Asymmetric interaural generalization of learning gains in a speech-in-noise identification task.

The pattern of generalization of learning gains to untrained conditions in adult human perceptual skill learning has been used as an effective behavioral probe for studying the functional organization of the learning system. Learning gains were previously reported to generalize symmetrically between the ears for tonal stimuli. However, given the open question concerning the specialization of the hemispheres in the processing of speech sounds, it is not clear whether symmetrical interaural generalization will follow training on such stimuli. Here the effect of monaural single-session training on the identification of consonant-vowel stimuli in noise was examined. Participants showed similar robust gains in performance at 24 h post-training in both trained ears. There was, however, an asymmetrical generalization of the learning gains from the trained to the untrained ear, with more transfer from the right-trained to the left-untrained ear than vice versa. Training and transfer gains were retained for both ears over an interval of several months, although for the untrained ear a brief exposure was necessary to relearn the task. These results provide first-time evidence for an asymmetry in interaural generalization for speech sounds following training and provide further support to the lateralization of speech sounds along the auditory system.

Newborn screening for congenital cytomegalovirus using real-time polymerase chain reaction in umbilical cord blood.

BACKGROUND: Congenital cytomegalovirus (C-CMV) infection affects 0.4-2% of newborn infants in Israel, most of whom are asymptomatic. Of these, 10-20% will subsequently develop hearing impairment and may have benetitted from early detection by neonatal screeing. OBJECTIVES: To retrospectively anaIyze the results of a screening program for C-CMV performed at the Sheba Medical Center, Tel, Hashomer, during a 1 year period, using real-time polymerase chain reaction (rt-PCR) from umbilical cord blood. METHODS: CMV DNA was detected by rt-PCR performed on infants' cord blood. C-CMV was confirmed by urine culture (Shell-vial). All confirmed cases were further investigated for C-CMV manifestations by head ultrasound, complete blood count, liver enzyme measurement, ophthalmology examination and hearing investigation. RESULTS: During the period 1 June 2009 to 31 May 2010, 11,022 infants were born at the Sheba Medical Center, of whom 8105 (74%) were screened. Twenty-three (0.28%) were positive for CMV and 22 of them (96%) were confirmed by urine culture. Two additional infants, who had not been screened, were detected after clinical suspicion. All 24 infants were further Investigated, and 3 (12.5%) had central nervous system involvement (including hearing impairment) and were offered intravenous ganciclovir for 6 weeks. Eighteen infants (82%) would not otherwise have been diagnosed. CONCLUSION: The relatively low incidence of C-CMV detected in our screening program probably reflects the low sensitivity of cord blood screening. Nevertheless, this screening program reliably detected a non-negligible number of infants who could benefit from early detection. Other screening methods using saliva should be investigated further.

Evidence for atypical auditory brainstem responses in young children with suspected autism spectrum disorders.

AIM: The aim of this study was to characterize the auditory brainstem responses (ABRs) of young children with suspected autism spectrum disorders (ASDs) and compare them with the ABRs of children with language delay and with clinical norms. METHOD: The ABRs of 26 children with suspected ASDs (21 males, five females; mean age 32.5 mo) and an age- and sex-matched group of 26 children with language delay (22 males, four females) were analysed. All children had normal hearing. The absolute latencies of waves I, III, and V, and interpeak latencies (IPLs) I to III, I to V, and III to V of the group with ASDs and the group with language delay were compared. Data from both groups were further compared with clinical norms. RESULTS: All absolute latencies and IPLs were significantly prolonged in the group with suspected ASDs compared with the group with language delay, excluding IPL III-V (all p-values <0.05) and with clinical norms (all p-values <0.001; IPL III-V, p<0.05). Significant prolongation of absolute and IPLs was also evident in the group with language delay compared with clinical norms, excluding IPL III to V (all p-values <0.001). The prevalence of abnormal findings in two or more absolute latencies was found to be significantly higher in the group with ASDs (50%) than in the group with language delay (8%; p=0.002). INTERPRETATION: The results provide first-time evidence for a neurodevelopmental brainstem abnormality that is already apparent in young children with suspected ASD and language delay. The overlap in ABR findings supports the assertion that an auditory processing deficit may be at the core of these two disorders.

