicate that elamipretide treatment adaptively alters the aging visual system. They also provide a rationale to investigate whether mitochondrial dysfunction is a treatable pathophysiology of human visual aging and age-related visual disease.

Summary: Age-related decline in vision in mice is substantially prevented or restored in response to treatment with a peptide that comprises mitochondrial affinity and improves mitochondrial function.

Differential Circuit Mechanisms of Young and Aged Visual Cortex in the Mammalian Brain

The main goal of this review is to summarize and discuss (1) age-dependent structural reorganization of mammalian visual cortical circuits underlying complex visual behavior functions in primary visual cortex (V1) and multiple extrastriate visual areas, and (2) current evidence supporting the notion of compensatory mechanisms in aged visual circuits as well as the use of rehabilitative therapy for the recovery of neural plasticity in normal and diseased aging visual circuit mechanisms in different species. It is well known that aging significantly modulates both the structural and physiological properties of visual cortical neurons in V1 and other visual cortical areas in various species. Compensatory aged neural mechanisms correlate with the complexity of visual functions; however, they do not always result in major circuit alterations resulting in age-dependent decline in performance of a visual task or neurodegenerative disorders. Computational load and neural processing gradually increase with age, and the complexity of compensatory mechanisms correlates with the intricacy of higher form visual perceptions that are more evident in higher-order visual areas. It is particularly interesting to note that the visual perceptual processing of certain visual behavior functions does not change with age. This review aims to comprehensively discuss the effect of normal aging on neuroanatomical alterations that underlie critical visual functions and more importantly to highlight differences between compensatory mechanisms in aged neural circuits and neural processes related to visual disorders. This type of approach will further enhance our understanding of inter-areal and cortico-cortical connectivity of visual circuits in normal aging and identify major circuit alterations that occur in different visual deficits, thus facilitating the design and evaluation of potential rehabilitation therapies as well as the assessment of the extent of their rejuvenation.

Age-related decline in motion contrast sensitivity due to lower absorption rate of cones and calculation efficiency

Motion perception is affected by healthy aging, which impairs the ability of older adults to perform some daily activities such as driving. The current study investigated the underlying causes of age-related motion contrast sensitivity losses by using an equivalent noise paradigm to decompose motion contrast sensitivity into calculation efficiency, the temporal modulation transfer function (i.e., temporal blur) and 3 sources of internal noise: stochastic absorption of photons by photoreceptors (i.e., photon noise), neural noise occurring at the retinal level (i.e., early noise) and at the cortical level (i.e., late noise). These sources of internal noise can be disentangled because there impacts on motion contrast sensitivity vary differently as a function of luminance intensity. The impact of healthy aging on these factors was evaluated by measuring motion contrast sensitivity of young and older healthy adults at different luminance intensities, temporal frequencies and with/without external noise. The older adults were found to have higher photon noise, which suggests a lower photon absorption rate of cones. When roughly equating the amount of photons being absorbed by the photoreceptors, older adults had lower calculation efficiencies, but no significant aging effect was found on temporal modulation transfer function, early noise and late noise.

Different luminance- and texture-defined contrast sensitivity profiles for school-aged children

Our current understanding of how the visual brain develops is based largely on the study of luminance-defined information processing. This approach, however, is somewhat limiting, since everyday scenes are composed of complex images, consisting of information characterized by physical attributes relating to both luminance and texture. Few studies have explored how contrast sensitivity to texture-defined information develops, particularly throughout the school-aged years. The current study investigated how contrast sensitivity to luminance- (luminance-modulated noise) and texture-defined (contrast-modulated noise) static gratings develops in school-aged children. Contrast sensitivity functions identified distinct profiles for luminance- and texture-defined gratings across spatial frequencies (SFs) and age. Sensitivity to luminance-defined gratings reached maturity in childhood by the ages of 9–10 years for all SFs (0.5, 1, 2, 4 and 8 cycles/degree or cpd). Sensitivity to texture-defined gratings reached maturity at 5–6 years for low SFs and 7–8 years for high SFs (i.e., 4 cpd). These results establish that the processing of luminance- and texture-defined information develop differently as a function of SF and age.

Age-related changes in the neural dynamics of bottom-up and top-down processing during visual object recognition: an electrophysiological investigation

When recognizing objects in our environments, we rely on both what we see and what we know. While older adults often display increased sensitivity to top-down influences of contextual information during object recognition, the locus of this increased sensitivity remains unresolved. To examine the effects of aging on the neural dynamics of bottom-up and top-down visual processing during rapid object recognition, we probed the differential effects of object perceptual ambiguity and scene context congruity on specific EEG event-related potential components indexing dissociable processes along the visual processing stream. Older adults displayed larger behavioral scene congruity effects than young adults. Older adults' larger visual P2 amplitudes to object perceptual ambiguity (as opposed to the scene congruity P2 effects in young adults) suggest continued resolution of perceptual ambiguity that interfered with scene congruity processing, while post-perceptual semantic integration (as indexed by N400) remained largely intact. These findings suggest that compromised bottom-up perceptual processing in healthy aging leads to an increased involvement of top-down processes to resolve greater perceptual ambiguity during object recognition.

Second-order visual sensitivity in the aging population

Most visual and cognitive functions are affected by aging over the lifespan. In this study, our aim was to investigate the loss in sensitivity to different classes of second-order stimuli-a class of stimuli supposed to be mainly processed in extrastriate cortex-in the aging population. These stimuli will then allow one to identify specific cortical deficit independently of visibility losses in upstream parts of the visual pathway. For this purpose, we measured the sensitivity to first-order stimuli and second-order stimuli: orientation-modulated, motion-modulated or contrast-modulated as a function of spatial frequency in 50 aged participants. Overall, we observed a sensitivity loss for all classes of stimuli, but this loss differentially affects the three classes of second-order stimuli tested. It involves all modulation spatial frequencies in the case of motion modulation, but just high modulation spatial frequencies in the case of contrast- and orientation modulations. These observations imply that aging selectively affects the sensitivity to second-order stimuli depending on their type. Since there is evidence that these different second-order stimuli are processed in different regions of extrastriate cortex, this result may suggest that some visual cortical areas are more susceptible to aging effects than others.

