Impaired timing of audiovisual events in the elderly

Age-Related Changes in Sensorimotor Temporal Binding

The causal relationship between a voluntary movement and a sensory event is crucial for experiencing agency. Sensory events must occur within a certain delay from a voluntary movement to be perceived as self-generated. Therefore, temporal sensitivity, i.e., the ability to discriminate temporal asynchronies between motor and sensory events, is important for sensorimotor binding. Moreover, differences in the physical propagation of external stimuli can sometimes challenge sensorimotor binding, generating illusory asynchrony. To overcome this problem, the brain adjusts the perceptual timing of sensory and motor events. This mechanism, named sensorimotor recalibration, helps keeping causality judgments accurate. As humans age, the broad decline in sensory and motor processing may reduce temporal sensitivity, and compromise sensorimotor recalibration. In the current study, we investigated the effect of aging on sensorimotor temporal binding by measuring changes in both temporal sensitivity and recalibration. Young and elderly adults were exposed to a prolonged physical delay between a voluntary movement (a keypress) and its perceptual consequence (a visual stimulus). Before and after this exposure, participants performed a sensorimotor temporal order judgment (TOJ) task. As expected, elderly adults showed reduced sensorimotor recalibration and sensitivity as compared to young adults, suggesting that aging affects sensorimotor temporal binding.

Shifts in Audiovisual Processing in Healthy Aging

Purpose of Review

The integration of information across sensory modalities into unified percepts is a fundamental sensory process upon which a multitude of cognitive processes are based. We review the body of literature exploring aging-related changes in audiovisual integration published over the last five years. Specifically, we review the impact of changes in temporal processing, the influence of the effectiveness of sensory inputs, the role of working memory, and the newer studies of intra-individual variability during these processes.

Recent Findings

Work in the last five years on bottom-up influences of sensory perception has garnered significant attention. Temporal processing, a driving factors of multisensory integration, has now been shown to decouple with multisensory integration in aging, despite their co-decline with aging. The impact of stimulus effectiveness also changes with age, where older adults show maximal benefit from multisensory gain at high signal-to-noise ratios. Following sensory decline, high working memory capacities have now been shown to be somewhat of a protective factor against age-related declines in audiovisual speech perception, particularly in noise. Finally, newer research is emerging focusing on the general intra-individual variability observed with aging.

Summary

Overall, the studies of the past five years have replicated and expanded on previous work that highlights the role of bottom-up sensory changes with aging and their influence on audiovisual integration, as well as the top-down influence of working memory.

Improving therapeutic outcomes in autism spectrum disorders: Enhancing social communication and sensory processing through the use of interactive robots

For children with autism spectrum disorders (ASDs), social robots are increasingly utilized as therapeutic tools in order to enhance social skills and communication. Robots have been shown to generate a number of social and behavioral benefits in children with ASD including heightened engagement, increased attention, and decreased social anxiety. Although social robots appear to be effective social reinforcement tools in assistive therapies, the perceptual mechanism underlying these benefits remains unknown. To date, social robot studies have primarily relied on expertise in fields such as engineering and clinical psychology, with measures of social robot efficacy principally limited to qualitative observational assessments of children's interactions with robots. In this review, we examine a range of socially interactive robots that currently have the most widespread use as well as the utility of these robots and their therapeutic effects. In addition, given that social interactions rely on audiovisual communication, we discuss how enhanced sensory processing and integration of robotic social cues may underlie the perceptual and behavioral benefits that social robots confer. Although overall multisensory processing (including audiovisual integration) is impaired in individuals with ASD, social robot interactions may provide therapeutic benefits by allowing audiovisual social cues to be experienced through a simplified version of a human interaction. By applying systems neuroscience tools to identify, analyze, and extend the multisensory perceptual substrates that may underlie the therapeutic benefits of social robots, future studies have the potential to strengthen the clinical utility of social robots for individuals with ASD.

One bout of open skill exercise improves cross-modal perception and immediate memory in healthy older adults who habitually exercise

One single bout of exercise can be associated with positive effects on cognition, due to physiological changes associated with muscular activity, increased arousal, and training of cognitive skills during exercise. While the positive effects of life-long physical activity on cognitive ageing are well demonstrated, it is not well established whether one bout of exercise is sufficient to register such benefits in older adults. The aim of this study was to test the effect of one bout of exercise on two cognitive processes essential to daily life and known to decline with ageing: audio-visual perception and immediate memory. Fifty-eight older adults took part in a quasi-experimental design study and were divided into three groups based on their habitual activity (open skill exercise (mean age = 69.65, SD = 5.64), closed skill exercise, N = 18, 94% female; sedentary activity-control group, N = 21, 62% female). They were then tested before and after their activity (duration between 60 and 80 minutes). Results showed improvement in sensitivity in audio-visual perception in the open skill group and improvements in one of the measures of immediate memory in both exercise groups, after controlling for baseline differences including global cognition and health. These findings indicate that immediate benefits for cross-modal perception and memory can be obtained after open skill exercise. However, improvements after closed skill exercise may be limited to memory benefits. Perceptual benefits are likely to be associated with arousal, while memory benefits may be due to the training effects provided by task requirements during exercise. The respective role of qualitative and quantitative differences between these activities in terms of immediate cognitive benefits should be further investigated. Importantly, the present results present the first evidence for a modulation of cross-modal perception by exercise, providing a plausible avenue for rehabilitation of cross-modal perception deficits, which are emerging as a significant contributor to functional decline in ageing.

