| Summary: | The logopenic variant of primary progressive aphasia (lvPPA) has been associated with impaired phonological short-term memory (STM; Gorno-Tempini et al., 2008). In contrast, people with mild Alzheimer’s dementia (AD) are thought to not have impaired phonological STM. Therefore, one would predict that people with lvPPA would score significantly lower than a matched AD group on tasks that require phonological STM, but not on tasks that require visuospatial STM. We tested this prediction in the current study. For tasks that are not widely available, the lvPPA group was also compared to unimpaired participants.
Subjects. The lvPPA group consisted of 11 participants who were diagnosed based on the currently accepted criteria (Gorno-Tempini et al, 2011). The AD group consisted of 12 participants who were matched with the lvPPA group on age (lvPPA: M = 70.7, SD = 8.3; AD: M = 69.7, SD = 9.3), education (lvPPA: M = 17.3, SD = 1.6; AD: M = 17.0, SD = 1.9), and MMSE (lvPPA: M = 22.1, SD = 3.8; AD: M = 22.4, SD = 2.0). The unimpaired control group consisted of 16 participants who were matched on age (M = 71.2, SD = 9.6) and education (M = 17.6, SD = 1.5). A few participants from each group did not complete every task.
Procedure. Participants with lvPPA and AD completed tasks requiring phonological STM: digit span, BDAE repetition subtests, pseudoword repetition, and reading and spelling of pseudowords and matched real words. They also completed tasks requiring visuospatial STM: spatial span and block design. The control participants completed the pseudoword and matched real word tasks.
Results. The Mann-Whitney U Test was utilized for group comparisons. The lvPPA group scored significantly lower than the AD group on word repetition (p < .05), sentence repetition (p < .01), forward digit span (p < .01), backward digit span (p < .05), and scaled total digit span (p < .01). In contrast, there were no significant differences between these groups on scaled block design or forward, backward, or scaled total spatial span (all p’s > .05).
The lvPPA group scored significantly lower on pseudoword repetition, compared to both the AD group (p < .05) and the controls (p < .01). For the reading and spelling tasks, difference scores were calculated by subtracting each participant’s word reading or spelling score from his or her pseudoword reading or spelling score (see Figure 1). Compared to the AD and control groups, the lvPPA group had a greater difference score for both tasks (lvPPA vs. AD: both p’s < .05; lvPPA vs. Controls, Reading: p < .05; Spelling: p < .01).
These findings are consistent with the hypothesis that phonological STM is impaired in lvPPA. The logopenic participants were more impaired than the AD group on multiple tests requiring phonological STM. In contrast, there were no differences between these groups on tests requiring visuospatial STM.
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