Age Affects How Task Difficulty and Complexity Modulate Perceptual Decision-Making

Decisions differ in difficulty and rely on perceptual information that varies in richness (complexity); aging affects cognitive function including decision-making, and yet, the interaction between difficulty and perceptual complexity have rarely been addressed in aging. Using a parametric fMRI modulation analysis and psychophysics, we address how task difficulty affects decision-making when controlling for the complexity of the perceptual context in which decisions are made. Perceptual complexity was varied in a factorial design while participants made perceptual judgments on the spatial frequency of two patches that either shared the same orientation (simple condition) or were orthogonal in orientation (complex condition). Psychophysical thresholds were measured for each participant in each condition and served to set individualized levels of difficulty during scanning. Findings indicate that discriminability interacts with complexity, to influence decisional difficulty. Modulation as a function of difficulty is maintained with age, as indicated by coupling between increased activation in fronto-parietal regions and suppression in the lateral hubs, however, age has a specific effect in the ventral anterior cingulate cortex (ACC), driven by performance at near-threshold (difficult) levels for the simpler stimulus combination condition, but not the more complex one. Taken together, our findings suggest that the context of difficulty, or what is perceived as important, changes with age, and that decisions that would seem neutral to younger participants, may carry more emphasis with age.

Reconciling age-related changes in behavioural and neural indices of human perceptual decision-making

Ageing impacts on decision-making behaviour across a range of cognitive tasks and scenarios. Computational modelling has proved valuable in providing mechanistic interpretations of these age-related differences; however, the extent to which model parameter differences accurately reflect changes to the underlying neural computations remains unclear. Here, we report that age-related effects on neural signatures of decision formation are inconsistent with behavioural fits derived from a prominent accumulation-to-bound model. Most notably, model-predicted bound differences were absent neurophysiologically. However, constraining the model to match the decision-predictive elements of the brain signals provided more parsimonious fits to behaviour and generated predictions regarding the neural data that were empirically validated. These included a task-dependent slowing of evidence accumulation among older adults and reduced between-trial accumulation rate variability, which was linked to enhanced attentional engagement. Our findings highlight how combining neurophysiological measurements with computational modelling can yield unique insights into group differences in neural decision mechanisms.

The Combination of Functional and Structural MRI Is a Potential Screening Tool in Alzheimer's Disease

Introduction: This study aimed to survey the discrimination power of parameters from cerebrospinal fluid (CSF) biomarkers, fluorodeoxyglucose uptake on PET (FDG-PET), structural magnetic resonance imaging (MRI), and functional MRI in high- and low-risk subjects or in converters and stable subjects of normal and mild cognitive impairment (MCI) statuses. Methods: We used baseline resting-state functional MRI (rfMRI) from the Alzheimer's Disease Neuroimaging Initiative (ADNI) dataset to analyze functional networks and recorded subjects' characteristics and results of the CSF study, FDG-PET, and structural MRI from the ADNI website. All parameters were evaluated based on the between-group difference among normal (NC), MCI, and Alzheimer's disease (AD) groups. The parameters other than CSF results were included to study the difference between high- and low-AD-risk subjects in NC or MCI groups, based on CSF results. On the basis of two-year follow-up conditions, all parameters were compared between stable subjects and converters in NC and MCI. Results: CSF biomarkers, FDG-PET, structural MRI, and functional MRI are all able to differentiate AD from MCI or NC but not between MCI and NC. As compared with low-AD-risk subjects, high-risk subjects present decreased FDG-PET in both MCI and NC groups but structural MRI change only in MCI status and rfMRI alteration only in NC status. As compared with stable subjects, converters have decreased FDG-PET, functional network changes, and structural changes in both MCI and NC groups. Conclusion: The combination of functional and structural MRI is a safer screening tool but with similar power as FDG-PET to reflect CSF change in the AD pathological process and to identify high-risk subjects and converters in NC and MCI.

Audiovisual Temporal Perception in Aging: The Role of Multisensory Integration and Age-Related Sensory Loss

Within each sensory modality, age-related deficits in temporal perception contribute to the difficulties older adults experience when performing everyday tasks. Since perceptual experience is inherently multisensory, older adults also face the added challenge of appropriately integrating or segregating the auditory and visual cues present in our dynamic environment into coherent representations of distinct objects. As such, many studies have investigated how older adults perform when integrating temporal information across audition and vision. This review covers both direct judgments about temporal information (the sound-induced flash illusion, temporal order, perceived synchrony, and temporal rate discrimination) and judgments regarding stimuli containing temporal information (the audiovisual bounce effect and speech perception). Although an age-related increase in integration has been demonstrated on a variety of tasks, research specifically investigating the ability of older adults to integrate temporal auditory and visual cues has produced disparate results. In this short review, we explore what factors could underlie these divergent findings. We conclude that both task-specific differences and age-related sensory loss play a role in the reported disparity in age-related effects on the integration of auditory and visual temporal information.

