Index of content:
Volume 34, Issue 9B, September 1962
34(1962); http://dx.doi.org/10.1121/1.1918337View Description Hide Description
The traveling‐wave theories are traced historically from their earliest formulation to modern times. Special consideration is given to the weighty influence on the later developments of these theories exerted by Békésy's direct visual observations of the movements of cochlear structures in response to sounds. Finally, a résumé is given of the characteristics of the tonal patterns and their dependence upon the physical variables operating within the cochlea, according to Békésy's experiments on mechanical models and specimens of human and animalears. Hereby are brought into focus the many conditions that a final theory of hearing must meet.
Bone Conduction: A Review of the Present Position with Especial Reference to the Contributions of Dr. Georg von Békésy34(1962); http://dx.doi.org/10.1121/1.1918339View Description Hide Description
The very great advances in our knowledge of bone conduction that have been made by Békésy's fundamental investigations are outlined and considered in relationship to the influence they have brought to bear upon the investigations of later workers in this field. The topics considered include the mode of vibration of the skull, the theoretical mechanisms of bone conduction, the so‐called occlusion effect, bone conduction in a free sound field, and the interaural attenuation across the head.
34(1962); http://dx.doi.org/10.1121/1.1918341View Description Hide Description
The audiometer that Békésy described in 1947 and the audiometric technique have permitted the measurement of auditory thresholds as a continuous function of frequency or of time, and have simultaneously provided a measure of the listener's variability. The clinical value of the instrument is seen in the detailed frequency characteristics of the threshold and other features that appear to have diagnostic significance. In the laboratory, the principles of the audiometer have been incorporated in ways that have permitted new kinds of problems to be studied. Particular reference is made to masked audiograms as a function of frequency and continuous recovery curves after exposure to sound.
34(1962); http://dx.doi.org/10.1121/1.1918343View Description Hide Description
With respect to the present inquiry, cochlear analysis of an applied signal is considered to be given by the distribution of amplitudes along the partition. Since Ohm and Helmholtz, this form of resolution has been thought to correspond to the result of a straightforward Fourier analysis. The present paper intends to show that cochlear models of the Békésy‐type perform a time/frequency analysis in the sense of Gabor. Along the existing time/frequency continuum, the response to sinusoidal signals represents one extreme, approaching a pure Fourier (frequency) analysis, and the response to transients the other extreme, approaching a pure time (waveform) analysis. Responses to all other signals arrange themselves between those two extremes; i.e., the resolution depends upon spectral as well as temporal features of the applied signal.
With modulated signals, a process of demodulation occurs. Its origin was finally traced to hydrodynamic events which take place in the region of rapid phase changes of the traveling waves. Since it occurs only along partitions in which stiffness varies with distance, this demodulation appears to be a characteristic property of Békésy models. From the analytic standpoint, demodulation is the detection of a temporal property of the signal.
34(1962); http://dx.doi.org/10.1121/1.1918345View Description Hide Description
Electron‐microscope studies of cross sections of hair bundles on the outer hair cells in the organ of Corti show a consistent orientation of the sensory hairs. In the cuticle, a basal body is regularly found on the side of the cell toward the Hensen's cells. The sensory hairs are organized in the shape of w pointing towards the basal body. The morphological polarization of the hair cells in the organ of Corti is discussed in the light of similar polarization of the hair cells in the vestibular sensory epithelia and the lateral‐line canal organs. A close relation is to be found between the morphological and electrophysiological polarization of the mechanoreceptors in the sense organs of hearing and equilibrium.
34(1962); http://dx.doi.org/10.1121/1.1918347View Description Hide Description
The structure and relationships of the hairs of the cochlear and vestibular sensory cells have been investigated in fixed and fresh tissue by light, phase contrast, and electron microscopy. The cochlear hairs closely resemble the stereocilia of the vestibular cells, but there are differences in size, number, and arrangement between those of the inner and outer hair cells. In the cuticlefree region of the cell surface, a basal body is found, corresponding to the single kinocilium on each vestibular cell. The stiff cochlear stereocilia are regarded simply as levers, transmitting mechanical energy from the overlying tectorial membrane by way of the cuticular plate to the basal body. It seems unlikely that their bending as such has the importance generally ascribed to it. In view of the great functional significance of modified kinocilia in other sense organs, the basal body, like the vestibular kinocilium with its associated mitochondria,membranes, granules, appears to be the essential excitable structure of the hair cells.
