Pitch Sensation Research Articles

Hearing aid delay in open-fit devices – coloration-pitch discrimination in normal-hearing and hearing-impaired

Objective The delay in digital hearing aids is known to cause distortions due to the mixing of the delayed hearing aid sound with the undelayed direct sound. The most apparent delay-based distortion is a pitch sensation referred to as coloration-pitch. This study investigated coloration-pitch discrimination at the lower end of typical hearing aid delays and aimed at establishing thresholds where a large change in coloration-pitch is just perceptible. Design Simulations were verified against a reference hearing aid for numerous conditions of delay, insertion gain and incident direction. The simulations were used in a psycho-acoustics experiment in which coloration-pitch discrimination thresholds were measured as a function of hearing aid delay and gain. Participants discriminated between coloration-pitches produced by delay changes of 12%. Insertion gains compensating for mild to moderate hearing losses were used. Study Sample Nine normal-hearing and twelve hearing-impaired participants with mild to moderate hearing loss participated. Results The simulations accurately reflected the acoustics of the open-fit hearing aid. Discrimination thresholds were between 0.3 ms and 1 ms depending on insertion gain and hearing status. Conclusions High sensitivity for changes in coloration-pitch was found for delays >1 ms. For shorter delays participants were increasingly insensitive to changes in coloration-pitch.

Rate and Temporal Coding of Regular and Irregular Pulse Trains in Auditory Midbrain of Normal-Hearing and Cochlear-Implanted Rabbits.

Although pitch is closely related to temporal periodicity, stimuli with a degree of temporal irregularity can evoke a pitch sensation in human listeners. However, the neural mechanisms underlying pitch perception for irregular sounds are poorly understood. Here, we recorded responses of single units in the inferior colliculus (IC) of normal hearing (NH) rabbits to acoustic pulse trains with different amounts of random jitter in the inter-pulse intervals and compared with responses to electric pulse trains delivered through a cochlear implant (CI) in a different group of rabbits. In both NH and CI animals, many IC neurons demonstrated tuning of firing rate to the average pulse rate (APR) that was robust against temporal jitter, although jitter tended to increase the firing rates for APRs ≥ 1280Hz. Strength and limiting frequency of spike synchronization to stimulus pulses were also comparable between periodic and irregular pulse trains, although there was a slight increase in synchronization at high APRs with CI stimulation. There were clear differences between CI and NH animals in both the range of APRs over which firing rate tuning was observed and the prevalence of synchronized responses. These results suggest that the pitches of regular and irregular pulse trains are coded differently by IC neurons depending on the APR, the degree of irregularity, and the mode of stimulation. In particular, the temporal pitch produced by periodic pulse trains lacking spectral cues may be based on a rate code rather than a temporal code at higher APRs.

No interaction between fundamental-frequency differences and spectral region when perceiving speech in a speech background

Differences in fundamental frequency (F0) or pitch between competing voices facilitate our ability to segregate a target voice from interferers, thereby enhancing speech intelligibility. Although lower-numbered harmonics elicit a stronger and more accurate pitch sensation than higher-numbered harmonics, it is unclear whether the stronger pitch leads to an increased benefit of pitch differences when segregating competing talkers. To answer this question, sentence recognition was tested in young normal-hearing listeners in the presence of a single competing talker. The stimuli were presented in a broadband condition or were highpass or lowpass filtered to manipulate the pitch accuracy of the voicing, while maintaining roughly equal speech intelligibility in the highpass and lowpass regions. Performance was measured with average F0 differences (ΔF0) between the target and single-talker masker of 0, 2, and 4 semitones. Pitch discrimination abilities were also measured to confirm that the lowpass-filtered stimuli elicited greater pitch accuracy than the highpass-filtered stimuli. No interaction was found between filter type and ΔF0 in the sentence recognition task, suggesting little or no effect of harmonic rank or pitch accuracy on the ability to use F0 to segregate natural voices, even when the average ΔF0 is relatively small. The results suggest that listeners are able to obtain some benefit of pitch differences between competing voices, even when pitch salience and accuracy is low.

