The mechanism of physiological height vertigo. I. Theoretical approach and psychophysics.

A theory is presented supporting a geometrical explanation of physiological height vertigo as a 'distance vertigo' created by visual destabilization of posture when the distance between the observer and visible stationary contrasts becomes critically large. Though height vertigo is generally regarded as a psychopathological process, we hypothesize that it might instead result from an intersensory mismatch when visual information is at variance with vestibular and proprioceptive inputs. Psychophysical experiments confirming the hypothesis revealed that: 1) height vertigo is clearly related to body position, being the greatest in the upright stance; 2) it is the eye-object distance rather than the direction of gaze which is critical; 3) there is a saturation of height vertigo magnitude. Subjective vertigo increases with increasing altitude only below 20 metres. Physiological 'distance vertigo' must be distinguished from psychological 'acrophobia'. Its postural consequences may be ameliorated by strategies gleaned from knowledge of its mechanism such as providing nearby stationary contrasts in the peripheral visual field.

The mechanism of physiological height vertigo. II. Posturography.

In order to validate the hypothesis that height vertigo is based on visual destabilization of free stance when the distance between eye and object becomes critically large, several of its consequences were demonstrated in posturographic experiments: (1) Visual signals conflicting with simultaneous vestibular and somatosensory inputs provided by sinusoidally tilting rooms may destabilize postural sway in the fore-aft as well as in the lateral direction. (2) In natural surrounding sway amplitudes increase with increasing eye-object distance up to 5 meters. Thus, teleologically, subjective height vertigo serves as an appropriate warning signal to withdraw the body from a stimulus situation inducing postural imbalance. (3) Postural height vertigo problems can be alleviated (a) by adjusting the head relative to the gravitational vector, and (b) by the presence of nearby stationary contrasts in the visual periphery according to the dominance of retinal periphery for dynamic spatial orientation.

[Rehabilitation possibilities in presbycusis]. / Revalidatiemogelijkheden bij presbyacusis.

Although several types of hearing loss in aged people can be distinguished, the word presbyacusis has grown to common use. It is not primarily the decrease of sensitivity for sounds, but rather the decrease of the ability for discrimination and the increase of being troubled by noisy circumstances, that impair understanding of speech. Conversation with aged people have to be practised slowly and in a well pronounced way in favourite circumstances for listening. The hearing impairment in aged people can grow to a problem, especially by the social circumstances, so rehabilitation may not be restricted to the aged themselves. A good insight in the remaining abilities of the hearing is the base for the prescription and the acceptance of a hearing aid. In this the fitting of the earmold and the adjustment of the output level-limiter are the most important factors. The participation in the verbal communication can become more easy and relaxed by a clever usage of the aid's abilities, but the partners in the conversation have to understand the difficulties and to be cooperative.

[Rehabilitation possibilities for hearing-impaired subjects]. / Revalidatiemogelijkheden voor slechthorenden.

Hearing impairment is a symptom, not a diagnosis. A number of types of hearing impairment can be distinguished. The self-reported hearing problems cluster around six hearing factors, the most important of which are speech understanding in noise and localisation of a sound source. For these capabilities equivalent functioning of both ears is important. The general practitioner can determine diagnosis and severity of the impairment using rather simple tools. When the cause of the impairment cannot be reduced in a proper way an adaptation of the sound to the impaired ear will be indicated. This can be arranged by either an ENT specialist or a centre for audiology. The selection of a proper hearing aid requires expertise and particular attention for the complaints. It is of the utmost importance that the hearing-impaired person can try out the effects of the hearing aid in daily circumstances for some weeks. If the patient, members of the family or the prescriber are not satisfied with the results, supplementary help is required, for example training in communication skills or special devices.

Satisfaction with fitted hearing aids. I. An analysis of technical information.

