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Timothy G. Turkington
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Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2003) 15 (3): 475–487.
Published: 01 April 2003
Abstract
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Positron emission tomography data (Madden, Langley, et al., 2002) were analyzed to investigate adult age differences in the relation between neural activation and the lexical (word frequency) and sublexical (word length) components of visual word identification. The differential influence of these components on reaction time (RT) for word/nonword discrimination (lexical decision) was generally similar for the two age groups, with word frequency accounting for a greater proportion of lexical decision RT variance relative to word length. The influence of word length on RT, however, was relatively greater for older adults. Activation in regions of the ventral occipito-temporal cortex was related to the RT changes associated with word frequency and length for older adults, but not for younger adults. Specifically, older adults' frequency effects were related to activation in both anterior (Brodmann's area [BA] 37) and posterior (BAs 17 and 18) regions of the occipito-temporal pathway, whereas word length effects were only associated with posterior activation (BA 17). We conclude that aging affects the neural mechanisms supporting word identification performance although behavioral measures of this ability are generally constant as a function of age.
Journal Articles
David J. Madden, Lawrence R. Gottlob, Laura L. Denny, Timothy G. Turkington, James M. Provenzale ...
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (1999) 11 (5): 511–520.
Published: 01 September 1999
Abstract
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We used H 2 15 O positron emission tomography (PET) to measure age-related changes in regional cerebral blood flow (rCBF) during a verbal recognition memory task. Twelve young adults (20 to 29 years) and 12 older adults (62 to 79 years) participated. Separate PET scans were conducted during Encoding, Baseline, and Retrieval conditions. Each of the conditions involved viewing a series of 64 words and making a two-choice response manually. The complete reaction time (RT) distributions in each task condition were characterized in terms of an ex-Gaussian model (convolution of exponential and Gaussian functions). Parameter estimates were obtained for the mean of the exponential component (τ), representing a task-specific decision process and the mean of the Gaussian component (μ), representing residual sensory coding and response processes. Independently of age group, both μ and τ were higher in the Encoding and Retrieval conditions than in the Baseline condition, and τ was higher during Retrieval than during Encoding. Age-related slowing in task performance was evident primarily in μ. For young adults, rCBF activation in the right prefrontal cortex, in the Retrieval condition, was correlated positively with μ but not with τ. For older adults, rCBF changes (both increases and decreases) in several cortical regions were correlated with both μ and τ. The data suggest that the attentional demands of this task are relatively greater for older adults and consequently lead to the recruitment of additional neural systems during task performance.