The development of human visual cortex and clinical implications

The primary visual cortex (V1) is the first cortical area that processes visual information. Normal development of V1 depends on binocular vision during the critical period, and age-related losses of vision are linked with neurobiological changes in V1. Animal studies have provided important details about the neurobiological mechanisms in V1 that support normal vision or are changed by visual diseases. There is very little information, however, about those neurobiological mechanisms in human V1. That lack of information has hampered the translation of biologically inspired treatments from preclinical models to effective clinical treatments. We have studied human V1 to characterize the expression of neurobiological mechanisms that regulate visual perception and neuroplasticity. We have identified five stages of development for human V1 that start in infancy and continue across the life span. Here, we describe these stages, compare them with visual and anatomical milestones, and discuss implications for translating treatments for visual disorders that depend on neuroplasticity of V1 function.

The Effect of Practice and Visual Feedback on Oral-Diadochokinetic Rates for Younger and Older Adults

Assessments of oral-diadochokinetic rates are commonly performed to evaluate oral-motor skills. However, the appropriate administration protocol is not defined, and varies across therapists, clinics and laboratories. In three experiments and an auxiliary one, this study analyzes the effects of brief (motor) practice and visual feedback on the performance of 98 younger (20-40 years old) and 78 older adults (over 65) with the sequential motion rate (SMR) version. Overall rates were significantly faster for younger over older adults. Irrespective of age-group, averaged performance was significantly better on the second round, but the third round was found to be superfluous, across experiments and age-groups. Visual feedback (using a mirror) was found to be detrimental for younger adults, eliminating the advantage reaped from a practice round. For older adults, visual feedback did not alter the effect of a practice round. Sensory (visual) degradation is presented as a possible source for this age-related difference. We discuss these findings and suggest an administration protocol for younger and older adults with the SMR version, including a total of two rounds and no visual feedback.

Effect of age and stereopsis on a multiple-object tracking task

3D vision develops during childhood and tends to diminish after 65 years of age. It is still relatively unknown how stereopsis is used in more complex/ecological contexts such as when walking about in crowds where objects are in motion and occlusions occur. One task that shares characteristics with the requirements for processing dynamic crowds is the multiple object-tracking task (MOT). In the present study we evaluated the impact of stereopsis on a MOT task as a function of age. A total of 60 observers consisting of three groups of 20 subjects (7–12 years old, 18–40 years old and 65 years and older) completed the task in both conditions (with and without stereoscopic effects). The adult group obtained the better scores, followed by the children and the older adult group. The performance difference between the stereoscopic and non-stereoscopic conditions was significant and similar for the adults and the children but was non significant for the older observers. These results show that stereopsis helps children and adults accomplish a MOT task, but has no impact on older adults’ performances. The present results have implications as to how populations differ in their efficiency of using stereoscopic cues for disambiguating complex dynamic scenes.

Overcoming indecision by changing the decision boundary

The dominant theoretical framework for decision making asserts that people make decisions by integrating noisy evidence to a threshold. It has recently been shown that in many ecologically realistic situations, decreasing the decision boundary maximizes the reward available from decisions. However, empirical support for decreasing boundaries in humans is scant. To investigate this problem, we used an ideal observer model to identify the conditions under which participants should change their decision boundaries with time to maximize reward rate. We conducted 6 expanded-judgment experiments that precisely matched the assumptions of this theoretical model. In this paradigm, participants could sample noisy, binary evidence presented sequentially. Blocks of trials were fixed in duration, and each trial was an independent reward opportunity. Participants therefore had to trade off speed (getting as many rewards as possible) against accuracy (sampling more evidence). Having access to the actual evidence samples experienced by participants enabled us to infer the slope of the decision boundary. We found that participants indeed modulated the slope of the decision boundary in the direction predicted by the ideal observer model, although we also observed systematic deviations from optimality. Participants using suboptimal boundaries do so in a robust manner, so that any error in their boundary setting is relatively inexpensive. The use of a normative model provides insight into what variable(s) human decision makers are trying to optimize. Furthermore, this normative model allowed us to choose diagnostic experiments and in doing so we present clear evidence for time-varying boundaries. (PsycINFO Database Record

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.

Utilising psychophysical techniques to investigate the effects of age, typeface design, size and display polarity on glance legibility

Psychophysical research on text legibility has historically investigated factors such as size, colour and contrast, but there has been relatively little direct empirical evaluation of typographic design itself, particularly in the emerging context of glance reading. In the present study, participants performed a lexical decision task controlled by an adaptive staircase method. Two typefaces, a 'humanist' and 'square grotesque' style, were tested. Study I examined positive and negative polarities, while Study II examined two text sizes. Stimulus duration thresholds were sensitive to differences between typefaces, polarities and sizes. Typeface also interacted significantly with age, particularly for conditions with higher legibility thresholds. These results are consistent with previous research assessing the impact of the same typefaces on interface demand in a simulated driving environment. This simplified methodology of assessing legibility differences can be adapted to investigate a wide array of questions relevant to typographic and interface designs. Practitioner Summary: A method is described for rapidly investigating relative legibility of different typographical features. Results indicate that during glance-like reading induced by the psychophysical technique and under the lighting conditions considered, humanist-style type is significantly more legible than a square grotesque style, and that black-on-white text is significantly more legible than white-on-black.

Negative arousal increases the effects of stimulus salience in older adults

BACKGROUND/STUDY CONTEXT: Stimuli compete for mental representation, with salient stimuli attracting more attention than less salient stimuli. In a recent study, we found that presenting an emotionally negative arousing sound before briefly showing an array of letters with different levels of salience increased the reporting of the more salient letters but decreased reporting of the less salient letters (Sutherland & Mather, 2012, Emotion, 12, 1367-1372). In the current study we examined whether negative arousal produces similar effects on attention in older adults.

METHODS

Data from 55 older adults (61-80 years; M = 70.7, SD = 5.1) were compared with those from 110 younger adults (18-29 years; M = 20.3, SD = 2.3) from Sutherland and Mather (2012). Neutral or negative arousing sound clips were played before a brief presentation of eight letters, three of which were presented in a darker font than the others to create a group of high- and low-salience targets. Next, participants recalled as many of the letters as they could. At the end of the study, participants rated the emotional arousal and the valence of the sounds.