Cues to monaural edge pitch in single auditory nerve fibers

The spectral edge of a bandlimited noise can create a pitch sensation, called “edge pitch,” which is slightly mismatched to the edge frequency. This pitch is usually speculated to reflect neural lateral inhibition but could also reflect temporal cues. We looked for such cues recording responses of single auditory nerve fibers in the anesthetized chinchilla to edge pitch stimuli. For every stimulus, we compute shuffled autocorrelograms for all recorded fibers and pool them in a population interval distribution (PID) from which we obtain the most common interval. We also quantify the slower “envelope” fluctuations in firing resulting from cochlear bandpass filtering of the bandlimited noise stimulus. Single fibers shows systematic temporal changes related to the spectral edge of the stimulus when it does not cover the fiber's frequency filter. Across the population of fibers, the estimated pitch based on the dominant interspike interval shows trends that are similar, qualitatively and quantitatively, to those observed behaviorally. Slower envelope fluctuations also systematically vary with the relationship of edge frequency to fiber CF, and are another potential temporal cue to the presence of the edge frequency. We conclude that temporal cues to edge-pitch are present in the auditory nerve at multiple time scales.

Effect of Pitch on the Asymmetry in Global Loudness Between Rising- and Falling-Intensity Sounds

The global loudness of a varying intensity sound is greater when the intensity increases than when it decreases. This global loudness asymmetry was found to be larger for pure tones than for broadband noises. In this study, our aim was to determine whether this difference between pure tones and noises is due to the difference in bandwidth between sounds or to the difference in the strength of the sensation of pitch. The loudness asymmetry was measured for broadband and for narrow-band signals that do or do not elicit a sensation of pitch. The asymmetry was greater for sounds that elicit a sensation of pitch whatever their bandwidth. The loudness model for time varying sounds [1] predicted well the asymmetry for the broadband noise that does not elicit a sensation of pitch and for a multi-tonal sound. For the other sounds the asymmetry was greater than predicted. It is known that loudness and pitch interact. The difference in asymmetry between sounds that elicit pitch and sounds that do not elicit pitch might be due to this interaction.

Electric and acoustic harmonic integration predicts speech-in-noise performance in hybrid cochlear implant users

BackgroundPitch perception of complex tones relies on place or temporal fine structure-based mechanisms from resolved harmonics and the temporal envelope of unresolved harmonics. Combining this information is essential for speech-in-noise performance, as it allows segregation of a target speaker from background noise. In hybrid cochlear implant (H-CI) users, low frequency acoustic hearing should provide pitch from resolved harmonics while high frequency electric hearing should provide temporal envelope pitch from unresolved harmonics. How the acoustic and electric auditory inputs interact for H-CI users is largely unknown. Harmonicity and inharmonicity are emergent features of sound in which overtones are concordant or discordant with the fundamental frequency. We hypothesized that some H-CI users would be able to integrate acoustic and electric information for complex tone pitch perception, and that this ability would be correlated with speech-in-noise performance. In this study, we used perception of inharmonicity to demonstrate this integration. MethodsFifteen H-CI users with only acoustic hearing below 500 Hz, only electric hearing above 2 kHz, and more than 6 months CI experience, along with eighteen normal hearing (NH) controls, were presented with harmonic and inharmonic sounds. The stimulus was created with a low frequency component, corresponding with the H-CI user's acoustic hearing (fundamental frequency between 125 and 174 Hz), and a high frequency component, corresponding with electric hearing. Subjects were asked to identify the more inharmonic sound, which requires the perceptual integration of the low and high components. Speech-in-noise performance was tested in both groups using the California Consonant Test (CCT), and perception of Consonant-Nucleus-Consonant (CNC) words in quiet and AzBio sentences in noise were tested for the H-CI users. ResultsEight of the H-CI subjects (53%), and all of the NH subjects, scored significantly above chance level for at least one subset of the inharmonicity detection task. Inharmonicity detection ability, but not age or pure tone average, predicted speech scores in a linear model. These results were significantly correlated with speech scores in both quiet and noise for H-CI users, but not with speech in noise performance for NH listeners. Musical experience predicted inharmonicity detection ability, but did not predict speech performance. ConclusionsWe demonstrate integration of acoustic and electric information in H-CI users for complex pitch sensation. The correlation with speech scores in H-CI users might be associated with the ability to segregate a target speaker from background noise using the speaker's fundamental frequency.

