Age-related changes in auditory and visual interactions in temporal rate perception

Multisensory Integration and Causal Inference in Typical and Atypical Populations

Multisensory perception is critical for effective interaction with the environment, but human responses to multisensory stimuli vary across the lifespan and appear changed in some atypical populations. In this review chapter, we consider multisensory integration within a normative Bayesian framework. We begin by outlining the complex computational challenges of multisensory causal inference and reliability-weighted cue integration, and discuss whether healthy young adults behave in accordance with normative Bayesian models. We then compare their behaviour with various other human populations (children, older adults, and those with neurological or neuropsychiatric disorders). In particular, we consider whether the differences seen in these groups are due only to changes in their computational parameters (such as sensory noise or perceptual priors), or whether the fundamental computational principles (such as reliability weighting) underlying multisensory perception may also be altered. We conclude by arguing that future research should aim explicitly to differentiate between these possibilities.

Older adults with a history of falling exhibit altered cortical oscillatory mechanisms during continuous postural maintenance

Background and Aim

The significant risk of falling in older adults 65 years or older presents a substantial problem for these individuals, their caretakers, and the health-care system at large. As the proportion of older adults in the United States is only expected to grow over the next few decades, a better understanding of physiological and cortical changes that make an older adult more susceptible to a fall is crucial. Prior studies have displayed differences in postural dynamics and stability in older adults with a fall history (FH) and those who are non-fallers (NF), suggesting surplus alterations that occur in some older adults (i.e., FH group) in addition to the natural aging process.

Methods

The present study measured postural dynamics while the FH, NF, and young adult (YA) groups performed continuous postural maintenance. In addition, electroencephalography activity was recorded while participants performed upright postural stance to examine any group differences in cortical areas involved in postural control.

Results

As expected, older participants (FH and NF) exhibited worse postural stability, as evidenced by increased excursion, compared to the YA group. Further, while NF and YA show increased alpha activity in occipital areas during the most demanding postural task (eyes closed), the FH group did not show any differences in occipital alpha power between postural tasks.

Conclusions

As alpha activity reflects suppression of bottom-up processing and thus diversion of cognitive resources toward postural centers during more demanding postural maintenance, deficits in this regulatory function in the FH group are a possible impaired cortical mechanism putting these individuals at greater fall risk.

Relevance for Patients

Impaired inhibitory function in older adults may impact postural control and increase their risk of falling. Interventions that aim at addressing cortical processing deficits may improve postural stability and facilitate independent living in this population.

Perceptual training narrows the temporal binding window of audiovisual integration in both younger and older adults

There is a growing body of evidence to suggest that multisensory processing changes with advancing age-usually in the form of an enlarged temporal binding window-with some studies linking these multisensory changes to negative clinical outcomes. Perceptual training regimes represent a promising means for enhancing the precision of multisensory integration in ageing; however, to date, the vast majority of studies examining the efficacy of multisensory perceptual learning have focused solely on healthy young adults. Here, we measured the temporal binding windows of younger and older participants before and after training on an audiovisual temporal discrimination task to assess (i) how perceptual training affected the shape of the temporal binding window and (ii) whether training effects were similar in both age groups. Our results replicated previous findings of an enlarged temporal binding window in older adults, as well as providing further evidence that both younger and older participants can improve the precision of their audiovisual timing estimation via perceptual training. We also show that this training protocol led to a narrowing of the temporal binding window associated with the sound-induced flash illusion in both age groups indicating a general refinement of audiovisual integration. However, while younger adults also displayed a general reduction in crossmodal interactions following training, this effect was not observed in the older adult group. Together, our results suggest that perceptual training narrows the temporal binding window of audiovisual integration in both younger and older adults but has less of an impact on prior expectations regarding the source of audiovisual signals in older adults.