Does feedback matter in an auditory frequency discrimination learning task?

While it is well known that an auditory training of normal-hearing adults can result in significant learning gains, less in known about the influence of feedback on such gains. The objectives of the present study were: (1) to investigate the influence of feedback on the performance of a frequency discrimination task; (2) to compare the learning-dependent gains between different feedback training protocols, and (3) to evaluate the influence of background noise on the efficiency of the auditory learning. Two groups of normal-hearing subjects participated in a single-session training. The session comprised of nine difference limen frequency (DLF) thresholds for 1 kHz in background noise using a three-interval, two-alternative forced choice paradigm (n = 17). One group of eight participants ('feedback-first' group) was trained using visual feedback in the first three thresholds estimations followed by three estimations with no feedback and then by another three estimations with feedback. For the second group of nine participants ('feedback-later' group), feedback was provided in the reversed order. Additional two DLF measurements were performed with feedback in both groups in quiet. Our results show that: 1) auditory learning of a frequency discrimination task using an adaptive procedure can occur whether feedback is provided or not; 2) changing the strategy of feedback in the middle of the training session discontinued the effect of training; and 3) the protocol of feedback by which listeners started with, seemed to determine their strategy of learning. The results support the notion that the adult learning mechanism may be limited by the initial strategy of learning to which it is introduced. Nevertheless, similar gains in performance can be obtained, regardless of the provision of the strategy adopted by the listener.

Logarithmic Versus Linear Change in Step Size When Using an Adaptive Threshold-Seeking Procedure in a Frequency Discrimination Task: Does It Matter?

Different rules for changing step sizes (e.g., logarithmic, linear) are alternately used in adaptive threshold-seeking procedures, with no clear justification. We hypothesized that the linear rule may yield more accurate thresholds for poor performers because the step sizes are predetermined and fixed across listeners and thus can be small, in contrast to the logarithmic rule, in which step sizes are changed with respect to the listener's performance. Purpose The aim of this study was to test the effect of logarithmic and linear rules on frequency discrimination (FD) thresholds. Method Three experiments involving human subjects and Monte Carlo computer simulations were designed and conducted. In the 1st experiment, FD thresholds were estimated in 40 young adults with either 3-interval 2-alternative forced choice (3I2AFC; n = 19) or 2-interval 2AFC (n = 21) in a within-subject design. In the 2nd experiment, thresholds were estimated in 16 children (7-8 years old) in a within-subject design, using 3I2AFC. In the 3rd experiment, thresholds were estimated in 30 young adults in a between-subjects design using 3I2AFC. Results No significant differences were shown between the 2 rules, regardless of age group, method, or level of FD performance. Computer simulations supported the empirical findings, predicting similar FD thresholds for both rules in the majority of runs. However, they also yielded more accurate thresholds with the linear rule, but with a larger number of outliers, which increased as the listener's attention level decreased. Conclusion Overall, the use of a particular rule has little influence on FD thresholds. Possible outliers may be minimized by monitoring the participant's attention at the beginning of the run.

Training of Speech Perception in Noise in Pre-Lingual Hearing Impaired Adults With Cochlear Implants Compared With Normal Hearing Adults.

BACKGROUND: Speech perception in noise remains a significant challenge for cochlear implant (CI) users in everyday life. It has been argued that training to use the information provided by the CI is as important as technological advances. So far, however, only few studies have trained speech perception in noise, most (if not all) included postlingually deafened CI adult users using non-sentence training material. OBJECTIVE: To assess the effect of training on a speech perception in noise task in prelingually hearing-impaired CI users with years of CI experience, as compared with normal-hearing (NH) young adults, following single- and multi-session training using the same training protocol. METHODS: Participants included 22 CI users with prelingual hearing loss and 30 NH. The Hebrew version of the Matrix sentence-in-noise test was used for training. All participants took part in a single training session. Six NH and seven CI continued training for four additional training sessions. All seven CI users trained for additional 5 days, totaling 10 training sessions. Generalization and retention of learning gains were assessed. RESULTS: Following single-session training, CI users showed speech reception thresholds in noise (SRTn) that were 9 to 10 dB higher than NH. After 5 first days of training, five of seven CI users reduced this disadvantage by half. After 10 days of training the CI improved performance by 4.1 dB SNR. No generalization and partial retention of learning were demonstrated. CONCLUSIONS: The present study is the first to demonstrate the course of learning and improvements in SRTn following training speech perception in noise in CI users with prelingual hearing loss.

