A new paradigm for assessing postural stability.

BACKGROUND: The sensory organization test (SOT) is an established and effective method for assessing postural stability and determining fall risk. SOT equilibrium scores are derived from the relationship between an individual's peak sway amplitude and a standard, theoretically-derived normal limits of stability (tLOS). Determining an individual's postural stability and fall risk based on this one-size-fits-all tLOS may overestimate functional equilibrium scores and underestimate fall risk when personal stability limits (pLOS) are reduced. RESEARCH QUESTION: The purpose of this study is to investigate whether LOS measured from a group of healthy adults is different from the tLOS, and whether SOT equilibrium scores are significantly different when calculated using pLOS versus the standard tLOS. METHODS: Sixty healthy volunteers were recruited into three age-groups: young (18-39), middle-aged (40-64), and elderly (65-80), with 10 males and 10 females in each age-group. Outcome measures included SOT and LOS. Additional measures o balance perception and functional mobility were obtained including the Activities Balance Confidence (ABC) scale and the timed-up-and-go test (TUG). The tLOS and pLOS were used to calculate standard (tSOT) and personalized (pSOT) equilibrium scores. RESULTS: The mean pLOS from the group of healthy adults was significantly lower than the tLOS. Consequently, the pSOT equilibrium scores were significantly lower than the standard SOT scores derived using the tLOS. SIGNIFICANCE: Individual measures of LOS are significantly lower than theoretical estimates of the LOS in healthy adults. This suggests that use of tLOS in the calculation of SOT equilibrium scores often overestimates postural stability and may have implications for the determination of fall risk.

Bimodal Cochlear Implant Listeners' Ability to Perceive Minimal Audible Angle Differences.

BACKGROUND: Bilateral inputs should ideally improve sound localization and speech understanding in noise. However, for many bimodal listeners [i.e., individuals using a cochlear implant (CI) with a contralateral hearing aid (HA)], such bilateral benefits are at best, inconsistent. The degree to which clinically available HA and CI devices can function together to preserve interaural time and level differences (ITDs and ILDs, respectively) enough to support the localization of sound sources is a question with important ramifications for speech understanding in complex acoustic environments. PURPOSE: To determine if bimodal listeners are sensitive to changes in spatial location in a minimum audible angle (MAA) task. RESEARCH DESIGN: Repeated-measures design. STUDY SAMPLE: Seven adult bimodal CI users (28-62 years). All listeners reported regular use of digital HA technology in the nonimplanted ear. DATA COLLECTION AND ANALYSIS: Seven bimodal listeners were asked to balance the loudness of prerecorded single syllable utterances. The loudness-balanced stimuli were then presented via direct audio inputs of the two devices with an ITD applied. The task of the listener was to determine the perceived difference in processing delay (the interdevice delay [IDD]) between the CI and HA devices. Finally, virtual free-field MAA performance was measured for different spatial locations both with and without inclusion of the IDD correction, which was added with the intent to perceptually synchronize the devices. RESULTS: During the loudness-balancing task, all listeners required increased acoustic input to the HA relative to the CI most comfortable level to achieve equal interaural loudness. During the ITD task, three listeners could perceive changes in intracranial position by distinguishing sounds coming from the left or from the right hemifield; when the CI was delayed by 0.73, 0.67, or 1.7 msec, the signal lateralized from one side to the other. When MAA localization performance was assessed, only three of the seven listeners consistently achieved above-chance performance, even when an IDD correction was included. It is not clear whether the listeners who were able to consistently complete the MAA task did so via binaural comparison or by extracting monaural loudness cues. Four listeners could not perform the MAA task, even though they could have used a monaural loudness cue strategy. CONCLUSIONS: These data suggest that sound localization is extremely difficult for most bimodal listeners. This difficulty does not seem to be caused by large loudness imbalances and IDDs. Sound localization is best when performed via a binaural comparison, where frequency-matched inputs convey ITD and ILD information. Although low-frequency acoustic amplification with a HA when combined with a CI may produce an overlapping region of frequency-matched inputs and thus provide an opportunity for binaural comparisons for some bimodal listeners, our study showed that this may not be beneficial or useful for spatial location discrimination tasks. The inability of our listeners to use monaural-level cues to perform the MAA task highlights the difficulty of using a HA and CI together to glean information on the direction of a sound source.

