The validity of LENA technology for assessing the linguistic environment and interactions of infants learning Hebrew and Arabic.

The present study assessed LENA's suitability as a tool for monitoring future language interventions by evaluating its reliability, construct validity, and criterion validity in infants learning Hebrew and Arabic, across low and high levels of maternal education. Participants were 32 infants aged 3 to 11 months (16 in each language) and their mothers, whose socioeconomic status (SES) was determined based on their years of education (H-high or L-low ME-maternal education). The results showed (1) good reliability for the LENA's automatic count on adult word count (AWC), conversational turns (CTC), and infant vocalizations (CVC), based on the positive associations and fair to excellent agreement between the manual and automatic counts; (2) good construct validity based on significantly higher counts for HME vs. LME and positive associations between LENA's automatic vocal assessment (AVA) and developmental questionnaire (DA) and age; and (3) good concurrent criterion validity based on the positive associations between the LENA counts for CTC, CVC, AVA, and DA and the scores on the preverbal parent questionnaire (PRISE). The present study supports the use of LENA in early intervention programs for infants whose families speak Hebrew or Arabic. The LENA could be used to monitor the efficacy of these programs as well as to provide feedback to parents on the amount of language experience their infants are getting and their progress in vocal production. The results also indicate a potential utility of LENA in assessing linguistic environments and interactions in Hebrew- and Arabic-speaking infants with developmental disorders, such as hearing impairment and cerebral palsy.

Practice Makes Transfer Imperfect: Evidence From Auditory Learning.

BACKGROUND: Evidence from motor and visual studies suggests that the ability to generalize learning gains to untrained conditions decreases as the training progresses. This decrease in generalization was suggested to reflect a shift from higher to lower levels of neuronal representations of the task following prolonged training. In the auditory modality, however, the few studies that tested the influence of prolonging training on generalization ability showed no decrease and sometimes even an increase in generalization. OBJECTIVE: To test the impact of extending training in a basic psychoacoustic task on the ability to generalize the gains attained in training to untrained conditions. DESIGN: Eighty-two young adults participated in two experiments that differed in the specific training regimen. In both experiments, training was conducted using a difference limen for frequency (DLF) task with an adaptive forced-choice procedure, for either a single- or nine-session training. Following training, generalization to the untrained ear and to an untrained frequency was assessed. RESULTS: (a) Training induced significant learning (i.e., smaller DLF thresholds) following a single session of training, and more so following nine training sessions; (b) results from the combined data from both experiments showed that the ability to generalize the learning gains to the untrained ear and frequency was limited after the extended DLF training; (c) larger improvements under the trained condition resulted in smaller generalization to the untrained conditions. CONCLUSIONS: The findings of increased specificity with training in the auditory modality support the notion that gradual changes, both quantitative and qualitative, occur in the neural representations of an auditory task during its acquisition. These findings suggest common underlying mechanisms in basic skill learning across different modalities.

Children With Normal Hearing Are Efficient Users of Fundamental Frequency and Vocal Tract Length Cues for Voice Discrimination.