By means of a questionnaire, satisfaction with fitted hearing aids has been judged 6 months after prescription. An analysis of the information obtained, together with some audiological features of 155 patients with hearing aids is reported. The influence of the most important factors is discussed and the findings are compared with those of other surveys. The relationship between satisfaction, and the degree of hearing loss and discrimination loss is very weak. The conclusion is that the population consists of sub-populations in which different criteria apply to hearing aid satisfaction. These criteria may be more closely related to psycho-social factors than to technical aspects. A second part of the study is devoted to that subject.

Satisfaction with fitted hearing aids. II. An investigation into the influence of psycho-social factors.

In the first article an analysis of technical information about hearing aid satisfaction, obtained by a questionnaire, was presented. To obtain complementary information, interviews were held with patients who showed a low satisfaction. This has led to an inventory of the factors in the psycho-social field of importance in the process of rehabilitation. The questionnaire has been modified and 165 hearing aid patients have been evaluated with this updated questionnaire. Analysis of the information obtained shows that the answers given intercorrelate well. It may be surmised that the approach is based on a sort of "attitude" incorporated in the given score and defining the hearing aid satsifaction. The audiometric features of the patients intercorrelate as well. It is surprising that the correlation between the audiometric features and the satisfaction with the aid is low, and this is discussed. The question arises as to what degree the routine audiometric tests reveal the relevant features and the impaired hearing. Where it seems to be impossible to use the available audiometric features for making a prediction about the satisfaction, the conclusion is drawn that full attention must be given to training in the use of the hearing aid.

Factors in the appreciation of a prosthetic rehabilitation.

6 months after the prescription of a hearing aid, the appreciation of the aid was judged in a group of 160 patients by a questionnaire. The analysis of the answers in combination with the audiometric features is reported. The answers given in a questionnaire have a good interrelation and agree with the score given for the aid. The audiometric features also showed a good correlation for every one but only a weak relation was found with the subjects' appreciations of the aid. The implications of this hearing aid evaluation for the improvement of the fitting procedure are discussed.

Technical possibilities in the school situation for the education of hearing-impaired children.

For hearing-impaired children, the main problem in the classroom is the signal-to-noise ratio. To improve the signal-to-noise ratio, several class systems have been developed, three of which have been investigated in this study. The systems are shown to be equivalent in a situation without a channel for pupil response. Application of such pupil response channels will decrease the improvement in signal-to-noise ratio brought about by the class system. It is argued that the choice among several combinations of class system and pupil response channel is governed by the primary goal of education and how this goal is to be achieved.

Effect of time scale modification of speech on the speech recognition threshold in noise for elderly listeners.

The effect of time scale modification of speech on the speech recognition threshold in noise (SRTN) was investigated for a group of 44 elderly subjects, varying in age from 56 to 88 years with sloping mild-to-moderate sensorineural hearing losses. Subjects' pure-tone average thresholds at 500, 1,000 and 2,000 Hz (PTA1) ranged from 3 to 58 dB. The study confirms the well-known fact that speech recognition in noise deteriorates with increasing age. Furthermore, time-compressing speech results in an even greater influence of age on the SRTN. The apparent age effect on SRTN values referenced to SRTN in the control condition is mostly caused indirectly by the significant correlation between age and PTA1, although there was a slight tendency for age to have a greater independent effect on relative SRTN values when the amount of time compression increased. The percentage of explained variance in relative SRTN values by the subject variables in this study was limited, indicating that there are other factors not investigated in this study (e.g. cochlear mechanisms, short-term memory, feature extractors) that significantly influence the effect of time compression on SRTN.

A proposal for a model to calculate hearing disability.

The present paper presents an alternative method to calculate hearing disability. As opposed to existing models to calculate hearing disability, the present method is not just based on the pure-tone audiogram. Hearing activities playing an important role in daily listening are taken into account: detection of sounds, distinction of sounds, intelligibility in quiet and in noise, auditory localization. Psycho-acoustical tests to measure each of these activities are described. Test scores are used to calculate overall hearing disability. A comparison is made between the present model and the method of the American Medical Association (AMA). Calculations are based on theoretical cases only. Further study has to be undertaken to verify the calculations by examining the scores of real cases to improve the validity and internal consistency of the present model.

