Shifts in Audiovisual Processing in Healthy Aging

Audiovisual n-Back Training Alters the Neural Processes of Working Memory and Audiovisual Integration: Evidence of Changes in ERPs

(1) Background: This study investigates whether audiovisual n-back training leads to training effects on working memory and transfer effects on perceptual processing. (2) Methods: Before and after training, the participants were tested using the audiovisual n-back task (1-, 2-, or 3-back), to detect training effects, and the audiovisual discrimination task, to detect transfer effects. (3) Results: For the training effect, the behavioral results show that training leads to greater accuracy and faster response times. Stronger training gains in accuracy and response time using 3- and 2-back tasks, compared to 1-back, were observed in the training group. Event-related potentials (ERPs) data revealed an enhancement of P300 in the frontal and central regions across all working memory levels after training. Training also led to the enhancement of N200 in the central region in the 3-back condition. For the transfer effect, greater audiovisual integration in the frontal and central regions during the post-test rather than pre-test was observed at an early stage (80-120 ms) in the training group. (4) Conclusion: Our findings provide evidence that audiovisual n-back training enhances neural processes underlying a working memory and demonstrate a positive influence of higher cognitive functions on lower cognitive functions.

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.

Visual and Auditory Spatial Localization in Younger and Older Adults

Visual and auditory localization abilities are crucial in real-life tasks such as navigation and social interaction. Aging is frequently accompanied by vision and hearing loss, affecting spatial localization. The purpose of the current study is to elucidate the effect of typical aging on spatial localization and to establish a baseline for older individuals with pathological sensory impairment. Using a verbal report paradigm, we investigated how typical aging affects visual and auditory localization performance, the reliance on vision during sound localization, and sensory integration strategies when localizing audiovisual targets. Fifteen younger adults (N = 15, mean age = 26 years) and thirteen older adults (N = 13, mean age = 68 years) participated in this study, all with age-adjusted normal vision and hearing based on clinical standards. There were significant localization differences between younger and older adults, with the older group missing peripheral visual stimuli at significantly higher rates, localizing central stimuli as more peripheral, and being less precise in localizing sounds from central locations when compared to younger subjects. Both groups localized auditory targets better when the test space was visible compared to auditory localization when blindfolded. The two groups also exhibited similar patterns of audiovisual integration, showing optimal integration in central locations that was consistent with a Maximum-Likelihood Estimation model, but non-optimal integration in peripheral locations. These findings suggest that, despite the age-related changes in auditory and visual localization, the interactions between vision and hearing are largely preserved in older individuals without pathological sensory impairments.

A Dynamic Mechanistic Model of Perceptual Binding

The brain’s ability to create a unified conscious representation of an object by integrating information from multiple perception pathways is called perceptual binding. Binding is crucial for normal cognitive function. Some perceptual binding errors and disorders have been linked to certain neurological conditions, brain lesions, and conditions that give rise to illusory conjunctions. However, the mechanism of perceptual binding remains elusive. Here, I present a computational model of binding using two sets of coupled oscillatory processes that are assumed to occur in response to two different percepts. I use the model to study the dynamic behavior of coupled processes to characterize how these processes can modulate each other and reach a temporal synchrony. I identify different oscillatory dynamic regimes that depend on coupling mechanisms and parameter values. The model can also discriminate different combinations of initial inputs that are set by initial states of coupled processes. Decoding brain signals that are formed through perceptual binding is a challenging task, but my modeling results demonstrate how crosstalk between two systems of processes can possibly modulate their outputs. Therefore, my mechanistic model can help one gain a better understanding of how crosstalk between perception pathways can affect the dynamic behavior of the systems that involve perceptual binding.

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.

