Body Mass and Tail Girth Predict Hibernation Expression in Captive Dwarf Lemurs.

AbstractHibernation, a metabolic strategy, allows individuals to reduce energetic demands in times of energetic deficits. Hibernation is pervasive in nature, occurring in all major mammalian lineages and geographical regions; however, its expression is variable across species, populations, and individuals, suggesting that trade-offs are at play. Whereas hibernation reduces energy expenditure, energetically expensive arousals may impose physiological burdens. The torpor optimization hypothesis posits that hibernation should be expressed according to energy availability. The greater the energy surplus, the lower the hibernation output. The thrifty female hypothesis, a variation of the torpor optimization hypothesis, states that females should conserve more energy because of their more substantial reproductive costs. Contrarily, if hibernation's benefits offset its costs, hibernation may be maximized rather than optimized (e.g., hibernators with greater fat reserves could afford to hibernate longer). We assessed torpor expression in captive dwarf lemurs, primates that are obligate, seasonal, and tropical hibernators. Across 4.5 mo in winter, we subjected eight individuals at the Duke Lemur Center to conditions conducive to hibernation, recorded estimates of skin temperature hourly (a proxy for torpor), and determined body mass and tail fat reserves bimonthly. Across and between consecutive weigh-ins, heavier dwarf lemurs spent less time in torpor and lost more body mass. At equivalent body mass, females spent more time torpid and better conserved energy than did males. Although preliminary, our results support the torpor optimization and thrifty female hypotheses, suggesting that individuals optimize rather than maximize torpor according to body mass. These patterns are consistent with hibernation phenology in Madagascar, where dwarf lemurs hibernate longer in more seasonal habitats.

On the modulation and maintenance of hibernation in captive dwarf lemurs.

In nature, photoperiod signals environmental seasonality and is a strong selective "zeitgeber" that synchronizes biological rhythms. For animals facing seasonal environmental challenges and energetic bottlenecks, daily torpor and hibernation are two metabolic strategies that can save energy. In the wild, the dwarf lemurs of Madagascar are obligate hibernators, hibernating between 3 and 7 months a year. In captivity, however, dwarf lemurs generally express torpor for periods far shorter than the hibernation season in Madagascar. We investigated whether fat-tailed dwarf lemurs (Cheirogaleus medius) housed at the Duke Lemur Center (DLC) could hibernate, by subjecting 8 individuals to husbandry conditions more in accord with those in Madagascar, including alternating photoperiods, low ambient temperatures, and food restriction. All dwarf lemurs displayed daily and multiday torpor bouts, including bouts lasting ~ 11 days. Ambient temperature was the greatest predictor of torpor bout duration, and food ingestion and night length also played a role. Unlike their wild counterparts, who rarely leave their hibernacula and do not feed during hibernation, DLC dwarf lemurs sporadically moved and ate. While demonstrating that captive dwarf lemurs are physiologically capable of hibernation, we argue that facilitating their hibernation serves both husbandry and research goals: first, it enables lemurs to express the biphasic phenotypes (fattening and fat depletion) that are characteristic of their wild conspecifics; second, by "renaturalizing" dwarf lemurs in captivity, they will emerge a better model for understanding both metabolic extremes in primates generally and metabolic disorders in humans specifically.

Influence of aided audibility on speech recognition performance with frequency composition for children and adults.

OBJECTIVE: The primary purpose of this project was to evaluate the influence of speech audibility on speech recognition with frequency composition, a frequency-lowering algorithm used in hearing aids. DESIGN: Participants were tested to determine word and sentence recognition thresholds in background noise, with and without frequency composition. The audibility of speech was quantified using the speech intelligibility index (SII). STUDY SAMPLE: Participants included 17 children (ages 6-16) and 21 adults (ages 19 to 72) with bilateral mild-to-severe sensorineural hearing loss. RESULTS: Word and sentence recognition thresholds did not change significantly with frequency composition. Participants with better aided speech audibility had better speech recognition in noise, regardless of processing condition, than those with poorer aided audibility. For the child participants, changes in the word recognition threshold between processing conditions were predictable from aided speech audibility. However, this relationship depended strongly on one participant with a low SII and otherwise, changes in speech recognition between frequency composition off and on were not predicable from aided speech audibility. CONCLUSION: While these results suggest that children who have a low-aided SII may benefit from frequency composition, further data are needed to generalise these findings to a greater number of participants and variety of stimuli.

