Working Memory Demands and Semantic Sensitivity for Prose in Mild Alzheimer's Disease

The debate continues with regard to whether degradation of semantic knowledge or deficits in information processing lead to impaired memory performance in patients with Alzheimer's disease (AD). This study examined the effects of semantic content and working memory demands on the recall and recognition abilities of patients with mild AD. Nineteen patients with probable AD and 19 demographically matched normal control participants were asked to remember prose passages that varied in semantic content (high, medium, and low level of idea importance) and working memory demands (narrative and expository passages). Compared to the controls, patients with mild AD lost the ability to recall prose in a manner consistent with the semantic structure of the passages as the demands on working memory increased. Furthermore, as the demands on working memory increased, patients recognized information in a manner that suggested their initial processing was of isolated details rather than by semantic structure. This study provides support for the hypothesis that information processing deficits contribute to impaired semantic processing in patients with mild AD.     

Modulation sensitivity in the perceptual organization of speech

In a spoken utterance, a talker expresses linguistic constituents in serial order. A listener resolves these linguistic properties in the rapidly fading auditory sample. Classic measures agree that auditory integration occurs at a fine temporal grain. In contrast, recent studies have proposed that sensory integration of speech occurs at a coarser grain, approximate to the syllable, on the basis of indirect and relatively insensitive perceptual measures. Evidence from cognitive neuroscience and behavioral primatology has also been adduced to support the claim of sensory integration at the pace of syllables. In the present investigation, we used direct performance measures of integration, applying an acoustic technique to isolate the contribution of short-term acoustic properties to the assay of modulation sensitivity. In corroborating the classic finding of a fine temporal grain of integration, these functional measures can inform theory and speculation in accounts of speech perception.