Impoverished Inhibitory Control Exacerbates Multisensory Impairments in Older Fallers

Impaired temporal perception of multisensory cues is a common phenomenon observed in older adults that can lead to unreliable percepts of the external world. For instance, the sound induced flash illusion (SIFI) can induce an illusory percept of a second flash by presenting a beep close in time to an initial flash-beep pair. Older adults that have enhanced susceptibility to a fall demonstrate significantly stronger illusion percepts during the SIFI task compared to those older adults without any history of falling. We hypothesize that a global inhibitory deficit may be driving the impairments across both postural stability and multisensory function in older adults with a fall history (FH). We investigated oscillatory activity and perceptual performance during the SIFI task, to understand how active sensory processing, measured by gamma (30–80 Hz) power, was regulated by alpha activity (8–13 Hz), oscillations that reflect inhibitory control. Compared to young adults (YA), the FH and non-faller (NF) groups demonstrated enhanced susceptibility to the SIFI. Further, the FH group had significantly greater illusion strength compared to the NF group. The FH group also showed significantly impaired performance relative to YA during congruent trials (2 flash-beep pairs resulting in veridical perception of 2 flashes). In illusion compared to non-illusion trials, the NF group demonstrated reduced alpha power (or diminished inhibitory control). Relative to YA and NF, the FH group showed reduced phase-amplitude coupling between alpha and gamma activity in non-illusion trials. This loss of inhibitory capacity over sensory processing in FH compared to NF suggests a more severe change than that consequent of natural aging.

Temporal Alignment but not Complexity of Audiovisual Stimuli Influences Crossmodal Duration Percepts

Reliable duration perception is an integral aspect of daily life that impacts everyday perception, motor coordination, and subjective passage of time. The Scalar Expectancy Theory (SET) is a common model that explains how an internal pacemaker, gated by an external stimulus-driven switch, accumulates pulses during sensory events and compares these accumulated pulses to a reference memory duration for subsequent duration estimation. Second-order mechanisms, such as multisensory integration (MSI) and attention, can influence this model and affect duration perception. For instance, diverting attention away from temporal features could delay the switch closure or temporarily open the accumulator, altering pulse accumulation and distorting duration perception. In crossmodal duration perception, auditory signals of unequal duration can induce perceptual compression and expansion of durations of visual stimuli, presumably via auditory influence on the visual clock. The current project aimed to investigate the role of temporal (stimulus alignment) and nontemporal (stimulus complexity) features on crossmodal, specifically auditory over visual, duration perception. While temporal alignment revealed a larger impact on the strength of crossmodal duration percepts compared to stimulus complexity, both features showcase auditory dominance in processing visual duration.

Aging and working memory modulate the ability to benefit from visible speech and iconic gestures during speech-in-noise comprehension

When comprehending speech-in-noise (SiN), younger and older adults benefit from seeing the speaker's mouth, i.e. visible speech. Younger adults additionally benefit from manual iconic co-speech gestures. Here, we investigate to what extent younger and older adults benefit from perceiving both visual articulators while comprehending SiN, and whether this is modulated by working memory and inhibitory control. Twenty-eight younger and 28 older adults performed a word recognition task in three visual contexts: mouth blurred (speech-only), visible speech, or visible speech + iconic gesture. The speech signal was either clear or embedded in multitalker babble. Additionally, there were two visual-only conditions (visible speech, visible speech + gesture). Accuracy levels for both age groups were higher when both visual articulators were present compared to either one or none. However, older adults received a significantly smaller benefit than younger adults, although they performed equally well in speech-only and visual-only word recognition. Individual differences in verbal working memory and inhibitory control partly accounted for age-related performance differences. To conclude, perceiving iconic gestures in addition to visible speech improves younger and older adults' comprehension of SiN. Yet, the ability to benefit from this additional visual information is modulated by age and verbal working memory. Future research will have to show whether these findings extend beyond the single word level.

Age-Related Changes in Audiovisual Simultaneity Perception and Their Relationship With Working Memory

OBJECTIVES

Perceiving simultaneity of a visual and an auditory signal is critical for humans to integrate these multisensory inputs effectively and respond properly. We examined age-related changes in audiovisual simultaneity perception, and the relationships between this perception and working memory performances with aging.