BACKGROUND: The ability to discriminate between talkers assists listeners in understanding speech in a multitalker environment. This ability has been shown to be influenced by sensory processing of vocal acoustic cues, such as fundamental frequency (F0) and formant frequencies that reflect the listener's vocal tract length (VTL), and by cognitive processes, such as attention and memory. It is, therefore, suggested that children who exhibit immature sensory and/or cognitive processing will demonstrate poor voice discrimination (VD) compared with young adults. Moreover, greater difficulties in VD may be associated with spectral degradation as in children with cochlear implants. OBJECTIVES: The aim of this study was as follows: (1) to assess the use of F0 cues, VTL cues, and the combination of both cues for VD in normal-hearing (NH) school-age children and to compare their performance with that of NH adults; (2) to assess the influence of spectral degradation by means of vocoded speech on the use of F0 and VTL cues for VD in NH children; and (3) to assess the contribution of attention, working memory, and nonverbal reasoning to performance. DESIGN: Forty-one children, 8 to 11 years of age, were tested with nonvocoded stimuli. Twenty-one of them were also tested with eight-channel, noise-vocoded stimuli. Twenty-one young adults (18 to 35 years) were tested for comparison. A three-interval, three-alternative forced-choice paradigm with an adaptive tracking procedure was used to estimate the difference limens (DLs) for VD when F0, VTL, and F0 + VTL were manipulated separately. Auditory memory, visual attention, and nonverbal reasoning were assessed for all participants. RESULTS: (a) Children' F0 and VTL discrimination abilities were comparable to those of adults, suggesting that most school-age children utilize both cues effectively for VD. (b) Children's VD was associated with trail making test scores that assessed visual attention abilities and speed of processing, possibly reflecting their need to recruit cognitive resources for the task. (c) Best DLs were achieved for the combined (F0 + VTL) manipulation for both children and adults, suggesting that children at this age are already capable of integrating spectral and temporal cues. (d) Both children and adults found the VTL manipulations more beneficial for VD compared with the F0 manipulations, suggesting that formant frequencies are more reliable for identifying a specific speaker than F0. (e) Poorer DLs were achieved with the vocoded stimuli, though the children maintained similar thresholds and pattern of performance among manipulations as the adults. CONCLUSIONS: The present study is the first to assess the contribution of F0, VTL, and the combined F0 + VTL to the discrimination of speakers in school-age children. The findings support the notion that many NH school-age children have effective spectral and temporal coding mechanisms that allow sufficient VD, even in the presence of spectrally degraded information. These results may challenge the notion that immature sensory processing underlies poor listening abilities in children, further implying that other processing mechanisms contribute to their difficulties to understand speech in a multitalker environment. These outcomes may also provide insight into VD processes of children under listening conditions that are similar to cochlear implant users.

Intelligibility of bandpass filtered speech: The effect of filter types.

Many studies have examined the contribution of different spectral bands to speech intelligibility, measuring recognition scores of filtered speech stimuli. For a given filter bandwidth, the influence of filter properties on such experiments has been studied mainly with respect to transition band slopes. The objective of the present study was to determine whether nominal transition band slope is a sufficient characterization of filter properties. Several types of filters, both finite impulse response and infinite impulse response types were examined in three experiments to determine if details of the transition band behavior, as well as group delay properties, had any influence on recognition scores. The results of a total of 72 participants showed that for 1/3 octave passbands, differences between filters having the same nominal transition band slopes, but of different types, were large and statistically significant. Linearity of phase response, however, did not influence the results. Further experiments using passband widths of 1/2 and 2/3 octaves revealed that only for the latter the difference in recognition scores between filter types ceased to be significant. These results have important implications for studies which involve filtered speech as well as models that employ different types of filters to emulate peripheral auditory processing.

Comprehension of "Narrow Focus" by Adolescents in the Autism Spectrum.

OBJECTIVE: The study compared the performance of adolescents with autistic spectrum disorder (ASD) to that of age-matched peers with typical development (TD) and cognitive language-matched peers with TD on measures of identification and comprehension of "narrow focus." PARTICIPANTS: Forty-nine participants, 17 autistic, 17 TD peers matched for age and sex, and 15 TD children matched for expressive vocabulary participated in the study. METHOD: The Hebrew Narrow Focus Test (HNFT) was used. The HNFT includes 3 subtests. The first subtest (A) required identification of the stressed word in the sentence based on psychoacoustic abilities alone. The second (B) and third (C) subtests required understanding the meaning of focused stress in different contexts. In subtest B, the meaning of "narrow focus" was to contrast other possibilities related to the lexical-grammatical role of the stressed word in the sentence, whereas in subtest C, the meaning was to indicate a mistake. RESULTS: ASD participants showed reduced performance compared to peers across all the subtests of the HNFT, but similar performance compared to TD children in subtests A and B and better performance on subtest C. A significant correlation was found between the Raven test for assessing nonverbal intelligence and subtests B and C of the HNFT in the group of adolescents with ASD. CONCLUSIONS: Comprehension of narrow focus in adolescents with ASD who study in a special educational system is related to their cognitive-linguistic abilities and not to the autistic condition by itself or to its severity.

Auditory Discrimination of Lexical Stress Patterns in Hearing-Impaired Infants with Cochlear Implants Compared with Normal Hearing: Influence of Acoustic Cues and Listening Experience to the Ambient Language.