Speech perception and short-term memory deficits in persistent developmental speech disorder.

Children with developmental speech disorders may have additional deficits in speech perception and/or short-term memory. To determine whether these are only transient developmental delays that can accompany the disorder in childhood or persist as part of the speech disorder, adults with a persistent familial speech disorder were tested on speech perception and short-term memory. Nine adults with a persistent familial developmental speech disorder without language impairment were compared with 20 controls on tasks requiring the discrimination of fine acoustic cues for word identification and on measures of verbal and nonverbal short-term memory. Significant group differences were found in the slopes of the discrimination curves for first formant transitions for word identification with stop gaps of 40 and 20 ms with effect sizes of 1.60 and 1.56. Significant group differences also occurred on tests of nonverbal rhythm and tonal memory, and verbal short-term memory with effect sizes of 2.38, 1.56, and 1.73. No group differences occurred in the use of stop gap durations for word identification. Because frequency-based speech perception and short-term verbal and nonverbal memory deficits both persisted into adulthood in the speech-impaired adults, these deficits may be involved in the persistence of speech disorders without language impairment.

Effects of temporal and spectral alterations of speech feedback on speech production by persons with hearing loss.

OBJECTIVE: To evaluate the effects of delay and spectral alteration of speech feedback (SF) on the speaking rate and voice pitch in adult users of hearing aids (HAs) and cochlear implants (CIs). METHODS: Repeated-measure, completely crossed, 2-factor design. Spectral alterations were implemented by replacing SF with noise that was filtered into 1-, 2-, or 4-frequency bands and speech-modulated in real time. Delays varied from 25 to 200 milliseconds. SUBJECTS: Seven HA users with severe to profound hearing loss and 6 CI users were randomly recruited by public advertising. All were postlingually deafened adults with intelligible speech. RESULTS: The average speaking rate significantly decreased and rate variability significantly increased with increase in SF delay for both groups. Spectral alterations of SF reduced the effect on speaking rate in the HA group but not in the CI group. Spectral alterations did not significantly affect rate variability in the HA group but did so in the CI group. Average voice pitch increased significantly with increase in SF delay and with spectral alterations of SF in the HA group. No significant effects on average pitch of CI users were noted. CONCLUSIONS: The 2 groups were affected differently by the delay and spectral alterations of SF. The differences possibly reflect greater spectral resolution ability in the case of CI users and greater audibility of bone-conducted SF (particularly in the low-frequency region) among the HA users.

Semantic aspects of morphological processing: transparency effects in Serbian.

We examined the contribution of semantics to morphological facilitation in the visual lexical decision task at two stimulus onset asynchronies (SOAs) with Serbian materials. Primes appeared in Roman or Cyrillic characters. Targets always were printed in Roman. When primes were presented at an SOA of 250 msec, decision latencies to verbal targets (e.g., VOLIM) showed greatest facilitation after inflectionally (e.g., VOLE) related primes, significantly less after semantically transparent derived primes (e.g., ZAVOLE), and less again after semantically opaque derived primes (e.g., PREVOLE). Latencies after semantically transparent and opaque derived target words did not differ at an SOA of 48 msec. Both were slower than after inflectionally related primes. Stated generally, effects of semantic transparency among derivationally related verb forms were evident at long SOAs, but not at short ones. Under alphabet-alternating conditions, magnitudes of facilitation were greater overall, but the pattern was similar. The outcome suggests that restricted processing time for the prime limits the contribution of semantics to morphological processing and calls into question accounts that posit a task-invariant semantic criterion for morphological decomposition within the lexicon.