Eric Waldron | PubMed Health

PubMed2006

FMRI of past tense processing: the effects of phonological complexity and task difficulty.

The generation of regular and irregular past tense verbs has been an important issue in cognitive science and has been used to advance different models of the organization of language in the brain. The dual-system view holds that the regular past tense forms are generated by a rule while irregular forms are retrieved from memory. The single-system view, on the other hand, holds that both forms are generated by a single integrated system and differ only in their reliance on factors such as phonology and semantics. We conducted an event-related fMRI study to examine the activation patterns associated with the generation and reading of regular and irregular past tense forms, in addition to the reading of their stems. Regular and irregular past tense generation activated similar brain regions compared to the reading of their respective stems. The areas activated more for irregular generation compared to regular generation included inferior frontal, precentral, and parietal regions bilaterally. This activation can be interpreted as reflecting the greater attentional and response selection demands of irregular generation. Compared to irregular generation, regular generation activated a small region in the left superior temporal gyrus when the regular and irregular past tense forms were mismatched on phonological complexity. No areas were more activated for regulars than irregulars when the past tense forms were matched on this variable. This suggests that the activation specific to regulars was related to the higher phonological complexity of their past tense forms rather than to their generation. A contrast of the reading of regular and irregular past tense forms was consistent with this hypothesis. These results support a single-system account of past tense generation.

Adult↗

PubMed2005

Volumetric vs. surface-based alignment for localization of auditory cortex activation.

The high degree of intersubject structural variability in the human brain is an obstacle in combining data across subjects in functional neuroimaging experiments. A common method for aligning individual data is normalization into standard 3D stereotaxic space. Since the inherent geometry of the cortex is that of a 2D sheet, higher precision can potentially be achieved if the intersubject alignment is based on landmarks in this 2D space. To examine the potential advantage of surface-based alignment for localization of auditory cortex activation, and to obtain high-resolution maps of areas activated by speech sounds, fMRI data were analyzed from the left hemisphere of subjects tested with phoneme and tone discrimination tasks. We compared Talairach stereotaxic normalization with two surface-based methods: Landmark Based Warping, in which landmarks in the auditory cortex were chosen manually, and Automated Spherical Warping, in which hemispheres were aligned automatically based on spherical representations of individual and average brains. Examination of group maps generated with these alignment methods revealed superiority of the surface-based alignment in providing precise localization of functional foci and in avoiding mis-registration due to intersubject anatomical variability. Human left hemisphere cortical areas engaged in complex auditory perception appear to lie on the superior temporal gyrus, the dorsal bank of the superior temporal sulcus, and the lateral third of Heschl's gyrus.

Acoustic Stimulation↗