OBJECTIVES: To assess discrimination of lexical stress pattern in infants with cochlear implant (CI) compared with infants with normal hearing (NH). While criteria for cochlear implantation have expanded to infants as young as 6 months, little is known regarding infants' processing of suprasegmental-prosodic cues which are known to be important for the first stages of language acquisition. Lexical stress is an example of such a cue, which, in hearing infants, has been shown to assist in segmenting words from fluent speech and in distinguishing between words that differ only the stress pattern. To date, however, there are no data on the ability of infants with CIs to perceive lexical stress. Such information will provide insight to the speech characteristics that are available to these infants in their first steps of language acquisition. This is of particular interest given the known limitations that the CI device has in transmitting speech information that is mediated by changes in fundamental frequency. DESIGN: Two groups of infants participated in this study. The first group included 20 profoundly hearing-impaired infants with CI, 12 to 33 months old, implanted under the age of 2.5 years (median age of implantation = 14.5 months), with 1 to 6 months of CI use (mean = 2.7 months) and no known additional problems. The second group of infants included 48 NH infants, 11 to 14 months old with normal development and no known risk factors for developmental delays. Infants were tested on their ability to discriminate between nonsense words that differed on their stress pattern only (/dóti/ versus /dotí/ and /dotí/ versus /dóti/) using the visual habituation procedure. The measure for discrimination was the change in looking time between the last habituation trial (e.g., /dóti/) and the novel trial (e.g., /dotí/). RESULTS: (1) Infants with CI showed discrimination between lexical stress pattern with only limited auditory experience with their implant device, (2) discrimination of stress patterns in infants with CI was reduced compared with that of infants with NH, (3) both groups showed directional asymmetry in discrimination, that is, increased discrimination from the uncommon to the common stress pattern in Hebrew (/dóti/ versus /dotí/) compared with the reversed condition. CONCLUSIONS: The CI device transmitted sufficient acoustic information (amplitude, duration, and fundamental frequency) to allow discrimination between stress patterns in young hearing-impaired infants with CI. The present pattern of results is in support of a discrimination model in which both auditory capabilities and "top-down" interactions are involved. That is, the CI infants detected changes between stressed and unstressed syllables after which they developed a bias for the more common weak-strong stress pattern in Hebrew. The latter suggests that infants with CI were able to extract the statistical distribution of stress patterns by listening to the ambient language even after limited auditory experience with the CI device. To conclude, in relation to processing of lexical stress patterns, infants with CI followed similar developmental milestones as hearing infants thus establishing important prerequisites for early language acquisition.

Soft tissue conduction as a possible contributor to the limited attenuation provided by hearing protection devices.

CONTEXT: Damage to the auditory system by loud sounds can be avoided by hearing protection devices (HPDs) such as earmuffs, earplugs, or both for maximum attenuation. However, the attenuation can be limited by air conduction (AC) leakage around the earplugs and earmuffs by the occlusion effect (OE) and by skull vibrations initiating bone conduction (BC). AIMS: To assess maximum attenuation by HPDs and possible flanking pathways to the inner ear. SUBJECTS AND METHODS: AC attenuation and resulting thresholds were assessed using the real ear attenuation at threshold (REAT) procedure on 15 normal-hearing participants in four free-field conditions: (a) unprotected ears, (b) ears covered with earmuffs, (c) ears blocked with deeply inserted customized earplugs, and (d) ears blocked with both earplugs and earmuffs. BC thresholds were assessed with and without earplugs to assess the OE. RESULTS: Addition of earmuffs to earplugs did not cause significantly greater attenuation than earplugs alone, confirming minimal AC leakage through the external meatus and the absence of the OE. Maximum REATs ranged between 40 and 46 dB, leading to thresholds of 46-54 dB HL. Furthermore, calculation of the acoustic impedance mismatch between air and bone predicted at least 60 dB attenuation of BC. CONCLUSION: Results do not support the notion that skull vibrations (BC) contributed to the limited attenuation provided by traditional HPDs. An alternative explanation, supported by experimental evidence, suggests transmission of sound to inner ear via non-osseous pathways such as skin, soft tissues, and fluid. Because the acoustic impedance mismatch between air and soft tissues is smaller than that between air and bone, air-borne sounds would be transmitted to soft tissues more effectively than to bone, and therefore less attenuation is expected through soft tissue sound conduction. This can contribute to the limited attenuation provided by traditional HPDs. The present study has practical implications for hearing conservation protocols.

Delay in auditory behaviour and preverbal vocalization in infants with unilateral hearing loss.

