Pitch Sensation Research Articles

A behavioral study on electrical stimulation of the cochlea and central auditory pathways of the cat

This behavioral study on cats has shown stimulus generalization for acoustic to electrical stimulation of the cochlea at frequenies from 100 to 8,000 pulse/sec. Response thresholds were determined for electrical stimulation of the apical and basal turns of the cochlea. The results show a linear increase in response threshold with rate of electrical stimulation up to a frequency of 2,000 pulse/sec. The response threshold was also lower for electrical stimulation of the basal rather than the apical electrode. Difference limen measurements for electrical stimulation of the cochlea were similar to those obtained for acoustic stimuli at 100 and 200 Hz, but were greater at higher rates of stimulation. The difference limen was also lower for electrical stimulation of the apical rather than the basal electrode. The results of this study show that electrical stimulation of the cochlea may produce a pitch sensation for rates of stimulation up to 200 pulse/sec. The results also emphasize the importance of the volley theory in the coding of low frequencies.

The Case of the “Missing MLD”

The decrease in the size of the MLD with signal frequency is presumably caused by the inability of the auditory fibers to follow details of the waveform at high frequencies. The ear appreciates slow frequency envelope variations even at high carrier frequency, however, as the residue attests. Using amplitude modulation, we attempted to obtain an MLD by manipulating the phase of a 250-Hz envelope on a 2000-Hz carrier. Essentially no MLD was observed. Attempting to create a more salient low-frequency pitch sensation we used a high-pass filtered pulse train. Delaying the pulse train, 250 ips, by half a period in the opposite ear had essentially no effect on the detectability of the binaural stimulus in wide-band masking noise. Our procedure is different from that used by Small who showed that simply inverting the waveforms at the two ears produced no MLD. These results replicate some of a more extensive series of measurements carried out by Dr. G. Bruce Henning. [Research supported by the National Institutes of Health, Public Health Service, U. S. Department of Health, Education, and Welfare, and by a research grant awarded to the Center for Human Information Processing.

Pitch as a voicing cue.

The pitch change at the onset of voicing after a period of articulatory closure for a consonant reflects the state of the glottis during that closure. In initial position, a low rising pitch indicates a closed glottis and high falling pitch a glottis that is still partly open. An experiment is reported which shows that, for about 90% of the subjects, this pitch change in the vowel can cue the voiced/voiceless distinction for a preceding stop consonant in English. Control conditions suggest that this cue depends not upon low-frequency energy content, but upon the pitch sensation.

Some parameters influencing the perceptibility of pitch.

A sound signal added to its repetition after a delay time τ is able to produce a pitch, repetition pitch, corresponding to 1/τ. When the repetition is attenuated relative to the original sound, the strength of the pitch sensation (the perceptibility of pitch) decreases. For white noise with its attenuated repetition and for sequences of pulse pairs with each second pulse attenuated, the threshold of perceptibility of pitch has been determined as a function of the pulse-pair interval T̄, the sensation level (SL), the bandpass center frequency f0, and the delay time (pulse interval) τ. The following conclusions can be drawn: (a) Somewhere in the hearing organ, timing information is preserved, rather perfectly, by means of some kind of autocorrelation process; (b) Above a certain minimum SL, the perceptibility of pitch is independent of the sensation level; (c) Dependent on the frequency value of the pitch, there is a specific spectral region for which the perceptibility of pitch is at a maximum; (d) The threshold as a function of f0 and τ shows a conformity between the existence region of repetition pitch and the existence region of the tonal residue.

Loudness and pitch sensations of an impulsive sound of very short duration

From the measured waveform caused by firing a pistol shot in anechoic listening conditions theoretical evaluations of the absolute loudness and pitch sensations have been investigated. Experimental results give support to the method of evaluation used and show that, for short duration transient sounds, the ear integrates the weighted sound energy —to form a loudness judgment.