Tinnitus evaluation: relationship between pitch matching and loudness, visual analog scale and tinnitus handicap inventory

IntroductionTinnitus is a subjective auditory symptom usually associated with a sound, even in the absence of external sound sources. Its diagnosis is complex, and some of the forms of measurement alone or in combination, include self-assessment questionnaires, such as the tinnitus handicap inventory, the visual analog scale and/or pitch and loudness matching. ObjectiveTo analyze the correlation among three tinnitus measurement methods: tinnitus handicap inventory, visual analog scale and pitch and loudness matching. MethodsThe study consisted of 148 patients complaining of chronic tinnitus. An otorhinolaryngological evaluation, anamnesis directed to tinnitus, audiometry (pure tone and speech), imitanciometry, tinnitus handicap inventory, visual analog scale, and pitch and loudness matching were performed. The study was registered in the Ethics Committee of the Institution with no. 0129/12. ResultsRegarding the frequency of tinnitus handicap inventory responses, a higher occurrence of the mild degree was observed. An average of 6 points was observed on the visual analog scale. The mean loudness matching in the right ear was 20dBNS, and in the left ear was 17dBNS. As for the type of stimulus, the most found was continuous pure tone. The frequency of the pitch sensation was 6000Hz in the largest number of cases. Regarding the measures of tinnitus handicap inventory and the visual analogical scale, a significant correlation was observed, and as one value increases the other also increases. Pitch and loudness matching and the visual analogical scale results are also significant. ConclusionThere was a significant correlation between the values measured by the tinnitus handicap inventory, visual analogical scale (annoyance) and loudness matching in the evaluation of tinnitus. The selection of any one of the three evaluative methods for tinnitus investigation provides different dimensions of the tinnitus and complements the others.

Effect of stimulus type and pitch salience on pitch-sequence processing.

Using a same-different discrimination task, it has been shown that discrimination performance for sequences of complex tones varying just detectably in pitch is less dependent on sequence length (1, 2, or 4 elements) when the tones contain resolved harmonics than when they do not [Cousineau, Demany, and Pessnitzer (2009). J. Acoust. Soc. Am. 126, 3179-3187]. This effect had been attributed to the activation of automatic frequency-shift detectors (FSDs) by the shifts in resolved harmonics. The present study provides evidence against this hypothesis by showing that the sequence-processing advantage found for complex tones with resolved harmonics is not found for pure tones or other sounds supposed to activate FSDs (narrow bands of noise and wide-band noises eliciting pitch sensations due to interaural phase shifts). The present results also indicate that for pitch sequences, processing performance is largely unrelated to pitch salience per se: for a fixed level of discriminability between sequence elements, sequences of elements with salient pitches are not necessarily better processed than sequences of elements with less salient pitches. An ideal-observer model for the same-different binary-sequence discrimination task is also developed in the present study. The model allows the computation of d' for this task using numerical methods.

Pure-Tone Masking Patterns for Monopolar and Phantom Electrical Stimulation in Cochlear Implants.

Monopolar stimulation of the most apical electrode produces the lowest pitch sensation in cochlear implants clinically. A phantom electrode that uses out-of-phase electrical stimulation between the most apical and the neighboring basal electrode can produce a lower pitch sensation than that associated with the most apical electrode. However, because of the absence of contacts beyond the apical tip of the array, the ability to assess the spread of electrical excitation associated with phantom stimulation is limited in the typical cochlear implant subject with no residual hearing. In the present study, the spread of electrical excitation associated with monopolar and phantom stimulation of the most apical electrode was assessed using electrical masking of acoustic thresholds in cochlear implant subjects with residual, low-frequency, acoustic hearing. Eight subjects with an Advanced Bionics cochlear implant and residual hearing in the implanted ear participated in this study (nine ears in total). Unmasked and masked thresholds for acoustic pure tones were measured at 125, 250, 500, 750, 1000, and 2000 Hz in the presence of monopolar and phantom electrode stimulation presented at the apical-most end of the array. The current compensation for phantom electrode stimulation was fixed at 50%. The two electrical maskers were loudness balanced. Differences between the unmasked and masked acoustic thresholds can be attributed to (1) the electrical stimulus-induced interference in the transduction/conduction of the acoustic signal through cochlear periphery and the auditory nerve and/or (2) masking at the level of the central auditory system. The results show a significant elevation in pure-tone thresholds in the presence of the monopolar and phantom electrical maskers. The unmasked thresholds were subtracted from the masked thresholds to derive masking patterns as a function of the acoustic probe frequency. The masking patterns show that phantom stimulation was able to produce more masking than that associated with the monopolar stimulation of the most apical electrode. These results suggest that for some cochlear implant subjects, phantom electrode stimulation can shift the neural stimulation pattern more apically in the cochlea, which is consistent with reports that phantom electrode stimulation produces lower pitch sensations than those associated with monopolar stimulation of the most apical electrode alone.

