Background: Temporal constraints of perceiving, generating and updating information in the central nervous system are crucial for human behaviour, since the complex interplay of cortical structures needs to be synchronized and coordinated. Different levels of temporal sensory processing have been found to be associated with different time ranges, longer temporal ranges suggesting the involvement of higher cortical areas. For example, 1. Range of a few milliseconds: Processing in this range (around 1-3 ms) allows the differentiation between simultaneity vs. non-simultaneity, e.g. as in sensory fusion threshold tasks. It primarily depends on peripheral sensory structures and primary cortex. 2. Range of some tens of milliseconds: Processing in this range (around 30-50 ms) is associated with the perception of succession, the identification of the temporal order of events, e.g. as in temporal order detection tasks. It involves secondary cortical structures, especially temporal and inferior parietal regions. 3. Range of some hundreds of milliseconds: Processing in this range (around 150-300 ms) is associated with perceptual grouping, as e.g. required for the identification of illusory contours. It primarily depends on secondary and higher-order cortical structures. Although these temporal ranges were found to alter with different kinds of brain lesions, the influence of normal brain aging on temporal processing is little understood.
Objective: Is there age-related general slowing of temporal processing, or is age-related slowing specific for temporal processes requiring interactions in higher-order cortical structures?
Design: Group comparison.
Materials and Methods: Two groups of healthy subjects (aged between 20-35 years, and between 60-86 years) with normal hearing and vision were psychophysically tested on three temporal ranges: a) 1-3ms: auditory fusion thresholds, b) 30-50ms: auditory order thresholds, c) 150-300ms: illusory figure perception.
Results: Preliminary analyses show a general decline of temporal processing in the elderly: fusion thresholds tended to be higher, temporal order detection required significantly longer intervals, and reaction times for the identification of illusory and real figures were longer than in younger subjects. Moreover, an interaction effect between age and task was found for the illusory contour task, revealing that reaction times of the elderly, but not of younger subjects, were significantly longer for illusory than for real figures.
Conclusion: Although our results favor general age-related slowing of temporal processing, the visual processing difference for illusory and real figures in elderly subjects indicates that decline might be more pronounced in secondary and higher cortical regions than in primary cortex. Additional analyses, including EEG data, shall provide further insights into temporal processing in the normal aging brain.
Outlook: Since histopathological findings in patients with Alzheimer’s disease (AD) let suggest specific decline of secondary and higher cortical regions, we test whether temporal processing assumed to be related to such regions is specifically altered in these patients, and could thus serve as early indicator for pathological brain aging.
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