RESUMEN
We studied the cortical activation underlying perception of variations in speech fundamental frequency (F0) as indexed by the amplitude, latency and source location of the auditory N100m response registered with magnetoencephalography (MEG). Ten subjects were presented with Finnish vowels with either a constant or an ascending/descending F0. We found that the human auditory cortex is sensitive to these time-varying changes in the F0 of speech: vowels with a constant F0 elicited more prominent N100m responses than did vowels with ascending or descending changes in F0. These results suggest that the speech-related behavior of the N100m arises out of cortical sensitivity to variations in the F0 and its harmonics which underlie the perception of pitch and intonation. The present observations are interpreted in terms of the interrelatedness of speech production and perception.
Asunto(s)
Estimulación Acústica/métodos , Corteza Auditiva/fisiología , Acústica del Lenguaje , Percepción del Habla/fisiología , Adulto , Análisis de Varianza , Femenino , Humanos , MasculinoRESUMEN
Voiced speech is created by the fluctuating vocal folds generating the glottal pulseform. This excitation signal is the source of the speech fundamental frequency and its harmonic integer multiples. Periodic glottal excitation is required for the elicitation of speech-specific cortical processes indexed by the auditory N100m response. Here, we studied the cortical processing underlying the perception of the vowels /a/ and /u/ produced using normal and aperiodic phonation. The behavior of the N100m, registered with magnetoencephalography (MEG), was studied in 10 subjects. The amplitude and latency of the N100m as well as the center of gravity of the activated cortical areas varied as a function of stimulus periodicity. Further, the presence of glottal excitation had differential effects on the latency of the N100m elicited by the vowels /a/ and /u/. Thus, changes affecting the perceptual quality of speech signals without changing their phonetic content modify the dynamics of human auditory cortex.
Asunto(s)
Estimulación Acústica/métodos , Potenciales Evocados Auditivos/fisiología , Glotis , Magnetoencefalografía/métodos , Percepción del Habla/fisiología , Adulto , Corteza Auditiva/fisiología , Femenino , Humanos , Masculino , Fonética , Tiempo de Reacción/fisiologíaRESUMEN
Cortical activity underlying speech perception has been studied mostly by using isolated vowels with constant formant frequencies. Speech, however, is characterized by formant transitions whereby formant frequencies change as a function of time. We used magnetoencephalography (MEG) to investigate cortical activity elicited by isolated vowels and diphthongs containing formant transitions. Ten subjects were presented with two isolated vowels /a/ and /u/ and diphthongs /au/ and /ua/. Stimulus duration was 200 ms, and the diphthongs started and ended with a 50-ms constant-formant period and included a 100-ms linear transition period. Apart from studying the auditory N100m response, we examined subsequent brain activity in a 500-ms poststimulus time window, as the transitions were expected to elicit activity also in later stages of cognitive processing. All the stimuli elicited prominent N100m responses. Thereafter, both the isolated vowels and diphthongs elicited sustained brain activity lasting up to 500 ms. The present observations indicate that identification of the speech sounds as well as changes in their identity are reflected in the auditory N100m. Notably, the stimuli appeared to elicit left-hemispheric activity resembling the N400, typically obtained by using more complicated speech stimuli such as words and sentences.
Asunto(s)
Estimulación Acústica/métodos , Corteza Auditiva/fisiología , Percepción del Habla/fisiología , Adulto , Análisis de Varianza , Femenino , Lateralidad Funcional/fisiología , Humanos , Masculino , LecturaRESUMEN
We recorded evoked magnetic fields while short words were visually presented in different languages with an oddball paradigm. The task was to count how many words were in a target language when most of the words were in another language and there were also non-target deviants in a third language. When native words (Finnish) were targets, they evoked a selection response at the latency of 300-600 ms. However, when the task was to count non-native words among native standards, in addition to the targets, also the non-target foreign words evoked the selection response. These results may reflect differences in the selection process for native versus non-native words brought about by different proficiency levels of the languages.
Asunto(s)
Atención/fisiología , Potenciales Evocados Visuales/fisiología , Lenguaje , Magnetoencefalografía , Percepción Visual/fisiología , Adulto , Mapeo Encefálico , Corteza Cerebral/fisiología , Femenino , Lateralidad Funcional/fisiología , Humanos , Imagen por Resonancia Magnética , Masculino , Persona de Mediana EdadRESUMEN
The effects of stimulus duration on the elicitation and equivalent current dipole (ECD) localization of the auditory N400(m) were studied in two subject groups, either familiar or unfamiliar with Finnish language, using a sentence-processing paradigm with incongruent ending words of either short or long duration. Long-duration words elicited a broad response at around 400 ms, the generator location(s) of which could not be reliably determined using ECD estimation. In contrast, short-duration words elicited a sharp, strong-amplitude response at about 400 ms latency and it's source location could be reliably determined as being in the vicinity of auditory cortex. Subjects unfamiliar with the Finnish language elicited no response at the 400 ms range. Thus, the use of short-duration words appears to be an important prerequisite for the elicitation and localization of N400m. The differential amplitude behaviour of the N400m between the two subject groups further suggests that comprehension of the semantic content of the speech message is also required.