Perceptual changes with monopolar and phantom electrode stimulation

Phantom electrode (PE) stimulation is achieved by simultaneously stimulating out-of-phase from two adjacent intra-cochlear electrodes with different amplitudes. If the basal electrode stimulates with a smaller amplitude than the apical electrode of the pair, the resulting electrical field is pushed away from the basal electrode producing a lower pitch. There is great interest in using PE stimulation in a processing strategy as it can be used to provide stimulation to regions of the cochlea located more apically than the most apical contact on the electrode array. The result is that even lower pitch sensations can be provided without additional risk of a deeper insertion. However, it is unknown if there are perceptual differences between monopolar (MP) and PE stimulation other than a shift in place pitch. Furthermore, it is unknown if the effect and magnitude of changing from MP to PE stimulation is dependent on electrode location. This study investigates the perceptual differences (including pitch and other sound quality differences) at multiple electrode positions using MP and PE stimulation using both a multidimensional scaling procedure (MDS) and a traditional scaling procedure.10 Advanced Bionics users reported the perceptual distances between 5 single electrode (typically 1, 3, 5, 7, and 9) stimuli in either MP or PE (σ = 0.5) mode. Subjects were asked to report how perceptually different each pair of stimuli were using any perceived differences except loudness. Subsequently, each stimulus was presented in isolation and subjects scaled how “high” or how “clean” each sounded.Results from the MDS task suggest that perceptual differences between MP and PE stimulation can be explained by a single dimension. The traditional scaling suggests that the single dimension is place pitch. PE stimulation elicits lower pitch perceptions in all cochlear regions. Analysis of Cone Beam Computer Tomography (CBCT) data suggests that PE stimulation may be more effective at the apical part of the cochlea. PE stimulation can be used for new sound coding strategies in order to extend the pitch range for cochlear implant (CI) users without perceptual side effects.

Does a pitch center exist in auditory cortex? A mismatch negativity study

Pitch sensation can be evoked by different acoustic cues which should be processed by different strategies for extracting pitch. However, in resent studies a general pitch center was hypothesized exist at some level of the auditory pathway for a general pitch sensation independent of other acoustic features. In this study, the existence of pitch center was examined by testing that whether the mismatch negativity (MMN) response, an index of pre-attentive auditory processing, can be elicited by pitch deviations in a passive oddball paradigm that composed of four different pitch-evoking stimuli (i.e., sinusoidal tone, resolved complex, iterated rippled noise, and pulse train). Although the pitch-evoking cues in these pitch-evoking stimuli were disparate, they evoked a fixed pitch of 200 Hz (or 283 Hz in a reversed oddball paradigm). Occasionally a deviant sound was encountered which evoked a different pitch (283 Hz, or 200 Hz in the reversed oddball paradigm). The results showed no significant MMN response was elicited by the deviant, regardless of the type of pitch-evoking stimuli, suggesting the absence of pitch center in the pre-attentive auditory processing stage.

Virtual Pitch and Pitch Shifts in Church Bells

It is well established that musical sounds comprising multiple partials with frequencies approximately in the ratio of small integers give rise to a strong sensation of pitch even if the lowest or fundamental partial is missing—the so-called virtual pitch effect. Experiments on thirty test subjects demonstrate that this virtual pitch is shifted significantly by changes in the spacing of the constituent partials. The experiments measured pitch by comparison of sounds of similar timbre and were automated so that they could be performed remotely across the Internet. Analysis of the test sounds used shows that the pitch shifts are not predicted by Terhardt’s classic model of virtual pitch. The test sounds used were modelled on the sounds of church bells, but a further experiment on seventeen test subjects showed that changes in partial amplitude only had a minor effect on the pitch shifts observed, and that a pitch shift was still observed when two of the lowest frequency partials were removed, so that the effects reported are of general interest.

Modeling of Breathy Voice Quality Using Pitch-strength Estimates

The characteristic voice quality of a speaker conveys important linguistic, paralinguistic, and vocal health-related information. Pitch strength refers to the salience of pitch sensation in a sound and was recently reported to be strongly correlated with the magnitude of perceived breathiness based on a small number of voice stimuli. The current study examined the relationship between perceptual judgments of breathiness and computational estimates of pitch strength based on the Aud-SWIPE (P-NP) algorithm for a large number of voice stimuli (330 synthetic and 57 natural). Similar to the earlier study, the current results confirm a strong relationship between estimated pitch strength and listener judgments of breathiness such that low pitch-strength values are associated with voices that have high perceived breathiness. Based on this result, a model was developed for the perception of breathy voice quality using a pitch-strength estimator. Regression functions derived between the pitch-strength estimates and perceptual judgments of breathiness obtained from matching task revealed a linear relationship for a subset of the natural stimuli. We then used this function to obtain predicted breathiness values for the synthetic and the remaining natural stimuli. Predicted breathiness values from our model were highly correlated with the perceptual data for both types of stimuli. Systematic differences between the breathiness of natural and synthetic stimuli are discussed.

