Degenerative Encephalopathy in Nova Scotia Duck Tolling Retrievers Presenting with a Rapid Eye Movement Sleep Behavior Disorder.

BACKGROUND: Neurodegenerative diseases are a heterogeneous group of disorders characterized by loss of neurons and are commonly associated with a genetic mutation. HYPOTHESIS/OBJECTIVES: To characterize the clinical and histopathological features of a novel degenerative neurological disease affecting the brain of young adult Nova Scotia Duck Tolling Retrievers (NSDTRs). ANIMALS: Nine, young adult, related NSDTRs were evaluated for neurological dysfunction and rapid eye movement sleep behavior disorder. METHODS: Case series review. RESULTS: Clinical signs of neurological dysfunction began between 2 months and 5 years of age and were progressive in nature. They were characterized by episodes of marked movements during sleep, increased anxiety, noise phobia, and gait abnormalities. Magnetic resonance imaging documented symmetrical, progressively increasing, T2-weighted image intensity, predominantly within the caudate nuclei, consistent with necrosis secondary to gray matter degeneration. Abnormalities were not detected on clinicopathological analysis of blood and cerebrospinal fluid, infectious disease screening or urine metabolite screening in most cases. Postmortem examination of brain tissue identified symmetrical malacia of the caudate nuclei and axonal dystrophy within the brainstem and spinal cord. Genealogical analysis supports an autosomal recessive mode of inheritance. CONCLUSIONS AND CLINICAL IMPORTANCE: A degenerative encephalopathy was identified in young adult NSDTRs consistent with a hereditary disease. The prognosis is guarded due to the progressive nature of the disease, which is minimally responsive to empirical treatment.

Hemiclonal analysis reveals significant genetic, environmental and genotype x environment effects on sperm size in Drosophila melanogaster.

Spermatozoa are the most diverse of all animal cells. Variation in size alone is enormous and yet there are still no clear evolutionary explanations that can account for such diversity. The basic genetics of sperm form is also poorly understood, although sperm size is known to have a strong genetic component. Here, using hemiclonal analysis of Drosophila melanogaster, we demonstrate that there is not only a significant additive genetic component contributing to phenotypic variation in sperm length but also a significant environmental effect. Furthermore, the plasticity of sperm size has a significant genetic component to it (a genotype x environment interaction). A genotype x environment interaction could contribute to the maintenance of the substantial genetic variation in this trait and thereby explain the persistent inter-male differences in sperm size seen in numerous taxa. We suggest that the low conditional dependence and high heritability but low evolvability (the coefficient of additive genetic variation) of sperm length is more consistent with a history of stabilizing selection rather than either sexual selection or strong directional selection.

Predicted and measured speech recognition performance in noise with linear amplification.

OBJECTIVE: The purpose of this study was to investigate the applicability of the Speech Intelligibility Index (SII) in hearing aid fitting. It was hypothesized that estimated speech intelligibility, based on the SII, could be a more reliable measure than real speech recognition results for comparing hearing aid characteristics. DESIGN: The test subjects were 29 elderly persons (66 to 80 yr) with mild-to-moderate hearing loss, who were using monaurally fitted linear hearing aids. They were selected from the files at Sahlgrenska hearing clinic. Speech recognition scores were obtained at fixed speech-to-noise ratios with Phonemically Balanced (PB) words in speech-weighted noise and in low-frequency noise. A Just-Follow-Conversation (JFC) test was performed with connected speech presented in the same background noises. The subjects were tested without hearing aid and with their hearing aids set at three different frequency responses. Predicted speech recognition scores were calculated for each condition based on the SII, complemented with a correction for sensorineural hearing impairment. The calculations involved speech and noise spectra, pure tone thresholds and insertion gain responses. RESULTS: For each condition, the measured speech recognition scores were, on average, well predicted by the calculated scores. The intra-individual standard deviation of the predicted scores was estimated to be about one percent unit. The group results of the JFC test were in agreement with the word recognition results for the aided conditions, but a floor effect was observed for the unaided conditions. CONCLUSIONS: Speech intelligibility prediction based on the modified SII is a valid estimate of speech recognition performance of hearing-impaired persons with mild-to-moderate hearing loss. Estimated intelligibility based on the SII is more reliable than actually measured speech recognition performance, for comparing amplification conditions within subjects.