Detection and Recognition of Asynchronous Auditory/Visual Speech: Effects of Age, Hearing Loss, and Talker Accent

This investigation examined age-related differences in auditory-visual (AV) integration as reflected on perceptual judgments of temporally misaligned AV English sentences spoken by native English and native Spanish talkers. In the detection task, it was expected that slowed auditory temporal processing of older participants, relative to younger participants, would be manifest as a shift in the range over which participants would judge asynchronous stimuli as synchronous (referred to as the "AV simultaneity window"). The older participants were also expected to exhibit greater declines in speech recognition for asynchronous AV stimuli than younger participants. Talker accent was hypothesized to influence listener performance, with older listeners exhibiting a greater narrowing of the AV simultaneity window and much poorer recognition of asynchronous AV foreign-accented speech compared to younger listeners. Participant groups included younger and older participants with normal hearing and older participants with hearing loss. Stimuli were video recordings of sentences produced by native English and native Spanish talkers. The video recordings were altered in 50 ms steps by delaying either the audio or video onset. Participants performed a detection task in which they judged whether the sentences were synchronous or asynchronous, and performed a recognition task for multiple synchronous and asynchronous conditions. Both the detection and recognition tasks were conducted at the individualized signal-to-noise ratio (SNR) corresponding to approximately 70% correct speech recognition performance for synchronous AV sentences. Older listeners with and without hearing loss generally showed wider AV simultaneity windows than younger listeners, possibly reflecting slowed auditory temporal processing in auditory lead conditions and reduced sensitivity to asynchrony in auditory lag conditions. However, older and younger listeners were affected similarly by misalignment of auditory and visual signal onsets on the speech recognition task. This suggests that older listeners are negatively impacted by temporal misalignments for speech recognition, even when they do not notice that the stimuli are asynchronous. Overall, the findings show that when listener performance is equated for simultaneous AV speech signals, age effects are apparent in detection judgments but not in recognition of asynchronous speech.

A Scoping Review of Audiovisual Integration Methodology: Screening for Auditory and Visual Impairment in Younger and Older Adults

With the rise of the aging population, many scientists studying multisensory integration have turned toward understanding how this process may change with age. This scoping review was conducted to understand and describe the scope and rigor with which researchers studying audiovisual sensory integration screen for hearing and vision impairment. A structured search in three licensed databases (Scopus, PubMed, and PsychInfo) using the key concepts of multisensory integration, audiovisual modality, and aging revealed 2,462 articles, which were screened for inclusion by two reviewers. Articles were included if they (1) tested healthy older adults (minimum mean or median age of 60) with younger adults as a comparison (mean or median age between 18 and 35), (2) measured auditory and visual integration, (3) were written in English, and (4) reported behavioral outcomes. Articles that included the following were excluded: (1) tested taste exclusively, (2) tested olfaction exclusively, (3) tested somatosensation exclusively, (4) tested emotion perception, (5) were not written in English, (6) were clinical commentaries, editorials, interviews, letters, newspaper articles, abstracts only, or non-peer reviewed literature (e.g., theses), and (7) focused on neuroimaging without a behavioral component. Data pertaining to the details of the study (e.g., country of publication, year of publication, etc.) were extracted, however, of higher importance to our research question, data pertaining to screening measures used for hearing and vision impairment (e.g., type of test used, whether hearing- and visual-aids were worn, thresholds used, etc.) were extracted, collated, and summarized. Our search revealed that only 64% of studies screened for age-abnormal hearing impairment, 51% screened for age-abnormal vision impairment, and that consistent definitions of normal or abnormal vision and hearing were not used among the studies that screened for sensory abilities. A total of 1,624 younger adults and 4,778 older participants were included in the scoping review with males composing approximately 44% and females composing 56% of the total sample and most of the data was obtained from only four countries. We recommend that studies investigating the effects of aging on multisensory integration should screen for normal vision and hearing by using the World Health Organization's (WHO) hearing loss and visual impairment cut-off scores in order to maintain consistency among other aging researchers. As mild cognitive impairment (MCI) has been defined as a “transitional” or a “transitory” stage between normal aging and dementia and because approximately 3–5% of the aging population will develop MCI each year, it is therefore important that when researchers aim to study a healthy aging population, that they appropriately screen for MCI. One of our secondary aims was to determine how often researchers were screening for cognitive impairment and the types of tests that were used to do so. Our results revealed that only 55 out of 72 studies tested for neurological and cognitive function, and only a subset used standardized tests. Additionally, among the studies that used standardized tests, the cut-off scores used were not always adequate for screening out mild cognitive impairment. An additional secondary aim of this scoping review was to determine the feasibility of whether a meta-analysis could be conducted in the future to further quantitatively evaluate the results (i.e., are the findings obtained from studies using self-reported vision and hearing impairment screening methods significantly different from those measuring vision and hearing impairment in the lab) and to assess the scope of this problem. We found that it may not be feasible to conduct a meta-analysis with the entire dataset of this scoping review. However, a meta-analysis can be conducted if stricter parameters are used (e.g., focusing on accuracy or response time data only).

