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that switched continuously between ears. At slow switching rates, listeners could easily follow the speech however, as switching rates became faster, intelligibility dropped consid- erably, with a maximum dip at a switching rate of 3 cycles per second. The authors interpreted their findings as reflecting a limit to the rate at which attention could switch between ears. However, it was later found that when noise was presented to the ear contralateral to the one receiving the speech signal, so that both ears received input simultaneously, performance rose again to a high level, showing that a slow switching
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Weber30 on the perceived ticking of two pocket watches that were placed one to each ear. Weber’s experiment is perhaps even more closely related to one by Axelrod and coworkers68 who asked listeners to compare the repetition rates of two series of clicks under various conditions. When the clicks were presented to the two ears in alternation, their rates were considerably underestimated relative to monotic presenta- tion, and the degree of underestimation increased with increasing presentation rate. We may surmise that in the dichotic condition the perceived rate was a compromise between the rate perceived on listening to each ear separate- ly and that perceived on listening dichotically.
Concerning Wells’ early speculation10 that different sounds presented simultaneously but separately to the two ears would not coalesce perceptually, recent work has shown that binaural fusion can indeed occur, particularly for sounds
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As a related finding, the contribution of a single mistuned har- monic to the pitch of a complex tone was almost as great when it is presented to a different ear as when it is presented
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also considered binaural rivalry that was stimulated by work on the simultaneous presentation of different colors to each eye. It has been shown recently that for certain dichotic con- figurations, the listener tends to follow the pitches presented to one (dominant) ear rather than the other, and this can happen even when the amplitude of the signal to the non-
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mechanism could not account for the results.
The above experiments can also be related to that of
More specifically, the early suggestion by Wheatstone27 that presenting two harmonics separately to each ear would not result in the perception of the fundamental has been disconfirmed. When two adjacent harmonics of the same fundamental are fed to different ears, listeners can identify the pitch of the fundamental,70 and the identification of the pitch of a two-tone complex with miss- ing fundamental is only weakly affected by whether the com-
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to the same ear.
As described above, early thinking about binaural fusion
built on the same fundamental.
ponents are fed to the same ear or to different ears.
dominant ear is considerably higher in amplitude.
Dove’s early report of the existence of binaural beats has been confirmed by twentieth century studies that showed that such beats were heard at low rather than high frequencies, and
were most salient at frequencies around 400-600 Hz.
The investigations of Wells, Venturi, Alison and others on binaural hearing were conducted without the instruments that could adequately control the stimuli and their delivery to the ears. The questions that they posed have been addressed in the twentieth century and their thoughtful conjectures have been
confirmed in some cases and disconfirmed in others. Their revolutionary research should be applauded because of the leaps of their imaginations—they used their (binocular) vision to derive insights into their (binaural) hearing.
Conclusion
The study of binocular vision has had a profound influ- ence on that of binaural hearing. Both Wells10 and Venturi6-9 were led to the examination of binaural hearing following their studies of dichoptic color mixing. However, it proved more difficult to manipulate the temporal characteristics of sound stimuli than the spatial aspects of light. Alison’s stetho- phone12 could have opened the way to more systematic stud- ies of binaural hearing, but it was Thompson’s pseudophone49 that was to have a greater impact. Modern studies have drawn attention to complexities of the binaural stimuli that were unknown to its early pioneers.AT
References
1 R. T. Beyer, Sounds of Our Times: Two Hundred Years of Acoustics (American Institute of Physics, Melville, 1998).
2 E. F. F. Chladni, Entdeckungen über die Theorie des Klanges (Weidmanns Erben und Reich, Leipzig, 1787).
3 E. F. F. Chladni, Die Akustik (Breitkopf und Härtel, Leipzig, 1802).
4 E. F. F. Chladni, Traité d’Acoustique (Courcier, Paris, 1809).
5 J. Tyndall, Sound. A Course of Eight Lectures Delivered at The Royal Institution of Great Britain (Longmans, Green, London,
1867).
6 J. B. Venturi, “Considérations sur la connaissance de l’étendue
que nous donne le sens de l’ouïe,” Magasin Encyclopédique, ou
Journal des Sciences, des Lettres et des Arts 3, 29-37 (1796).
7 J. B. Venturi, “Betrachtungen über die Erkenntniss des Raums durch den Sinn des Gohörs,” Magazin für den neuesten Zustand
der Naturkunde 2, 1-16 (1800).
8 G. Venturi, “Riflessioni sulla conoscenza dello spazio, che noi
possiamo ricavar dall’udito,” in Indagine Fisica sui Colori by G.
Venturi (Tipografica, Modena, 1801), pp. 133-149.
9 J. B. Venturi, “Betrachtungen über die Erkenntniss der Entfernung, die wir durch das Werkzeug des Gehörs erhalten,”
Archiv für die Physiologie 5, 383-392 (1802).
10 W. C. Wells, An Essay upon Single Vision with two Eyes: together
with Experiments and Observations on several other Subjects in
Optics. (Cadell, London, 1792).
11 Wells’s book on binocular single vision, as well as his autobio-
graphical sketch, have been reprinted in: N. J. Wade, Destined for Distinguished Oblivion: The Scientific Vision of William Charles Wells (1757-1817) (Kluwer/Plenum, New York, 2003).
12 S. S. Alison, “On the differential stethophone, and some new phenomena observed by it,” Proceedings of the Royal Society of London 9, 196-209 (1859).
13 N. J. Wade, “Light and sight since antiquity,” Perception 27, 637- 670 (1998).
14 N. J. Wade, “On the late invention of the stereoscope,” Perception 16, 785-818 (1987).
15 N. J. Wade, A Natural History of Vision (MIT Press, Cambridge, MA, 1998).
16 N. J. Wade, and H. Ono, “From dichoptic to dichotic: historical contrasts between binocular vision and binaural hearing,” Perception 34, 645-668 (2005).
24 Acoustics Today, July 2008