Generalization to untrained conditions following training with identical stimuli.

It has recently been documented that perceptual learning occurs in the absence of perceived differences between stimuli. This finding supports the notion that stimuli do not have to be highly discriminable in order to elicit learning effects. It is not clear, however, whether additional characteristics of perceptual learning, such as generalization of the learning gains, will be demonstrated in this type of training. Thus, the goals of the present study were to compare the effects of type of training, i.e. adaptive versus fixed with identical stimuli on (1) difference limen for frequency (DLF) thresholds; and (2) the extent of generalization of the learning gains to an untrained frequency and the untrained ear. Twelve adult participants with normal hearing were randomly assigned into two experimental groups: an 'adaptive' group and a 'fixed' group. A single-session frequency discrimination training/testing protocol was conducted in which participants were assessed using three 1,000 Hz DLF testing intervals separated by two training intervals. In the 'adaptive' group, each training interval consisted of tone pairs that varied in a 2-down 1-up adaptive procedure. In the 'fixed' group, each training interval consisted of identical 1,000 Hz tone pairs. Following the training/testing protocol, two untrained conditions were tested: a 2,000 Hz untrained frequency and the untrained ear. Results show that: (1) training on a DLF task with identical stimuli improved performance; (2) the type of training (i.e., 'adaptive' versus 'fixed' with identical stimuli) did not influence the amount of gains in performance; (3) learning generalized to an untrained frequency but to a lesser extent in the 'fixed' group with identical stimuli compared to the 'adaptive' group; and (4) learning generalized to the untrained ear for both groups. Thus, training with identical stimuli appears to promote auditory perceptual learning in a frequency discrimination task that generalizes, to some extent, to untrained conditions. These findings support the hypothesis that top-down attention processes and not only bottom-up processes may play an important role in auditory perceptual learning.

Speech perception enhanced by noise in listeners with normal hearing.

Most often, noise is considered a major factor in the degradation of listening conditions. Recently, however, there is increasing evidence suggesting that the addition of low-intensity noise can improve signal detection in non-linear systems. While this phenomenon has been described in physical systems, very little has been documented regarding its functional significance in the human sensory system in general, and in the auditory system in particular. The purpose of the present study was to investigate the benefit of adding noise to the recognition of speech already embedded in background noise. Participants included 27 adults with normal hearing, between 20 and 30 years of age. Speech stimuli were consonant-vowel-consonant monosyllabic words. Babble noise (BN) was added until word recognition dropped to threshold levels (below 50%). Additional low-level noise (LLN) was added to the words + BN in an alternating design (i.e., words + BN + LLN, words + BN, etc.). For each participant, word recognition scores were based on 25 words in BN and 25 words in BN + LLN. The number of words was distributed unequally across the conditions. The results show that for 63% of the participants, adding LLN enhanced scores significantly by 4-32%. Of these participants, 70% showed that adding LLN to speech-in-noise improved performance by more than 12%. Additional noise seems to help when word recognition score in BN was lower than 50%. These results provide first-time evidence for the benefit of low-intensity noise in order to enhance speech-in-noise in hearing listeners.

Is the Role of External Feedback in Auditory Skill Learning Age Dependent?

