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Six subjects with VIIIth nerve audiometric profiles tracked thresholds for periodically interrupted tones on a Bekesy audiometer. When on-time was held constant and off-time was varied, a critical off-time (COT) appeared at one or more frequencies in each subject.

According to Witmaack (1911), division of the VIIIth nerve in the cat results in widespread degeneration of the cochlear neurones peripheral to the point of section; the morphological integrity of all other cochlear elements being maintained. These findings have been confirmed by later observers (Kaida 1931; Hallpike and Rawdon-Smith 1934 b ), who have in addition shown that these results require for their production the avoidance of damage to the cochlear vessels, which is found to bring about a generalized necrosis of the contents of the internal ear. A study of the electrical response of the internal ear (cochlear component of the Wever and Bray phenomenon) found to occur in the cochlea of a cat denervated in the manner described, has been the subject of a previous publication (Hallpike and Rawdon-Smith 1934 b ). In this, absence of electrical response was found to occur in a cochlea morphologically normal apart from the elimination of the neural elements. The results of a further series of observations upon these lines are now available and form the subject of the present paper.

A variety of psychoacoustic procedures was administered to three subjects—one with normal hearing, one with cochlear disorder, and one with VIIIth nerve disorder. Auditory tasks included discrimination of loudness, pitch, and temporal order; critical off-time; and speech intelligibility. A number of differences in response pattern were noted. Both theoretical and applied implications are discussed.

In precollicular decerebrate cats, stimulation of the VIIIth cranial nerve increases the discharge of muscle spindle receptors of the gastrocnemius muscle of the cat at low frequencies of stimulation (2–25 pulses/sec). Extrafusal contraction is induced only at higher frequencies of stimulation (16–100 pulses/sec). Both spindle receptor acceleration and extrafusal contraction increase with increase in frequency of VIIIth nerve stimulation to an optimum value at about 100 pulses/sec and then fall progressively with further increase in frequency of stimulation from 200 to 500 pulses/sec. Effects similar to those from the VIIIth cranial nerve are obtained from the medial and descending vestibular nuclei.

Examination of click-evoked VIIIth nerve actio potentials (AP) recorded from the round windw of anesthetized rats at ages of one, six, 12, 18 and 24 months reveals that: 1. Visual detectio levels for AP increase by 17.5 db from six to 24 months of age; 2. N1 voltage increases to a maximum at six or 12 months, depending on click level, and then declines to 24 months; 3. N2 voltage increases from one to six months but does not show a regular decline thereafter: 4. The voltage of the positive peak separating N1 from N2 shows irregular age changes; 5. N1 latency does not change significantly with advancing age; and 6. N1-N2 latency is reduced between one and 12 months but remains relatively stable thereafter.

The course and distribution of the vestibulospinal tract in the toad have been studied in silver-impregnated sections following electrolytic lesions of the terminal nuclei of the VIIIth cranial nerve. The tract originates from the ventral, vestibular nucleus of the VIIIth nerve and descends bilaterally in the ventral funiculi throughout the whole length of the spinal cord. Contralateral fibers are less numerous than ipsilateral and cross the midline in the caudal medulla oblongata. Some fibers cross in the spinal gray matter ventral to the central canal.The vestibulospinal fibers terminate in the ventromedial region of the ventral horn which harbors the medial column of motoneurons, innervating the axial musculature. Silver-impregnated sections suggest that some fibers might terminate on the cell bodies and proximal dendrites of these motoneurons. Preliminary electron microscopical observations, however, confirm only the presence of degenerating boutons in the neuropile of this region.Short comment has been devoted to other descending fiber systems which were observed following hemisection of the high cervical cord.

Early auditory evoked potentials (EAEPs) were measured in rabbits. After establishing normative data an operative method was developed to expose the cerebello-pontine angle. Compression of the VIIIth nerve and a reduction of blood supply to the cochlea via the labyrinthine artery altered the EAEP systematically. In all cases of an VIIIth nerve lesion wave 1 continued to be elicited whereas waves 2–5 disappeared. Circulatory disturbances had an effect upon wave 1. The results indicate that the generator of wave 1 is the unit cochlea/acoustic nerve and of waves 2–5 the auditory pathway within the brain stem. The resultant data help to understand wave alterations in patients with acoustic neuromas.