RESULTS

Higher ratings of emotional arousal for the sounds predicted a greater advantage for high-salience letters in recall. This influence of arousal did not significantly differ by age.

CONCLUSION

The effects of negative arousal on subsequent attention were similar in older adults as in younger adults. Moreover, the results support arousal-biased competition theory (Mather & Sutherland, 2011, Perspectives on Psychological Science, 6, 114-133), which predicts that emotional arousal amplifies the effects of stimulus salience in attention and memory.

First- and Second-Order Stimuli Reaction Time Measures Are Highly Sensitive to Mild Traumatic Brain Injuries

Mild traumatic brain injury (mTBI) has subtle effects on several brain functions that can be difficult to assess and follow up. We investigated the impact of mTBI on the perception of sine-wave gratings defined by first- and second-order characteristics. Fifteen adults diagnosed with mTBI were assessed at 15 days, 3 months, and 12 months postinjury. Fifteen matched controls followed the same testing schedule. Reaction times (RTs) for flicker detection and motion direction discrimination were measured. Stimulus contrast of first- and second-order patterns was equated to control for visibility, and correct-response RT means, standard deviations (SDs), medians, and interquartile ranges (IQRs) were calculated. The level of symptoms was also evaluated to compare it to RT data. In general in mTBI, RTs were longer, and SDs as well as IQRs larger, than those of controls. In addition, mTBI participants' RTs to first-order stimuli were shorter than those to second-order stimuli, and SDs as well as IQRs larger for first- than for second-order stimuli in the motion condition. All these observations were made over the three sessions. The level of symptoms observed in mTBI was higher than that of control participants, and this difference did also persist up to 1 year after the brain injury, despite an improvement. The combination of RT measures with particular stimulus properties is a highly sensitive method for measuring mTBI-induced visuomotor anomalies and provides a fine probe of the underlying mechanisms when the brain is exposed to mild trauma.

Age-related changes in resting-state networks of a large sample size of healthy elderly

AIMS

Population aging is burdening the society globally, and the evaluation of functional networks is the key toward understanding cognitive changes in normal aging. However, the effect of age on default mode subnetworks has not been documented well, and age-related changes in many resting-state networks remain debatable. The purpose of this study was to propose more precise results for these issues using a large sample size.

METHODS

We used group-level meta-ICA analysis and dual regression approach for identifying resting-state networks from functional magnetic resonance imaging data of 430 healthy elderly participants. Partial correlation was used to observe age-related correlations within and between resting-state networks.

RESULTS

In the default mode network, only the ventral subnetwork negatively correlated with age. Age-related decrease in functional connectivity was also noted in the auditory, right frontoparietal, sensorimotor, and visual medial networks. Further, some age-related increases and decreases were observed for between-network correlations.

CONCLUSION

The results of this study suggest that only the ventral default mode subnetwork had age-related decline in functional connectivity and several reverse patterns of resting-state networks for network development. Understanding age-related network changes may provide solutions for the impact of population aging and diagnosis of neurodegenerative diseases.

Delayed signal transmission in area 17, area 18 and the posteromedial lateral suprasylvian area of aged cats

To investigate the effect of senescence on signal transmission, we have compared the visual response latency and spontaneous activity of cells in the lateral geniculate nucleus (LGN), area 17, area 18 and posteromedial lateral suprasylvian area (PMLS) of young and old cats. We found that LGN cells in old cats exhibit largely normal visual response latency. In contrast, all the other three areas exhibited significant aging-related delays in the visual response latency. On average, PMLS showed most pronounced delays among these three areas. Area 18 slowed more than area 17, but this was not significant. The degradation of signal timing in the visual cortex might provide insight into neuronal response mechanism underlying perception slowing during aging.

Brightness induction and suprathreshold vision: effects of age and visual field

A variety of visual capacities show significant age-related alterations. We assessed suprathreshold contrast and brightness perception across the lifespan in a large sample of healthy participants (N=155; 142) ranging in age from 16 to 80 years. Experiment 1 used a quadrature-phase motion cancelation technique (Blakeslee & McCourt, 2008) to measure canceling contrast (in central vision) for induced gratings at two temporal frequencies (1 Hz and 4 Hz) at two test field heights (0.5° or 2°×38.7°; 0.052 c/d). There was a significant age-related reduction in canceling contrast at 4 Hz, but not at 1 Hz. We find no age-related change in induction magnitude in the 1 Hz condition. We interpret the age-related decline in grating induction magnitude at 4 Hz to reflect a diminished capacity for inhibitory processing at higher temporal frequencies. In Experiment 2 participants adjusted the contrast of a matching grating (0.5° or 2°×38.7°; 0.052 c/d) to equal that of both real (30% contrast, 0.052 c/d) and induced (McCourt, 1982) standard gratings (100% inducing grating contrast; 0.052 c/d). Matching gratings appeared in the upper visual field (UVF) and test gratings appeared in the lower visual field (LVF), and vice versa, at eccentricities of ±7.5°. Average induction magnitude was invariant with age for both test field heights. There was a significant age-related reduction in perceived contrast of stimuli in the LVF versus UVF for both real and induced gratings.