METHODS

Audiovisual simultaneity perception of young, middle-aged, and older adults was measured using a simultaneity judgment (SJ) task, in which a flash and a beep were presented at 1 of 11 stimulus-onset asynchronies (SOAs). Participants judged whether these two stimuli were perceived simultaneously. Precision of simultaneity perception, the SOA corresponding to the point of subjective simultaneity (PSS), and response errors at each SOA were estimated using model fitting. The precision and PSS are associated with multisensory perception per se, whereas the response error reflects executive ability when performing the SJ task. Visual working memory of the same middle-aged and older adults was measured using the Cambridge Neuropsychological Test Automated Battery (CANTAB) beforehand.

RESULTS

Compared to young adults' performances, middle-aged and older adults showed a decreased precision, a shift of PSS toward the visual-leading SOAs, and increased response errors at the visual-leading SOAs. Among these changes, only the increased response errors correlated with worse spatial recognition memory in middle-aged and older adults.

DISCUSSION

Age-related decrements in audiovisual simultaneity perception start from middle age and are manifested in both perceptual and executive parameters. Furthermore, higher-order executive ability is plausibly a common cause for age-related degenerations in the audiovisual simultaneity perception and visual working memory.

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.

Effects of age and left hemisphere lesions on audiovisual integration of speech

Neuroimaging studies have implicated left temporal lobe regions in audiovisual integration of speech and inferior parietal regions in temporal binding of incoming signals. However, it remains unclear which regions are necessary for audiovisual integration, especially when the auditory and visual signals are offset in time. Aging also influences integration, but the nature of this influence is unresolved. We used a McGurk task to test audiovisual integration and sensitivity to the timing of audiovisual signals in two older adult groups: left hemisphere stroke survivors and controls. We observed a positive relationship between age and audiovisual speech integration in both groups, and an interaction indicating that lesions reduce sensitivity to timing offsets between signals. Lesion-symptom mapping demonstrated that damage to the left supramarginal gyrus and planum temporale reduces temporal acuity in audiovisual speech perception. This suggests that a process mediated by these structures identifies asynchronous audiovisual signals that should not be integrated.

Age-related hearing loss influences functional connectivity of auditory cortex for the McGurk illusion

Age-related hearing loss affects hearing at high frequencies and is associated with difficulties in understanding speech. Increased audio-visual integration has recently been found in age-related hearing impairment, the brain mechanisms that contribute to this effect are however unclear. We used functional magnetic resonance imaging in elderly subjects with normal hearing and mild to moderate uncompensated hearing loss. Audio-visual integration was studied using the McGurk task. In this task, an illusionary fused percept can occur if incongruent auditory and visual syllables are presented. The paradigm included unisensory stimuli (auditory only, visual only), congruent audio-visual and incongruent (McGurk) audio-visual stimuli. An illusionary precept was reported in over 60% of incongruent trials. These McGurk illusion rates were equal in both groups of elderly subjects and correlated positively with speech-in-noise perception and daily listening effort. Normal-hearing participants showed an increased neural response in left pre- and postcentral gyri and right middle frontal gyrus for incongruent stimuli (McGurk) compared to congruent audio-visual stimuli. Activation patterns were however not different between groups. Task-modulated functional connectivity differed between groups showing increased connectivity from auditory cortex to visual, parietal and frontal areas in hard of hearing participants as compared to normal-hearing participants when comparing incongruent stimuli (McGurk) with congruent audio-visual stimuli. These results suggest that changes in functional connectivity of auditory cortex rather than activation strength during processing of audio-visual McGurk stimuli accompany age-related hearing loss.