In anesthetized albino rabbits, the inferior olive was mapped for the effect of its local stimulation upon the vestibulo-ocular reflex. The reflex evoked by electric stimulation of the VIIIth nerve in the medial rectus muscle was inhibited specifically from the caudal part, and those to the inferior oblique and superior rectus muscles from the rostral part, of the dorsal cap of the principal olive. No such effect could be induced from the medial accessory olive. It is concluded that olivary neurons connected with different components of the vestibulo-ocular reflex via the flocculus are differentially localized within the inferior olive.

A combined regimen of kanamycin sulfate treatment (175 mg/kg/day) and behavioral evaluation of resulting audiometric threshold shifts was used to produce selective outer hair cells (OHC) loss in chinchillas. This protocol resulted in a 3-7 mm region in the cochlear base in which OHCs were completely absent and inner hair cells (IHCs) were largely resent and normal at both light and electron microscopic levels. Partial OHC loss was associated with audiometric threshold shifts in excess of 15 dB, while complete OHC loss was associated with audiometric threshold shifts in excess of 40 dB. After recovery periods of at least three weeks, phase-locking was examined across frequency for auditory nerve (VIIIth nerve) and ventral cochlear nucleus (VCN) neurons. The frequency range for neural phase-locking in normal subjects extended up to approximately 4 kHz for VIIIth nerve fibers and 3 kHz for VCN neurons. Following kanamycin intoxication, however, the frequency range for neural phase-locking in both of these auditory regions varied with characteristic frequency (CF): neurons whose CF corresponded to normal cochlear regions exhibited phase-locking throughout the normal frequency range; neurons whole CF corresponded to cochlear regions with selective OHC loss exhibited a marked reduction in the frequency range over which they could phase-lock.

The ABR interaural latency difference (ILD) from 15 patients with brain stem lesions was compared to the ILDs from patients with VIIIth nerve tumors, cochlear pathology, and a normal control group. All patients in the study had to meet the criteria of bilaterally symmetrical hearing for pure-tone thresholds in order to offset the effect of hearing loss on the ILD. Although the ILDs for the brain stem lesion group were larger than for the cochlear or normal groups, they were significantly smaller than for the VIIIth nerve tumor group. It appears that the ILD is not as sensitive a measure for detecting brain stem involvement as VIIIth nerve tumors.

The stapedius reflex was investigated in 61 patients with cerebellopontine angle tumours, in order to evaluate the reliability of the reflex-decay test in VIIIth nerve disorders. The reflex was completely normal in 11% of the patients. The 2 most frequently observed abnormalities were (1) an absence of the reflex when stimulating the ear on the side of the tumour, and (2) the conjunction of pathological reflex-decay at 0.5 kHz with a unilateral threshold elevation and/or absence of the reflex at other frequencies. The decay test was normal in one-third of the patients with a preserved reflex.

Frequency-specific compound action potentials (CAP) of the VIIIth nerve were registered in patients in which surgery confirmed retrocochlear pathology. A different pathologic behaviour of threshold latency was encountered for 2 and 4 kHz CAP, respectively. This was due to the question of whether transmission of neural information by the acoustic nerve's fibres was blocked completely by retrocochlear pathology or not. A totally reversible hearing loss in a case of cystic arachnitis can offer a reasonable explanation.

After injecting a solution of a fluorescent retrograde neuronal tracer (Fast blue, Diamidino compound 253/50) into the perilymphatic space of the frog labyrinth (Rana esculenta), labeled cells were found in the ventral and dorsal nuclei of the VIIIth nerve and in the nucleus reticularis medius. We consider these labeled cells to be the origin of the afferent innervation of the frog labyrinth. No evidence was found for the existence of a direct cerebello-labyrinthine connection.

Since the first single unit recordings obtained from the VIIIth nerve of the frog (Ross, 1936) a great deal of knowledge has been accumulated in this field of research. In the following a state of the art description of the qualitative and quantitative response characteristics to natural stimulation of semicircular canal and otolith afferents of the frog will be given. Reference will be made to data obtained from other species by other investigators only when essential to the understanding of functional properties of the afferent system as a whole.