Self-motion perception in the elderly

Self-motion through space generates a visual pattern called optic flow. It can be used to determine one's direction of self-motion (heading). Previous studies have already shown that this perceptual ability, which is of critical importance during everyday life, changes with age. In most of these studies subjects were asked to judge whether they appeared to be heading to the left or right of a target. Thresholds were found to increase continuously with age. In our current study, we were interested in absolute rather than relative heading judgments and in the question about a potential neural correlate of an age-related deterioration of heading perception. Two groups, older test subjects and younger controls, were shown optic flow stimuli in a virtual-reality setup. Visual stimuli simulated self-motion through a 3-D cloud of dots and subjects had to indicate their perceived heading direction after each trial. In different subsets of experiments we varied individually relevant stimulus parameters: presentation time, number of dots in the display, stereoscopic vs. non-stereoscopic stimulation, and motion coherence. We found decrements in heading performance with age for each stimulus parameter. In a final step we aimed to determine a putative neural basis of this behavioral decline. To this end we modified a neural network model which previously has proven to be capable of reproduce and predict certain aspects of heading perception. We show that the observed data can be modeled by implementing an age related neuronal cell loss in this neural network. We conclude that a continuous decline of certain aspects of motion perception, among them heading, might be based on an age-related progressive loss of groups of neurons being activated by visual motion.

Do older individuals have difficulty processing motion or excluding noise? Implications for safe driving

This study aimed to determine if difficulties extracting signal from noise explained poorer coherent motion thresholds in older individuals, particularly women. In four experimental conditions the contrast of the signal and noise dots used in a random dot kinematogram was manipulated. Coherence thresholds were highest when the signal dots were of a lower contrast than the noise dots and lowest when the signal dots were of a higher contrast than the noise dots. In all conditions the older group had higher coherence thresholds than the younger group, and women had higher thresholds than men. Significant correlations were found between coherence thresholds and self-reported driving difficulties in conditions in which the signal dots had to be extracted from noise only. The results indicate that older individuals have difficulties extracting signal from noise in cluttered visual environments. The implications for safe driving are discussed.

Declined contrast sensitivity of neurons along the visual pathway in aging cats

Changes in the visual cortex appear to mediate much of the visual degradation during normal aging. However, how aging affects different stages along the visual pathway is unclear. In the current study, the contrast response function, one of the most important properties of neurons from early visual areas to high brain areas, was systematically compared along the visual pathway, including the lateral geniculate nucleus (LGN), early visual cortices (A17 and A18), and posteromedial lateral suprasylvian cortex (PMLS, analog to the medial temporal area (MT) in monkeys) of young and old cats. We found that the effects of aging on the LGN were negligible, whereas those in the striate cortex were substantial, with even more severe degradation in the PMLS. Reduced contrast sensitivity of neurons in the three cortical areas was accompanied by enhanced maximal visual response, increased spontaneous activity, and decreased signal-to-noise ratio, while LGN neurons exhibited largely normal response properties. Our results suggested that there was a progressively greater effect of aging on neurons at successively higher stages in the visual pathway.

Changes of spatial and temporal frequency tuning properties of neurons in the middle temporal area of aged rhesus monkeys

Aged humans exhibit severe deficits in visual motion perception and contrast sensitivity under various levels of spatial and temporal modulation. Previous studies indicated that many of these deficits are probably mediated by the neural degradation of the central visual system. To clarify the neuronal response mechanisms underlying the visual degradation during aging, we examined the spatial and temporal frequency tuning properties of neurons from anesthetised and paralysed aged monkeys at the middle temporal area (area MT), which is downstream of the primary visual cortex in the visual processing pathway and thought to be critical for motion perception. We found that the preferred spatial and temporal frequencies, spatial resolution and high temporal frequency cutoff of area MT neurons were reduced in aged monkeys, and were accompanied by the broadened tuning width of spatial frequency, elevated spontaneous activity, and decreased signal-to-noise ratio. These results showed that, for neurons in area MT, aging significantly changed both the spatial and temporal frequency response tuning properties. Such evidence provides new insight into the changes occurring at the electrophysiological level that may be related to the aging-related visual deficits, especially in processing spatial and temporal information.

Luminance- and texture-defined information processing in school-aged children with autism

According to the complexity-specific hypothesis, the efficacy with which individuals with autism spectrum disorder (ASD) process visual information varies according to the extensiveness of the neural network required to process stimuli. Specifically, adults with ASD are less sensitive to texture-defined (or second-order) information, which necessitates the implication of several cortical visual areas. Conversely, the sensitivity to simple, luminance-defined (or first-order) information, which mainly relies on primary visual cortex (V1) activity, has been found to be either superior (static material) or intact (dynamic material) in ASD. It is currently unknown if these autistic perceptual alterations are present in childhood. In the present study, behavioural (threshold) and electrophysiological measures were obtained for static luminance- and texture-defined gratings presented to school-aged children with ASD and compared to those of typically developing children. Our behavioural and electrophysiological (P140) results indicate that luminance processing is likely unremarkable in autistic children. With respect to texture processing, there was no significant threshold difference between groups. However, unlike typical children, autistic children did not show reliable enhancements of brain activity (N230 and P340) in response to texture-defined gratings relative to luminance-defined gratings. This suggests reduced efficiency of neuro-integrative mechanisms operating at a perceptual level in autism. These results are in line with the idea that visual atypicalities mediated by intermediate-scale neural networks emerge before or during the school-age period in autism.

Multisensory integration compensates loss of sensitivity of visual temporal order in the elderly

Here, we examined sensitivity of visual, auditory, and audiovisual temporal order in five age-groups (20 to 70 years old). We also measured multisensory integration (MSI) using a phenomenon known as "temporal ventriloquism," in which click sounds improve sensitivity of visual temporal order. Results showed that sensitivity of visual, auditory, and audiovisual temporal order declined from 50 years on. However, there was no corresponding decline in MSI as the click sounds actually compensated the loss of sensitivity of visual temporal order in the elderly. Sensitivity of audiovisual temporal order did not correlate with MSI, suggesting that well-preserved explicit judgments about cross-modal temporal order are not required for MSI to occur.