34(1962); http://dx.doi.org/10.1121/1.1918349View Description Hide Description
Calculations were made of the dimensions of traveling‐wave envelopes in four species. The calculations were based on Békésy's measurements of the tuning curves of single points on the basilar membrane of each species, and on four empirical functions, one per species, relating frequency to position of maximum amplitude on the basilar membrane. The functions were in approximate agreement with other observations by Békésy. It was found that the distances over which a traveling wave damps from maximum amplitude to fractions of maximum amplitude—i.e., to one‐half maximum, to two‐tenths maximum, or to “zero” amplitude, respectively—appear to be approximately constant, independent of the position of maximum amplitude on the membrane. In comparing the traveling wave envelopes of the four species, elephant, man, guinea pig, and chicken, it was found that (1) the shape of a traveling‐wave envelope is quite similar among the four species, (2) the distance over which a traveling wave damps from maximum to “zero” amplitude is the greater the longer the basilar membrane, (3) this distance, in the species compared, seems to be an approximately constant fraction of the length of the basilar membrane, independent of the length of the membrane.
34(1962); http://dx.doi.org/10.1121/1.1918351View Description Hide Description
A computational model is described for estimating basilar membrane displacement in the human ear when the sound pressure at the eardrum is known. The model embodies rational‐function approximations of middle ear transmission and of stapes to‐membrane transmission. The physiological data upon which it is based stem primarily from the researches of Békésy. Besides computational convenience, the rational‐function format has the additional advantage that the model can, if desired, be realized in terms of lumped‐constant electrical circuits. The model has been found to be a useful analytical tool for relating subjective auditory behavior and the acoustomechanical operation of the ear.
34(1962); http://dx.doi.org/10.1121/1.1918353View Description Hide Description
This review deals with a few selected areas in which significant advances have recently been made or are being made. The topics relate to the origin and significance of the dc polarization of scala media of the cochlea, to the variety and distribution of nerve endings, to the possible peripheral effects of the efferent nerve fibers, and to the pattern of activity of individual fibers of the auditory nerve.
Functional Implications of the Nature and Submicroscopic Structure of the Tectorial and Basilar Membranes34(1962); http://dx.doi.org/10.1121/1.1918355View Description Hide Description
The nature and the submicroscopic structure of the tectorial and basilar membranes have been studied with phase‐contrast, polarized‐light, and electron microscopy; x‐ray diffraction; and analytical chemistry. It is shown that the protein found in these membranes has nothing to do with collagen and elastic substance. Perhaps it may be classed in the same group as keratin, epidermin, myosin, and fibrinogen. The tectorial membrane consists of submicroscopic filaments which have a diameter of 96±4 Å, arranged fairly compactly, to form numerous transverse and a few longitudinal fibrous bundles. The basilar membrane consists of a supporting layer which is covered on the tympanic face by the basilar‐membrane cells. The supporting layer is made of filaments with a diameter of 85±105 Å, strictly, arranged in a transverse direction. In the pars recta, they lie side by side, whereas, in the pars pectinata, they are grouped in variously sized fibers, separated by a cottony ground substance. These results are compared with those of Békésy's experiments, in order to find a relationship between structure and mechanical properties. The mechanical anisotropy observed in the tectorial membrane by Békésy finds a perfect agreement with the results of the submicroscopic investigations. The mechanical isotropy shown by Békésy in the basilar membrane apparently contrasts with the evident structural anisotropy. It could be explained by the lack of independence in the oriented structures and by the presence of the cottony ground substance which forms a system binding the filaments and the fibers. The transverse orientation of filaments and fibers is not the effect of mechanical forces alone, but could also be connected to other factors, such as those of morphogenesis and growth.
34(1962); http://dx.doi.org/10.1121/1.1918357View Description Hide Description
The cochlear nerve of the monkey is composed only of the axons of the primary neurons. In Part I of this article, the properties of the primary auditory neuron—i.e., tonotopic organization, response pattern, and response area—have been studied. Two groups of neurons could be stochastically separated in terms of threshold in the low‐ and middle‐frequency range and not in the high‐frequency range. The rate of increase of impulse frequency with the change of sound intensity was examined at the characteristic frequency (CF) of a neuron after the measurement of its response area. The rate of increase and the threshold of a neuron were found to be well‐correlated. This result seems to show the validity of Békésy's hypothesis on the pitch‐intensity coordinate system of the inner and outer hair cells.
Part II is concerned with the responses of the cortical neurons of unanesthetized monkeys. Two types of response areas, wide as well as narrow, were obtained with single‐tone bursts. By the simultaneous delivery of two sounds, these areas were found to be altered in different ways, even though they were originally similar. The response patterns for beat sounds also were different from neuron to neuron. The cortical neurons are characterized by the phasic on, off, and on‐off response patterns. Intracellular recording of the membrane potentials of neurons revealed that a brief depolarization was often found before or after a long hyperpolarization by a sound stimulation. Owing to such types of responses, very many cortical neurons may be able to discriminate such complex sounds as musical sounds or voices which are always changing. The spatial and temporal funneling action in the neural mechanism of hearing is discussed.