Threshold-based fitting methods for non-linear (WDRC) hearing instruments--comparison of acoustic characteristics.

Six threshold-based prescriptive methods for non-linear hearing instruments were compared for a standard audiogram and three simulated listening situations. Six hearing aids were programmed according to the manufacturers' recommended initial fittings for the specified audiogram. Coupler gain measurements were then made with speech-like signals, and loudness and speech intelligibility index (SII) were calculated. Large differences between estimated insertion gain-frequency responses were seen. These differences resulted in large differences in calculated loudness, whereas the SII calculations showed only small differences between the fitting methods. For two of the methods, DSL[i/o] and FIG6. a comparison between the original prescriptions and the hearing aid manufacturers' implementations of the prescriptions was made. The results showed large differences between prescribed and implemented gain.

Noise analysis of real-life listening situations for maximal speech audibility in hearing aid fitting.

This study attempts to prescribe hearing aid characteristics for one listening environment selected by an individual hearing aid user in order to provide better speech intelligibility than standard insertion gain prescriptions. The procedure is based on acoustic analyses of noise recorded by the user. The main purpose is to show the feasibility of the measurement and analysis procedure as a tool to investigate the consequences of the noise characteristics of everyday hearing aid use. The Speech Intelligibility Index (SII) is used as a criterion to optimize the insertion gain frequency response of the hearing aid. The results indicate that realistic background noise information is essential to achieve the best possible speech audibility. Maximizing the SII required higher insertion gain above 5000 Hz than assumed in conventional fitting procedures. Different insertion gain frequency responses are required for different listening conditions. The measurement procedure could identify acoustic listening conditions where hearing instruments would probably give no benefit.

Loudness discomfort levels and saturation levels in hearing aids prescribed for young persons.

Hearing aids were re-evaluated for 18 persons aged 11-16 years. Since these aids were fitted mainly using an informal test of aided loudness discomfort, the saturation levels were re-evaluated with a new magnitude-estimation procedure for measuring unaided and aided loudness discomfort levels. Sixteen subjects had used hearing aids capable of producing uncomfortably loud warble tones. New hearing aids were fitted according to the new loudness discomfort data and the NAL recommendation for insertion gain. When forced to choose between the previously prescribed hearing aids and the new aids after three weeks of real life comparison, most subjects preferred the new instruments, but three persons finally decided to wear hearing aids with saturation levels exceeding their loudness discomfort levels. The magnitude estimation procedure was found to be clinically feasible, although problems with the instruction caused uncertainty in some cases. Measured loudness discomfort levels increased 5-10 dB between test and retest sessions.

Quantization error in clinical pure-tone audiometry.

The current clinical procedure for pure-tone audiometry was analysed for statistical measurement errors. Theoretically, the root-mean-square (RMS) error in a single threshold measurement is always greater than the standard deviation (SD) of measured intra-individual test-retest differences, divided by the square root of two. The RMS error includes an additional quantization component, caused by the finite step size between presented signal levels. In Monte-Carlo simulations with 2-dB and 5-dB steps the quantization error was negligible compared with other errors. Therefore, the single-test RMS error can be estimated with sufficient accuracy from the test-retest SD. The simulated single-test RMS error decreased from about 2.7 dB about 2.3 dB when the audiometric step size was reduced from 5 dB to 2 dB. Hearing thresholds appeared to be about 1.7 dB better with 2-dB steps than with 5-dB steps.

Hearing aid gain for loudness-density normalization in cochlear hearing losses with impaired frequency resolution.

A theoretical criterion for preliminary prescription of hearing aid gain and frequency response was formulated on the basis of Zwicker's loudness model, modified for impaired auditory frequency resolution in cochlear hearing losses. The procedure was designed to restore normal relative loudness contributions from each frequency band of input speech. Prescribed frequency responses had less steep bass cut than recommended by either the Prescription of Gain/Output or the National Acoustic Laboratories' procedures, regardless of various model assumptions. Prescribed overall gain depended on the loudness growth assumed in the model. In cases where auditory filters are wider than normal and loudness recruitment is complete, the procedure yielded a nonlinear relation between hearing aid gain and hearing loss: Required insertion gain (in dB) was 25 to 30% of hearing threshold loss (in dB HL) for mild to moderate losses, but this percentage increased for more severe impairments. For cases with incomplete loudness recruitment, the model prescribed that insertion gain should be 40 to 50% of hearing threshold loss for a wide range of impairments.