Brain stem auditory evoked potential (BAEP) testing has been demonstrated to be a useful diagnostic tool in the presence of severe or complete sensorineural hearing loss. From a series of 38 patients with tumors in the vicinity of the VIIIth nerve, 13 patients with tumors larger than 2 cm had abnormal BAEP results contralateral to the involved side. The abnormalities observed on the noninvolved side included prolonged peak latencies, reduced amplitudes, poor wave shape and poor response stability. The significance of these findings is twofold: 1. Large tumors may disrupt BAEP test results on the side contralateral to the lesions, 2. Important information may be obtained on patients having complete sensorineural hearing loss on the involved side.

The averaged VIIIth nerve response to third-octave clicks at 500, 2 000 and 8 000 Hz was recorded from the promontory of four normal-hearing young adultsAs click frequency is lowered, the N1 latency increases in a manner consistent with the changes in velocity of the cochlear traveling wave. This finding suggests that clicks of different spectral content stimulate different regions of the basilar membraneN1 amplitude shows a general increase with frequency; this observation appears related to the increased synchrony of neural firing that results from the higher velocity of the traveling wave in the more basal portions of the cochlea

The surgical plane between the VIIth nerve and acoustic tumor is often elusive. This histological relationship was reviewed in three patients who underwent VII-VII neuroanastomosis at tumor removal disclosing an inseparable surgical plane in two. In the third patient, tissue sections did not accurately show the relationship. In all three, surgical planes were not apparent at tumor removal. Another patient had a second, isolated tumor in the same VIIIth nerve proximally at the brain stem root entry zone. This was seen only on permanent section. In considering "total" tumor removal by microsurgical standards, these histological findings should be kept in mind. We advocate removal of the entire VIIIth nerve to the brain stem root entry zone along with smaller tumors.

Field and intracellular potentials were recorded in the vestibular nuclei of the lizard following stimulation of the ipsi- and contralateral vestibular nerves. The field potentials induced by ipsilateral VIIIth nerve stimulation consisted of an early negative or positive-negative wave (presynaptic component) followed by a slow negativity (transsynaptic component). The spatial distribution of the field potential complex closely paralleled the extension of the vestibular nuclei. Mono- and polysynaptic EPSPs were recorded from vestibular neurons after ipsilateral VIIIth nerve stimulation. In some neurons early depolarizations preceded the EPSPs. These potentials may be elicited by electrical transmission. Often spikelike partial responses were superimposed on the EPSPs. It is assumed that these potentials represent dendritic spikes. Contralateral VIIIth nerve stimulation generated disynaptic and polysynaptic IPSPs in some neurons and EPSPs in others. The possible role of commissural inhibition in phylogeny is discussed. In a group of vestibular neurons stimulation of the ipsilateral VIIIth nerve evoked full action potentials with latencies ranging from 0.25-1.1msec. These potentials are caused by antidromic activation of neurons which send their axons to the labyrinth.

Delayed pattern evoked electrical cortical potentials provide a very sensitive index of clinically silent optic nerve lesions, but are not specific for multiple sclerosis. Apart from the influence of retinal illumination and of some ophthalmological diseases, delayed responses may also occur when optic nerve fibres are compressed. We observed them in Bell's palsy and octavus VIIIth nerve neuropathy.

A case of acute renal failure associated with severe uraemic hearing loss is presented. Audiometric site-of-lesion testing revealed cochlear as well as neural involvement.After therapy hearing recovered up to an almost normal level, with normal auditory nerve conduction velocities.This case report supports the suggestion that the improvement of hearing after renal transplantation or dialysis might be correlated with the influences of these forms of therapy upon the peripheral neuropathy.

12 cases of unilateral labyrinthectomy, 3 cases of VIIIth nerve section, 22 cases of streptomycin sulfate infusion into the middle ear cavity and 8 cases of bilateral vestibular a-functions underwent vestibular training. Our training is very useful for regaining equilibrium and for evaluating the effects of training on equilibrium by recording the gravity center movements.

