No abstract

A quantitative theory of the middle-ear acoustics is developed and expressed in terms of an electric analog.The analog network is based on the functional anatomy of the middle ear. The numerical values of its elements are derived from impedance measurements on normal and pathological ears and from anatomical data. It is shown that the input impedance of the analog agrees within the experimental error with the acoustic impedance at the eardrum, and that changes in analog parameters corresponding to known anatomical changes produce the same effect on its impedance characteristics as measured at the eardrum. • G. von Bik6sy and W. A. Rosenblith, "The Early Histo W of HearingsObservations and Theories," J. Acoust. Soc. Am. 20, 727 (1948).They should vanish gradually, as the experimental redundancy accumulates.The knowledge of the acoustic function of the middle ear may be synthesized in various ways. The most primitive way would be to build an artificial middle ear that would replicate the natural middle ear in every detail. This is impractical, however, and the analytic information that could be derived from such an undertaking would be low. Any more sophisticated model must be based on mathematical theory, explicitly or implicitly. As a consequence, the theory developed in further portions of this paper is essentially mathematical, although it is presented in the disguise of an electric analog. Equations describing the action of various parts of the middle ear, as well as of the whole middle ear, are complex and their solution is tedious. It is more economical to express them by means of electrical networks and to study the input-output relation4 ships. In this form, the theory appears reasonably simple and straightforward. ANATOMICAL EVIDENCEThe acoustically important parts of the middle ear are shown schematically in Fig. 1. Proceeding from the outer-ear canal, the first part is the eardrum. To it is connected the chain of ossicles that consists of the malleus, incus, and stapes (hammer, anvil, and stirrup). The foot plate of the stapes is imbedded in the oval window of the inner ear and its motions are transmitted to the inner-ear fluids. The volume displacements produced by the stapes are compensated by nearly 1514

A theory of temporal auditory summation is developed and applied to the threshold of audibility for various temporal patterns of pulses and sinusoidal vibrations. The theory is based on the assumption of an exponential decay of neural excitation and, for the threshold of audibility, it includes only one time constant. Various factors that may affect temporal auditory summation are discussed. It is shown that the same theory applies to muscle contractions.

No abstract

The just noticeable difference in dichotic phase, as a function of sensation level and of frequency, has been determined on a number of listeners with normal hearing. The test tones were transmitted by earphones, and the phase difference between the ears was varied by means of an electronic phase shifter. The psychophysical method used combined paired comparisons and forced choice. The first tone pulse of each pair presented was kept at a constant phase difference at which the subject localized the sound source as equidistant from his ears. The dichotic phase difference of the second pulse was varied irregularly (“randomly”). The results show that the sensitivity to dichotic phase difference is highest (2° of phase) at medium sensation levels, and that the jnd increases with positive acceleration as the sound frequency increases. Around 1300 cps the jnd becomes so great that it cannot be measured. The dichotic time difference calculated from the measured jnd in phase has a minimum near 800 cps.