Refinement but not maintenance of visual receptive fields is independent of visual experience

Visual deprivation is reported to prevent or delay the development of mature receptive field (RF) properties in primary visual cortex (V1) in several species. In contrast, visual deprivation neither prevents nor delays refinement of RF size in the superior colliculus (SC) of Syrian hamsters, although vision is required for RF maintenance in the SC. Here, we report that, contrary to expectation, visual cortical RF refinement occurs normally in dark-reared animals. As in the SC, a brief period of visual experience is required to maintain V1 RF refinement in adulthood. Whereas in the SC, 3 days of visual experience within a sensitive period (P37-40) was sufficient to protect RFs from deprivation-induced enlargement in adulthood, 7 days (P33-40) were required for RF size maintenance in V1. Thus, spontaneous activity is sufficient for RF refinement at these 2 levels of the visual pathway, and visual input is necessary only to prevent deprivation-induced RF enlargement in adulthood. These studies show that sensory experience during a late juvenile sensitive period protects the visual pathway against sensory deprivation in adulthood, and suggest that more importance may have been placed on the role of early visual experience in visual RF development than is warranted.

Differential effects of aging on spatial contrast sensitivity to linear and polar sine-wave gratings

Changes in visual function beyond high-contrast acuity are known to take place during normal aging. We determined whether sensitivity to linear sine-wave gratings and to an elementary stimulus preferentially processed in extrastriate areas could be distinctively affected by aging. We measured spatial contrast sensitivity twice for concentric polar (Bessel) and vertical linear gratings of 0.6, 2.5, 5, and 20 cycles per degree (cpd) in two age groups (20-30 and 60-70 years). All participants were free of identifiable ocular disease and had normal or corrected-to-normal visual acuity. Participants were more sensitive to Cartesian than to polar gratings in all frequencies tested, and the younger adult group was more sensitive to all stimuli tested. Significant differences between sensitivities of the two groups were found for linear (only 20 cpd; P<0.01) and polar gratings (all frequencies tested; P<0.01). The young adult group was significantly more sensitive to linear than to circular gratings in the 20 cpd frequency. The older adult group was significantly more sensitive to linear than to circular gratings in all spatial frequencies, except in the 20 cpd frequency. The results suggest that sensitivity to the two kinds of stimuli is affected differently by aging. We suggest that neural changes in the aging brain are important determinants of this difference and discuss the results according to current models of human aging.

Reading performance in middle-aged adults with declines in accommodation

The present study investigated the effects of presbyopia on the reading ability of middle-aged adults in a Japanese reading context, using the rapid serial visual presentation paradigm. Japanese words, each consisting of three characters, were sequentially presented at the same location on a display screen. Participants were instructed to read the words aloud as accurately as possible, irrespective of their order within the sequence. Experiment 1 showed that the reading performance for the presbyopes was far worse for the near-viewing (35 cm) than for the far-viewing (70 cm) conditions when the words were presented at 0.4° in character size. Experiment 2 investigated in detail the effect of luminance contrast on reading at a viewing distance of 35 cm. The minimums of the exposure durations within which the participants could read the words above 89.9 % correct (minimum exposure duration) were 498 ms/word for the presbyopes and 134 ms/word for the nonpresbyopes, both of which values were obtained at 100 % contrast. The critical contrast-that is, the contrast that doubled the minimum exposure duration that had been obtained at 100 % contrast-was considerably higher for the presbyopes (39.2 %) than for the nonpresbyopes (16.4 %). However, the reading performance for the presbyopes was improved more than threefold when the contrast was increased to 100 % in both experiments. Thus, our results provide psychophysical evidence for the dependency of presbyopes' reading on viewing distance and luminance contrast.

Feature tracking and aging

There are conflicting results regarding the effect of aging on second-order motion processing (i.e., motion defined by attributes other than luminance, such as contrast). Two studies (Habak and Faubert, 2000; Tang and Zhou, 2009) found that second-order motion processing was more vulnerable to aging than first-order motion processing. Conversely, Billino et al. (2011) recently found that aging affected first- and second-order motion processing by similar proportions. These three studies used contrast-defined motion as a second-order stimulus, but there can be at least two potential issues when using such a stimulus to evaluate age-related sensitivity losses. First, it has been shown that the motion system processing contrast-defined motion varies depending on the stimulus parameters. Thus, although all these three studies assumed that their contrast-defined motion was processed by a low-level second-order motion system, this was not necessarily the case. The second potential issue is that contrast-defined motion consists in a contrast modulation of a texture rich in high spatial frequencies and aging mainly affects contrast sensitivity at high spatial frequencies. Consequently, some age-related sensitivity loss to second-order motion could be due to a lower sensitivity to the texture rather than to motion processing per se. To avoid these two potential issues, we used a second-order motion stimulus void of high spatial frequencies and which has been shown to be processed by a high-level feature tracking motion system, namely fractal rotation (Lagacé-Nadon et al., 2009). We found an age-related deficit on second-order motion processing at all temporal frequencies including the ones for which no age-related effect on first-order motion processing was observed. We conclude that aging affects the ability to track features. Previous age-related results on second-order and global motion processing are discussed in light of these findings.

