Pitch Shift Research Articles

Monaural edge pitch and models of pitch perception

Noise with a sharp spectral edge produces a definite, perceived pitch. The pitch of lowpass noise lies slightly below the edge and the pitch of highpass noise slightly above it. The pitch shifts away from the edge, expressed in semitones, increase with the decreasing edge frequency. A neural timing model based on positive peaks of the autocorrelation function accounts for the broad features of the shifts. So, does a place model based on the peak of an excitation pattern as enhanced by lateral inhibition. As the edge frequency decreases below 150 Hz, the pitch persists for a lowpass noise but disappears for highpass noise. This result is consistent with the timing model but not with the place model. For high edge frequencies, the pitch is stronger for highpass noise than for lowpass noise—consistent with both timing and place models. As the edge frequency approaches 5000 Hz, the pitch disappears for most listeners, but for some listeners, a pitch persists for edge frequencies beyond 8000 Hz. The latter res...

Pitch Shift in Exsomatized Cochlea Observed by Laser Interferometry**Supported by the National Natural Science Foundation of China under Grant Nos 11374118 and 90820001.

Pitch is one of the most important auditory perception characteristics of sound; however, the mechanism underlying the pitch perception of sound is unclear. Although theoretical researches have suggested that perception of virtual pitch is connected with physics in cochlea of inner ear, there is no direct experimental observation of virtual pitch processing in the cochlea. By laser interferometry, we observe shift phenomena of virtual pitch in basilar membrane vibration of exsomatized cochlea, which is consistent with perceptual pitch shift observed in psychoacoustic experiments. This means that the complex mechanical vibration of basilar membrane in cochlea plays an important role in pitch information processing during hearing.

Control of Fundamental Frequency in Dysphonic Patients During Phonation and Speech

PurposeThe pitch-shift reflex (PSR) is the adaptation of the fundamental frequency during phonation and speech and describes the auditory feedback control. Speakers without voice and speech disorders mostly show a compensation of the pitch change in the auditory feedback and adapt their fundamental frequency to the opposite direction. Dysphonic patients often display problems with the auditory perception and control of their voice during therapy. Our study focuses on the auditory and kinesthetic control mechanisms of patients with muscle tension dysphonia (MTD) and speakers without voice and speech problems. Main purpose of the study is the analysis of the functionality of the control mechanisms within phonation and speech between patients with MTD and normal speakers. MethodSixty-one healthy subjects (17 male, 44 female) and 22 patients with MTD (7 male, 15 female) participated following two paradigms including a sustained phonation (vowel /a/) and speech ([‘mama]). Within both paradigms the fundamental frequency of the auditory feedback was increased synthetically. For the analysis of the PSR the electroencephalogram, electroglottography, the voice signal, and the high-speed endoscopy data were recorded simultaneously. The PSR in the electroencephalogram was detected via the N100 and the mismatch negativity. Statistical tests were applied for the detection of the PSR in the physiological response within the electroglottography, voice, and high-speed endoscopy signals. The results were compared between both groups. ResultsNo differences were found between the controls and patients with MTD regarding latency and magnitude of the perception of the pitch shift in both paradigms, but for the magnitude of the behavioral response. Differences also could be found for both groups between the “no pitch” and “pitch” condition of the two paradigms regarding vocal fold dynamics and voice quality. Patients with MTD showed more vibrational irregularities during the PSR than the controls, especially regarding the symmetry of vocal fold dynamics. ConclusionPatients with MTD seem to have a disturbed interaction between the auditory and kinesthetic feedback inducing the execution of an overriding behavioral response.

Self-monitoring in the cerebral cortex: Neural responses to small pitch shifts in auditory feedback during speech production

Speaking is a complex motor skill which requires near instantaneous integration of sensory and motor-related information. Current theory hypothesizes a complex interplay between motor and auditory processes during speech production, involving the online comparison of the speech output with an internally generated forward model. To examine the neural correlates of this intricate interplay between sensory and motor processes, the current study uses altered auditory feedback (AAF) in combination with magnetoencephalography (MEG). Participants vocalized the vowel/e/and heard auditory feedback that was temporarily pitch-shifted by only 25 cents, while neural activity was recorded with MEG. As a control condition, participants also heard the recordings of the same auditory feedback that they heard in the first half of the experiment, now without vocalizing. The participants were not aware of any perturbation of the auditory feedback. We found auditory cortical areas responded more strongly to the pitch shifts during vocalization. In addition, auditory feedback perturbation resulted in spectral power increases in the θ and lower β bands, predominantly in sensorimotor areas. These results are in line with current models of speech production, suggesting auditory cortical areas are involved in an active comparison between a forward model's prediction and the actual sensory input. Subsequently, these areas interact with motor areas to generate a motor response. Furthermore, the results suggest that θ and β power increases support auditory-motor interaction, motor error detection and/or sensory prediction processing.