AIM: To evaluate the impact of unilateral hearing loss (UHL) on early aural/oral communication skills of infants by comparing performance to infants with bilateral normal hearing (BNH). METHOD: Thirty-four infants with UHL (median age 9.4mo, 25th-75th centile 7.34-12.15) and 331 control infants with BNH (median age 9mo, 6.0-13.38) were divided into two subgroups based on risk factors known to cause developmental delay: low risk and high risk. Early auditory skills and preverbal vocalizations were assessed using two parent questionnaires: the Infant-Toddler Meaningful Auditory Integration Scale and the Production of Infants Scale Evaluation. RESULTS: Of the infants with UHL, 21% showed delays in auditory behaviour and 41% delays in preverbal vocalizations, compared to their peers with BNH (p<0.01). After adjusting for risk level, delayed auditory behaviour and preverbal vocalizations were approximately four and nine times more common in infants with UHL compared to BNH respectively (p<0.01). INTERPRETATION: This is the first study to show that infants with UHL are at higher risk of delay in early aural/oral communication abilities compared to infants with BNH even in the absence of other known risk factors for developmental delay. This has important implications for early intervention and habilitation of infants with UHL, in order to reduce some of the negative long-term consequences of what was once considered 'minor' hearing loss.

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.

Parent report of the development of auditory skills in infants and toddlers who use hearing aids.

OBJECTIVES: This study investigated the use of the Infant-Toddler Meaningful Auditory Integration Scale (IT-MAIS) as a measure of early auditory skill development in aided infants and toddlers with varying degrees of hearing loss. Specific goals were (1) to rate the change in IT-MAIS score as a function of change in hearing thresholds achieved through amplification; (2) to establish the hierarchy of early auditory skill development for infants who use hearing aids (HAs) relative to what is known in infants with normal hearing; and (3) to analyze background information variables that may account for differences in IT-MAIS performance, as age and duration of HAs use. DESIGN: The study included 106 infants and toddlers (47 girls and 59 boys) aged 7 to 36 months (mean = 19.02, SD = 7.7) with various degrees of sensorineural hearing loss (mean = 86.42 dB, SD = 22.52). Infants used bilateral digital HAs with a mean experience of 8 months. All participants attended the same early intervention program. After at least 2 months of HA use, parents were interviewed with the IT-MAIS questionnaire regarding the auditory behavior of their infants in everyday situations. RESULTS: The results of the present study support the following outcomes: (1) on average, every 10 dB gain in pure-tone average scores (PTA4) threshold improved the IT-MAIS score by 10%; (2) infants who were part of the same unaided hearing categories appeared to have derived different benefits from amplification; (3) when reaching the same aided category, those infants who were originally in a better unaided hearing category achieved higher IT-MAIS scores than those who belonged to a worse unaided hearing category; (4) the hierarchy of auditory development in young aided infants with hearing loss followed that of normal hearing peers; and (5) 62.9% of the variance of IT-MAIS performance was explained by aided hearing level (50.3%), unaided hearing level (6.4%), and duration of HA use (6.2)%. CONCLUSIONS: The present study provides important information to assist clinicians and parents in setting realistic expectations regarding the auditory behavior of infants as a function of aided and unaided thresholds. It emphasizes the need for assessing functional hearing in young infants and not relying on hearing thresholds alone. Such data can also contribute to the decision-making process when selecting a sensory device (e.g., HA versus cochlear implant) for infants with hearing loss.

Judging emotions in lexical-prosodic congruent and incongruent speech stimuli by adolescents in the autism spectrum.

OBJECTIVE: The purpose of the present study was to assess how adolescents with autism who vary in the severity of autistic characteristics judge the emotional state of the speaker when lexical and prosodic information is congruent or incongruent. PARTICIPANTS: Eighty participants, 24 autistic and 56 typically developing (TD) subjects participated: (a) 11 autistic adolescents between 9.5 and 16.83 years old, studying at general education settings (AA1), (b) 13 autistic adolescents between 15.91 and 20.33 years old, studying at a special school (AA2), and (c) 56 TD subjects between 6 and 29 years old. Listeners were required to judge the emotional meaning of words (sad/happy) in congruent conditions and incongruent conditions. RESULTS: (a) All participants judged lexical and prosodic meaning separately with high accuracy, (b) all participants showed prolonged reaction times in the incongruent compared to the congruent condition, (c) AA1 relied on prosodic information in the incongruent condition similarly to TD 9-15 year olds and TD adults, (d) AA2 and TD 6-8 year olds did not rely on prosodic information in the incongruent condition, and (e) both education placements, the severity of autistic characteristics and nonverbal IQ contributed to prosodic judgment in the incongruent condition in autistic adolescents. CONCLUSIONS: The two groups of autistic adolescents processed both lexical and prosodic information in the incongruent condition. However, the severity of autistic characteristics influenced the preference for prosody.