Contour integration and aging: the effects of element spacing, orientation alignment and stimulus duration

The ability to extract contours in cluttered visual scenes, which is a crucial step in visual processing, declines with healthy aging, but the reasons for this decline are not well understood. In three experiments, we examined how the effect of aging on contour discrimination varies as a function of contour and distracter inter-element spacing, collinearity, and stimulus duration. Spiral-shaped contours composed of Gabors were embedded within a field of distracter Gabors of uniform density. In a four alternative forced-choice task, younger and older subjects were required to report the global orientation of the contour. In Experiment 1, the absolute contour element spacing varied from two to eight times the Gabor wavelength and contour element collinearity was disrupted with five levels of orientation jitter. Contour discrimination accuracy was lower in older subjects, but the effect of aging did not vary with contour spacing or orientation jitter. Experiment 2 found that decreasing stimulus durations from 0.8 to 0.04 s had a greater effect on older subjects' performance, but only for less salient contours. Experiment 3 examined the effect of the background on contour discrimination by varying the spacing and orientation of the distracter elements for contours with small and large absolute spacing. As in Experiment, the effect of aging did not vary with absolute contour spacing. Decreasing the distracter spacing, however, had a greater detrimental effect on accuracy in older subjects compared to younger subjects. Finally, both groups showed equally high accuracy when all distracters were iso-oriented. In sum, these findings suggest that aging does not affect the sensitivity of contour integration to proximity or collinearity. However, contour integration in older adults is slower and is especially vulnerable when distracters are denser than contour elements.

Healthy older observers show equivalent perceptual-cognitive training benefits to young adults for multiple object tracking

The capacity to process complex dynamic scenes is of critical importance in real life. For instance, traveling through a crowd while avoiding collisions and maintaining orientation and good motor control requires fluent and continuous perceptual-cognitive processing. It is well documented that effects of healthy aging can influence perceptual-cognitive processes (Faubert, 2002) and that the efficiency of such processes can improve with training even for older adults (Richards et al., 2006). Here we assess the capacity of older participants to improve their tracking speed thresholds in a dynamic, virtual reality environment. Results show that this capacity is significantly affected by healthy aging but that perceptual-cognitive training can significantly reduce age-related effects in older individuals, who show an identical learning function to younger healthy adults. Data support the notion that learning in healthy older persons is maintained for processing complex dynamic scenes.

Foveal visual acuity is worse and shows stronger contour interaction effects for contrast-modulated than luminance-modulated Cs

Contrast-modulated (CM) stimuli are processed by spatial mechanisms that operate at larger spatial scales than those processing luminance-modulated (LM) stimuli and may be more prone to deficits in developing, amblyopic, and aging visual systems. Understanding neural mechanisms of contour interaction or crowding will help in detecting disorders of spatial vision. In this study, contour interaction effects on visual acuity for LM and CM C and bar stimuli are assessed in normal foveal vision. In Experiment 1, visual acuity is measured for all-LM and all-CM stimuli, at ~3.5× above their respective modulation thresholds. In Experiment 2, visual acuity is measured for Cs and bars of different type (LM C with CM bars and vice versa). Visual acuity is degraded for CM compared with LM Cs (0.46 ± 0.04 logMAR vs. 0.18 ± 0.04 logMAR). With nearby bars, CM acuity is degraded further (0.23 ± 0.01 logMAR or ~2 lines on an acuity chart), significantly more than LM acuity (0.11 ± 0.01 logMAR, ~1 line). Contour interaction for CM stimuli extends over greater distances (arcmin) than it does for LM stimuli, but extents are similar with respect to acuities (~3.5× the C gap width). Contour interaction is evident when the Cs and bars are defined differently: it is stronger when an LM C is flanked by CM bars (0.17 ± 0.03 logMAR) than when a CM C is flanked by LM bars (0.08 ± 0.02 logMAR). Our results suggest that contour interaction for foveally viewed acuity stimuli involves feature integration, such that the outputs of receptive fields representing Cs and bars are combined. Contour interaction operates at LM and CM representational stages, it can occur across stage, and it is enhanced at the CM stage. Greater contour interaction for CM Cs and bars could hold value for visual acuity testing and earlier diagnosis of conditions for which crowding is important, such as in amblyopia.

Aging effects on visual evoked potentials (VEPs) for motion direction discrimination

Age-related declines in motion perception have been well documented. We investigated the impact of age on electrophysiological correlates of motion perception, namely the P1 and N2 components of motion onset visual evoked potentials (MO-VEPs). Additionally, we used a model of response times based on the diffusion model to pinpoint the cognitive processes affected by aging. Twelve healthy adults (age <55 years) and 19 elderly (age >55 years) performed a motion direction discrimination task during EEG recording. Behaviorally, younger and older participants had similar, high accuracy rates--98% correct, but older adults exhibited 85 ms longer response times. Fitting behavioral results with a diffusion model revealed differences between young adults and elderly in non-decision time, which we argue reflects an early perceptual stage. Electrophysiologically, aging effects were present at MO-VEPs P1 and N2 components at the posterior sites. For the P1 component, older as compared to younger adults showed greater topographical voltage distribution. For the N2 component of elderly as compared to young adults we found delayed onsets and diminished amplitudes. We did not find any significant correlations between behavioral and MO-VEP measures. However, regression analysis showed that N2 amplitude and latency were significant age predictors. Overall, our results indicate that in motion perception, age-related changes occur in early stages of visual processing, most likely in striate and extrastriate visual cortices.

Aging and audio-visual and multi-cue integration in motion

The perception of naturalistic events relies on the ability to integrate information from multiple sensory systems, an ability that may change with healthy aging. When two objects move toward and then past one another, their trajectories are perceptually ambiguous: the objects may seem to stream past one another or bounce off one another. Previous research showed that auditory or visual events that occur at the time of disks' coincidence could bias the percept toward bouncing or streaming. We exploited this malleable percept to assay age-related changes in the integration of multiple inter- and intra-modal cues. The disks' relative luminances were manipulated to produce stimuli strongly favoring either bouncing or streaming, or to produce ambiguous motion (equal luminances). A sharp sound coincident with the disks' overlap increased both groups' perception of bouncing, but did so significantly less for older subjects. An occluder's impact on motion perception varied with its duration: a long duration occluder promoted streaming in both groups; a brief occluder promoted bouncing in younger subjects, but not older ones. Control experiments demonstrated that the observed differences between younger and older subjects resulted from neither age-related changes in retinal illuminance nor age-related changes in hearing, pointing to weakened inter- and intra-modal integration with aging. These changes could contribute to previously demonstrated age-related perceptual and memory deficits.