The effects of involvement of the general practitioner and guidance of the hearing impaired on hearing-aid use.

A number of international and national publications report that hearing aids are sometimes under used. In this paper, results are reported of a project to increase the effective use of hearing aids. The first intervention was aimed at a more effective exchange of information between the general practitioner (GP) and the ENT specialist. This was achieved by the introduction of a structured referral form. In addition, a simple hearing aid was placed at the GP's disposal for demonstration purposes. As a second, independent intervention, 50% of the patients were visited at home by a trained volunteer. A measure of effective use that combines the effectiveness and actual use had been developed. After the first intervention the non-effective use of hearing aids decreased from 38% to 30%, this being just below statistical significance (p = 0.12). The protocol approach by the GP in combination with the demonstration hearing aid proved to be especially useful. Patients with a counselling visit at home had a significantly lower level of non-effective use (27% versus 37%; p < 0.05) than patients who had not been visited.

The cancellation method for an accurate determination of an air-bone gap.

For a reliable detection of the bone conduction threshold blocking of the contralateral ear can be necessary but then the noise will affect the threshold in the test ear. To resolve this problem the cancellation method is used. The equalization of air and bone conduction sound level in the inner ear is very accurate, the relation between the intensities has been proved to be linear and independent of noise at the contralateral ear. An application for calibration of the bone conduction vibrator to the head phone is discussed. The benefit of the method for measuring an air-bone gap in an accurate way in patients suffering bilaterally from a severe conductive hearing loss is shown.

Effect of time-scale modification of speech on the speech recognition threshold in noise for hearing-impaired and language-impaired children.

In this study, the effect of time-compression and expansion of speech on speech perception in noise was measured for a group of hearing-impaired and a group of language-impaired children relative to control groups of normal children and normal adults. The children's ages ranged from 9 to 12 years. For all time-scale modified conditions, both hearing-impaired and language-impaired children had significantly higher speech recognition thresholds in noise (SRTN) than their normal peers, who performed almost equally well as the adult control group. Time-expansion was shown to have a negligible effect on SRTN for all groups when compared to the control condition, i.e. 0% time-compression. The difference in SRTN between the control and the impaired groups was, in general, not significantly altered by the degree of time-compression or expansion of speech, although a clear trend towards greater differences for increasing time-compression was observed. Five tests of auditory discrimination and auditory memory were also administered to both groups of impaired children. In a step-wise multiple regression procedure, 94% of variation in SRTN in the control condition could be explained by the score on the ADIT C (type Wepman; discrimination task) and the maximum speech recognition score for monosyllables in quiet.

The self-reported handicapping effect of hearing disabilities.

This study investigates the extent to which individuals see themselves as being handicapped by a hearing disability. Self-reports were obtained with the Amsterdam Inventory for Auditory Disability and Handicap which distinguishes five basic disabilities: intelligibility in noise, intelligibility in quiet, localization of sounds, distinction of sounds and detection of sounds. Responses of 239 hearing-impaired people with varying types of hearing loss have been examined. The occurrence of the five disabilities in the population as well as the self-reported limiting and annoying effect per disability has been examined. This study shows that the handicapping effects of the disabilities do not have equal weights. Handicap resulting from the inability to understand speech in noise is most strongly felt. This paper argues that the type of disability jointly determines the severity of a person's handicap.

Height vertigo and human posture.

A theory is presented supporting a geometrical explanation for physiological height vertigo being a distance vertigo through visual destabilization of postural balance when the distance between the eyes and visible stationary contrasts becomes critically large. Physiological and posturographic data obtained under natural height vertigo conditions are consistent with this hypothesis.