Anna Shestakova

Speech–sound-selective auditory impairment in children with autism: They can perceive but do not attend

In autism, severe abnormalities in social behavior coexist with aberrant attention and deficient language. In the attentional domain, attention to people and socially relevant stimuli is impaired the most. Because socially meaningful stimulus events are physically complex, a deficiency in sensory processing of complex stimuli has been suggested to contribute to aberrant attention and language in autism. This study used event-related brain potentials (ERP) to examine the sensory and early attentional processing of sounds of different complexity in high-functioning children with autism. Acoustically matched simple tones, complex tones, and vowels were presented in separate oddball sequences, in which a repetitive “standard” sound was occasionally replaced by an infrequent “deviant” sound differing from the standard in frequency (by 10%). In addition to sensory responses, deviant sounds elicited an ERP index of automatic sound-change discrimination, the mismatch negativity, and an ERP index of attentional orienting, the P3a. The sensory sound processing was intact in the high-functioning children with autism and was not affected by sound complexity or “speechness.” In contrast, their involuntary orienting was affected by stimulus nature. It was normal to both simple- and complex-tone changes but was entirely abolished by vowel changes. These results demonstrate that, first, auditory orienting deficits in autism cannot be explained by sensory deficits and, second, that orienting deficit in autism might be speech–sound specific.

Abstract phoneme representations in the left temporal cortex: magnetic mismatch negativity study.

We investigated the brain mechanisms enabling one auto-matically discriminate phoneme category irrespective of the large inter-speaker variability in the acoustic features of the voices. For this purpose, subjects were presented with 450 different speech stimuli, each uttered by a different speaker, belonging to three vowel categories, while a 306-channel magnetoencephalogram (MEG) was obtained to record the magnetic counterpart of the mismatch negativity (MMNm), elicited only when sensory memory traces for repetitive sounds are formed in the auditory cortex. Despite this wide acoustic variation, category changes elicited prominent MMNm responses, which were considerably stronger in the left than in the right hemisphere in the right-handed subjects. These results implicate the presence of long-term memory traces for vowels, which can recognize the vowel-specific invariant code enabling correct vowel percept even in the presence of realistic acoustic variation.

Event-related potentials associated with second language learning in children.

OBJECTIVE In this study, we investigated learning-related changes in auditory event-related potentials (ERPs) of Finnish-speaking 3-6-year-old children caused by learning French language. METHODS Using an oddball paradigm, ERPs to sounds of French language were recorded in the two groups of healthy children: those who were learning French (experimental group) and those who were not learning any foreign language (control peers). RESULTS When the children from the experimental group were exposed to the foreign language, they automatically developed French-specific memory traces that helped them to discriminate, categorize, and pronounce utterances of the new language as indicated by the mismatch negativity (MMN) component of the ERPs in a previous study. We found that the learning process was also reflected by changes in P3a and late difference negativity (LDN) responses. Unlike MMN and P3a, the LDN has been discovered relatively recently and its functional role remains unclear. Similarly, as the MMN magnitude increased during the learning process, an increase of the P3a (known to reflect the involuntary attention switching toward deviant stimuli) and LDN amplitudes was observed. The ERPs of the control peers did not change significantly over the test period. CONCLUSIONS When phonemes of a foreign language are learned, this process is accompanied with the increase in the MMN, P3a, and LDN amplitudes in children. Though the functional significance of LDN remains to be further investigated, our results support its possible link to reorienting processes following distraction.

Linguistic relevance of duration within the native language determines the accuracy of speech-sound duration processing.

As indexed by electrophysiological measures, in native speakers of a language with linguistically significant opposition between short and long phonemes, the pre-attentive detection accuracy of duration changes in speech sounds was tuned in comparison with that in non-speech sounds. This was not observed in advanced second-language users of the same language, suggesting that second-language acquisition does not lead to speech-specific tuning of the duration processing as does native language acquisition in early childhood.