Systematic Review Registration:https://doi.org/10.17605/OSF.IO/GTUHD.

Ageing and multisensory integration: A review of the evidence, and a computational perspective

The processing of multisensory signals is crucial for effective interaction with the environment, but our ability to perform this vital function changes as we age. In the first part of this review, we summarise existing research into the effects of healthy ageing on multisensory integration. We note that age differences vary substantially with the paradigms and stimuli used: older adults often receive at least as much benefit (to both accuracy and response times) as younger controls from congruent multisensory stimuli, but are also consistently more negatively impacted by the presence of intersensory conflict. In the second part, we outline a normative Bayesian framework that provides a principled and computationally informed perspective on the key ingredients involved in multisensory perception, and how these are affected by ageing. Applying this framework to the existing literature, we conclude that changes to sensory reliability, prior expectations (together with attentional control), and decisional strategies all contribute to the age differences observed. However, we find no compelling evidence of any age-related changes to the basic inference mechanisms involved in multisensory perception.

Sensory- and memory-related drivers for altered ventriloquism effects and aftereffects in older adults

The manner in which humans exploit multisensory information for subsequent decisions changes with age. Multiple causes for such age-effects are being discussed, including a reduced precision in peripheral sensory representations, changes in cognitive inference about causal relations between sensory cues, and a decline in memory contributing to altered sequential patterns of multisensory behaviour. To dissociate these putative contributions, we investigated how healthy young and older adults integrate audio-visual spatial information within trials (the ventriloquism effect) and between trials (the ventriloquism aftereffect). With both a model-free and (Bayesian) model-based analyses we found that both biases differed between groups. Our results attribute the age-change in the ventriloquism bias to a decline in spatial hearing rather than a change in cognitive processes. This decline in peripheral function, combined with a more prominent influence from preceding responses rather than preceding stimuli in the elderly, can also explain the observed age-effect in the ventriloquism aftereffect. Our results suggest a transition from a sensory-to a behavior-driven influence of past multisensory experience on perceptual decisions with age, due to reduced sensory precision and change in memory capacity.

Brain Computer Interfaces for Improving the Quality of Life of Older Adults and Elderly Patients

All people experience aging, and the related physical and health changes, including changes in memory and brain function. These changes may become debilitating leading to an increase in dependence as people get older. Many external aids and tools have been developed to allow older adults and elderly patients to continue to live normal and comfortable lives. This mini-review describes some of the recent studies on cognitive decline and motor control impairment with the goal of advancing non-invasive brain computer interface (BCI) technologies to improve health and wellness of older adults and elderly patients. First, we describe the state of the art in cognitive prosthetics for psychiatric diseases. Then, we describe the state of the art of possible assistive BCI applications for controlling an exoskeleton, a wheelchair and smart home for elderly people with motor control impairments. The basic age-related brain and body changes, the effects of age on cognitive and motor abilities, and several BCI paradigms with typical tasks and outcomes are thoroughly described. We also discuss likely future trends and technologies to assist healthy older adults and elderly patients using innovative BCI applications with minimal technical oversight.