[Aging affects early stage direction selectivity of MT cells in rhesus monkeys]

The middle temporal area (MT/V5) plays an important role in motion processing. Neurons in this area have a strongly selective response to the moving direction of objects and as such, the selectivity of MT neurons was proposed to be a neural mechanism for the perception of motion. Our previous studies have found degradation in direction selectivity of MT neurons in old monkeys, but this direction selectivity was calculated during the whole response time and the results were not able to uncover the mechanism of motion perception over a time course. Furthermore, experiments have found that direction selectivity was enhanced by attention at a later stage. Therefore, the response should be excluded in experiments with anesthesia. To further characterize the neural mechanism over a time course, we investigated the age-related changes of direction selectivity in the early stage by comparing the proportions of direction selective MT cells in old and young macaque monkeys using in vivo single-cell recording techniques. Our results show that the proportion of early-stage-direction-selective cells is lower in old monkeys than in young monkeys, and that the early stage direction bias (esDB) of old MT cells decreased relative to young MT cells. Furthermore, the proportion of MT cells having strong early stage direction selectivity in old monkeys was decreased. Accordingly, the functional degradation in the early stage of MT cells may mediate perceptual declines of old primates in visual motion tasks.

Aging of low and high level vision: from chromatic and achromatic contrast sensitivity to local and 3D object motion perception

The influence of normal aging in early, intermediate and high-level visual processing is still poorly understood. We have addressed this important issue in a large cohort of 653 subjects divided into five distinct age groups, [20;30[, [30;40[, [40;50[, [50;60[and [60;[. We applied a broad range of psychophysical tests, testing distinct levels of the visual hierarchy, from local processing to global integration, using simple gratings (spatial contrast sensitivity -CS- using high temporal/low spatial frequency or intermediate spatial frequency static gratings), color CS using Landolt patches, moving dot stimuli (Local Speed Discrimination) and dot patterns defining 3D objects (3D Structure from Motion, 3D SFM). Aging data were fitted with linear or quadratic regression models, using the adjusted coefficient of determination (R²_a) to quantify the effect of aging. A significant effect of age was found on all visual channels tested, except for the red-green chromatic channel. The high temporal low spatial frequency contrast sensitivity channel showed a mean sensitivity loss of 0.75 dB per decade (R²_a = 0.17, p<0.001), while the lower intermediate spatial frequency channel showed a more pronounced decrease, around 2.35 dB (R²_a = 0.55, p<0.001). Concerning low-level motion perception, speed discrimination decreased 2.71°/s (R²_a = 0.18, p<0.001) and 3.15°/s (R²_a = 0.13, p<0.001) only for short presentations for horizontal and oblique meridians, respectively. The 3D SFM task, requiring high-level integration across dorsal and ventral streams, showed the strongest (quadratic) decrease of motion coherence perception with age, especially when the task was temporally constrained (R²_a = 0.54, p<0.001). These findings show that visual channels are influenced by aging into different extent, with time presenting a critical role, and high-level dorso-ventral dominance of deterioration, which accelerates with aging, in contrast to the other channels that show a linear pattern of deterioration.

Perceptuo-motor learning rate declines by half from 20s to 70/80s

This study examined perception-action learning in younger adults in their 20s compared to older adults in their 70s and 80s. The goal was to provide, for the first time, quantitative estimates of perceptuo-motor learning rates for each age group and to reveal how these learning rates change between these age groups. We used a visual coordination task in which participants are asked to learn to produce a novel-coordinated rhythmic movement. The task has been studied extensively in young adults, and the characteristics of the task are well understood. All groups showed improvement, although learning rates for those in their 70s and 80s were half the rate for those in their 20s. We consider the potential causes of these differences in learning rates by examining performance across the different coordination patterns examined as well as recent results that reveal age-related deficits in motion perception.

Individual and age-related variation in chromatic contrast adaptation

Precortical color channels are tuned primarily to the LvsM (stimulation of L and M cones varied, but S cone stimulation held constant) or SvsLM (stimulation of S cones varied, but L and M cone stimulation held constant) cone-opponent (cardinal) axes, but appear elaborated in the cortex to form higher-order mechanisms tuned to both cardinal and intermediate directions. One source of evidence for these higher-order mechanisms has been the selectivity of color contrast adaptation for noncardinal directions, yet the degree of this selectivity has varied widely across the small sample of observers tested in previous studies. This study explored the possible bases for this variation, and in particular tested whether it reflected age-related changes in the distribution or tuning of color mechanisms. Observers included 15 younger (18-22 years of age) and 15 older individuals (66-82), who adapted to temporal modulations along one of four chromatic axes (two cardinal and two intermediate axes) and then matched the hue and contrast of test stimuli lying along eight different directions in the equiluminant plane. All observers exhibited aftereffects that were selective for both the cardinal and intermediate directions, although selectivity was weaker for the intermediate axes. The degree of selectivity increased with the magnitude of adaptation for all axes, and thus adaptation strength alone may account for much of the variance in selectivity among observers. Older observers showed a stronger magnitude of adaptation thus, surprisingly, more conspicuous evidence for higher-order mechanisms. For both age groups the aftereffects were well predicted by response changes in chromatic channels with linear spectral sensitivities, and there was no evidence for weakened channel tuning with aging. The results suggest that higher-order mechanisms may become more exposed in observers or conditions in which the strength of adaptation is greater, and that both chromatic contrast adaptation and the cortical color coding it reflects remain largely intact in the aging visual system.