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 brains 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.

Children's Auditory Event-Related Potentials Index Sound Complexity and “Speechness”

Childrens long-latency auditory event-related potential (LLAEP) structure differs from that of adults. Functional significance of childhood ERP components is largely unknown. In order to look for the functional correlates in adult and childrens LLAEPs, stimulus-complexity effects were investigated in 8–10-year old children. To this end, auditory ERPs to vowels, acoustically matched complex tones, and sinusoidal tones were recorded. All types of stimuli elicited P100-N250-N450 ERP complex. Differences between the sinusoidal and complex tones were confined to the P100 and N250 peaks, complex tones eliciting larger responses. Vowels elicited smaller-amplitude N250 but larger-amplitude N450 than the complex tones. Some stimulus-complexity effects observed for N250 in children corresponded to those observed for the Nl in adults, whereas the N450 peak exhibited behaviour resembling that of the adult ERP components subsequent to the Nl wave.

Speech-sound duration processing in a second language is specific to phonetic categories

The mismatch negativity (MMN) component of the auditory event-related potential was used to determine the effect of native language, Russian, on the processing of speech-sound duration in a second language, Finnish, that uses duration as a cue for phonological distinction. The native-language effect was compared with Finnish vowels that either can or cannot be categorized using the Russian phonological system. The results showed that the duration-change MMN for the Finnish sounds that could be categorized through Russian was reduced in comparison with that for the Finnish sounds having no Russian equivalent. In the Finnish sounds that can be mapped through the Russian phonological system, the facilitation of the duration processing may be inhibited by the native Russian language. However, for the sounds that have no Russian equivalent, new vowel categories independent of the native Russian language have apparently been established, enabling a native-like duration processing of Finnish.

Auditory stream segregation processes operate similarly in school-aged children and adults

Our previous research with adults suggests that pre-attentive (bottom-up) brain processes govern auditory stream segregation [Sussman et al., 1998. Brain Res. 789, 130--138; Sussman et al., 1999. Psychophysiology 36, 22--34; Winkler et al., submitted for publication]. We investigated whether the pre-attentive mechanisms underlying auditory stream segregation operate similarly in school-aged (7--10 years of age) children and adults. We used an electrophysiological index of auditory change detection that does not require the experimental participant to focus on the sounds to be evoked. In Experiment 1, children were presented with mixtures of high and low frequency tones in different conditions and were instructed to watch a silent video and ignore the sounds. In Experiment 2, children were asked to listen to the same sets of sounds as presented in Experiment 1 and tell whether they heard one or two auditory streams. The pre-attentive processing of the mixture of sounds as one or two auditory streams (Experiment 1), matched with the perception of the sounds as one or two distinct streams (Experiment 2). Our results demonstrate that the mechanisms for auditory stream segregation operate similarly in school-aged children and adults when frequency proximity is the cue for segregation.

Mismatch negativity (MMN) elicited by changes in phoneme length: A cross-linguistic study

Speech sounds representing different phonetic categories are typically easier to discriminate than sounds belonging to the same category. This phenomenon is referred to as the phoneme boundary effect. We aimed to determine whether, at neural level, this effect is indeed due to crossing the phoneme boundary. The mismatch negativity (MMN) brain response was measured for across- and within-category changes in Finnish phoneme length in native speakers and second-language users of Finnish as well as non-Finnish-speaking subjects. The results showed that the MMN amplitude was enhanced in the native speakers in comparison with the two non-native groups which, in turn, did not differ from each other in MMN amplitude. The response pattern to across- and within-category changes, however, was the same in all groups regardless of whether or not they had the phoneme categories. Thus, the responses could not be determined by crossing the phoneme boundary. Rather, the enhancement of MMN amplitude in the native speakers is likely to be due to the activation of native-language phonetic prototypes. The second-language users, however, did not seem to have automatic access to Finnish prototypes.

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.