1. Glass micropipettes were inserted into the oculomotor nucleus of the cat and electrical activities and properties of the neurons were studied with intracellular recordings.2. The properties of ocular motoneurons were, in many respects, alike to those of lumbar spinal motoneurons. However, when compared with the latters, several characteristics of ocular motoneurons were noted; rather smaller time constant, shorter duration of after-hyperpolarization, lack or scarcity of collateral inhibition, much more frequent rates of tonic and phasic discharges and so on.3. The local reflex activity in the oculomotor system was scarcely observed, but a few cases were encountered that seemed to be alike to those of proprioceptive responses in the spinal motor system.4. Synaptic potentials in ocular motoneurons due to the VIIIth nerve stimulations were visualized by the intracellular recording, and their relations with focal potentials in the oculomotor nucleus and with discharge outflows to the IIIrd nerve, elicited by the same stimulations, were examined in concern with the vestibulo-ocular reflex.

Repetitive stimulation of the VIIIth nerve or of the medial and descending vestibular nuclei increases the excitability of the intrageniculate optic fibres endings with a time course typical for presynaptic inhibition.

Cochlear microphonics (CM) and masked and unmasked VIIIth nerve action potentials (AP) were measured in rats at ages of one, six, 12, 18 and 24 months in order to explore an animal model for presbycusis. These rats were raised in quiet surroundings and were given no antibiotics. Mean CM 1 microvolt sensitivity levels showed a 7 db augmentation from one month to one year followed by a 13 db decline from one to two years of age. Similarly, unmasked AP amplitudes increased from one to 12 months, then declined through 18 to 24 months. Masked AP amplitudes demonstrated a similar growth and decline with age, showing the greatest losses in those AP components originating from the high frequency regions of the basilar membrane.

The early diagnosis of dizziness of vascular origin in the face of few positive historical, physical and clinical findings can be made when mild internuclear ophthalmoplegia in lateral gaze is noted in association with central or peripheral VIIIth nerve involvement. Early symptoms and physical findings are described and certain relevant diagnostic studies recommended. Functional correlation with the central anatomical areas supplied by the vertebral-basilar artery system are reviewed.

Preliminary investigations indicate that contralateral masking exerts a significant influence on auditory diagnostic procedures in which a sustained stimulation is involved. In Bekesy tracings, masking caused separation between curves for interrupted and continuous tones and reduction of tracing width of the latter. In the SISI-test the scores improved at higher frequencies. In patients with VIIIth nerve lesion excessive temporary threshold shifts appeared when the unaffected ear was stimulated with continuous white noise.

The temperature dependence of the response of single primary auditory nerve fibers (n = 31) was investigated in the European edible frog, Rana esculenta (seven ears). Nerve fiber responses were analyzed with Wiener kernel analysis and polynomial correlation. The responses were described with a cascade model, consisting of a linear bandpass filter, a static nonlinearity, and a linear lowpass filter. From the computed Wiener kernels and the polynomial correlation functions, the characteristics of the three model components were obtained. With increasing temperature (1) tuning of the first filter increased in the majority (n = 16) of amphibian papilla fibers (best excitatory frequency, BEF 1 kHz, n = 11), (2) the gain of the first filter remained unchanged, (3) the shape of nonlinear IO function remained unchanged, (4) the combined gain of the static nonlinearity and the second filter usually increased, but displayed considerable scatter across fibers (from -0.7 dB/degrees C to 3 dB/degrees C), and (5) the cutoff frequency of the second lowpass filter increases, with average 0.13 oct/ degrees C. The immunity of the shape of the nonlinearity is considered evidence of a temperature independent gating mechanism in the transduction channels. The temperature dependence of the second filter may have resulted from a decrease of the hair cell membrane resistance, but may also reflect changes in subsequent staging of nerve fiber excitation. (C) 1997 Elsevier Science B.V.

