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Repetitive rotational stimuli simulating natural head movements have been applied to the study of the vestibular evoked response in normal subjects and 12 patients with complete loss of vestibular function. Special precautions were taken to eliminate all possible sources of artefacts, in particular, all eye movements were restrained by requiring the subject to fixate upon a target light attached to the rotating chair throughout the course of the test. With a stimulus of 2 sec duration the typical response took the form of a slow negative wave with a mean peak amplitude of approximately 24 microV and maximally recorded from the vertex. It was characteristically absent in the patient group. Occasionally, both in normal subjects and patients it was preceded by a long latency complex thought to be non-vestibular in origin. Tests carried out both in total darkness and in the light show a statistically significant increase in the potential in the latter condition indicating an influence of the optokinetic effect exerted by the visual surround. Further studies have explored the phase changes brought about by varying the amplitude and duration of the stimulus. These have revealed certain parallels in the results of recent animal experimental studies.

The effect of peripheral vision upon the suppression of caloric induced nystagmus has been studied in normal subjects and patients with Parkinson's disease and cerebellar lesions. In normal subjects, caloric responses in the presence of optic fixation upon a target light viewed in darkness are further suppressed by a factor of two when background illumination is introduced. In both patient groups background illumination had significantly less effect. Additionally, optokinetic and pursuit test have revealed specific abnormalities consistent with the notion of a peripheral retinal feed-back mechanism deranged by disease. These in turn appear to have particular relevance to certain visuo-vestibular disturbances characteristic of patients in both groups.

Publisher Summary This chapter reviews the music appreciation capabilities of deaf people. Different types of deafness because of a variety of conditions are collectively known as conductive deafness as they impair the conduction of sound from the outer ear to the inner ear. They result in a simple attenuation of sounds that can be rectified with a hearing aid given sufficient amplification to overcome the deafness. Although complete restoration of speech recognition can be accomplished in this way, miniaturization imposes severe restrictions on the frequency response of hearing aids. As a result, the full spectrum of sounds so necessary for musical appreciation and enjoyment is lacking. Loudness recruitment is essentially a disorder of the loudness function whereby the deafness present at threshold intensities seems to disappear at higher sound intensities. The surprising result is that such patients, although deaf for all practical purposes, will complain bitterly about the irritating loudness of, for example, pop music played too loudly or the shouting of children at play.

Publisher Summary This chapter focuses on the dilemma of electronystagmography. One of the considerable advantages of the caloric test is that by isolating the stimulus, it enables the function of one labyrinth to be determined independently of the other. The resulting heat transfer across the labyrinth brings about convection currents in the canals that produce copular deflections in much the same way as if the patient had been subjected to an angular acceleration about the vertical axis. However, in the case of the caloric test, the copular movement is restricted to only one canal. These copular movements, in turn, give rise to induced nystagmic movements of the eyes, which can be observed by direct observation. Results of caloric tests carried out in this way are now well documented in a wide range of pathological processes affecting the vestibular system. A particular feature of the test is that it is normally carried out with the patient fixating a target immediately above his head.

Publisher Summary This chapter discusses the psychological and physiological aspects of hearing. It is highly probable that the auditory characteristics of each species have evolved in ways most suited to the animals' requirements, which at times take on a remarkable specificity. The hearing mechanism is similar in all higher mammals and consists essentially of an outer ear, a middle ear, and an inner ear. The auricle or pinna is the visible portion of the ear. For it to collect and deflect sound into the ear, it is a matter of physical acoustics that its dimensions be at least comparable to or larger than the wavelength of the sound reaching it. Wavelength varies inversely with frequency, and in man, this condition prevails only at the highest audible frequencies. All sounds in air consist of rapid vibrations of the air particles that move backward and forward, imparting this movement to their neighbours so that waves of sound energy are propagated, which on reaching the tympanic membrane set it into sympathetic vibration.