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Title: Aging effect on audiovisual integrative processing in spatial discrimination task
Authors: Zou, Zhi
Degree: Ph.D.
Issue Date: 2018
Abstract: Delivery of information from multiple sensory modalities is useful for enhancing perceptual discrimination and subsequently behavioral performance. Older adults have been reported having greater enhancement in the behavioral performance. The mechanism underlying how the multisensory modulation occurs among older adults remains unclear. The aim of this thesis was to investigate how aging impacts on the multisensory integration process which in turn influences the sensory, response selection and generation, and motor execution processes. There are two studies in this thesis. The first study (Study 1, Chapter Four) was to validate the audiovisual discrimination task used in this study for generating the multisensory integration process among a group of younger participants. In this study, adults performed in a spatial discrimination task based on visual or auditory information or a combination of both, while electroencephalogram (EEG) as well as electromyography (EMG) data was captured. The behavioral measures were accuracy rate and reaction time on the audiovisual discrimination task. The neurophysiology measures included event-related potentials (ERP), lateralized response potentials (LRP), and muscle activities based on EMG. The results obtained were compared with those reported in previous studies on audiovisual integration. Behavioral results demonstrated higher accuracy rate in the audiovisual (AV) condition compared with both auditory (A) and visual (V) conditions. The results were consistent with the previous findings. Moreover, ERP results also showed a sub-additive pattern of fronto-central P2 in the AV condition which was also consistent with those reported in previous findings. The results of first study indicated that the audiovisual discrimination task used in this thesis was valid for generating the multisensory integration process. The measurements used were capable to generating meaningful data for the next study.
The second study recruited older participants of who completed the same audiovisual discrimination task and same parameters of measurements in Study 1. The aim was to investigate the impact of aging on the audiovisual integration process affecting the subsequent sensory, response selection and generation, and motor execution processes. Due to the observations of obvious speed-accuracy trade-off existed in the older group, inverse effectiveness score (IES) was used to normalized the task-related behavioral measures. Results of Study 2 demonstrated that older participants could benefit more from the audiovisual integration process than their younger counterparts in terms of lower IES in the AV condition. The super-additive patterns of the fronto-central P2 were significantly and negatively correlated with the IES scores. These suggested that the enhanced task performance is likely to be due to the modulated audiovisual integration influencing perceptual and feedback processes. Furthermore, the fronto-central P2 was also positively correlated with participants' MoCA attention sub-score. These findings indicated that audiovisual integration may play a role in compensating the deteriorated attention function among the older participants. For the post-audiovisual integration motor responses, between-group differences were only revealed in the response generation process. Older participants showed less negative-going r-LRP in audiovisual condition while no significant differences in the r-LRP were observed among the younger participants. The r-LRP amplitudes were further revealed to be negatively correlated with the IES score. These results suggested that the audiovisual integration could have modulated the response generation process, which enhanced older participants' performances on the task. These observations were not found among the younger participants. In summary, the results of the two studies indicated that the enhanced performances on audiovisual discrimination task observed among the older participants would have contributed by the super-additive audiovisual integration processes, which modulated the perceptual and feedback stages as well as response generation process. The super-additive audiovisual integration may serve a functional role to compensate the deterioration of attention function as well as the response generation due to aging.
Subjects: Hong Kong Polytechnic University -- Dissertations
Senses and sensation
Pages: xxi, 150 pages : color illustrations
Appears in Collections:Thesis

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