Purpose: The purpose of this study is to investigate the role of external feedback in auditory perceptual learning of school-age children as compared with that of adults. Method: Forty-eight children (7-9 years of age) and 64 adults (20-35 years of age) conducted a training session using an auditory frequency discrimination (difference limen for frequency) task, with external feedback (EF) provided for half of them. Results: Data supported the following findings: (a) Children learned the difference limen for frequency task only when EF was provided. (b) The ability of the children to benefit from EF was associated with better cognitive skills. (c) Adults showed significant learning whether EF was provided or not. (d) In children, within-session learning following training was dependent on the provision of feedback, whereas between-sessions learning occurred irrespective of feedback. Conclusions: EF was found beneficial for auditory skill learning of 7-9-year-old children but not for young adults. The data support the supervised Hebbian model for auditory skill learning, suggesting combined bottom-up internal neural feedback controlled by top-down monitoring. In the case of immature executive functions, EF enhanced auditory skill learning. This study has implications for the design of training protocols in the auditory modality for different age groups, as well as for special populations.

Can learning a frequency discrimination task occur without discrimination?

Following a recent report by Moore (Auditory learning: implications for speech perception. Proceedings of ISCA Workshop on Plasticity in Speech Perception [PSP2005], London, UK, 2005), showing in a frequency discrimination task that perceptual learning can occur in the absence of perceived stimuli, we further investigated the effects of training with identical stimuli (i.e. no perceptual difference between the stimuli) on frequency discrimination thresholds (DLF) and evaluated the influence of task demands on the degree of improvement following such training. A total of 20 adult normal-hearing participants were randomly assigned into three experimental groups: a "DLF-task" group, a "DLI-task" group, and a control group. For all groups, three DLF thresholds were obtained using an adaptive technique with feedback. For the two experimental groups, training was provided using two intervals of identical tone pairs. The participants in the "DLF-task" group were asked to select the tone with the higher pitch, whereas the participants in the "DLI-task" group, were instructed to select the louder of two tones. For the control group, DLF threshold-seeking tests were separated by two time intervals with no training. The results showed that: (1) training on a DLF task with identical stimuli can improve performance; (2) limited exposure to the stimuli and task in a group of naive listeners can already induce significant fast changes in performance; and (3) changing the task demands (i.e. to a DLI task) reduced improvement compared to the control group, which may suggest an interference with DLF learning. These results support the notion that perceptual learning can occur even in the absence of perceived stimuli. These findings shed light on the mechanisms that are involved in and influence auditory perceptual learning.

The effect of number of perceptual categories on identification functions of non-speech stimuli and the relationship to categorization of Hebrew voicing.

Category boundary (CB) of Hebrew voicing on voice-onset time (VOT) continuum was found to be different from non-speech stimuli on tone-onset time (TOT) continuum. This is in contrast to data in English, thus suggesting that CB for speech stimuli may be determined not only by general auditory sensitivities but by additional factors that may be speech specific. The data in Hebrew voicing, however, can also be explained by the fact that in Hebrew voicing, two categories were available to the listener, whereas for the TOT stimuli there were three: leading, simultaneous and lagging temporal events. The purpose of the present study was to investigate the effect of number of perceptual categories on CB of non-speech analogs of voicing in Hebrew-speaking subjects and compare them to those obtained on a VOT continuum. Twenty-four Hebrew-speaking adults participated in this study. Stimuli consisted of (a) a two-tone complex continuum that varied in the relative onset time of the lower frequency tone, and (b) a /ba-pa/ continuum which varied in VOT values similar to (a). The same TOT continuum was tested twice. In one, subjects identified TOT stimuli as belonging to one of three categories (TOT3): leading, simultaneous, or lagging; and in the other to two categories of TOT (TOT2): leading or lagging. VOT stimuli were labeled as /ba/ or /pa/. Results show that (1) when listeners were offered only two perceptual categories of temporal events, the pattern of identification functions matched one of the two functions shown for TOT3, and (2) the category boundary of VOT stimuli was similar for all subjects regarding the value calculated for TOT2. The present study supports the hypotheses that (1) CB of non-speech stimuli is not influenced by the number of perceptual categories available to the listener, and (2) different mechanisms may underlie the categorical perception of speech versus non-speech stimuli.

Frequency discrimination training: is there ear symmetry?