Sonification of Animal Tracks as an Alternative Representation of Multi-Dimensional Data: A Northern Elephant Seal Example

Understanding movement of marine megafauna across the ocean is largely based on approaches and models based on analysis of tracks of single animals. While this has led to major progress, the possibility of concerted group dynamics has not been sufficiently examined, possibly due to challenges in exploring massive amounts of data required to this end. Here we report a sonification experiment, where the collective movement of northern elephant seals (Mirounga angustirostris) was explored by coding their group dynamics into sound. Specifically, we converted into sound data derived from a tagging program involving a total of 321 tagged animals tracked over a decade, between 20 February 2004 and 30 May 2014, consisting of an observation period of 90063 hours, composed of 1,027,839 individual positions. The data parameters used to provide the sound are position (longitude) and spread (degree of displacement taken for the active group). These data parameters are mapped to the sonic parameters of frequency (pitch) and amplitude (volume), respectively. Examination of the resulting sound revealed features of motion that translate into specific patterns in space. The serial departure of elephant seals to initiate their trips into waves is clearly reflected in the addition of tonalities, with coherent swimming of the animals conforming a wave reflected in the modulated fluctuations in volume, suggesting coordinated fluctuations in dispersion of the wave. Smooth changes in volume, coordinated with pitch variability, indicate that the animals spread out as they move further away from the colony, with one or a few animals exploring an ocean area away from that explored by the core wave. The shift in volume and pitch also signals at group coordination in initiating the return home. Coordinated initiation of the return to the colony is also clearly revealed by the sonification, as reflected in an increase in volume and pitch of the notes denoting the movement of each animal in a migration wave. This sonification reveals clear patterns of covariation in movement data, which drivers and triggers, whether intrinsic or environental, cannot be elucidated here but allow to formulate a number of non-trivial questions on the synchronized nature of group

GBVS360, BMS360, ProSal: Extending existing saliency prediction models from 2D to omnidirectional images

In this paper it is studied how existing visual saliency models designed for 2D images can be extended and applied to Omnidirectional images in the equirectangular format. Three different frameworks, BMS360, GBVS360 and Projected Saliency were designed to address this task. In the particular case of BMS360 and GBVS360, the 2D models Boolean Map Saliency (BMS) and Graph-Based Visual Saliency (GBVS) were rigorously extended to integrate the specific properties of equirectangular images to model visual attention in omnidirectional images watched using Head Mounted Displays (HMDs). With the proposed extensions, the saliency prediction performance in comparison to their original design could significantly be improved. Another key result of this paper comes from the design of a framework called projected saliency which allows applying existing saliency models on equirectangular images without requiring in-depth adaptation of the prediction algorithms. The projected saliency framework enabled to study the interaction of features in the feature activation process of computational saliency models. It shows that the activation should not be done per-viewport, but should account for neighboring regions. As a consequence, we argue that the feature activation process should be performed at a global level instead of a local one. Here, the use of a local approach with a large FOV was found to be a good compromise between global activation and appropriate feature computation to directly port existing saliency models designed for rectilinear images to the domain of equirectangular images. In this paper an adaptive equatorial prior is also described. This equatorial prior allows to account for pitch shift of the horizon line. Finally, results show that the newly designed BMS360 and GVBS360 outperform even recent state-of-the-art models at head motion prediction and are competitive at head/eye saliency-map prediction. Moreover, all models and their code are made publicly available on GitHub allowing to further iterate on this work.

Incongruent pitch cues are associated with increased activation and functional connectivity in the frontal areas

Pitch plays a crucial role in music and speech perception. Pitch perception is characterized by multiple perceptual dimensions, such as pitch height and chroma. Information provided by auditory signals that are related to these perceptual dimensions can be either congruent or incongruent. To create conflicting cues for pitch perception, we modified Shepard tones by varying the pitch height and pitch chroma dimensions in either the same or opposite directions. Our behavioral data showed that most listeners judged pitch changes based on pitch chroma, instead of pitch height, when incongruent information was provided. The reliance on pitch chroma resulted in a stable percept of upward or downward pitch shift, rather than alternating between two different percepts. Across the incongruent and congruent conditions, consistent activation was found in the bilateral superior temporal and inferior frontal areas. In addition, significantly stronger activation was observed in the inferior frontal areas during the incongruent compared to congruent conditions. Enhanced functional connectivity was found between the left temporal and bilateral frontal areas in the incongruent than congruent conditions. Increased intra-hemispheric and inter-hemispheric connectivity was also observed in the frontal areas. Our results suggest the involvement of the frontal lobe in top-down and bottom-up processes to generate a stable percept of pitch change with conflicting perceptual cues.

Timbral Shepard-illusion reveals ambiguity and context sensitivity of brightness perception.

