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dc.contributorDepartment of Rehabilitation Sciencesen_US
dc.creatorAu, Kai-ming Brian-
dc.publisherHong Kong Polytechnic University-
dc.rightsAll rights reserveden_US
dc.titleAging effect on egocentric and allocentric frames of reference in visual attention : an event-related potential (ERP) studyen_US
dcterms.abstractVisual attention is the cognitive process that some visual stimuli are selected for processing over others. This process involves directing attention to a spatial location which can improve the accuracy and speed of responses to target stimuli that occur in that location. Visual attention could be modulated by the frame of reference which individual takes when perceiving external visual stimuli. Egocentric (viewer-based) as well as allocentric (object-based) processing can affect visuospatial attention. Nevertheless, not much is known about the mental and cognitive processes which mediate the two encoding reference frames. Besides, not much studies in aging effect on the modulation of visual attention by these two frames of reference. This study aimed to 1) investigate the cognitive processes involved in the allocentric and egocentric reference frames for visual attention; and 2) investigate the possible changes in these cognitive processes in normal aging.en_US
dcterms.abstractSeventeen young individuals (7 female and 10 male) aged 18-23 years (mean ± SD = 20.82 ± 1.19 years) and sixteen older healthy individuals (9 females) aged 60-66 years (mean ± SD = 62.75 ± 1.57 years) were successfully recruited in the final data analyses. The behavioral data showed that both groups responded more accurately in valid (Young: 95.11 ± 1.25%; Older: 91.22 ± 0.87%) than invalid trial (Young: 90.67 ± 2.02%; Older: 76.52 ± 2.50%) (p<0.001) but the young group responded faster when the stimuli were presented to their right (651.75 ± 25.86 ms) compared to their left (689.24 ± 27.12 ms) visual hemi-fields, F(1, 16)=18.39, p=0.001. On the other hand, the older group responded more accurately in egocentric (85.64 ± 1.31%) than allocentric (82.09 ± 1.64%) but no such difference was found in the young group (p>0.05). The ERP findings shows that greater P1 amplitude was found in the older group, F(1, 31)=6.28, p=0.018. Interaction effect between group and hemi-field was found in the P1, F(1.00, 31.00)=13.04, p=0.001. It was found larger in the young group when the visual stimuli were presented at right hemi-field than left hemi-field. Similarly, interaction effect between group and hemi-field was also found in the P3, F(1.00, 31.00)=9.91, p=0.004. Larger P3 was found when stimuli appeared at RHF (1.22 ± 0.48 μV) than LHF (0.86 ± 0.55 μV) in the young group. However, it is the other way round for the older adults. Their P3 was larger for the stimuli presented at the LHF (3.25 ± 0.52 μV) than the RHF (2.90 ± 0.49 μV).For the N2, interaction effects were found between group and frames of reference, F(1.00, 31.00)=5.59, p=0.025, suggesting that the young group had shorter latency in egocentric than allocentric conditions. For the contralateral delay activity (CDA), interaction effects were found between group and condition, F(1.00, 31.00)=5.74, p=0.023, suggesting that its amplitude was found larger in egocentric (-0.64 ± 0.09 μV) than allocentric condition for the older adults (-0.47 ± 0.07 μV). Overactivation and posterior-anterior shift in aging were also found which indicate the compensation for the age-related decline in the posterior regions. Although both young and older adults have similar findings in responding faster in egocentric than allocentric condition under behavioral observation, the reasons for having this phenomenon are different in terms of the cognitive processes involved.en_US
dcterms.extentxxiii, 234 leaves : illustrations (some color) ; 30 cmen_US
dcterms.isPartOfPolyU Electronic Thesesen_US
dcterms.educationalLevelAll Doctorateen_US
dcterms.LCSHVisual perception.en_US
dcterms.LCSHHong Kong Polytechnic University -- Dissertationsen_US
dcterms.accessRightsopen accessen_US

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