While it is well documented that significant improvements in a frequency discrimination task occur following training of normal-hearing adult subjects, less is known about the symmetry between the ears. The objectives of the present study were (1) to compare the first obtained DLF thresholds between left and right ears, (2) to determine whether single-session training would result in similar improvements in those subjects trained in the right ear versus those trained in the left ear, and (3) to evaluate the generalization of learning to the untrained ear and compare its extent between the left and right ears. Two groups of 10 normal-hearing subjects participated in a single-session training. One group of 10 subjects was trained in the left ear and the second group of 10 additional subjects was trained in the right ear. Single-session training consisted of 10 difference limen frequency (DLF) thresholds for 1 kHz using a two-interval, two-alternative forced choice paradigm. Generalization to the untrained ear was tested 24 hours post-training. Our results show that: (1) No significant differences were found in the first obtained DLF thresholds between left and right ears; (2) Similar improvement in DLF thresholds occurred in both ears for single-session training; and (3) Twenty-four hours post-training, learning generalized to the untrained ear with similar generalization to both ears. Future studies are required in order to establish whether this symmetry is maintained with verbal stimuli and/or after multi-session training.

Frequency discrimination thresholds: the effect of increment versus decrement detection of frequency.

Difference limen for frequency (DLF) is traditionally tested using a frequency increment detection paradigm in which listeners are requested to distinguish between a reference tone and a series of comparison tones of higher frequency. Sporadic findings indicated that an increment paradigm is not necessarily comparable to a decrement paradigm, in which the comparison tones are lower than the reference tone. The purpose of the present study was to test whether the ability to detect frequency increments is different from that of frequency decrements. DLFs of 16 young women were measured at 200 Hz and 1,000 Hz, using detection of both frequency increment and decrement paradigms. Results indicated that: (1) the frequency increment detection paradigm was significantly smaller (i.e., superior) to the decrement paradigm for the DLF task at 200 Hz, (2) for both frequencies, the number of participants who exhibited better DLF using the frequency increment detection paradigm was significantly larger than the number of those who had better DLFs using the frequency decrement paradigm, and (3) for both frequencies, strong correlations were found between DLFs obtained in the increment versus the decrement paradigms. These results have implications: (1) to studies whose subjects may have reduced sensitivities at frequencies higher than the reference tone (such as the hearing impaired), and (2) to models related to the role of auditory feedback on voice accuracy and to the underlying processes of frequency discrimination.

The effect of gender on a frequency discrimination task in children.

BACKGROUND: Physiological and behavioral sex-related differences have been previously reported in the human auditory system, although data are limited to adults and are equivocal. While physiological evidence showed some advantage for females, psychophysical data tended to show greater sensitivity for males in several auditory tasks. Possible explanations for the gender effect in the auditory system include differences between the sexes in physical dimensions of the ear, brain anatomy, exposure to androgens prenatally and/or at puberty, and/or environmental factors (e.g., auditory experience). The purpose of the present study was to investigate sex-related differences in an auditory frequency discrimination task in children prior to puberty. METHODS: A total of 24 normal-hearing children were divided into two age groups: 7- and 8-year-olds, with six girls and six boys in each age group. All children took part in a testing session that consisted of three Difference Limen for Frequency (DLF) measurements. Cognitive tests were also conducted. RESULTS: RESULTS showed that (a) boys outperformed the girls regardless of age; (b) age effect was significant, with older children performing better than the younger ones, irrespective of gender; (c) intrameasurement variance was smaller for the older children; and (d) age, gender, and auditory working memory and capacity explained over 65% of the variance in DLF thresholds. This is the first evidence of a gender effect in the auditory system in children prior to puberty. CONCLUSIONS: This evidence suggests that it is more likely that inherent physiological differences between the sexes influence the differential outcomes reported in the present study.

Evidence for a right cochlear implant advantage in simultaneous bilateral cochlear implantation.