Physics underlying the physiology of the ear.

Physics underlying the physiology of the ear.

Harmonic fusion and pitch affinity: Is there a direct link?

Simultaneous pure tones approximately one octave apart tend to be fused perceptually and to evoke a single pitch sensation. Besides, sequentially presented pure tones show a subjective “affinity” or similarity in pitch when their frequency ratio is close to one octave. The aim of the study reported here was to determine if these two perceptual phenomena are directly related. Each stimulus was a triplet of simultaneous or successive pure tones forming frequency ratios varying across stimuli between 0.96 and 1.04 octaves. The tones were presented at a low sensation level (15 dB) within broadband threshold-equalizing noise, in order to prevent them from interacting in the cochlea when they were simultaneous. A large set of stimulus comparisons made by 18 listeners indicated that: (1) when the tones were simultaneous, maximal fusion was obtained for a mean frequency ratio deviating by less than 0.2% from one octave, and fusion decreased less rapidly above this frequency ratio than below it; (2) when the tones were presented successively, maximal pitch affinity was obtained for a mean frequency ratio significantly larger than one octave, and pitch affinity decreased more rapidly above this frequency ratio than below it. The differences between the results obtained for simultaneous and successive tones suggest that harmonic fusion and pitch affinity are unrelated phenomena.

Classification of urban park soundscapes through perceptions of the acoustical environments

The aim of this study is to classify the soundscape characteristics in urban parks based on perceptions of acoustic environments and to examine useful acoustic indicators to identify soundscape classifications. Both acoustic measurements and subjective evaluations of the soundscape were conducted at various locations in three urban parks. Using hierarchical cluster analysis (HCA), the soundscape perceptions in urban parks were classified into three clusters characterized by the dominance of sound sources, such as traffic noise, natural and human-made sounds. Both discriminant function analysis (DFA) and artificial neural network (ANN) analysis were performed using various acoustic parameters to discern which of them best differentiate the soundscape classifications in urban parks. It was found that the indicators representing sound strength (LAeq), perceived pitch sensation (τ1) and strength of the pitch components (Φ1) of sound scenes could effectively identify the clusters. In particular, autocorrelation function (ACF) parameters τ1 and Φ1 were significantly correlated with identification of traffic noise and human sounds. It was revealed that sounds caused by various human activities in parks play an important role to influence eventfulness of soundscape perception. Soundscape perceptions were also closely correlated with esthetic quality, simplicity and sense of enclosure of landscape. Despite the fact that the results might be limited to the local conditions in Seoul, the findings could provide useful information for designing appropriate soundscapes in urban parks.

Pitch perception and representations of frequency in the peripheral auditory system: What’s missing in cochlear implants?

Pitch is a crucial feature of auditory perception. It conveys information about melody and harmony in music, and conveys prosodic and (in tone languages) lexical information in speech. Although pitch has been studied formally for many decades, there still remains considerable uncertainty regarding how frequency and pitch information is coded and represented in the auditory periphery. This uncertainty means it is unclear whether and how pitch information can best be conveyed via cochlear implants. Cochlear-implant users have been shown to be sensitive to changes in the place of stimulation within the cochlea (“place” pitch) and to changes in the pulse rate presented to the electrode (“rate” pitch), at least up to rates of around 300 Hz. Place pitch in cochlear implants is probably best compared to “brightness” and rate pitch has most in common with the relatively weak pitch produced by temporal-envelope fluctuations in normal-hearing listeners. Neither type of pitch seems to provide the salient and accurate pitch sensations associated with normal hearing. Studies in both normal-hearing listeners and cochlear-implant users will be reviewed to shed light on the mechanisms of pitch perception and on the challenges involved in restoring pitch to cochlear-implant users. [Work supported by NIH grant R01DC005216.]

Effects of fundamental frequency removal and low-pass filtering on pitch comparisons.