Aging Impairs Temporal Sensitivity, but not Perceptual Synchrony, Across Modalities

Encoding the temporal properties of external signals that comprise multimodal events is a major factor guiding everyday experience. However, during the natural aging process, impairments to sensory processing can profoundly affect multimodal temporal perception. Various mechanisms can contribute to temporal perception, and thus it is imperative to understand how each can be affected by age. In the current study, using three different temporal order judgement tasks (unisensory, multisensory, and sensorimotor), we investigated the effects of age on two separate temporal processes: synchronization and integration of multiple signals. These two processes rely on different aspects of temporal information, either the temporal alignment of processed signals or the integration/segregation of signals arising from different modalities, respectively. Results showed that the ability to integrate/segregate multiple signals decreased with age regardless of the task, and that the magnitude of such impairment correlated across tasks, suggesting a widespread mechanism affected by age. In contrast, perceptual synchrony remained stable with age, revealing a distinct intact mechanism. Overall, results from this study suggest that aging has differential effects on temporal processing, and general impairments with aging may impact global temporal sensitivity while context-dependent processes remain unaffected.

Audio-visual integration in cochlear implant listeners and the effect of age difference

This study aimed to investigate differences in audio-visual (AV) integration between cochlear implant (CI) listeners and normal-hearing (NH) adults. A secondary aim was to investigate the effect of age differences by examining AV integration in groups of older and younger NH adults. Seventeen CI listeners, 13 similarly aged NH adults, and 16 younger NH adults were recruited. Two speech identification experiments were conducted to evaluate AV integration of speech cues. In the first experiment, reaction times in audio-alone (A-alone), visual-alone (V-alone), and AV conditions were measured during a speeded task in which participants were asked to identify a target sound /aSa/ among 11 alternatives. A race model was applied to evaluate AV integration. In the second experiment, identification accuracies were measured using a closed set of consonants and an open set of consonant-nucleus-consonant words. The authors quantified AV integration using a combination of a probability model and a cue integration model (which model participants' AV accuracy by assuming no or optimal integration, respectively). The results found that experienced CI listeners showed no better AV integration than their similarly aged NH adults. Further, there was no significant difference in AV integration between the younger and older NH adults.

Age-Related Effects on Cross-Modal Duration Perception

Reliable duration perception of external events is necessary to coordinate perception with action, precisely discriminate speech, and for other daily functions. Visual duration perception can be heavily influenced by concurrent auditory signals; however, age-related effects on this process have received minimal attention. In the present study, we examined the effect of aging on duration perception by quantifying (1) duration discrimination thresholds, (2) auditory temporal dominance, and (3) visual duration expansion/compression percepts induced by an accompanying auditory stimulus of longer/shorter duration. Duration discrimination thresholds were significantly greater for visual than auditory tasks in both age groups, however there was no effect of age. While the auditory modality retained dominance in duration perception with age, older adults still performed worse than young adults when comparing durations of two target stimuli (e.g., visual) in the presence of distractors from the other modality (e.g., auditory). Finally, both age groups perceived similar visual duration compression, whereas older adults exhibited visual duration expansion over a wider range of auditory durations compared to their younger counterparts. Results are discussed in terms of multisensory integration and possible decision strategies that change with age.

High cognitive load enhances the susceptibility to non-speech audiovisual illusions

The role of attentional processes in the integration of input from different sensory modalities is complex and multifaceted. Importantly, little is known about how simple, non-linguistic stimuli are integrated when the resources available for sensory processing are exhausted. We studied this question by examining multisensory integration under conditions of limited endogenous attentional resources. Multisensory integration was assessed through the sound-induced flash illusion (SIFI), in which a flash presented simultaneously with two short auditory beeps is often perceived as two flashes, while cognitive load was manipulated using an n-back task. A one-way repeated measures ANOVA revealed that increased cognitive demands had a significant effect on the perception of the illusion while post-hoc tests showed that participants' illusion perception was increased when attentional resources were limited. Additional analysis demonstrated that this effect was not related to a response bias. These findings provide evidence that the integration of non-speech, audiovisual stimuli is enhanced under reduced attentional resources and it therefore supports the notion that top-down attentional control plays an essential role in multisensory integration.