Difficulties Experienced by Older Listeners in Utilizing Voice Cues for Speaker Discrimination.

Human listeners are assumed to apply different strategies to improve speech recognition in background noise. Young listeners with normal hearing (NH), e.g., have been shown to follow the voice of a particular speaker based on the fundamental (F0) and formant frequencies, which are both influenced by the gender, age, and size of the speaker. However, the auditory and cognitive processes that underlie the extraction and discrimination of these voice cues across speakers may be subject to age-related decline. The present study aimed to examine the utilization of F0 and formant cues for voice discrimination (VD) in older adults with hearing expected for their age. Difference limens (DLs) for VD were estimated in 15 healthy older adults (65-78 years old) and 35 young adults (18-35 years old) using only F0 cues, only formant frequency cues, and a combination of F0 + formant frequencies. A three-alternative forced-choice paradigm with an adaptive-tracking threshold-seeking procedure was used. Wechsler backward digit span test was used as a measure of auditory working memory. Trail Making Test (TMT) was used to provide cognitive information reflecting a combined effect of processing speed, mental flexibility, and executive control abilities. The results showed that (a) the mean VD thresholds of the older adults were poorer than those of the young adults for all voice cues, although larger variability was observed among the older listeners; (b) both age groups found the formant cues more beneficial for VD, compared to the F0 cues, and the combined (F0 + formant) cues resulted in better thresholds, compared to each cue separately; (c) significant associations were found for the older adults in the combined F0 + formant condition between VD and TMT scores, and between VD and hearing sensitivity, supporting the notion that a decline with age in both top-down and bottom-up mechanisms may hamper the ability of older adults to discriminate between voices. The present findings suggest that older listeners may have difficulty following the voice of a specific speaker and thus implementing doing so as a strategy for listening amid noise. This may contribute to understanding their reported difficulty listening in adverse conditions.

Identification and Comprehension of Narrow Focus by Arabic-Speaking Adolescents With Moderate-to-Profound Hearing Loss.

PURPOSE: Processing narrow focus (NF), the stressed word in the sentence, includes both the perceptual ability to identify the stressed word in the sentence and the pragmatic-semantic ability to comprehend the nonexplicit linguistic message. NF and its underlying meaning can be conveyed only via the auditory modality. Therefore, NF can be considered as a measure for assessing the efficacy of the hearing aid (HA) and cochlear implants (CIs) for acquiring nonexplicit language skills. The purpose of this study was to assess identification and comprehension of NF by HA and CI users who are native speakers of Arabic and to associate NF outcomes with speech perception and cognitive and linguistic abilities. METHOD: A total of 46 adolescents (age range: 11;2-18;8) participated: 18 with moderate-to-severe hearing loss who used HAs, 10 with severe-to-profound hearing loss who used CIs, and 18 with typical hearing (TH). Test materials included the Arabic Narrow Focus Test (ANFT), which includes three subtests assessing identification (ANFT1), comprehension of NF in simple four-word sentences (ANFT2), and longer sentences with a construction list at the clause or noun phrase level (ANFT3). In addition, speech perception, vocabulary, and working memory were assessed. RESULTS: All the participants successfully identified the word carrying NF, with no significant difference between the groups. Comprehension of NF in ANFT2 and ANFT3 was reduced for HA and CI users compared with TH peers, and speech perception, hearing status, and memory for digits predicted the variability in the overall results of ANFT1, ANFT2, and ANFT3, respectively. CONCLUSIONS: Arabic speakers who used HAs or CIs were able to identify NF successfully, suggesting that the acoustic cues were perceptually available to them. However, HA and CI users had considerable difficulty in understanding NF. Different factors may contribute to this difficulty, including the memory load during the task as well as pragmatic-linguistic knowledge on the possible meanings of NF.

