Biomedical subjects

Paavo Alku

Publications and source records attributed to Paavo Alku.

At least 37 records · Page 2Linked to original sources

PubMed2005

Long-term exposure to occupational noise alters the cortical organization of sound processing.

OBJECTIVE: Long-term exposure to noise may cause an altered hemispheric lateralization of speech processing even in silent conditions. We examined whether this lateralization shift is speech specific or occurs also for other sounds. METHODS: Brain responses from 10 healthy noise-exposed workers (>5 years) and 10 matched controls were recorded with a 32-channel electroencephalogram in two conditions, one including standard and deviant speech sounds, the other non-speech sounds, with novel sounds in both. RESULTS: The deviant-sound elicited mismatch negativity (MMN) was larger to non-speech than speech sounds in control subjects, while it did not differ between the sound types in the noise-exposed subjects. Moreover, the MMN to speech sounds was lateralized to the right hemisphere in exposed workers, while it was left-hemisphere predominant in control subjects. No group topography difference was found for non-speech sounds. The deviant sounds that were close in formant space to the standards elicited a longer MMN latency in both speech and non-speech conditions in exposed subjects than controls. No group differences were found for cortical responses to novel sounds. CONCLUSIONS: Long-term noise exposure altered the strength and the hemispheric organization of speech-sound discrimination and decreased the speed of sound-change processing. SIGNIFICANCE: Subpathological changes in cortical responses to sounds may occur even in subjects without a peripheral damage but continuously exposed to noisy auditory environments.

Adult↗

PubMed2005

Voice symptoms of call-centre customer service advisers experienced during a work-day and effects of a short vocal training course.

Occupational voice users often suffer from voice symptoms to varying extents. The first goal of this study was to find out how telephone customer service advisers experience voice symptoms at different moments of the working day. The second goal was to investigate the effects of a short vocal training course arranged for telephone workers. The results indicate that although the subjects did not suffer from severe voice problems, the short vocal training course significantly reduced some of the vocal symptoms they had experienced. The results suggest that systematic consultation and training for occupational voice users in the field of occupational voice care would be advantageous.

Adult↗

PubMed2005

The perception of phonological quantity based on durational cues by native speakers, second-language users and nonspeakers of Finnish.

Some languages, such as Finnish, use speech-sound duration as the primary cue for a phonological quantity distinction. For second-language (L2) learners, quantity is often difficult to master if speech-sound duration plays a less important role in the phonology of their native language (L1). By comparing the categorization performance of native speakers of Finnish, Russian L2 users of Finnish, and non-Finnish-speaking Russians, the present study aimed to determine whether the L2 users, whose native language does not have a quantity distinction, have been able to establish categories for Finnish quantity. The results suggest that the native speakers and some of the L2 users that have been exposed to Finnish for a longer time have access to phonological quantity categories, whereas the L2 users with shorter exposure and the non-Finnish-speaking subjects do not. In addition, by comparing categorization and discrimination tasks it was found that the native speakers show a phoneme-boundary effect for quantity that is cued by duration only, whereas the non-Finnish-speaking subjects and the subjects with low proficiency in Finnish do not.

Adolescent↗

PubMed2004

The processing of speech and non-speech sounds in aphasic patients as reflected by the mismatch negativity (MMN).

This study compared the discrimination of speech and non-speech sounds in left-hemisphere stroke patients with aphasia and healthy controls by recording event-related potentials (ERPs) and behavioural responses. It was found that the mismatch negativity (MMN) amplitude for vowel and duration changes in speech sounds was diminished in the patients. In contrast, there was no significant difference between the groups in the MMN for comparable frequency and duration changes in non-speech sounds. In the behavioural session, the patients were slower than the control subjects in discriminating duration changes of both types of sounds. These results suggest that left-hemisphere lesions have differential effects on the discrimination of speech and acoustic features indicating that they have separate neural substrates.

Acoustic Stimulation↗

PubMed2004

Glides in speech fundamental frequency are reflected in the auditory N1m response.

The cortical dynamics underlying the perception of constant and gliding speech fundamental frequency (F0) was investigated in 10 subjects using magnetoencephalography (MEG). The stimuli comprised vowels having either constant, ascending or descending F0s and tones of corresponding frequencies, matched with the vowels in intensity or loudness. The amplitude of the N1m response was highly sensitive to F0 variation embedded in vowels and insensitive to corresponding variation in tones. The latency of the N1m elicited by the tones with respect to vowels was significantly delayed. Thus, the speech-specific behavior of the N1m arises out of cortical sensitivity to the acoustic structure of voiced speech, that is to the F0 and its harmonics, which underlie the perception of pitch and intonation in speech.

Acoustic Stimulation↗

PubMed2004

Estimating perceived phonatory pressedness in singing from flow glottograms.