Effects of Hearing Loss on School-Aged Children's Ability to Benefit From F0 Differences Between Target and Masker Speech.

OBJECTIVES: The objectives of the study were to (1) evaluate the impact of hearing loss on children's ability to benefit from F0 differences between target/masker speech in the context of aided speech-in-speech recognition and (2) to determine whether compromised F0 discrimination associated with hearing loss predicts F0 benefit in individual children. We hypothesized that children wearing appropriately fitted amplification would benefit from F0 differences, but they would not show the same magnitude of benefit as children with normal hearing. Reduced audibility and poor suprathreshold encoding that degrades frequency discrimination were expected to impair children's ability to segregate talkers based on F0. DESIGN: Listeners were 9 to 17 year olds with bilateral, symmetrical, sensorineural hearing loss ranging in degree from mild to severe. A four-alternative, forced-choice procedure was used to estimate thresholds for disyllabic word recognition in a 60-dB-SPL two-talker masker. The same male talker produced target and masker speech. Target words had either the same mean F0 as the masker or were digitally shifted higher than the masker by three, six, or nine semitones. The F0 benefit was defined as the difference in thresholds between the shifted-F0 conditions and the unshifted-F0 condition. Thresholds for discriminating F0 were also measured, using a three-alternative, three-interval forced choice procedure, to determine whether compromised sensitivity to F0 differences due to hearing loss would predict children's ability to benefit from F0. Testing was performed in the sound field, and all children wore their personal hearing aids at user settings. RESULTS: Children with hearing loss benefited from an F0 difference of nine semitones between target words and masker speech, with older children generally benefitting more than younger children. Some children benefitted from an F0 difference of six semitones, but this was not consistent across listeners. Thresholds for discriminating F0 improved with increasing age and predicted F0 benefit in the nine-semitone condition. An exploratory analysis indicated that F0 benefit was not significantly correlated with the four-frequency pure-tone average (0.5, 1, 2, and 4 kHz), aided audibility, or consistency of daily hearing aid use, although there was a trend for an association with the low-frequency pure-tone average (0.25 and 0.5 kHz). Comparisons of the present data to our previous study of children with normal hearing demonstrated that children with hearing loss benefitted less than children with normal hearing for the F0 differences tested. CONCLUSIONS: The results demonstrate that children with mild-to-severe hearing loss who wear hearing aids benefit from relatively large F0 differences between target and masker speech during aided speech-in-speech recognition. The size of the benefit increases with increasing age, consistent with previously reported age effects for children with normal hearing. However, hearing loss reduces children's ability to capitalize on F0 differences between talkers. Audibility alone does not appear to be responsible for this effect; aided audibility and degree of loss were not primary predictors of performance. The ability to benefit from F0 differences may be limited by immature central processing or aspects of peripheral encoding that are not characterized in standard clinical assessments.

Masking Release for Speech-in-Speech Recognition Due to a Target/Masker Sex Mismatch in Children With Hearing Loss.