Sound quality and speech reception for prescribed hearing aid frequency responses.

Four different prescriptions of hearing aid insertion gain versus frequency were validated with a group of 26 moderately hearing-impaired, elderly hearing aid users. Three prescriptions were based on calculating the loudness and articulation index (AI) for aided speech, and ranged from a frequency response with moderate high-frequency emphasis, restoring normal loudness for speech peaks, to a response with the greatest high-frequency emphasis, maximizing the AI. The fourth prescription was a well-established formula of the half-gain type. The frequency responses were evaluated by paired comparison ratings of the pleasantness and intelligibility of speech in noise, and by speech identification tests in noise. The subjects rated the flattest response as significantly more pleasant than the other responses, and significantly more intelligible than the prescription with maximal high-frequency emphasis. There were no detectable differences in signal/noise ratios required for 50% speech identification. These results indicate that a prescription that restores normal loudness for speech peaks in each critical band is probably more easily accepted than either a procedure which is intended to make all speech bands equally loud, or a prescription which maximizes the AI.

Preferred hearing aid gain in everyday use after prescriptive fitting.

The insertion gain preferred by a group of 26 moderately hearing-impaired, elderly hearing-aid users was investigated in everyday listening situations. The subjects used monaural behind-the-ear aids, carefully fitted according to a prescription formula of the half-gain type, validated and used at National Acoustic Laboratories, Australia. The fitting was checked with real-ear measurements of insertion gain and reviewed at one or more follow-up sessions. The subjects were strictly instructed to try the recommended volume control setting before reporting which setting they preferred. The prescription significantly over-estimated preferred gain by about 7 dB. No correlation could be detected between prescribed versus preferred gain differences and the amount of previous hearing-aid use or the degree of subjective hearing problems.

Multi-programmable hearing aid.

A basic problem in hearing-aid fitting is the difficulty in finding one setting optimal to all listening situations that might occur. The objective was to develop a behind-the-ear hearing-aid with a very flexible analog signal processor which is digitally controlled, and a memory with logic, so that the hearing-impaired person can select from eight completely different fittings. To program and adjust this multi-programmable hearing-aid (called MemoryMate) a hearing evaluation and recommendation system (called Master-Fit) has been developed, based on an IBM PS/2 computer. This system offers the dispenser prescriptive fitting methods and performance of real ear measurements. It can be used to manage a client database. Preliminary results from a clinical study conducted in 1988 are presented. The paper also describes the uniqueness of this multi-programmable hearing aid as a powerful new research tool.

Preferred hearing aid gain and bass-cut in relation to prescriptive fitting.

The insertion gain versus frequency, preferred by a group of moderately hearing-impaired, elderly, untrained hearing aid users was investigated both in everyday listening situations and in an acoustically specified test situation in the laboratory. The subjects used experimental binaural hearing aids with modified controls, which could be easily and accurately operated. They adjusted both gain and bass-cut while using the aids. Preferred insertion gain was compared with recommendations from three methods of prescriptive fitting. These methods significantly overestimated preferred gain by about 10 dB. Preliminary fittings should allow a gain reserve of about 15 db. Intra-individually, a gain range of about 11 dB is often sufficient for different everyday situations.

The reliability of insertion gain measurements using probe microphones in the ear canal.

Two methods are now available for measuring the insertion gain as a clinical procedure; the ear canal microphone- and the soft probe tube microphone-system. It was decided to investigate some of the variables affecting the reliability of the insertion gain measurements, such as the measurement location and head movement effects, as well as factors related to the presence of the ear canal microphone in the auditory canal. The last variable exhibited significant systematic differences of -2 to 4 dB in the measured insertion gain with the ear canal microphone compared to the measurement obtained with the probe tube microphone. The intrasubject standard deviations were about the same for both methods and less than 4 dB in the frequency range 0.25 to 4.0 kHz. Finally when making clinical hearing aid recommendations using the probe tube microphone technique the errors in one insertion gain measurement are within 95% probability +/- 2 to +/- 8 dB in the frequency range 0.25 to 4.0 kHz.

Analysis of hearing aid fittings using insertion gain measurements.