The normalized amplitude quotient (NAQ), defined as the ratio between the peak-to-peak amplitude of the flow pulse and the negative peak amplitude of the differentiated flow glottogram and normalized with respect to period time, has been shown to be related to glottal adduction. Glottal adduction, in turn, affects mode of phonation and hence perceived phonatory pressedness. The relationship between NAQ and perceived phonatory pressedness was analyzed in a material collected from a professional female singer and singing teacher who sang a triad pattern in breathy, flow, neutral, and pressed phonation in three different loudness conditions (soft, middle, loud). In addition, she also sang the same triad pattern in four different styles of singing, classical, pop, jazz, and blues, in the same three loudness conditions. A panel of experts rated the degree of perceived phonatory press along visual analogue scales. Comparing the obtained mean rated pressedness ratings with the mean NAQ values for the various triads showed that about 73% of the variation in perceived pressedness could be accounted for by variations of NAQ.

Acoustics↗

PubMed2004

Automatic and controlled processing of acoustic and phonetic contrasts.

Changes in the temporal properties of the speech signal provide important cues for phoneme identification. An impairment or inability to detect such changes may adversely affect one's ability to understand spoken speech. The difference in meaning between the Finnish words tuli (fire) and tuuli (wind), for example, lies in the difference between the duration of the vowel /u/. Detecting changes in the temporal properties of the speech signal, therefore, is critical for distinguishing between phonemes and identifying words. In the current study, we tested whether detection of changes in speech sounds, in native Finnish speakers, would vary as a function of the position within the word that the informational changes occurred (beginning, middle, or end) by evaluating how length contrasts in segments of three-syllable Finnish pseudo-words and their acoustic correlates were discriminated. We recorded a combination of cortical components of event-related brain potentials (MMN, N2b, P3b) along with behavioral measures of the perception of the same sounds. It was found that speech sounds were not processed differently than non-speech sounds in the early stages of auditory processing indexed by MMN. Differences occurred only in later stages associated with controlled processes. The effects of position and attention on speech and non-speech stimuli are discussed.

Acoustic Stimulation↗

PubMed2004

Neurophysiologic correlates of deficient phonological representations and object naming in prematurely born children.

OBJECTIVE: The aim of this follow-up study was to evaluate the development of object naming ability and auditory processing in prematurely born children. Furthermore, we investigated whether the mismatch negativity (MMN) parameters at the age of 4 years correlate with the MMN parameters and naming ability at the age of 6 years. METHODS: Twelve very low birth weight (VLBW) preterm children (mean age 5 years 7 months) and matched controls were studied. Object naming was measured by the Boston naming test. Auditory event-related potentials (ERPs), especially the MMN, were recorded for Finnish syllables (standard /taa/; deviants /ta/ and /kaa/) in an oddball paradigm. RESULTS: VLBW preterm children scored significantly lower in the object naming test than their controls. The MMN amplitude for consonant change was significantly smaller in the preterm group compared to the controls. The MMN amplitude at the age of 4 years correlated with the MMN amplitude at the age of 6 years. Furthermore, absence of the MMN at the age of 4 years predicted naming difficulties at the age of 6 years. CONCLUSIONS: VLBW preterm children with a difficulty to preattentively discriminate changes in syllables, as indexed by the diminished change detection response, MMN, seem to have sustained naming difficulty. Therefore, it is reasonable to record the MMN along with the language development from infancy, in order to identify the children at risk for language deficiencies and to provide appropriate rehabilitation.

Auditory Perception↗

PubMed2004

Automatic auditory processing of english words as indexed by the mismatch negativity, using a multiple deviant paradigm.