OBJECTIVES: The goal of the present study was to compare the extent to which children with hearing loss and children with normal hearing benefit from mismatches in target/masker sex in the context of speech-in-speech recognition. It was hypothesized that children with hearing loss experience a smaller target/masker sex mismatch benefit relative to children with normal hearing due to impairments in peripheral encoding, variable access to high-quality auditory input, or both. DESIGN: Eighteen school-age children with sensorineural hearing loss (7 to 15 years) and 18 age-matched children with normal hearing participated in this study. Children with hearing loss were bilateral hearing aid users. Severity of hearing loss ranged from mild to severe across participants, but most had mild to moderate hearing loss. Speech recognition thresholds for disyllabic words presented in a two-talker speech masker were estimated in the sound field using an adaptive, forced-choice procedure with a picture-pointing response. Participants were tested in each of four conditions: (1) male target speech/two-male-talker masker; (2) male target speech/two-female-talker masker; (3) female target speech/two-female-talker masker; and (4) female target speech/two-male-talker masker. Children with hearing loss were tested wearing their personal hearing aids at user settings. RESULTS: Both groups of children showed a sex-mismatch benefit, requiring a more advantageous signal to noise ratio when the target and masker were matched in sex than when they were mismatched. However, the magnitude of sex-mismatch benefit was significantly reduced for children with hearing loss relative to age-matched children with normal hearing. There was no effect of child age on the magnitude of sex-mismatch benefit. The sex-mismatch benefit was larger for male target speech than for female target speech. For children with hearing loss, the magnitude of sex-mismatch benefit was not associated with degree of hearing loss or aided audibility. CONCLUSIONS: The findings from the present study indicate that children with sensorineural hearing loss are able to capitalize on acoustic differences between speech produced by male and female talkers when asked to recognize target words in a competing speech masker. However, children with hearing loss experienced a smaller benefit relative to their peers with normal hearing. No association between the sex-mismatch benefit and measures of unaided thresholds or aided audibility were observed for children with hearing loss, suggesting that reduced peripheral encoding is not the only factor responsible for the smaller sex-mismatch benefit relative to children with normal hearing.

A Two-Interval, Forced-Choice, Observer-Based Procedure for Evaluating Hearing Sensitivity in Children With Motor and Developmental Impairments.

Purpose It can be challenging to collect reliable behavioral responses to sound from individuals with significant motor or developmental impairments, the most common types of comorbid disability found in children with hearing loss (e.g., Gallaudet Research Institute, 2011). The purpose of this study was to test the feasibility of using a 2-interval, forced-choice, observer-based method for individuals considered to be difficult-to-test using behavioral audiometric assessments. Method Participants were 5 children with motor and developmental impairments, ages 5-15 years (M = 11.6, SD = 4.6). The functional abilities of all participants were greater than 2 SDs below the mean, as measured by the Vineland-II Parent Caregiver Rating Form. Participants listened to either a male talker saying the word "playground" or a 1000-Hz warble tone, presented via an insert earphone or a sound field speaker. An observer, blind to signal presentation, selected 1 of 2 temporal intervals, determining which contained the signal based only on participant behavior. Criterion was reached when the observer correctly identified the interval containing the signal for 8 of the last 10 trials. Results An 80%-correct criterion was met for all participants, suggesting feasibility for use in children with motor or developmental impairment. Two participants were tested using an adaptive tracking procedure; a reliable threshold estimate was obtained for both children. This method offers promise for children who have difficulty performing behavioral audiometric assessments currently in use clinically.

Language Proficiency and Dominance Considerations When Working With Spanish-English Bilingual Adults.

Purpose As the Hispanic population continues to increase within the United States, there is a pressing need to incorporate rigorous and efficient clinical assessments of language dominance and proficiency when working with Spanish-English bilingual patients. The purpose of this study was to begin addressing this need by evaluating the association between language dominance and language proficiency. Method The association between scores for the English Versant Test (Pearson Education, 2010), an automated assessment of spoken language proficiency, and dominance and proficiency scores obtained using the Bilingual Language Profile, a self-report questionnaire was evaluated. Results The results indicated that half of the variance in the English Versant Test was explained by the response to a single question included in the Bilingual Language Profile. Conclusion These data support the inclusion of asking patients to not only indicate how many languages they speak but, for those patients that speak more than 1 language, to also ask how well they understand each of the languages.

Effects of Adaptive Hearing Aid Directionality and Noise Reduction on Masked Speech Recognition for Children Who Are Hard of Hearing.