“Polyacusis” Accompanying Hearing Loss

During audiometric test, H. F. Stimson observed that signals of above 3500 Hz produced different pitches in his right and left ears; the right ear's sensation was appropriate to a lower frequency. Upon raising the level, the pitch perceived in the right ear persisted, but another tone appeared. Further investigation of the right ear showed: Above 3700 Hz these tones remain fixed, independent of the frequency of the stimulus that evokes them. Pitch matches can be made either via the left ear, or by additional stimulus at the right ear, but no beats are heard. The tone perceived above threshold is matched by about 2200 Hz. At higher levels, an additional tone corresponding to 1400 Hz appears, and at still higher levels, one corresponding to 1700 Hz. Frequency matches were reproducible within 2% even over weeks. The absence of beats, the tonal purity and constancy of the spurious responses, and their coincidence with pitch sensations evoked by signals of lower frequency imply that the effect originates in a mechanism beyond the cochlea.

Frequencies Dominant in the Perception of Pitch of Complex Sounds

In an investigation of the pitch of complex sounds, the relative importance of selected bands of frequencies was evaluated by determining the minimum sensation levels (SL) at which the bands govern over-all pitch. The stimulus consisted of the sum of (1) a low-frequency band of fundamental frequency f0 and upper cutoff frequency fc and (2) a high-frequency band of fundamental frequency f0±Δf and lower cutoff frequency fc. The parameters used were f0, fc, Δf, and the SL's of the two bands. In most of the experiments, f0 was 200 Hz, Δf/f0 was either 3% or 6%, and over-all SL was between 30 and 50 dB. Dominance for pitch sensation was determined in terms of the “crossover” frequency fc as a function of relative level of the bands. It was found that, for a given fc, the low band tended to dominate the pitch sensation as long as its amplitude exceeded a minimum absolute level of 10–15 dB SL. Dominance was found to be independent of Δf. It is concluded that the most effective frequencies influencing pitch correspond to the third, fourth, and fifth harmonics for fundamental frequencies in the range of 100–400 Hz.

Further Investigations of Pitch Discrimination of Pulse-Train Bursts

Previous results have indicated that discrimination of pulse-train bursts, identical except for polarity pattern, with pulse separations of the order of 10 or 15 msec is associated with the magnitude of the difference in the number of polarity transitions between stimuli [J. Acoust. Soc. Am. 39, 1233(A) (1964)]. This interpretation of the result is not adequate for pulse separations less than 10 msec. In discussing the previous experiment, it was hypothesized that discrimination is based on distinct pitch sensations associated with homopolar and heteropolar pulse pairs. Then, the pitch sensation associated with a pulse-train burst is some additive combination of the pitch sensations of constituent pulse pairs. In the present experiment, this hypothesis is given further support. Moreover, it is shown that for pulse separations less than 10-msec pitch discrimination for some pulse-train bursts may be accounted for by simple extension of this hypothesis. Attaching greater weight to pulse pairs occurring latterly in a burst and admitting pitch sensations associated with pulse pairs formed from nonadjacent pulses are extensions suggested by the results.

Pitch of Frequency-Modulated Signals

This study deals with measurements carried out to determine the pitch of a quasi frequency-modulated signal consisting of only three frequency components. Such a signal was generated by modulating a sinusoid of center frequency f with a second sinusoid of frequency g and shifting the phase of the center-frequency component over 90 deg. Listening experiments showed that, with a ratio n = f/g ⩾ 9 and a modulation index m = 2, a better tonality was achieved for odd values of n than for even values. Moreover, the frequency values for pitch were found to vary as a function of the modulation index m. This was investigated at a center frequency of 2000 cps. The pitch values found are in good agreement with those calculated from the hypothesis that the distance between two positive peaks in the fine structure near two adjacent crests of the envelope of the signal constitutes a measure of the pitch of the complex. Finally, an explanation is given for the experimental evidence of a purely frequency-modulated signal giving rise to a low pitch sensation.

Three Experiments Concerned with Pitch Perception

Three experiments indicate that the place of the excitation along the basilar membrane determines pitch perception. (1) Without changing the periodicity of a tone, its pitch can be raised or lowered by masking. (2) The changes in the size of a sound image produced by masking can be explained in terms of the place theory of hearing. (3) Pitch sensations seem to be connected in an orderly way to place of excitation along the basilar membrane, since it is possible to observe the time differences required by the traveling waves to reach the different places along the membrane.