Differential effects of the temporal and spatial distribution of audiovisual stimuli on cross-modal spatial recalibration

Visual input constantly recalibrates auditory spatial representations. Exposure to isochronous audiovisual stimuli with a fixed spatial disparity typically results in a subsequent auditory localization bias (ventriloquism aftereffect, VAE), whereas exposure to spatially congruent audiovisual stimuli improves subsequent auditory localization (multisensory enhancement, ME). Here, we tested whether cross-modal recalibration is affected by the stimulation rate and/or the distribution of audiovisual spatial disparities during training. Auditory localization was tested before and after participants were exposed either to audiovisual stimuli with a constant spatial disparity of 13.5° (VAE) or to spatially congruent audiovisual stimulation (ME). In a between-subjects design, audiovisual stimuli were presented either at a low frequency of 2 Hz, as used in previous studies of VAE and ME, or intermittently at a high frequency of 10 Hz, which mimics long-term potentiation (LTP) protocols and which was found superior in eliciting unisensory perceptual learning. Compared to low-frequency stimulation, VAE was reduced after high-frequency stimulation, whereas ME occurred regardless of the stimulation protocol. In two additional groups, we manipulated the spatial distribution of audiovisual stimuli in the low-frequency condition. Stimuli were presented with varying audiovisual disparities centered around 13.5° (VAE) or 0° (ME). Both VAE and ME were equally strong compared to a fixed spatial relationship of 13.5° or 0°, respectively. Taken together, our results suggest (a) that VAE and ME represent partly dissociable forms of learning and (b) that auditory representations adjust to the overall stimulus statistics rather than to a specific audiovisual spatial relationship.

Spatial vision in older adults: perceptual changes and neural bases

PURPOSE

The number of older adults is rapidly increasing internationally, leading to a significant increase in research on how healthy ageing impacts vision. Most clinical assessments of spatial vision involve simple detection (letter acuity, grating contrast sensitivity, perimetry). However, most natural visual environments are more spatially complicated, requiring contrast discrimination, and the delineation of object boundaries and contours, which are typically present on non-uniform backgrounds. In this review we discuss recent research that reports on the effects of normal ageing on these more complex visual functions, specifically in the context of recent neurophysiological studies.

RECENT FINDINGS

Recent research has concentrated on understanding the effects of healthy ageing on neural responses within the visual pathway in animal models. Such neurophysiological research has led to numerous, subsequently tested, hypotheses regarding the likely impact of healthy human ageing on specific aspects of spatial vision.

SUMMARY

Healthy normal ageing impacts significantly on spatial visual information processing from the retina through to visual cortex. Some human data validates that obtained from studies of animal physiology, however some findings indicate that rethinking of presumed neural substrates is required. Notably, not all spatial visual processes are altered by age. Healthy normal ageing impacts significantly on some spatial visual processes (in particular centre-surround tasks), but leaves contrast discrimination, contrast adaptation, and orientation discrimination relatively intact. The study of older adult vision contributes to knowledge of the brain mechanisms altered by the ageing process, can provide practical information regarding visual environments that older adults may find challenging, and may lead to new methods of assessing visual performance in clinical environments.

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.

Changed crossmodal functional connectivity in older adults with hearing loss

Previous work compellingly demonstrates a crossmodal plastic reorganization of auditory cortex in deaf individuals, leading to increased neural responses to non-auditory sensory input. Recent data indicate that crossmodal adaptive plasticity is not restricted to severe hearing impairments, but may also occur as a result of high-frequency hearing loss in older adults and affect audiovisual processing in these subjects. We here used functional magnetic resonance imaging (fMRI) to study the effect of hearing loss in older adults on auditory cortex response patterns as well as on functional connectivity between auditory and visual cortex during audiovisual processing. Older participants with a varying degree of high frequency hearing loss performed an auditory stimulus categorization task, in which they had to categorize frequency-modulated (FM) tones presented alone or in the context of matching or non-matching visual motion. A motion only condition served as control for a visual take-over of auditory cortex. While the individual hearing status did not affect auditory cortex responses to auditory, visual, or audiovisual stimuli, we observed a significant hearing loss-related increase in functional connectivity between auditory cortex and the right motion-sensitive visual area MT+ when processing matching audiovisual input. Hearing loss also modulated resting state connectivity between right area MT+ and parts of the left auditory cortex, suggesting the existence of permanent, task-independent changes in coupling between visual and auditory sensory areas with an increasing degree of hearing loss. Our data thus indicate that hearing loss impacts on functional connectivity between sensory cortices in older adults.