Purpose The purpose of this study was to evaluate speech-in-noise and speech-in-speech recognition associated with activation of a fully adaptive directional hearing aid algorithm in children with mild to severe bilateral sensory/neural hearing loss. Method Fourteen children (5-14 years old) who are hard of hearing participated in this study. Participants wore laboratory hearing aids. Open-set word recognition thresholds were measured adaptively for 2 hearing aid settings: (a) omnidirectional (OMNI) and (b) fully adaptive directionality. Each hearing aid setting was evaluated in 3 listening conditions. Fourteen children with normal hearing served as age-matched controls. Results Children who are hard of hearing required a more advantageous signal-to-noise ratio than children with normal hearing to achieve comparable performance in all 3 conditions. For children who are hard of hearing, the average improvement in signal-to-noise ratio when comparing fully adaptive directionality to OMNI was 4.0 dB in noise, regardless of target location. Children performed similarly with fully adaptive directionality and OMNI settings in the presence of the speech maskers. Conclusions Compared to OMNI, fully adaptive directionality improved speech recognition in steady noise for children who are hard of hearing, even when they were not facing the target source. This algorithm did not affect speech recognition when the background noise was speech. Although the use of hearing aids with fully adaptive directionality is not proposed as a substitute for remote microphone systems, it appears to offer several advantages over fixed directionality, because it does not depend on children facing the target talker and provides access to multiple talkers within the environment. Additional experiments are required to further evaluate children's performance under a variety of spatial configurations in the presence of both noise and speech maskers.

Pure-Tone Frequency Discrimination in Preschoolers, Young School-Age Children, and Adults.

Purpose: Published data indicate nearly adultlike frequency discrimination in infants but large child-adult differences for school-age children. This study evaluated the role that differences in measurement procedures and stimuli may have played in the apparent nonmonotonicity. Frequency discrimination was assessed in preschoolers, young school-age children, and adults using stimuli and procedures that have previously been used to test infants. Method: Listeners were preschoolers (3-4 years), young school-age children (5-6 years), and adults (19-38 years). Performance was assessed using a single-interval, observer-based method and a continuous train of stimuli, similar to that previously used to evaluate infants. Testing was completed using 500- and 5000-Hz standard tones, fixed within a set of trials. Thresholds for frequency discrimination were obtained using an adaptive, two-down one-up procedure. Adults and most school-age children responded by raising their hands. An observer-based, conditioned-play response was used to test preschoolers and those school-age children for whom the hand-raise procedure was not effective for conditioning. Results: Results suggest an effect of age and frequency on thresholds but no interaction between these 2 factors. A lower proportion of preschoolers completed training compared with young school-age children. For those children who completed training, however, thresholds did not improve significantly with age; both groups of children performed more poorly than adults. Performance was better for the 500-Hz standard frequency compared with the 5000-Hz standard frequency. Conclusions: Thresholds for school-age children were broadly similar to those previously observed using a forced-choice procedure. Although there was a trend for improved performance with increasing age, no significant age effect was observed between preschoolers and school-age children. The practice of excluding participants based on failure to meet conditioning criteria in an observer-based task could contribute to the relatively good performance observed for preschoolers in this study and the adultlike performance previously observed in infants.

Spectro-temporal modulation detection in children.

Children's performance on psychophysical tasks improves with age. The relationship of spectro-temporal modulation detection to age, particularly in children who are hard of hearing, is not well-established. In this study, children with normal hearing (N = 22) and with sensorineural hearing loss (N = 15) completed measures of spectro-temporal modulation detection. Measures of aided audibility were completed in the children who are hard of hearing. Pearson product-moment correlations were completed with listener age and aided audibility as parameters. Spectro-temporal modulation detection performance increased with listener age and with greater aided audibility.

Preliminary evaluation of a two-interval, two-alternative infant behavioral testing procedure.

The purpose of this study was to evaluate the feasibility and efficiency of an observer-based, two-interval forced-choice infant psychophysical testing procedure. Ten of 11 infants (7-9 months of age) achieved a criterion of 80%-correct detection of a 50-dB sound pressure level noise band in a single testing session. Fewer trials were needed to reach criterion using the two-interval procedure than previously reported for the single-interval observer-based psychophysical procedure [Olsho, Koch, Halpin, and Carter (1987). Devel. Psychol. 23, 627-640]. These results provide preliminary evidence that the two-interval procedure is feasible and efficient while controlling for observer and listener response bias.