Listening preference for child-directed speech versus nonspeech stimuli in normal-hearing and hearing-impaired infants after cochlear implantation.

OBJECTIVES: The main purpose of the present study was to determine listening preference for child-directed speech (CDS) over static (white noise, WN) and dynamic (time-reversed speech, TRS) nonspeech stimuli in both normal-hearing (NH) infants and hearing-impaired infants with cochlear implants (CIs). A second purpose was to investigate the effect of auditory experience on listening preference for speech in both groups. METHOD: A total of 64 infants, 43 NH (age 6 to 20 mos) and 21 CI users (age 14 to 33 mos), were tested. Twenty-two NH infants and 12 infants with CIs were tested on their listening preference for CDS compared with WN. In addition, 21 NH infants and 9 infants with CIs were tested on their listening preference for CDS compared with TRS using the central fixation preference procedure. RESULTS: NH infants and infants with CIs preferred listening to speech compared with WN and TRS. This preference was shown in infants with limited listening experience and increased significantly with auditory exposure for both NH infants and infants with CIs. The extent of preference for speech versus nonspeech among infants with CIs was significantly correlated with gross auditory and preverbal production skills (as measured by ITMAIS and PRISE tests, respectively) as well as with duration of auditory experience. CONCLUSIONS: The CI device provides sufficient information for the infants with CIs to follow early language processes similarly to NH infants.

How specific is the learning in an auditory frequency discrimination task?

BACKGROUND: There is ample evidence showing that frequency discrimination can dramatically improve with practice. Nevertheless, the ability to generalize the learning gains to conditions that were not encountered during training is still controversial. Therefore, the purpose of the present study was to evaluate the extent of generalization to the untrained ear, to an untrained frequency (2000 Hz) and to an untrained (noisy) environment by continuing to train the generalization conditions. METHODS: Twenty-one participants took part in two training phases. The first training phase included nine training sessions that consisted each of six threshold measurements of difference limen for frequency (DLF) at 1000 Hz, and a 10th testing session that consisted of three DLF thresholds at 1000 Hz. The generalization phase included four training sessions that consisted each of six DLF threshold estimates, two days at each generalization condition (each participant was trained in two out of three generalization conditions, thus the total number of participants trained in each generalization condition was 14). All DLF thresholds were estimated using a three-interval, two-alternative forced choice adaptive procedure. RESULTS: Results showed that (1) the initial thresholds in the generalization conditions were reduced following training, and (2) new learning was observed in the subsequent training sessions suggesting that the learning was partially specific to the trained ear, frequency and environment. CONCLUSIONS: These results have important theoretical and clinical implications regarding the extent of the plasticity of the auditory system and the neural processes that underlie this plasticity.

Infants' Preference for Child-Directed Speech Over Time-Reversed Speech in On-Channel and Off-Channel Masking.

Purpose This study aims to examine the development of auditory selective attention to speech in noise by examining the ability of infants to prefer child-directed speech (CDS) over time-reversed speech (TRS) presented in "on-channel" and "off-channel" noise. Method A total of 32 infants participated in the study. Sixteen typically developing infants were tested at 7 and 11 months of age using the central fixation procedure with CDS and TRS in two types of noise at +10 dB signal-to-noise ratio. One type of noise was an "on-channel" masker with a spectrum overlapping that of the CDS (energetic masking), and the second was an "off-channel" masker with frequencies that were outside the spectrum of the CDS (distractive masking). An additional group of sixteen 11-month-old infants were tested in quiet and served as controls for the "off-frequency" masker condition. Results Infants preferred CDS over TRS in both age groups, but this preference was more pronounced with "off-channel" masker regardless of age. Also, older infants demonstrated longer looking time for the target stimuli when presented with an "off-channel" masker compared to the "on-channel" masker. Looking time in quiet was similar to looking time in the "off-channel" condition, and looking time for CDS was longer in quiet compared to the "on-channel" condition. Conclusions These findings support the notion that (a) infants as young as 7 months of age are already showing preference for speech in noise, regardless of type of masker; (b) by 11 months of age, listening with the "off-channel" condition did not yield different results than in quiet. Thus, by 11 months of age, infants' cognitive-attentional abilities may be more developed.

The Effect of Soft Tissue Stimulation on Skull Vibrations and Hearing Thresholds in Humans.