Wiener kernel analysis was used to characterize the auditory pathway from tympanic membrane to single primary auditory nerve fibers in the European edible frog, Rana esculenta. Nerve fiber signals were recorded in response to white Gaussian noise. By cross-correlating the noise stimulus and the nerve fiber response, we computed (1) the full second-order Wiener kernel, and (2) the diagonals of the zeroth-to fourth-order Wiener kernels. These diagonals are usually referred to as polynomial correlation functions. The measured Wiener kernels were fitted with a 'sandwich' model. A new fitting procedure was used to compute the response characteristics of(1) the first filter, (2) the static nonlinearity, and (3) the second filter, which form the functional components of the model. The first filter is a bandpass filter. In the majority of low frequency fibers, with best excitatory frequency (BEF)

The males of the species E. coqui produce a two‐note call; the first note (“co”) consists of a constant tone of duration 100 msec and frequency 1.1 kHz, and the second note (“qui”) sweeps upward in frequency from 1.8–2.2 kHz in about 170 msec. Acoustic playback experiments with males and females revealed a behavioral difference in the response of the males and females to the two‐note call. These experiments showed that the first note functions in male‐male interactions and probably serves to maintain spacing between adjacent males, but does not attract a female. The second note serves to attract conspecific females and apparently plays no role in male‐male encounters. An electrophysiological study of the response properties of auditory fibers was conducted in the VIIIth nerve of males and females to determine whether this selectivity could occurs as early as the peripheral auditory system. The results of this study revealed that the functional dichotomy of the two notes in the male's call is reflected by ...

In our clinic brain stem potentials recorded by a nonsurgical method have been used as a routine audiometric test for 4 years. The procedure has proved to be easier than ECoG and gives nearly the same information about cochlear and middle ear function if there is no VIIIth nerve or brain stem damage. For topical diagnosis of the lower auditory pathway additional recording of BCoG is necessary.

In a recent paper, J. V. Tobias and E. D. Schubert [J. Acoust. Soc. Am. 31, 1595–1605 (1959)] suggested an “effective onset‐duration” of 1–3 msec which they related to the “on‐effect” and to the minimum refractory period of fibers of the VIIIth nerve. In the present experiments, an attempt was made to measure the critical duration by playing pairs of binaural stimuli with interaural correlations of +1 and −1 (or −1 and +1) and determining the duration below which the two conditions could not be recognized as different. For both noise‐burst and click stimuli through PDR‐8 earphones, stimulus durations were varied down to 0.09 msec. Judgments were 100% correct for all conditions. Acoustic measurements showed that, although waveform varied with varying duration of electrical input, the acoustic period remained at least 1 msec long. Indeed, for a given short‐duration (less than a millisecond or so) burst of electrical noise, the acoustical waveform was surprisingly constant. The same sort of experiment, done with a comparison of +1 and 0 (uncorrelated) stimuli, produced similar results. The basic finding, then, is that stimuli delivered via PDR‐8's cannot be changed enough electrically to produce acoustically an “unsolvable” interaural‐correlation problem. It is apparent that the binaural system can solve any duration‐sensitive transform that is transduced through standard earphones. (This work was partially supported by the Bureau of Ships.)

Attempts to predict human auditory fatigue and permanent auditory damage by recourse to the animal have often suffered from two procedures used for expedience only, namely, the use of the cochlear microphonic as an index of hearing, and the use of anesthesia with its destruction of the protective acoustic reflexes. Chronic implantation of a round window electrode in the cat and recording N1 and N2 potentials help to diminish the blurring the earlier compromise procedures create. In one and the same cat it is possible to go from short durations and low SPL's to conditions approaching those giving rise to permanent damage, with or without anesthesia at random. Onset curves of N1 − N2 depression can be drawn, and recovery curves. For example, 105 db SPL at 2 kc/sec reduces the N1 − N2 potentials in negatively accelerated fashion to about 110 original in about 20 min, with recovery complete within about 5 min. At 100 db SPL, the reduction is about 13; and so on. Intensity‐time relationships will be drawn and ...

In the mammalian cochlea, primary fibers to inner hair cells synapse with one or a very few receptors, and thereby innervate only a restricted region, or point, on the basilar partition. In contrast, VIIIth nerve fibers innervating outer hair cells course toward the basal (high frequency) portion of the cochlea and then synapse with a number of receptors over a finite length of the basilar membrane. Because of these unique patterns of distribution, it seems possible that the two major afferent populations might respond differently to identical stimuli, if appropriate parameters are selected. In order to determine if these anatomical distinctions are reflected by physiological differences under a defined set of stimulus conditions, we have recorded the responses of a population of VIIIth nerve fibers in the cat utilizing a two‐tone stimulus paradigm. In these experiments, f1 was placed at the fiber's characteristic frequency (CF), and a higher frequency f2 was systematically changed to explore in and aroun...