34(1962); http://dx.doi.org/10.1121/1.1918359View Description Hide Description
The cochlear potentials were studied in rhesus and squirrel monkeys. Contrary to previous reports, the data revealed no important differences between the results obtained in these animals and those reported for the cat and guinea pig. Round‐window recording of responses to sound stimuli exhibited cochlear microphonics of nearly 2 mV at maximum. The input‐output curves showed that CM of these primates behaved not differently from those reported for the cat and guinea pig. When a micropipette was advanced from scala tympani into the organ of Corti, an increase in magnitude of CM was recorded, as well as a negative dc potential of about 75 mV. Perforation of the reticular lamina was associated with a change in polarity of CM and the appearance of an endocochlear potential (about +75 mV). Oxygen deprivation depressed CM and changed the polarity of the endocochlear potential from +75 to −20 mV. A comparative anatomical study showed that the cochleas of primates, cat, and guinea pig are similar.
34(1962); http://dx.doi.org/10.1121/1.1918360View Description Hide Description
The residue is defined as the joint perception of a number of Fourier components. Depending on circumstances outside the scope of this paper, it has a pronounced pitch. The consequences of this phenomenon for the theory of hearing are briefly reviewed in the light of past experiments. Special attention is then called to what are termed the first and second effects of pitch shift. The first effect is found when equidistantly shifting the entire Fourier spectrum. The second effect shows itself primarily in a slight drop in pitch when increasing the frequency spacing of the Fourier components. Presented are rather extensive measurements of these effects for a spectrum consisting of three components. Their inherent connection is shown along with their mathematical relationship. As an important experimental finding, the ambiguity of pitch is presented, measured in two more‐or‐less independent ways. All these phenomena strongly point towards a pitch‐extracting mechanism different from and subsequent to the basilar membrane and operating in the time domain.
34(1962); http://dx.doi.org/10.1121/1.1918362View Description Hide Description
Subjective comparisons of the sensations produced by frequency‐ and amplitude‐modulated octave‐band noises were made by the method of adjustment. The results indicate a general correlation between the sensations produced by the two kinds of modulation. Expressed in changes of level (ΔL) and shifts (Δz) along the critical‐band function, ΔL seems to be equal to C⋅Δz, where C = 10 dB/1.6 Bark. A second experiment shows the possibility of increasing and decreasing the sensation produced by amplitude modulation by adding in‐phase or out‐of‐phase frequency modulation. The conclusion is reached that at least for noises the sensation produced by amplitude changes and that produced by frequency changes are based on the same mechanism.
34(1962); http://dx.doi.org/10.1121/1.1918364View Description Hide Description
The model of binaural interaction proposed by Békésy in 1930 which has received very little attention in modern theories is re‐examined the light of recent anatomical and physiological findings. A modified model is proposed in which time and intensity are mapped independent of each other in the accessory nuclei of the superior olive; excitatory and inhibitory neural signals interact at the accessory nucleus neurons, giving rise to time‐intensity trade. The behavior of the model is in qualitative accord with psychophysical and physiological observations.
34(1962); http://dx.doi.org/10.1121/1.1918366View Description Hide Description
Intracochlear electrodes in the guinea pig are used to measure the relations among cochlear potentials in response to slow acoustic transients. The traveling wave of Békésy is described in terms of cochlear‐microphonic (CM) voltage as functions of time and place along the cochlear partition. The results are consistent with previous observations in the ear and on models of the basilar membrane. Interpolations of wavevelocity and wave amplitudes between places used for the measurements allow continuous representations of the traveling‐wave pattern of CM in either space or time. From these representations, it is clear that the duration of the stimulating phase of CM along the cochlear partition significantly exceeds the apparent duration of the whole‐nerve action‐potential (AP) response to these transients.
Selective changes in the waveforms of the AP responses, as opposed to simple reductions in amplitude, are observed when the transients are accompanied by bands of noise and after local chemical or mechanical injury to the organ of Corti. The selective changes in waveform allow consideration of the waveform removed from the normal AP response by the noise as well as the response remaining during noise. The responses removed by each of successive increases the bandwidth of the noise reveal the presence of AP responses at times not apparent in the normal whole‐nerve AP waveform. These observations are most easily explained by assuming that the basic neural response is diphasic as conventionally recorded. When neurons become active in an orderly sequence, the positive phases of the earlier individual responses coincide with and may conceal the negative phases of later responses. The whole‐nerve AP waveform is thus considered as the convolution (complex product) of two functions in time, the diphasic unit of response and the numerical sequence of newly active neurons. An empirical model for the diphasic unit of response “divided” into the AP waveform reveals patterns of neural activity that are compatible with the traveling wave of CM. The same model satisfactorily explains several details of the whole‐nerve AP waveform recorded during stimulation with a burst of high‐frequency tone.