OBJECTIVE: The aim of this study was to investigate mismatch negativity (MMN) responses to a variety of speech stimuli (/de:/, /ge:/, /deI/ "day", and /geI/ "gay") in a multiple deviant paradigm. It was hypothesized that all speech stimulus contrasts in the multiple deviant paradigm, including the fine acoustic speech contrast [d/g], would elicit robust MMN responses and that consonant vowel (CV) real word deviants (e.g., "day" and "gay") would elicit larger MMN responses than CV nonword deviants (e.g., "de" and "ge") within and across experimental contrasts. DESIGN: Ten healthy, right-handed, native English-speaking adults (23.4 +/- 2.27 yr) with normal hearing were presented with 12 blocks of stimuli, using a multiple deviant oddball paradigm. Each of the four speech stimuli were presented as standards (p = 0.7) in three blocks, with the remaining stimuli acting as deviants (p = 0.1 each). Subjects were also presented with the same stimuli in a behavioral discrimination task. RESULTS: MMN responses to the fine acoustic speech contrast [d/g] (e.g., "de" versus "ge", "day" versus "gay") did not reach significance. However, a significant and larger MMN response was obtained at an earlier latency to the real word deviants among nonword standards with the same initial consonant (i.e., de-->day, ge-->gay) when compared with the responses to nonword deviants among word standards (day-->de, gay-->ge). CONCLUSIONS: The results showed that MMN responses could be elicited by speech stimuli with large, single acoustic deviances, within a multiple deviant paradigm design. This result has positive clinical implications for the testing of subjects who may only tolerate short testing sessions (e.g., pathological populations) in that responses to a wider range of speech stimuli may be recorded without necessarily having to increase session length. The results also demonstrated that MMN responses were elicited by large, single acoustic deviances but not fine acoustic deviances within the speech stimuli. The poor results for the fine acoustic deviances support previous studies that have used single contrast paradigms and found that when carefully controlled methodological designs and strict methods of analysis are applied, robust responses to fine-grained CV syllable contrasts may be difficult to obtain. The enhanced MMN observed in response to the real word deviants among nonword standards may provide further evidence for the presence of long-term neural traces for words in the brain, however possible contextual effects limit the interpretation of these data. Further research is needed to investigate the ability of the MMN response to accurately reflect speech sounds with fine acoustic contrasts, as well as the ability of the MMN to reflect neural traces for words in the brain, before it can be reliably used as a clinical tool in the investigation of spoken word processing in pathological populations.

Adult↗

PubMed2004

Processing of English words with fine acoustic contrasts and simple tones: a mismatch negativity study.

The purpose of this study was to compare the robustness of the event-related potential (ERP) response, called the mismatch negativity (MMN), when elicited by simple tone stimuli (differing in frequency, duration, or intensity) and speech stimuli (CV nonword contrast /de:/ vs. /ge:/ and CV word contrast /del/ vs. /gel/). The study was conducted using 30 young adult subjects (Groups A and B; n = 15 each). The speech stimuli were presented to Group A at a stimulus onset asynchrony (SOA) of 610 msec and to Group B at an SOA of 900 msec. The tone stimuli were presented to both groups at an SOA of 610 msec. MMN responses were elicited by the simple tone stimuli (66.7%-96.7% of subjects with MMN "present," or significantly different from zero, p < 0.05) but not the speech stimuli (10% subjects with MMN present for nonwords, 10% for words). The length of the SOA (610 msec or 900 msec) had no effect on the ability to obtain consistent MMN responses to the speech stimuli. The results indicated a lack of robust MMN elicited by speech stimuli with fine acoustic contrasts under carefully controlled methodological conditions. The implications of these results are discussed in relation to conflicting reports in the literature of speech-elicited MMNs, and the importance of appropriate methodological design in MMN studies investigating speech processing in normal and pathological populations.

Acoustic Stimulation↗

PubMed2003

The auditory N1m reveals the left-hemispheric representation of vowel identity in humans.

The cortical correlates of the perception of the sustained vowels /a/, /o/ and /u/ were studied by using whole-head magnetoencephalography (MEG). The three vowels which were located on a line in the space spanned by the first (F1) and second (F2) formants and having equal F2-F1 differences evoked equally strong auditory N1m responses at 120 ms after stimulus onset. The left-hemispheric distribution of the source locations, estimated by equivalent current dipoles, reflected the acoustic similarity of the vowels: the growing distance of the vowels in the F2,F1-space was accompanied by a growing distance between the centres of gravity of activation elicited by each vowel. Thus, direct evidence for the orderly left-hemispheric representation of phonemes in human auditory cortex was found.

Adult↗

PubMed2003

Deficient speech-sound processing, as shown by the electrophysiologic brain mismatch negativity response, and naming ability in prematurely born children.

Very low birth weight (VLBW, <1500 g) preterm birth has been associated with anatomic abnormalities in brain development and cognitive and language disorders. We examined object naming ability, and an electrophysiologic index of auditory sensory discrimination of speech sounds (the mismatch negativity, MMN) in 4-year-old VLBW prematurely born children. We found that half of the VLBW children were inferior to their controls in the object naming ability. Also the MMN amplitudes were smaller in the preterm group as compared with the controls. Further, the MMN amplitude varied as a function of children's performance on object naming, such that the weaker object-naming performance of the preterm group was paralleled by the diminished MMN amplitudes. Therefore, difficulties in auditory discrimination seem to be implicated in language difficulties encountered in VLBW prematurely born children.

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↗

PubMed2003

Automatic pre-segmentation of running speech improves the robustness of several acoustic voice measures.

In order to study vocal loading, we developed a speech analysis environment for continuous speech. The objective was to build a robust system capable of handling large amounts of data while minimizing the amount of user-intervention required. The current version of the system can analyze up to five-minute recordings of speech at a time. Through a semiautomatic process it will classify a speech signal into segments of silence, voiced speech and unvoiced speech. Parameters extracted from the input signal include fundamental frequency, sound pressure level, alpha-ratio and speech segment information such as the ratio of speech to silence. This paper presents results from the performance evaluation of the system, which shows that the analysis environment is able to perform robust and consistent measurements of continuous speech.

