Akira Toyomura

Neural correlates of auditory feedback control in human

Auditory feedback plays an important role in natural speech production. We conducted a functional magnetic resonance imaging (fMRI) experiment using a transformed auditory feedback (TAF) method to delineate the neural mechanism for auditory feedback control of pitch. Twelve right-handed subjects were required to vocalize /a/ for 5 s, while hearing their own voice through headphones. In the TAF condition, the pitch of the feedback voice was randomly shifted either up or down from the original pitch two or three times in each trial. The subjects were required to hold the pitch of the feedback voice constant by changing the pitch of original voice. In non-TAF condition, the pitch of the feedback voice was not modulated and the subjects just vocalized /a/ continuously. The contrast between TAF and non-TAF conditions revealed significant activations; the supramarginal gyrus, the prefrontal area, the anterior insula, the superior temporal area and the intraparietal sulcus in the right hemisphere, but only the premotor area in the left hemisphere. This result suggests that auditory feedback control of pitch is mainly supported by the right hemispheric network.

Effect of external auditory pacing on the neural activity of stuttering speakers

External auditory pacing, such as metronome sound and speaking in unison with others, has a fluency-enhancing effect in stuttering speakers. The present study investigated the neural mechanism of the fluency-enhancing effect by using functional magnetic resonance imaging (fMRI). 12 stuttering speakers and 12 nonstuttering controls were scanned while performing metronome-timed speech, choral speech, and normal speech. Compared to nonstuttering controls, stuttering speakers showed a significantly greater increase in activation in the superior temporal gyrus under both metronome-timed and choral speech conditions relative to a normal speech condition. The caudate, globus pallidus, and putamen of the basal ganglia showed clearly different patterns of signal change from rest among the different conditions and between stuttering and nonstuttering speakers. The signal change of stuttering speakers was significantly lower than that of nonstuttering controls under the normal speech condition but was raised to the level of the controls, with no intergroup difference, in metronome-timed speech. In contrast, under the chorus condition the signal change of stuttering speakers remained lower than that of the controls. Correlation analysis further showed that the signal change of the basal ganglia and motor areas was negatively correlated with stuttering severity, but it was not significantly correlated with the stuttering rate during MRI scanning. These findings shed light on the specific neural processing of stuttering speakers when they time their speech to auditory stimuli, and provide additional evidence of the efficacy of external auditory pacing.

Neural substrates of irony comprehension: A functional MRI study.

In daily communication, we sometimes use ironic expressions to convey the opposite meaning. To understand these contradictory statements, we have to infer contextual implications and the speakers mental state. However, little is known about how our brains carry out these complex processes. In this study, we investigated the neural substrates involved in irony comprehension using echoic utterance (Sperber and Wilson, 1986, 1995). Participants read a short scenario that consisted of five sentences. The first four sentences explained the situation of the protagonists. The fifth connoted either an ironic, literal, or unconnected meaning. The participants had to press a button to indicate whether or not the final sentence expressed irony. In the ironic sentence condition, the bilateral superior frontal gyrus, middle frontal gyrus, inferior frontal gyrus, medial prefrontal cortex, superior temporal gyrus, inferior parietal lobule, caudate, thalamus, the left insula, and amygdala were activated. In the literal sentence condition, the right superior frontal gyrus, the bilateral middle frontal gyrus, inferior frontal gyrus, medial prefrontal cortex, superior temporal gyrus, inferior parietal lobule, caudate, the left insula, the right thalamus, and the left amygdala were activated. However, in the ironic sentence condition minus the literal sentence condition, we observed higher activation in the right medial prefrontal cortex (BA 10), the right precentral (BA 6), and the left superior temporal sulcus (BA 21). Our results suggest that irony comprehension is strongly related to mentalizing processes and that activation in these regions might be affected by higher-order cognitive operations.

Does simile comprehension differ from metaphor comprehension? A functional MRI study

Since Aristotle, people have believed that metaphors and similes express the same type of figurative meaning, despite the fact that they are expressed with different sentence patterns. In contrast, recent psycholinguistic models have suggested that metaphors and similes may promote different comprehension processes. In this study, we investigated the neural substrates involved in the comprehension of metaphor and simile using functional magnetic resonance imaging (fMRI) to evaluate whether simile comprehension differs from metaphor comprehension or not. In the metaphor and simile sentence conditions, higher activation was seen in the left inferior frontal gyrus. This result suggests that the activation in both metaphor and simile conditions indicates similar patterns in the left frontal region. The results also suggest that similes elicit higher levels of activation in the medial frontal region which might be related to inference processes, whereas metaphors elicit more right-sided prefrontal activation which might be related to figurative language comprehension.

Self-paced and externally triggered rhythmical lower limb movements: a functional MRI study.

Self-paced rhythmical lower limb movement is an important component of locomotive motion in humans. External stimuli are known to facilitate the generation of rhythmical motion. The importance of such self-paced and externally triggered movements is widely recognized, and these movements of the upper limbs have been studied in detail. However, the difference in neural mechanisms between the self-paced and externally triggered movements of the lower limbs is not clear even in healthy subjects. The present study investigated the neural regions involved in the lower limb movements by using functional magnetic resonance imaging (fMRI). The subjects were fixed face-up to an MRI bed and performed lower limb movements that mimicked walking under self-paced and externally triggered conditions. The results showed that the supplementary motor area, sensorimotor cortex and cerebellum were involved in both types of movement, but the basal ganglia and the thalamus were selectively recruited for the self-paced lower limb movement. These results are compatible with those of previous studies on the control of the lower limbs, and on upper limb movement under self-paced and externally triggered conditions.

A functional MRI study on auditory feedback control of pitch

Perception of one’s own speech plays an important role in fluent speech production. In this study, we conducted a functional magnetic resonance imaging (fMRI) experiment to delineate the neural mechanism for auditory feedback control of pitch, using a transformed auditory feedback (TAF) method. Subjects (n=12, right handed) were required to vocalize /a/ for 5 s while hearing their voice through a headphone. In the TAF condition, the feedback voice pitch was shifted randomly up or down from the original pitch two or three times. The subjects were required to hold the pitch of the feedback voice constant by changing the pitch of the original voice. In the non‐TAF condition, the pitch of feedback voice was not modulated and the subjects merely vocalized /a/ continuously. A contrast between TAF and non‐TAF conditions showed some significantly greater activations in the TAF condition (p<0.05 corrected). In the right hemisphere, the supramarginal gyrus, the prefrontal area, the anterior insula, and the superior...

Frequency modulated feedback of ones own voice can cause dysfluence of speech

Delayed auditory feedback (DAF) can cause speech dysfluency (e.g., stuttering) in healthy normal subjects. In previous studies, feedback frequency was changed linearly or to a constant value in FAF. In this study, we introduce frequency‐modulated feedback of pitch in a sine‐wave manner. The modulation depth of pitch (F0) of auditory feedback voice was six semitones, and the modulation frequencies of sinewaves were set at 0.05, 0.1, 0.5, 0.9, 2, 4, 6, 8, 10, 12, 14, and 16 Hz. In addition to the FAF experiment, we conducted DAF experiments with delay times of 50, 200, and 400 ms. Participants (18 Chinese and 18 Japanese) were instructed to read sentences as they listened to the altered feedback voice through a headphone under each condition. Speech dysfluency was apparent under all FAF and DAF conditions for both groups. Only when the modulation frequency was 14 Hz did Chinese subjects show significantly larger disturbance than Japanese in FAF. A significant greater disturbance of Chinese in DAF was observ...