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.

Temporal Information Processing and its Relation to Executive Functions in Elderly Individuals

Normal aging triggers deterioration in cognitive functions. Evidence has shown that these age-related changes concern also executive functions (EF) as well as temporal information processing (TIP) in a millisecond range. A considerable amount of literature data has indicated that each of these two functions sets a frame for our mental activity and may be considered in terms of embodied cognition due to advanced age. The present study addresses the question whether in elderly subjects the efficiency of TIP is related to individual differences in EF. The study involved 53 normal healthy participants aged from 65 to 78. In these subjects TIP was assessed by sequencing abilities measured with temporal-order threshold (TOT). It is defined as the minimum time gap separating two auditory stimuli presented in rapid succession which is necessary for a subject to report correctly their temporal order, thus the relation ‘before-after.’ The EF were assessed with regard to the efficiency of the executive planning measured with the Tower of London-Drexel University (TOL^DX) which has become a well-known EF task. Using Spearman’s rank correlations we observed two main results. Firstly, the indices of the TOL^DX indicated a coherent construct reflecting the effectiveness of executive planning in the elderly. Initiation time seemed dissociated from these coherent indices, which suggested a specific strategy of mental planning in the elderly based on on-line planning rather than on preplanning. Secondly, TOT was significantly correlated with the indices of TOL^DX. Although some of these correlations were modified by subject’s age, the correlation between TOT and the main index of TOL^DX (‘Total Move Score’) was rather age resistant. These results suggest that normal aging may be characterized by an overlapping of deteriorated TIP and deteriorated EF.

Audiovisual Integration Delayed by Stimulus Onset Asynchrony Between Auditory and Visual Stimuli in Older Adults

Although neuronal studies have shown that audiovisual integration is regulated by temporal factors, there is still little knowledge about the impact of temporal factors on audiovisual integration in older adults. To clarify how stimulus onset asynchrony (SOA) between auditory and visual stimuli modulates age-related audiovisual integration, 20 younger adults (21–24 years) and 20 older adults (61–80 years) were instructed to perform an auditory or visual stimuli discrimination experiment. The results showed that in younger adults, audiovisual integration was altered from an enhancement (AV, A ± 50 V) to a depression (A ± 150 V). In older adults, the alterative pattern was similar to that for younger adults with the expansion of SOA; however, older adults showed significantly delayed onset for the time-window-of-integration and peak latency in all conditions, which further demonstrated that audiovisual integration was delayed more severely with the expansion of SOA, especially in the peak latency for V-preceded-A conditions in older adults. Our study suggested that audiovisual facilitative integration occurs only within a certain SOA range (e.g., −50 to 50 ms) in both younger and older adults. Moreover, our results confirm that the response for older adults was slowed and provided empirical evidence that integration ability is much more sensitive to the temporal alignment of audiovisual stimuli in older adults.

Audiovisual Simultaneity Judgment and Rapid Recalibration throughout the Lifespan

Multisensory interactions are well established to convey an array of perceptual and behavioral benefits. One of the key features of multisensory interactions is the temporal structure of the stimuli combined. In an effort to better characterize how temporal factors influence multisensory interactions across the lifespan, we examined audiovisual simultaneity judgment and the degree of rapid recalibration to paired audiovisual stimuli (Flash-Beep and Speech) in a sample of 220 participants ranging from 7 to 86 years of age. Results demonstrate a surprisingly protracted developmental time-course for both audiovisual simultaneity judgment and rapid recalibration, with neither reaching maturity until well into adolescence. Interestingly, correlational analyses revealed that audiovisual simultaneity judgments (i.e., the size of the audiovisual temporal window of simultaneity) and rapid recalibration significantly co-varied as a function of age. Together, our results represent the most complete description of age-related changes in audiovisual simultaneity judgments to date, as well as being the first to describe changes in the degree of rapid recalibration as a function of age. We propose that the developmental time-course of rapid recalibration scaffolds the maturation of more durable audiovisual temporal representations.

Cognitive Aging and Time Perception: Roles of Bayesian Optimization and Degeneracy

This review outlines the basic psychological and neurobiological processes associated with age-related distortions in timing and time perception in the hundredths of milliseconds-to-minutes range. The difficulty in separating indirect effects of impairments in attention and memory from direct effects on timing mechanisms is addressed. The main premise is that normal aging is commonly associated with increased noise and temporal uncertainty as a result of impairments in attention and memory as well as the possible reduction in the accuracy and precision of a central timing mechanism supported by dopamine-glutamate interactions in cortico-striatal circuits. Pertinent to these findings, potential interventions that may reduce the likelihood of observing age-related declines in timing are discussed. Bayesian optimization models are able to account for the adaptive changes observed in time perception by assuming that older adults are more likely to base their temporal judgments on statistical inferences derived from multiple trials than on a single trial's clock reading, which is more susceptible to distortion. We propose that the timing functions assigned to the age-sensitive fronto-striatal network can be subserved by other neural networks typically associated with finely-tuned perceptuo-motor adjustments, through degeneracy principles (different structures serving a common function).