Does expanded retrieval produce benefits over equal-interval spacing? Explorations of spacing effects in healthy aging and early stage Alzheimer's disease.

Three experiments explored different schedules of retrieval practice in young adults, older adults, and individuals with dementia of the Alzheimer type. In each experiment, an initial acquisition phase was presented in which participants studied or attempted to retrieve response words to cues, followed by a later cued-recall test. Experiment 1 produced a benefit of expanded retrieval over equal-interval retrieval during acquisition, but this benefit was lost in final cued recall. In Experiments 2 and 3, participants received corrective feedback during acquisition and modified spacing schedules. There was again no evidence of a difference between expanded and equal-interval conditions in final cued recall. Discussion focuses on the potential benefits and costs of expanded retrieval on a theoretical and applied level.

Consistency and regularity in past-tense verb generation in healthy ageing, Alzheimer's disease, and semantic dementia.

Older adults, individuals with dementia of the Alzheimer's type (DAT), and individuals with semantic dementia (SD) produced the past tense of verbs based on present-tense carrier sentences (e.g., Everyday I ding the bell. Yesterday I_____the bell). Both regularity (i.e., whether or not -ed is used for the past tense) and consistency (i.e., the degree to which verbs of similar orthography and phonology in the present tense have similar past tenses to the target) were manipulated. Participants received regular consistent (e.g., land-landed), regular inconsistent (e.g., weed-weeded), irregular consistent (e.g., sting-stung), and irregular inconsistent (e.g., light-lit) verbs. The dependent measures were overall accuracy rates and error rate types (e.g., regularizations, analogies, and other errors). Both consistency and regularity influenced performance. In addition, individuals with DAT showed a disproportionate deficit for inconsistent verbs associated with a high summed frequency of enemies, whereas SD individuals produced disproportionate breakdowns in performance on regular inconsistent, irregular consistent, and irregular inconsistent verbs. These results are consistent with the perspective that semantic/lexical processes are involved in processing the past tense of both irregular verbs and regular inconsistent verbs, and that attention is used to select appropriate responses and control inappropriate responses.

Differing neuropsychological and neuroanatomical correlates of abnormal reading in early-stage semantic dementia and dementia of the Alzheimer type.

Individuals with semantic dementia (SD) were differentiated neuropsychologically from individuals with dementia of the Alzheimer type (DAT) at very mild-to-mild stages (clinical dementia rating 0.5 or 1). A picture naming and recognition memory experiment provided a particularly useful probe for early identification, with SD individuals showing preserved picture recognition memory and impaired naming, and DAT individuals tending to show the reverse dissociation. The identification of an early SD group provided the opportunity to inform models of reading by exploring the influence of isolated lexical semantic impairment on reading regular words. Results demonstrated prolonged latency in both SD and DAT group reading compared to a control group but exaggerated influence of frequency and length only for the SD group. The SD reading pattern was associated with focal atrophy of the left temporal pole. These cognitive-neuroanatomical findings suggest a role for the left temporal pole in lexical/semantic components of reading and demonstrate that cortical thickness differences in the left temporal pole correlate with prolonged latency associated with increased reliance on sublexical components of reading.

Visual word recognition of single-syllable words.

Speeded visual word naming and lexical decision performance are reported for 2428 words for young adults and healthy older adults. Hierarchical regression techniques were used to investigate the unique predictive variance of phonological features in the onsets, lexical variables (e.g., measures of consistency, frequency, familiarity, neighborhood size, and length), and semantic variables (e.g. imageahility and semantic connectivity). The influence of most variables was highly task dependent, with the results shedding light on recent empirical controversies in the available word recognition literature. Semantic-level variables accounted for unique variance in both speeded naming and lexical decision performance, level with the latter task producing the largest semantic-level effects. Discussion focuses on the utility of large-scale regression studies in providing a complementary approach to the standard factorial designs to investigate visual word recognition.

Spelling via semantics and phonology: exploring the effects of age, Alzheimer's disease, and primary semantic impairment.

Spelling performance across a common set of stimuli was examined in young adults, healthy older adults, individuals with early stage dementia of the Alzheimer's type (DAT), and four individuals with a primary semantic impairment (PSI). The stimuli included homophones and low-frequency sound-to-spelling consistent (i.e. words with more predictable spellings) and inconsistent words (i.e. words with less predictable spellings). The results indicate that when spelling homophonic words (spelling/pleIn/ as plane versus plain), younger adults and to a greater extent individuals with PSI placed relatively more emphasis on phonological information (i.e. spell the word based on sound-to-spelling principles) whereas healthy older adults and individuals with DAT placed relatively more emphasis on semantic information (i.e. spell the word based on the dominant usage). For non-homophonic words, large consistency effects (spelling plaid as plad) were observed for both individuals with DAT and individuals with PSI. It is proposed that the decrease in accuracy for inconsistent words has different bases in DAT and PSI. We propose that deficits in attentional control (i.e. selection) underlie performance in DAT whereas disruption of semantic representations underlies performance in PSI.