Binaural Pitch Phenomena

The possibility of having a sensation of pitch associated only with a bilateral presentation of acoustic stimuli to the listener was first discovered by Huggins [Cramer and Huggins, J. Acoust. Soc. Am. 30, 413–417 (1958)]. Huggins employed a single, smooth-frequency-spectrum noise generator, and fed its output directly to one ear, but via an all-pass phase-changing network to the other. In the present work, the possibility that this effect is a by-product of a process of auditory localization has been considered. This has led to the experimental use of a family of new binaural pitch-producing stimuli obtained from a multiplicity of independent, smooth-spectrum noise generators which operate in conjunction with continuously variable all-pass delay lines. Each stimulus configuration may be associated with a simple localization pattern. The pitch associated with a particular pattern depends both on its form and on the magnitudes of the delays involved. Pitch-matching measurements with these stimuli and a comparison with the more complex pattern of localization which might be associated with the Huggins stimuli support the view that these binaural pitch phenomena are mediated by a process akin to localization rather than by a central frequency-analysis mechanism.

Can We Feel the Nervous Discharges of the End Organs during Vibratory Stimulation of the Skin?

The vibratory pitch sensation is a complicated function of both the frequency and the amplitude of the vibrations, and frequency discrimination on the skin is thus inaccurate within a range of one or two octaves. Rutherford's telephone theory for pitch discrimination does not describe the pitch of vibratory sensations.

Magnitude Estimations of Pitch

Using the method of magnitude estimation, the experiments reported investigated the effect of the frequency of the standard upon the pitch functions for piano tones and randomly chosen pure tones. The pitch functions obtained are found to agree in an important respect with each other and with the function previously reported for pure tones chosen to correspond to notes on the musical scale. When the frequency of the standard was the lowest tone presented, the magnitude estimations yielded a function similar to the revised mel scale, and when the standard was a frequency nearer the middle of the series, the magnitude estimations yielded a steeper function closer to the original mel scale. Data are also presented showing that the numerical value of the standard can affect the magnitude estimation function. These results indicate that response biases relating to the frequency and numerical value of the standard may be expected to influence the pitch function determined by magnitude estimations. The nature and effect of these biases are discussed. It is concluded that care is required in viewing magnitude estimation judgments as reflecting a simple correspondence between frequency and the sensation of pitch.

Pitch Retention by Compensatory Frequency Tracking

The accuracy of compensatory tracking of a reference frequency of 250 cps was studied. Over a duration of 6 min this standard was changed at a rate of 3 cycles/second in such a way as to keep each of three programs within the limits of 114 cps on the low, and 370 cps on the high side. One program was symmetrical around 250 cps, one was always the same as or higher than 250 cps, another always the same or lower. Each program contained seven 10-sec plateaus interspersed at 30-sec intervals at 250 cps. Programs and tracking responses were displayed in terms of cps vs time on a paper tape recorder by the device of mounting rotary attenuators on the same shafts as those of the capacitors which allowed for frequency changes. Frequency could be read to the nearest couple of cycles. Analysis of variances showed that, while the 6 trained but generally unmusical S's were somewhat different, the three programs and the three replications of each program did not act as sources of variance. All S's were continuously “undershooting” the programs except on the plateaus. The errors ranged from less than the precision of recording up to 9 cps. It would thus seem that over a 6-min span even unmusical S's can retain rather precisely a pitch sensation in the face of drifts which could, if uncompensated, lead to pitch changes of more than an octave. Evidently the compensated program is sufficient to allow S to simulate a rudimentary form of absolute pitch.

Pitch Sensation and Its Relation to the Periodicity of the Stimulus. Hearing and Skin Vibrations

It has been suggested that the nervous system of the ear is capable of identifying the periodicity of a complex sound, as such, isolated from other factors. Because many phenomena in hearing have their counterparts in the vibratory sensations of the skin, the question is analyzed whether the skin also is able to identify and isolate periodicity of the stimulus. Since a phenomenon described by Seebeck 100 years ago seems to provide the best demonstration of periodicity perception in hearing, an analogous phenomenon the skin has been investigated for both mechanical and electrical stimulation. The skin too showed the Seebeck phenomenon. But it became obvious that on the skin it is possible to change the periodicity without altering the “pitch sensation” or to change the pitch sensation without having modified the periodicity. The pitch sensation for complex sounds and complex vibrations is probably not a simple process.