Algorithms↗

PubMed2002

Context modulates processing of speech sounds in the right auditory cortex of human subjects.

Using whole-head magnetoencephalography, we studied how context affects processing of speech sounds by recording the magnetic counterpart (MMNm) of the mismatch negativity (MMN) event-related potential, which is elicited in the auditory cortex by a contrast between infrequent and frequent auditory stimuli. In Experiment 1, in the right, but not in the left, hemisphere auditory cortex, a contrast of consonant-vowel syllables elicited a stronger MMNm when presented within a word context than when occurring alone. Further, in Experiment 2, these same syllable contrasts were processed in the right auditory cortex more strongly when embedded in a non-speech sound context than when presented alone. This facilitation thus was insensitive to the phonetic and semantic features of the context but might nevertheless reflect the participation of the right hemisphere in speech perception.

Acoustic Stimulation↗

PubMed2002

Mismatch negativity shows that 3-6-year-old children can learn to discriminate non-native speech sounds within two months.

Using 3-6-year-old children as subjects, we describe the neural plasticity accompanying the concurrent learning of a foreign language in a natural environment. Children were monitored for 6 months as they either enrolled in schools or daycare centers where only Finnish was spoken (Control group) or as they joined a French school or a daycare center where French was spoken 50-90% of the time (Experimental group). Whereas mismatch negativity (MMN)--a brain's electrical change-detection response--for a French speech contrast was initially absent or very small in both groups, it was conspicuous 2 months after Finnish children had joined a French kindergarten. Consequently, the data suggest that youngsters can learn to distinguish non-native speech sounds in natural language environment without any special training in just a couple of months. Accordingly, these data herald the vast potential MMN may entail for studying language learning, especially in situations where behavioral responses cannot be readily elicited.

Analysis of Variance↗

PubMed2002

Human cortical dynamics determined by speech fundamental frequency.

Evidence for speech-specific brain processes has been searched for through the manipulation of formant frequencies which mediate phonetic content and which are, in evolutionary terms, relatively "new" aspects of speech. Here we used whole-head magnetoencephalography and advanced stimulus reproduction methodology to examine the contribution of the fundamental frequency F0 and its harmonic integer multiples in cortical processing. The subjects were presented with a vowel, a frequency-matched counterpart of the vowel lacking in phonetic contents, and a pure tone. The F0 of the stimuli was set at that of a typical male (i.e., 100 Hz), female (200 Hz), or infant (270 Hz) speaker. We found that speech sounds, both with and without phonetic content, elicited the N1m response in human auditory cortex at a constant latency of 120 ms, whereas pure tones matching the speech sounds in frequency, intensity, and duration gave rise to N1m responses whose latency varied between 120 and 160 ms. Thus, it seems that the fundamental frequency F0 and its harmonics determine the temporal dynamics of speech processing in human auditory cortex and that speech specificity arises out of cortical sensitivity to the complex acoustic structure determined by the human sound production apparatus.

Adult↗

PubMed2002

Sound complexity and 'speechness' effects on pre-attentive auditory discrimination in children.

The evidence in adults suggests that at a cortical level simple and complex sounds are processed by partly divergent subsystems. In children, central processing of sounds differing in complexity has not been investigated. Therefore, the present study examined preconscious discrimination of the differences in sound frequency and duration as a function of sound complexity in 8-10-year-old children. A mismatch negativity (MMN) component of auditory event-related potentials was elicited in a paradigm where 'deviant' (rare) stimuli were either shorter in duration or higher in frequency than the 'standard' (repetitive) sounds. Vowels and vowel-matched complex and simple tones were presented in separate sequences. The stimulus complexity effects were sizable and appeared as larger areas and shorter and more consistent latencies of the MMNs, elicited by more complex stimuli. In addition, the vowel frequency MMN showed left hemisphere preponderance compared to the complex tone frequency MMN. No such effect was found for the duration decrement MMNs. In addition, the complex tone duration decrement MMN was distributed posteriorly to either the vowel or sinusoidal tone MMNs. A late discriminative negativity, LDN, did not show consistent effects of sound complexity. In conclusion, acoustically rich sound content facilitates auditory sensory discrimination in 8-10-year-old children. The sound 'speechness' effects were not as robust though present. Unlike adults, children demonstrated high intersubject variability in discriminating spectrally poor, but not rich, sounds. The discrimination of the sound duration appears to differ from that of the sound frequency in nature and, consequently, in the neural substrates.

Acoustic Stimulation↗