34(1962); http://dx.doi.org/10.1121/1.1918368View Description Hide Description
A series of experiments is reported in which the lateral position of the intracranial image resulting from acoustic transients presented via earphones is shown to vary with frequency content and sensation level (SL) as well as with interaural time differences. The experimental procedures followed, together with new physiological data from the inner ear and certain theoretical assumptions, permit an estimate of the effective neurophysiological waveforms for one of the acoustic signals. The data suggest that an anatomical substrate for a “timing signal,” if present at all in the auditory system, does not have its origin in the inner ear. The theoretical treatment suggests that the synchrony of the neural input may be a significant factor in localization.
34(1962); http://dx.doi.org/10.1121/1.1918370View Description Hide Description
By the methods of magnitude estimation and magnitude production, judgments of softness were shown to be the reciprocal of judgments of loudness. The instruction to judge “distance” produces the same results as instructions to judge softness. Attempts to partition a segment of the loudness continuum into equal‐appearing intervals results in a systematic error that is greater the more variable are the judgments.
34(1962); http://dx.doi.org/10.1121/1.1918372View Description Hide Description
In 40 anesthetized guinea pigs and one cat, the left middle‐ear apparatus and cochlea were destroyed in order to de‐afferent this side of the auditory pathway. Via the left internal meatus, glass electrodes were placed inside the cochlear nucleus. The de‐afferented secondary neurons in the cochlear nucleus were never found to be excited by sound, but their excitability could be checked by recording their spontaneous activity. In 34 out of 260 spontaneously discharging secondary neurons, the repetition rate was clearly depressed by sound given exclusively to the opposite intact ear. This sound‐produced inhibition must have been transmitted by centrifugal fibers. The degree of inhibition depended on the intensity and frequency of the sound. With pure tones, inhibition showed either a maximum or a minimum in a certain frequency range which was typical for the particular neuron. “Worst frequency” of centrifugal inhibition might be a correlate of “listening” to a certain frequency range; “best frequency” of inhibition might be a correlate of the reverse process, perhaps to be called “hearing‐off.” The view is offered for discussion that worst frequency and best frequency of centrifugal inhibition are possibly important for the function of focusing or defocusing the auditory system upon or away from a particular frequency range.
Auditory‐Evoked Potentials from Cochlea to Cortex as Influenced by Activation of the Efferent Olivo‐Cochlear Bundle34(1962); http://dx.doi.org/10.1121/1.1918374View Description Hide Description
The crossed olivo‐cochlear bundle (OCB) of Rasmussen was stimulated stereotaxically in acute experiments on cats immobilized by Flaxedil and prepared either under pentobarbital, or chloralose, or with a high‐spinal section. Middle‐ear muscles were cauterized. The efferent effects on sound‐evoked potentials were titrated as equivalent dB changes in soundenergy by a matching procedure taking into account the intensity function of the responses to sound alone. Maximal inhibition of the N1 auditory‐nerve response to click was equivalent to a −25‐dB decrease. The potentials evoked in cochlear nucleus, superior olive, inferior colliculus, medial geniculate, and auditory I area of the cerebral cortex when expressed similarly in equivalent dB changes disclosed a decrease proportional to that of N1. The anomalous Ruben‐Sekula effect—i.e., reduction of cortical auditory potential without concomitant change in N1 during brainstem stimulation—was shown not to involve the OCB inhibition but to depend on a cortical refractory state subsequent to spurious stimulation of second‐order auditory axons by inadequately placed electrodes. With suitable precautions, pure OCB stimulation was achieved in most of our experiments, and interference from this effect thus excluded. The OCB activation also paradoxically potentiates the cochlear microphonic potential (CM), but the change amounted at most to a +4‐equivalent‐dB increase in soundenergy. This increase receptor potential, while important for understanding the synaptic mechanisms of the inner ear, is ignored by the central nervous system, since acoustic signals are simultaneously suppressed in the auditory nerve (Fig. 13). Various parameters of OCB effects were analyzed in detail, e.g., voltage, duration, frequency and number of shocks delivered to the bundle, and interval between the conditioning stimulation and the testing sound. More than three shocks at a frequency higher than 50/sec are needed to produce detectable changes in N1 or CM, and 40 shocks at 400/sec will generally produce maximal effects. The dissipation of the changes after OCB stimulation is rather slow and has an exponential time constant of 90 to 180 msec. These and other intrinsic features of olivo‐cochlear axons may be reflected in the operational characteristics of the whole centrifugal extrareticular auditory control system (CERACS), for which the OCB is one of the peripheral effector links.