Functional magnetic resonance imaging (fMRI) was used to examine how the brain responds to temporal compression of speech and to determine whether the same regions are also involved in phonological processes associated with reading. Recorded speech was temporally compressed to varying degrees and presented in a sentence verification task. Regions involved in phonological processing were identified in a separate scan using a rhyming judgment task with pseudowords compared to a lettercase judgment task. The left inferior frontal and left superior temporal regions (Broca's and Wernicke's areas), along with the right inferior frontal cortex, demonstrated a convex response to speech compression; their activity increased as compression increased, but then decreased when speech became incomprehensible. Other regions exhibited linear increases in activity as compression increased, including the middle frontal gyri bilaterally. The auditory cortices exhibited compression-related decreases bilaterally, primarily reflecting a decrease in activity when speech became incomprehensible. Rhyme judgments engaged two left inferior frontal gyrus regions (pars triangularis and pars opercularis), of which only the pars triangularis region exhibited significant compression-related activity. These results directly demonstrate that a subset of the left inferior frontal regions involved in phonological processing is also sensitive to transient acoustic features within the range of comprehensible speech.

Individuals with developmental language disabilities, including developmental dyslexia and specific language impairment (SLI), exhibit impairments in processing rapidly presented auditory stimuli. It has been hypothesized that these deficits are associated with concurrent deficits in speech perception and, in turn, impaired language development. Additionally, postmortem analyses of human dyslexic brains have revealed the presence of focal neocortical malformations such as cerebrocortical microgyria. In an initial study bridging these research domains, we found that male rats with induced microgyria were impaired in discriminating rapidly presented auditory stimuli. In order to further assess this anatomical-behavioral association, we designed two experiments using auditory-reflex modification. These studies were intended to assess whether auditory processing deficits in microgyric male rats would be seen in threshold detection of a silent gap in white noise, and in oddball detection of a two-tone stimulus of variable duration. Results showed no differences between sham and microgyric subjects on gap detection, but did show that microgyric subjects were impaired in the discrimination of two-tone stimuli presented in an oddball paradigm. This impairment was evident for stimuli with total duration of 64 msec or less, while both groups were able to discriminate stimuli with duration of 89 msec or greater. The current results further support the relationship between malformations of the cerebral cortex and deficits in rapid auditory processing. They also suggest that the parameters characterizing rapid auditory processing deficits for a specific task may be influenced by stimulus features and/or cognitive demand of that particular task.

Clinical, behavioral, and neurophysiological studies of developmental language impairment (LI), including reading disability (RD), have variously emphasized different factors that may contribute to this disorder. These include abnormal sensory processing within both the auditory and visual modalities and deficits in linguistic skills and in general cognitive abilities. In this study we employed the event-related brain potential (ERP) technique in a series of studies to probe and compare Merent aspects of functioning within the same sample of LI/RD children. Within the group multiple aspects of processing were affected, but heterogeneously across the sample. ERP components linked to processing within the superior temporal gyrus were abnormal in a subset of children that displayed abnormal performance on an auditory temporal discrimination task. An early component of the visual ERP was reduced in amplitude in the group as a whole. The relevance of this effect to current conceptions of substreams within the visual system is discussed. During a sentence processing task abnormal hemispheric specialization was observed in a subset of children who scored poorly on tests of grammar. By contrast the group as a whole displayed abnormally large responses to words requiring contextual integration. The results imply that multiple factors can contribute to the profile of language impairment and that different and specific deficits occur heterogeneously across populations of LI/RD children.