Biomedical subjects

Kayoko Okada

Publications and source records attributed to Kayoko Okada.

4 recordsLinked to original sources

PubMed2006

Identification of lexical-phonological networks in the superior temporal sulcus using functional magnetic resonance imaging.

General agreement exists that dorsal aspects of the temporal lobe support the perception of speech but there is less agreement regarding the mapping between levels of speech processing and neural regions within the dorsal temporal lobe. The present experiment sought to identify temporal lobe regions that support one such level, namely, lexical-phonological representation/processing. To do this, we manipulated phonological neighborhood density, a variable that affects processing within lexical-phonological networks. In a functional magnetic resonance imaging experiment, 10 participants listened to blocks of either high-density or low-density words. High-density words produced significantly more activation in the posterior half of the superior temporal sulcus bilaterally, suggesting that these regions are involved in lexical-phonological processing networks.

Acoustic Stimulation↗

PubMed2006

Left posterior auditory-related cortices participate both in speech perception and speech production: Neural overlap revealed by fMRI.

Recent neuroimaging studies and neuropsychological data suggest that there are regions in posterior auditory cortex that participate both in speech perception and speech production. An outstanding question is whether the same neural regions support both perception and production or whether there exist discrete cortical fields subserving these functions. Previous neurophysiological studies suggest that there is indeed regional overlap between these systems, but those studies used a rehearsal task to assess production. The present study addressed this question in an event-related fMRI experiment in which subjects listened to speech and in separate trials, performed a covert object naming task. Single subject analysis revealed regions of coactivation for speech perception and production in the left posterior superior temporal sulcus (pSTS), left area Spt (a region in the Sylvian fissure at the parietal-temporal boundary), and left inferior frontal gyrus. These results are consistent with lesion data and previous physiological data indicating that posterior auditory cortex plays a role in both reception and expression of speech. We discuss these findings within the context of a neuroanatomical framework that proposes these neural sites are a part of an auditory-motor integration system.

Auditory Cortex↗

PubMed2004

Human cortical auditory motion areas are not motion selective.

The existence of a specialized mechanism supporting auditory motion processing in humans is a matter of debate in the psychophysical literature. Recent functional neuroimaging data appear to have resolved the debate in favor of a specialized motion system in that several studies have found cortical regions that seem to be motion selective. While all these studies contrast some form of moving auditory stimulation with a stationary stimulus, none have adequately controlled for the possibility that these areas are simply computing sound-source location and not motion per se: a moving stimulus varies in spatial location as well as motion, and so a system computing spatial location (and not motion) would be activated in response to both a moving and stationary sound source. To control for this possibility, ten subjects were scanned while listening to moving stimuli and while listening to stationary stimuli that varied randomly in spatial location. Consistent with previous imaging studies, we found that a motion stimulus when contrasted with rest (scanner noise) activated STG/planum temporale (bilaterally) and right parietal lobe. However, stationary stimuli presented at varying locations activated these regions equally well, arguing against the existence of specialized motion-processing areas in human cortex.

Acoustic Stimulation↗

PubMed2003

Word length modulates neural activity in auditory cortex during covert object naming.

Several lines of evidence show that posterior portions of left auditory cortex participate in aspects of speech production. A current hypothesis is that these regions play a specific role in processing phonological codes. We used event-related fMRI to test this hypothesis. Subjects covertly named objects that had names varying in length from one to four syllables. Behavioral data, both in previous work and in the present study, show an increase in naming reaction time as words get longer, reflecting the increase in phonological load. If left posterior auditory areas participate in phonological aspects of production, word length should modulate neural activity in this region. Object naming activated the left planum temporale in each subject, confirming previous findings of auditory cortex involvement in speech production. The timecourse of activation in this region showed a length effect, consistent with its hypothesized role in phonological processing. Similar effects were also observed in premotor cortex, but not in occipital-temporal cortex, which presumably supports visual processing of the pictures to be named.

Auditory Cortex↗