The effects of duration and of frequency on frequency discrimination are consistent with a neural‐based model that used the temporal information present in the phase‐locked response of VIIIth nerve units to estimate the frequency of a pure‐tone stimulus [J. L. Goldstein and P. Srulovicz, “Auditory‐nerve spike intervals as an adequate basis for aural frequency measurement” in Psychophysics and Physiology of Hearing, edited by E. F. Evans and J. P. Wilson (Academic, London, 1977), pp. 337–346]. We have extended this model to include the effects of intensity on the frequency difference limen by incorporating (1) the functional dependence of the synchronization index on intensity [D. H. Johnson, doctoral dissertation, MIT, 1974] and (2) an appropriate dependence of average discharge rate on intensity. When fit to the psychophysical data, the extended model accounts for much of the effect of intensity on the frequency DL above 10 dB SL. At levels lower than this, the model does not exhibit the same rapid incre...

The extensive use of Brainstem Evoked Response Testing (BSER) for the detection of mass lesions involving the VIIIth nerve necessitates knowledge of the effects of hearing loss of cochlear origin on BSER. Thirty‐one ears displaying varying degrees of sensorineural, high‐frequency (beginning above 500 Hz) loss of sensitivity of cochlear origin were tested with BSER. A 100‐μs rectangular pulse was used to excite TDH‐39 earphones at a rate of 11.3 pulses/s. Utilizing monaural stimulation at two to five intensities per ear, responses were obtained from a vertex to ipsilateral mastoid electrode montage. Linear regression analysis lines for waves I, III, and V latencies versus average degree of loss for various combinations of audiometric test frequencies are shown. The dependence of BSER wave latencies on individual and audiometric test frequencies and various combinations at and above 1 kHz are shown via the use of correlation coefficients. The results compare well with earlier results [A. C. Coats and J. L. ...

Previously we reported the release of auditory nerve activation substance (ANAS) into perilymph during sound stimulation [Soc. Neurosci. III, 11 (1977)]. Recently, experiments designed to increase the output of ANAS were carried out using more intense sound stimuli during the perilymphatic collection periods. In these experiments, compound VIIIth nerve action potentials and cochlear microphonics were measured. The more intense auditory stimuli caused reductions in these potentials reminiscent of auditory fatigue. Perilymph, collected during periods of auditory fatigue, when infused back into the guinea pig cochlea during silence caused reductions in cochlear potentials similar to those seen during auditory fatigue. Such cochlear electrical changes are not seen with perilymph collected during quiet periods. These results suggest that ANAS and/or another substance released during sound stimulation may be responsible for the changes in cochlear electrical activity seen during auditory fatigue. These results ...

Stanford Electronics Laboratories, Stanford, CA 94305 Two profoundly deaf multielectrode implant subjects were required to detect a probe signal (10 ms in duration) in a temporal gap between two pulse‐train maskers (each 300 ms in duration). The detection threshold was measured for a probe centered temporally in the gap, as well as for a probe offset from center by up to 97.5%. Also presented were the pure backward and pure forward masking cases. Qualitatively, both subject's forward and backward masking functions approximated those observed for normal hearing subjects [L.L. Elliott, J. Acoust. Soc. Am. 34, 1116–1117 (1962)] in that forward masking decayed more gradually than backward masking as a function of probe‐masker separation. Because mechanical (cochlear) contributions to masking [H. Duifhuis, J. Acoust. Soc. Am. 54, 1471–1488 (1973)] can be excluded in the case of direct VIIIth nerve stimulation, these data support the attribution of nonsimultaneous masking phenomena to VIIIth nerve or higher neural mechanisms. [Work supported by NIH.]

The response of the peripheral auditory system to digitally generated and human‐articulated vowels was modelled at the level of the cochlea and auditory nerve. The simulation operates upon the spectral density function to derive an estimate of the excitation pattern of the VIIIth nerve and thereby serves to illustrate the manner in which certain acoustic attributes of the vocalic signal such as fundamental frequency, formant pattern, formant bandwidth, and glottal pulse shape affect the simulated discharge pattern of the auditory nerve. [Research supported by NIH.]