Binaural Studies of Amplitude Modulated Signals

Experiments on the pitch sensations resulting from signals with low-frequency envelopes suggest that such signals might exhibit interaural phase (time) effects—masking level differences and localization displacements—associated with the low frequency of the envelope. In the present study, the principal signals used were a 5000-cps carrier modulated by 250 cps or by 500 cps. Various modulation percentages and various phase relations between the modulator and carrier were tested for binaural interaction both in a masking situation and in localization. In general, the results were negative—the signals showed no more binaural interaction than would occur with the high frequency alone. Other combinations of high-frequency stimuli which do exhibit binaural interaction will be discussed.

On the Relation between the Time Pattern of the Envelope of Complex Tones and the Periodicity Pitch Sensation

On the Relation between the Time Pattern of the Envelope of Complex Tones and the Periodicity Pitch Sensation

Synchronism of Neural Discharges and Their Demultiplication in Pitch Perception on the Skin and in Hearing

The role of the volleys in the sensation of “pitch” on the skin was investigated. It was shown that the existence of rotating skin sensations does not insure perfect synchrony between sinusoidal vibrations and the discharges in the neural pathway. Experiments seem rather to indicate that, just as vibration loudness is a complex result of summation and inhibition, so is pitch sensation on the skin also influenced by summation and inhibition of a large group of end organs. One experiment showed that the pulse rate experienced on the skin is much lower than the pulse rate of the stimulus. This suggests a sort of “demultiplication” in the rate of the neural discharges along the neural pathway. This is one possible way in which synchronism may be maintained between the stimulus and the neural discharges, even though the frequencies transmitted are lowered.

Neural Volleys and the Similarity between Some Sensations Produced by Tones and by Skin Vibrations

Some similarities and differences between skin sensations and hearing have been investigated. The sensation of pitch on the skin has little similarity to the pitch sensation in hearing. The pitch sensation on the skin changes very much with changes in loudness, and there is a strong diplacusis between different parts of the skin. But the rotating skin sensations and rotating tones (Drehton) have many aspects in common. It was further found that the apparent size of the sensation on the skin and in the ear vary similarly as the stimulus changes. From a neurophysiological point of view, it seems to be important that it is possible to find a situation on the skin where two stimuli of different frequencies cancel each other completely. In this case, one sensation is inhibited by another, but the inhibiting sensation is felt no more. In order to be able to extrapolate from the skin to the cochlea, for several phenomena on the skin, the changes are plotted which occur when the vibrator is moved from an insensitive spot on the skin to a more sensitive one.

A Test of the Frequency Theory of Hearing

“Tone-pips” with a basic frequency of 2000 c.p.s. were produced by passing rectangular pulses of 14-msec. duration through two sound-effects filter sections in cascade. The high pass and the low pass cut-offs (18 db per octave) of each unit were set to 2000 c.p.s. The transducer was an Atlas PM 25 loudspeaker. The tone-pips appear on the oscilloscope as brief trains of waves that begin gradually and reach maximum amplitude at the third wave. The amplitude then falls off only a little less rapidly. A single pip sounds like a metallic click. When the pulses were repeated at 123 per second at sensation levels from 5 to 40 db all of our subjects reported hearing a “buzz.” Other descriptive terms used were “metallic,” “high pitched,” “continuously interrupted,” and “rough.” No listener, even when directly questioned and even when a pure tone of 123 per second had been sounded a few seconds previously for comparison, ever reported any trace of a low pitched component corresponding to 123 per second. Inasmuch as the frequency of nerve impulses in each nerve fiber is 123 per second under these conditions, the absence of a sensation of low pitch is contrary to the frequency theory of pitch perception and favors the place theory even for very low tones.