Biomedical subjects

Teija Kujala

Publications and source records attributed to Teija Kujala.

24 records · Page 2Linked to original sources

PubMed2003

The N1 hypothesis and irrelevant sound: evidence from token set size effects.

This study investigated how increases in the number of different types of sound (token set size) within a heard but ignored sequence influence brain activity and performance in a serial recall task (the irrelevant sound effect). We tested the hypothesis that brain processes affected by the refractory state of the neuronal populations involved in generating the auditory N1 play a role in the memory disruption produced by irrelevant sound. Auditory event-related potentials (ERPs) were recorded when volunteers performed a serial recall task that required remembering lists of visually presented numbers that were followed by a distractor-filled retention interval. The results showed that both increments in set size from 1 to 2 and from 2 to 5 elicited an increase of the N1 amplitude. Furthermore, increases in set size from 2 to 5, but not from 1 to 2, caused a significant decrease of the serial recall performance. This result suggested that, if N1 were to play a role in the disruption produced by irrelevant sound, the processes underlying the N1 wave may only serve as a necessary rather than a sufficient condition for disruption.

Acoustic Stimulation↗

PubMed2003

The mismatch negativity and reaction time as indices of the perceptual distance between the corresponding vowels of two related languages.

Two experiments were conducted to determine whether vowel familiarity affects automatic and conscious vowel discrimination. Familiar (Finnish) and unfamiliar (Komi) vowels were presented to Finnish subjects. The good representatives of Finnish and Komi mid vowels were grouped into three pairs: front /e- epsilon /, central /ø-oe/, and back /o-o/. The acoustic difference for /e- epsilon / and /o-o/ was smaller than that for /ø-oe/. For /e- epsilon /, the Komi vowel / epsilon / was at the boundary between the Finnish /e/ and /ae/. The stimuli were presented in an oddball paradigm. In three different blocks, each Komi vowel in turn served as the standard (probability 0.86) and the corresponding Finnish vowel as the deviant stimulus (probability 0.14), and vice versa. In Experiment 1, subjects were instructed to press a button as soon as they detected a deviant stimulus. In Experiment 2, event-related potentials (ERPs) were recorded to these stimuli in order to use the mismatch negativity (MMN) as an index of the perceptual distance between the members of each vowel pair, while subjects did not attend to the stimuli. There were similar effects of the acoustic distance within a vowel pair for both the reaction time (RT) and the MMN amplitude; the RT decreased and the MMN amplitude increased when the acoustic difference between the stimuli increased. However, the RT was longer when the Komi / epsilon / was the standard and the Finnish /e/ was the deviant than vice versa. No such pattern was found for the MMN. Thus, the phonemic status of the standard stimulus seems to play a role at the attentive but not at the pre-attentive level.

Acoustic Stimulation↗

PubMed2003

Language context and phonetic change detection.

Event-related brain potentials (ERP) were recorded to two spoken words, /paeti/ and /peti/. The vowel difference between the two words results in a semantical difference in Finnish, but not in Hungarian, in which /ae/ and /e/ are perceived as allophones of the same vowel /epsilon/. As a consequence, native Hungarian speakers, who had not studied Finnish before being tested, could not categorize the two word stimuli. In the main experiment, native Hungarian speakers, who fluently spoke Finnish, were presented with two oddball sequences in which /paeti/ was the frequent standard stimulus, /peti/ the infrequent deviant. In addition, very rare target words were also included. In one condition, the targets were Hungarian words, whereas in the other, they were Finnish words. The participants' sense of being in two different language environments was further encouraged by having separate experimenters conducting the two conditions, one speaking with the subjects only in Hungarian, the other only in Finnish. Language context had no effect on the mismatch negativity ERP component elicited by the deviant word stimuli. This result suggests that language context does not affect the pre-attentive detection of auditory deviance.

Adult↗

PubMed2002

Distinct gamma-band evoked responses to speech and non-speech sounds in humans.

To understand spoken language, the human brain must have fast mechanisms for the representation and identification of speech sounds. Stimulus-induced synchronization of neural activity at gamma frequencies (20-80 Hz), occurring in humans at 200-300 msec from stimulus onset, has been suggested to be a possible mechanism for neural object representation. Auditory and visual stimuli also evoke an earlier (peak <100 msec) gamma oscillation, but its dependence on high-level stimulus parameters and, thereby, its involvement in object representation has remained unclear. Using whole-scalp magnetoencephalography, we show here that responses evoked by speech and non-speech sounds differed in the gamma-frequency but not in the low-frequency (0.1-20 Hz) band as early as 40-60 msec from stimulus onset. The gamma-band responses to the speech sound peaked earlier in the left than in the right hemisphere, whereas those to the non-speech sound peaked earlier in the right hemisphere. For the speech sound, there was no difference in the response amplitude between the hemispheres at low (20-45 Hz) gamma frequencies, whereas for the non-speech sound, the amplitude was larger in the right hemisphere. These results suggest that evoked gamma-band activity may indeed be sensitive to high-level stimulus properties and may hence reflect the neural representation of speech sounds. Consequently, speech-specific neuronal processing may commence no later than 40-60 msec from stimulus onset, possibly in the form of activation of language-specific memory traces.

Acoustic Stimulation↗

PubMed2002

The auditory sensory memory trace decays rapidly in newborns.

The present study investigated the temporal dynamics of auditory sensory memory in newborns as reflected by the mismatch negativity (MMN), a preattentive electric change-detection response. MMN was obtained from 24 full-term healthy newborns who were either awake or asleep (quiet or active sleep) during the experiments. Stimuli were 1,000 Hz tones (standards) that were occasionally replaced by 1,100 Hz tones (deviants). The constant stimulus onset asynchrony (SOA) was, in separate blocks, either 450, 800, or 1,500 ms. A prominent MMN was obtained at the 800 ms SOA in all three sleep or waking states, whereas no MMN occurred at 450 and 1,500 ms SOAs. In view of the fact that in adults MMN is elicited even with a 10s SOA, these results imply that the time span of auditory memory is considerably shorter in neonates than in adults and 8-12-year-old children.

Auditory Perception↗

PubMedDate not supplied

Mismatch negativity brain response as an index of speech perception recovery in cochlear-implant recipients.

Speech-discrimination performance and the mismatch negativity (MMN) response elicited by vowel changes were used to track vowel-perception improvement of 5 adult cochlear-implant (CI) recipients. The MMN was recorded several times during the first 3 years after CI activation. Artefacts, presumably caused by CI, contaminated most of the brain responses until 1 year after CI activation. We found that speech discrimination improved over time and the MMN, observed in all patients after 2.5 years of CI use, was first seen for the larger vowel difference and later for the smaller one.

Acoustic Stimulation↗