We reported that aspartate (asp) and glummate (glu) are significantly reduced in the ventral CN after surgical destruction of the organ of Corti, corresponding to the pattern of primary innervation [Thaimann et al., J. Acoust. Soc. Am. Suppl. 1 67, S77 (1980)]. More recently, we confirmed and extended Wenthold's finding [Brain Res. 143, 544 (1978)] that these substances decline similarly, although on a faster time scale, after VIIIth nerve section–no decline in molecular and fusiform layers of dorsal CN, but significant declines (p < 0.001) in deep dorsal CN (asp 29%, glu 24%) and in posteroventral CN (asp 48%, glu 45%). Analogous declines occurred in the phylogenetically older VN following VIIIth nerve section. In the heavily innervated central part of superior VN asp and glu decreased by 21% and 37%, respectively (p < 0.001), with no decline in the sparsely supplied peripheral part. In lateral VN, asp and glu declined significantly (35% and 21%, respectively) in the heavily innervated ventral portion, while in the sparsely innervated dorsal part, only asp declined (26%). The behavior of asp and glu after lesion (as well as their resting distribution) is consistent with the involvement of either or both in neurotransmission at the primary auditory and vestibular terminals. [Supported by NIH.]

Pure‐tone pitch anomalies such as pitch‐intensity effects and diplacusis have been traditionally considered as evidence against temporal theories of pitch. These phenomena, however, may at least in part, be correlated with stochastic model calculations of VIIIth nerve firing probabilities. These calculations predict shifts in the peaks of the ISI histogram as a function of the intensity of acoustic stimulation which are consistent with average human pitch‐intensity data. The same models suggest a temporal basis for some features of central‐processor‐type algorithms in complex‐tone pitch perception. They also account qualitatively for the frequency‐dependent deviation from unity of the ratio of the first ISI histogram peak to the stimulus period, as seen in ISI measurements. Physiological and psychophysical measurements, and detailed neural model studies which are designed to check the validity of these preliminary results, will be described. [Work supported by NIH Grant NS 15405 and NSF Grant BNS 8021529.]

Unit spikes were recorded from the VIIIth nerve branch innervating the amphibian papilla of a urethane‐anesthetized toad. Tonal stimuli were applied from an earphone through a coupling tube to the surface of the saccule. The tuning curve (TC) for fast rising tone bursts rose gradually toward both low and high frequencies (HF's) from the characteristic frequency (CF) of the unit. HF continuous tones had the effect of peripheral inhibition on the response to any test tones. As the rate of rise of tone bursts was decreased, the TC rose progressively at comparatively higher frequencies, while little change was seen near the CF and under. When the slow rising (90% rise per 20 ms and slower) test tone bursts were used, the rise of TC reached a saturation point, where HF cutoff of the TC was very steep. It seems that the sharp HF cutoff arises, because the thresholds are reached after the peripheral inhibition developed during the slow rising phase of the HF test tones themselves.

In order for a multichannel cochlear prosthesis to be more effective than a single‐channel prosthesis, the different channels of the stimulating electrode must be able to activate separate populations of the neurons in the auditory nerve. Earlier animal studies [C. van den Honert and P. Stypulkowski, Hear. Res. 14, 225–243 (1984); H. S. Lusted, Ph.D. thesis, Stanford University, 1980] have resulted in conflicting conclusions about whether this occurs for monopolar stimulation. To address this question, an eight‐channel electrode array was acutely placed in the scala tympani of seven cats. Recordings were then made in the VIIIth nerve, of single unit responses to electrical stimulation from each of the channels in the array. For each unit isolated, threshold current for biphasic monopolar stimulation was determined for each of the electrode channels. Some units were found to be highly selective in their response to the different channels of the electrode array, with the most effective electrode having a threshold lower than an adjacent electrode by up to a factor of 5 times. Adjacent electrodes were either 1.0 or 1.5 mm apart. Other units were found not to be very selective in their response. This suggests that some degree of spatial selectivity is achievable with monopolar stimulation. [Work supported by NIH.]