OBJECTIVES/HYPOTHESIS: To compare speech perception performance with right versus left cochlear implants (CIs) in children with bilateral CIs implanted simultaneously. STUDY DESIGN: Prospective case series of patients undergoing simultaneous bilateral cochlear implantation. METHODS: Speech perception performance was tested in 10, right-handed children who received bilateral CIs simultaneously between 11 and 36 months (mean, 21 months), had at least 18 months of bilateral CI use, and were 5.3 years of age during testing. All children exhibited bilateral symmetrical severe-to-profound hearing loss prior to implantation and did not benefit from hearing aids. Speech perception performance was evaluated with the right CI and the left CI by means of an open-set monosyllabic word test in quiet presented at 45 dB HL in a sound field. RESULTS: All children exhibited higher performance with the right CI compared to the left CI. Group mean performance with the right CI was 66.5% compared to 52% with the left CI (P = .002), yielding a 14.5% difference. With increasing duration of bilateral CI use and age at evaluation, the right-left difference increased (r = 0.72, P = .019 and r = 0.74, P = .014, respectively). CONCLUSIONS: Current preliminary data indicate that children with bilateral CIs implanted simultaneously exhibit a significant right ear advantage for speech. Similarly to reports on normal-hearing children, right ear preference for speech increased with increasing age and auditory-linguistic experience. Thus, simultaneous bilateral cochlear implantation may lead to normal development of auditory pathways and may be an important contributor to the superior auditory, language, and communication skills reported in children with bilateral versus unilateral CIs.

Preauricular skin tags and ear pits are associated with permanent hearing impairment in newborns.

OBJECTIVES: Our goals were to (1) study the prevalence of hearing impairment in a large cohort of infants with preauricular skin tags or ear pits and compare it with that among all other newborns participating in our universal newborn hearing screening program during the same period and (2) evaluate the effectiveness of transient evoked otoacoustic emissions as a hearing-screening tool in this population. PATIENTS AND METHODS: During the study period of 7.5 years, 68484 infants were screened for hearing impairment, of whom 637 (0.93%) had preauricular skin tags and/or ear pits. The population was divided into 3 groups: (1) a low-risk group for hearing impairment; (2) a high-risk group for hearing impairment; and (3) a very high-risk group for hearing impairment. The screening results and audiological follow-up for these infants were examined retrospectively. RESULTS: A significantly higher prevalence of permanent hearing impairment was found among infants with preauricular skin tags or ear pits (8 of 1000), compared with infants without tags or pits (1.5 of 1000). In the low-risk group, the prevalence was 3.4 of 1000, compared with 0.5 of 1000 in infants with and without preauricular tags or pits, respectively. In the high-risk group, the prevalence was 77 of 1000, compared with 20 of 1000 in infants with and without preauricular tags or pits, respectively. The odds ratio for hearing impairment associated with preauricular skin tags and/or ear pits after adjusting for level of risk group was 4.9. All infants diagnosed with permanent hearing impairment, with the exception of 1 with late-onset impairment, were detected by in-hospital transient-evoked otoacoustic emissions screening. CONCLUSIONS: Infants with preauricular skin tags or ear pits are at increased risk for permanent hearing impairment. Transient-evoked otoacoustic emissions were found to be an effective hearing-screening tool in this population.

A latent consolidation phase in auditory identification learning: time in the awake state is sufficient.

Large gains in performance, evolving hours after practice has terminated, were reported in a number of visual and some motor learning tasks, as well as recently in an auditory nonverbal discrimination task. It was proposed that these gains reflect a latent phase of experience-triggered memory consolidation in human skill learning. It is not clear, however, whether and when delayed gains in performance evolve following training in an auditory verbal identification task. Here we show that normal-hearing young adults trained to identify consonant-vowel stimuli in increasing levels of background noise showed significant, robust, delayed gains in performance that became effective not earlier than 4 h post-training, with most participants improving at more than 6 h post-training. These gains were retained for over 6 mo. Moreover, although it has been recently argued that time including sleep, rather than time per se, is necessary for the evolution of delayed gains in human perceptual learning, our results show that 12 h post-training in the waking state were as effective as 12 h, including no less than 6 h night's sleep. Altogether, the results indicate, for the first time, the existence of a latent, hours-long, consolidation phase in a human auditory verbal learning task, which occurs even during the awake state.