HYPOTHESIS: Hearing via soft tissue stimulation involves an osseous pathway. BACKGROUND: A recent study that measured both hearing thresholds and skull vibrations found that vibratory stimulation of soft tissue led to hearing sensation that correlated with skull vibrations, supporting the hypothesis of an osseous pathway. It is possible, however, that a lower application force of the vibrator on the stimulated soft tissue would not be sufficient to elicit skull vibration suggesting hearing via a nonosseous pathway. The purpose of the present study was to confirm the osseous pathway by measuring skull vibrations and behavioral thresholds using a low application force on a layer of ultrasound gel. Gel was used to mimic soft tissue because of its similar acoustic impedance and to control for variability between participants. METHODS: Hearing thresholds and the skull vibrations of five patients who were implanted with bone-anchored implants were assessed in two conditions when the bone vibrator was applied on the forehead: 1) direct application with 5N force; 2) through a layer of ultrasound gel with minimal application force. Skull vibrations were measured in both conditions by a laser Doppler vibrometer focused on the bone-anchored implant. RESULTS: Skull vibrations were present even when minimal application force was applied on soft tissue. The difference in skull vibrations when the vibrator was directly on the forehead compared with the gel condition was consistent with the variability in hearing thresholds between the two conditions. CONCLUSION: These results reinforce the hypothesis that skull vibrations are involved in hearing when sound is transmitted via either soft tissue or bone.

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.

Listening in Noise Remains a Significant Challenge for Cochlear Implant Users: Evidence from Early Deafened and Those with Progressive Hearing Loss Compared to Peers with Normal Hearing.

Cochlear implants (CIs) are the state-of-the-art therapy for individuals with severe to profound hearing loss, providing them with good functional hearing. Nevertheless, speech understanding in background noise remains a significant challenge. The purposes of this study were to: (1) conduct a novel within-study comparison of speech-in-noise performance across ages in different populations of CI and normal hearing (NH) listeners using an adaptive sentence-in-noise test, and (2) examine the relative contribution of sensory information and cognitive-linguistic factors to performance. Forty CI users (mean age 20 years) were divided into "early-implanted" <4 years (n = 16) and "late-implanted" >6 years (n = 11), all prelingually deafened, and "progressively deafened" (n = 13). The control group comprised 136 NH subjects (80 children, 56 adults). Testing included the Hebrew Matrix test, word recognition in quiet, and linguistic and cognitive tests. Results show poorer performance in noise for CI users across populations and ages compared to NH peers, and age at implantation and word recognition in quiet were found to be contributing factors. For those recognizing 50% or more of the words in quiet (n = 27), non-verbal intelligence and receptive vocabulary explained 63% of the variance in noise. This information helps delineate the relative contribution of top-down and bottom-up skills for speech recognition in noise and can help set expectations in CI counseling.

Cortical neural activity underlying speech perception in postlingual adult cochlear implant recipients.

Auditory event-related potentials (AERPs) and the simultaneously obtained behavioral measures (performance accuracy and reaction time) were used to study speech perception in postlingual adult cochlear implant (CI) recipients and in normal-hearing (NH) controls. AERPs were recorded while subjects were performing oddball discrimination tasks with increasing acoustic-phonetic demand. The tasks consisted of pairs of natural syllables that differed by one of the following phonetic contrasts: vowel place, voicing, vowel height, and place of articulation. Results indicated that the P3 potential was comparable in CI recipients and NH controls when the acoustic cues to the perception of the phonetic contrast were accessible. With the reduction in accessibility to the essential temporal and/or spectral cues, CI recipients exhibited delayed (prolonged P3 latency) and less synchronous (reduced amplitude) central speech-sound processing compared to NH controls. Among the phonetic contrasts used in the present study the place of articulation contrast yielded (1) the most prominent differences between CI recipients and NH controls across all measures, and (2) significant correlations between the neurophysiologic manifestation of speech discrimination (i.e. P3 latency), and conscious integration of perceptual information (i.e. performance accuracy and reaction time). Thus, P3 exposed the difficulties imposed on the impaired auditory system of CI recipients especially when elicited by speech contrasts that required processing of brief temporal-spectral cues. These findings support the P3 potential as a sensitive neural index of cortical processing that may provide information regarding accessibility and neural encoding of distinct acoustic-phonetic cues in CI recipients.