Insertion gain was measured in 166 persons after they were fitted with a hearing aid according to the Swedish prescription guidelines. Fitting was considered inadequate (1) when the levels of the long-term RMS speech spectrum were not amplified above the tone threshold at 1.0, 1.5 and 2.0 kHz, or (2) when the speech peak levels did not exceed the tone thresholds at 3.0 and 4.0 kHz. At least 40% of the subjects were found to have inadequate amplification according to these criteria. This number increased further when the measured insertion gain was compared with the gain recommended by other investigators. Our results indicate that real ear insertion gain measurements should be introduced as a routine clinical procedure in the fitting of hearing aids.

Hearing aid prescription rules using insertion gain measurements.

Many of the decisions regarding hearing aid selection and use are based mainly upon clinical impressions. It was therefore decided to investigate whether the old fitting of 25 aided subjects with moderate hearing loss could be improved by using more precise prescription rules and a real ear measuring technique. The rules formulated should give a frequency response of moderate low and pronounced high frequency gain. The application of these rules resulted in improved high frequency gain and better speech discrimination for consonants in noise. As a result of the investigation, the routine procedure of hearing aid fitting has been revised. Earmold modifications of different types should be used more often and real ear canal measurements are recommended for incorporation in the routine examination of hearing aid performance.

Audiometric earphone discomfort level and hearing aid saturation sound pressure level for a 90 decibel input signal (SSPL90) as measured in the human ear canal.

The acoustical problems involved in matching the saturation sound pressure level for a 90 dB input signal (SSPL90) of a hearing aid to individual discomfort level were investigated. The real ear SPL (RE/SSPL90) produced by a supra-aural earphone used when measuring uncomfortable loudness (UCL), and RE/SSPL90 produced by three different hearing aids at 90 dB SPL input, were measured for nine subjects, using a miniature microphone technique, and compared to the corresponding coupler levels used when matching hearing aid maximum output to UCL. It was found that a hearing aid often gives about 5 dB, and sometimes 10 dB, higher RE/SPLs than the earphone, if the hearing aid output levels, as measured in a 2-cc coupler (IEC126), are equal to the earphone output levels as measured in a 6-cc coupler (NBS9A). It is recommended that a safety margin of at least 5 dB be used in the preliminary fitting when matching hearing aid SSPL90 to the patient's UCL, converted to dB SPL.

A simplified real ear technique for verifying the maximum output of a hearing aid.

Real ear SPL (RE/SSPL90) produced by four different hearing aids was compared to the standard SSPL90 measurements for the same hearing aids on a 2-cc coupler. The effects of venting, location, and reliability for RE/SSPL90 were also studied. As expected, the real ear output level was greater than the coupler level. No systematic influence of earmold venting was found. An earmold that occludes an ear canal decreases the output in the high-frequency range so that only a small difference remains between RE/SSPL90 and 2-cc coupler levels above 2000 Hz. The difference seems to be affected slightly by the output impedance of the hearing aid receiver system. Individual variation for the RE/SSPL90 is as much as 10 dB. Finally, the saturated output levels measured were found to be insensitive to changes in actual microphone input levels caused by different procedures for calibrating ambient SPL. The RE/SSPL90 method is easy to use and reliability seems quite adequate for the typical clinical setting.

Analysis of the mechanical impedance of bone-anchored hearing aids.

Some patients who need hearing aids are unable to use an apparatus which transmits the sound via the external ear canal and have to use a bone conduction hearing aid. The bone vibration transducer of this aid is applied to the skin over the mastoid process and the sound is transmitted via the soft tissue and bone to the cochlea. The pressure needed to apply the transducer often gives the patient discomfort and the damping effect of the soft tissue gives poor quality of the sound transmitted. Advances in the ability to permanently implant foreign material in the body and perform permanent skin penetration has made it possible to develop a bone-anchored hearing aid. Fourteen patients have been equipped with such hearing aids. To be able to give these patients the best hearing aid, a new transducer has to be constructed to match the new situation. The impedance of the bone-anchored titaniumscrew/skull has been studied and the resistance and reactance of the mechanical impedance have been measured. The influence of a damping soft tissue layer over the bone has been analyzed. The difference between the impedance of the skull and the impedance of the soft tissue + skull was in the order of 10 to 25 dB depending on the frequency.