Page 17 - Summer 2008

BINAURAL HEARING—BEFORE AND AFTER THE STETHOPHONE
Nicholas J. Wade
School of Psychology, University of Dundee
Dundee DD1 4HN, United Kingdom
and
Diana Deutsch
Department of Psychology, University of California, San Diego La Jolla, California 92093
The late eighteenth century wit- nessed many revolutions in both sci- ence and society, but one of the former remains relatively unsung—the revolu- tion in binaural hearing. The experi- mental endeavors of Ernst Florens Friedrich Chladni (1756–1827) shown
1
in Fig. 1 are well known. Indeed,
Chladni has been called the father of acoustics. Chladni investigated the characteristics of vibrating strings and plates and advanced the physical
2-4
Battista Venturi (1746–1822), and repeated Venturi’s sugges- tion that localization of sounds was dependent upon inequali- ties at the two ears. Despite the fact that between 1796 and 1802, Venturi6-9 described essentially the same four experi- ments in French, German and Italian, few (other than Chladni) took note of them. Even earlier, in 1792, William Charles Wells (1757–1817) examined some theoretical aspects
However, he paid relatively little attention to the then contemporary deliberations on binaur- al hearing. In his Akustik of 1802 he did cite the experiments of Giovanni
analysis of sound.
10,11
Venturi on binaural hearing, as well as that of others in the
of binaural hearing.
We here describe the work of Wells and
“In much the same way that binocular vision was studied theoretically and experimentally before the invention of the stereoscope, binaural hearing was examined before suitably selected sounds could be delivered to each ear by means of the stethophone.”
early nineteenth century, particularly
12
1859 to listen to different sounds sep- arately with each ear. It was the audi- tory equivalent of the stereoscope. In much the same way that binocular vision was studied theoretically and experimentally before the invention of the stereoscope, binaural hearing was examined before suitably selected sounds could be delivered to each ear by means of the stethophone. The early studies on binaural hearing were informed by comparisons with binocular vision, and so we introduce this history with a contrast between
these two aspects of integrated perception.
Sound and sight
The nature of sound was appreciated long before that of light. First, sound was never associated with its production in
13
Alison and his stethophone.
The stethophone was invented in
It was not until the seven- teenth century, with Kepler’s analysis of optical image forma- tion in the eye, that a receptor theory of light was generally accepted. Prior to that, extramission theories (that light was produced within the eye) were accepted. This was principal- ly based on the observation that light could be seen in the dark when pressure was applied to the eye. Sound, on the other hand, has been associated with vibrations of bodies and their transmission through a medium at least since the time of the ancient Greeks. In short, the ear was not endowed with the generative properties that were attributed to the eye. Secondly, the nature of the stimulus for sound was appreciat- ed (if not fully understood) before that of light. The seven- teenth century disputes between corpuscular and wave theo- rists remain unresolved, as the duality of light is still with us. Thirdly, stimulus manipulations of sound have a longer his- tory than those for light. Light has been examined in terms of its reflections and refractions for centuries, but the nature of
the ears, as light was in the eyes.
the stimulus remains a mystery.
Paradoxically, although much was known about the nature
of sound in early times, experiments on hearing lagged behind those on vision until the twentieth century. In particular, differ- ences in the patterns of stimulation at each ear were not exam- ined with the consistent concern that was applied to differences in the stimuli to each eye. There were at least three reasons for this: First, phenomenal differences could readily be perceived
Fig. 1. “Chladni figures” by Nicholas Wade. The portrait of Ernst Chladni is embed- ded in an array of acoustic figures taken from his “Traité d’Acoustique.”4 The por- trait is derived from a frontispiece engraving in John Tyndall’s book on “Sound.”5
16 Acoustics Today, July 2008