Pitch has been defined as perceptual attribute which allows the ordering of sounds on a frequency-related scale ordered from low to high (Klapuri & Davy, 2006; p. 8). A primary acoustic dimension for determining the pitch of complex periodic sounds is fundamental frequency (Stevens & Volkmann, 1940; Idson & Massaro, 1978). Relationships between the spectral components of complex tones also contribute to pitch. Harmonic relations, in particular, strengthen the sensation of pitch (Plomp, 1976; Terhardt, 1974).In contrast, timbre traditionally has been defined by exclusion. For example, the American Standards Association (1960) defines timbre as attribute of auditory sensation in terms of which a listener can judge that two sounds similarly presented and having the same loudness and pitch are dissimilar. Part of the reason for the adherence to the traditional definition of timbre may be that timbre has repeatedly been demonstrated to consist of several perceptual dimensions. Yet, establishing an inclusive definition critically depends on understanding the nature of each of the various dimensions of timbre. Research that has sought to define timbre dimensions has typically involved the multidimensional scaling (MDS) of timbre dissimilarity judgments for musical instrument tones. Reported MDS solutions have tended to converge on several acoustic correlates for the perceptual dimensions of timbre. These associations are summarized below (Caclin, McAdams, Smith, & Winsberg, 2005; Grey, 1977; Krumhansl, 1989; McAdams, Winsberg, Donnadieu, De Soete, & Krimphoff, 1995; Miller & Carterette, 1975). The correspondence between some timbre dimensions and their putative acoustic correlates also has been confirmed by timbre discrimination tasks in response to acoustic manipulations (Grey & Moorer, 1977; also see McAdams, Beauchamp, & Meneguzzi, 1999).Dimensions of musical instrument timbre fall into three broad categories: temporal, spectrotemporal, and spectral.1 Important temporal information is conveyed during the attack portion of a tone, the most salient characteristic of which is the logarithm of rise time. For example, MDS studies have shown that the logarithm of rise time is strongly correlated with a perceptual dimension of timbre (Caclin et al., 2005; Krimphoff, McAdams, & Winsberg, 1994; McAdams et al., 1995). When attack transients are removed (Saldanha & Corso, 1964) or swapped across instru- ments (Thayer, 1974), the accuracy of instrument recognition suffers.The most commonly referenced spectrotemporal dimension is spectral flux, a measure of (the lack of) harmonic stability over the duration of a tone (e.g., see Krumhansl, 1989). However, this dimension has not always significantly correlated with MDS solutions, and sometimes corresponding perceptual dimensions have been accounted for equally well or better by spectral attributes such as spectral irregularity (Krimphoff et ah, 1994) or the relative intensity of odd versus even harmonics (Caclin et al., 2005), both of which contribute to the jaggedness of the spectrum. Several alternative spectrotemporal attributes have been determined to contribute to timbre when controlling for spectral flux, as well as spectral envelope shape and rise time (McAdams et ah, 1999; also see Beauchamp & Lakatos, 2002).The current investigation sought to understand the potential impact on pitch made by spectral timbre information. One primary spectral attribute of timbre is brightness, which is related to the relative amount of higher-frequency energy, and is strongly correlated with spectral centroid, an intensity-weighted average of the frequencies in a tone (Schubert & Wolfe, 2006). Because spectral centroid strongly correlates with a primary perceptual dimension in MDS solutions, it has repeatedly been inferred that listeners use perceived brightness to differentiate between musical instruments (Ehresman & Wessel, 1978). …

Mammalian pitch sensation shaped by the cochlear fluid

The perceived pitch of a complex harmonic sound changes if the partials of the sound are frequency-shifted by a fixed amount. Simple mathematical rules that the perceived pitch could be expected to follow ('first pitch-shift') are violated in psychoacoustic experiments ('second pitchshift'). For this, commonly cognitive cortical processes were held responsible. Here, we show that human pitch perception can be reproduced from a minimal, purely biophysical, model of the cochlea, by fully recovering the psychoacoustical pitch-shift data of G.F. Smoorenburg (1970) and related physiological measurements from the cat cochlear nucleus. For this to happen, the cochlear fluid plays a distinguished role.

Pitch sensation involves stochastic resonance

Pitch is a complex hearing phenomenon that results from elicited and self-generated cochlear vibrations. Read-off vibrational information is relayed higher up the auditory pathway, where it is then condensed into pitch sensation. How this can adequately be described in terms of physics has largely remained an open question. We have developed a peripheral hearing system (in hardware and software) that reproduces with great accuracy all salient pitch features known from biophysical and psychoacoustic experiments. At the level of the auditory nerve, the system exploits stochastic resonance to achieve this performance, which may explain the large amount of noise observed in the working auditory nerve.