Recent research has described strong effects of prior context on the perception of ambiguous pitch shifts of Shepard tones [Chambers, Akram, Adam, Pelofi, Sahani, Shamma, and Pressnitzer (2017). Nat. Commun. 8, 15027]. Here, similar effects are demonstrated for brightness shift judgments of harmonic complexes with cyclic spectral envelope components and fixed fundamental frequency. It is shown that frequency shifts of the envelopes are perceived as systematic shifts of brightness. Analogous to the work of Chambers et al., the perceptual ambiguity of half-octave shifts resolves with the presentation of prior context tones. These results constitute a context effect for the perceptual processing of spectral envelope shifts and indicate so-far unknown commonalities between pitch and timbre perception.

英語学習者の英語リスニングにプロソディ情報が及ぼす影響 : ピッチの変化に焦点をあてて(実証研究,第45回中部地区英語教育学会和歌山大会)

英語学習者の英語リスニングにプロソディ情報が及ぼす影響 : ピッチの変化に焦点をあてて(実証研究,第45回中部地区英語教育学会和歌山大会)

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.

Analysis of the Auditory Feedback and Phonation in Normal Voices.

The aim of this study was to investigate the auditory feedback mechanisms and voice quality during phonation in response to a spontaneous pitch change in the auditory feedback. Does the pitch shift reflex (PSR) change voice pitch and voice quality? Quantitative and qualitative voice characteristics were analyzed during the PSR. Twenty-eight healthy subjects underwent transnasal high-speed video endoscopy (HSV) at 8000 fps during sustained phonation [a]. While phonating, the subjects heard their sound pitched up for 700 cents (interval of a fifth), lasting 300 milliseconds in their auditory feedback. The electroencephalography (EEG), acoustic voice signal, electroglottography (EGG), and high-speed-videoendoscopy (HSV) were analyzed to compare feedback mechanisms for the pitched and unpitched condition of the phonation paradigm statistically. Furthermore, quantitative and qualitative voice characteristics were analyzed. The PSR was successfully detected within all signals of the experimental tools (EEG, EGG, acoustic voice signal, HSV). A significant increase of the perturbation measures and an increase of the values of the acoustic parameters during the PSR were observed, especially for the audio signal. The auditory feedback mechanism seems not only to control for voice pitch but also for voice quality aspects.

Delayed auditory feedback induces slow oscillations in vocal fundamental frequency and intensity

A system with negative feedback tends toward oscillation or instability when delay is introduced into the feedback loop. Given current evidence for feedback control of pitch and loudness, we hypothesized that delaying auditory feedback during sustained phonation would result in oscillations in fundamental frequency and vocal intensity. Subject produced a sustained vowel across seven auditory feedback conditions: 0, 100, 200, 300, 400, 500, 600, and 700 ms delay. Increasingly large oscillations in fundamental frequency and intensity were observed as delay increased. The frequency of oscillations as a function of delay appear to be subject-specific, with a range between 0.3 and 0.8 Hz. These oscillations carried over into the prosodic contour of subjects' connected speech produced under the same delay conditions. These results suggest that disfluencies induced by delayed feedback (e.g., sound prolongations) may be the result of compensation for shifts in pitch and loudness, rather than discrepancies in articulatory or segmental timing.

Speaker responses to indirect evidence of acoustic signal transmission conditions.

Evidence has been accumulating that speakers adjust their speech production to account for conditions of signal transmission to an interlocutor, in addition to speaker- and listener-related influences. This study manipulated acoustic transmission conditions between speakers and a researcher while they completed dyadic cooperative puzzle tasks. Speakers heard evidence of four transmission perturbations (intensity increase/decrease, pitch increase/decrease) only indirectly, i.e., via changes in the researcher's voice. Analysis of speakers' conversational turns across conditions (baseline + four partner-voice manipulations) showed significant group-level imitation of transmission manipulations of partner voice intensity, with no general response to shifts in partner voice pitch. Significant voice alterations were also observed for individual speakers in intensity, with substantial inter-talker variability in responses. Thirteen of 29 speakers exclusively imitated the manipulation of partner intensity, 4/29 speakers exclusively opposed the transmission manipulation, and 4/29 speakers showed both response types. The presence of opposition responses coupled with a relatively low-magnitude group-level convergence suggests the possibility of a compensatory force at work in at least some speakers, adjusting for changes made during signal transmission despite their lack of direct experience with the transmission manipulation effects.

A Study of Six-Dimensional Intrafractional Shifts During Frameless Image-Guided Radiosurgery and Pain Outcome for Trigeminal Neuralgia

Precision targeting is essential to successful stereotactic radiosurgery (SRS) for trigeminal neuralgia (TGN). We investigate the impact of intra-fractional 6-dimensional shifts during frameless image-guided stereotactic radiosurgery (IGRS) on pain relief outcome for TGN patients. A total of 41 sets of intra-fractional shifts from 35 patients with idiopathic TGN treated by a dedicated Linac-based radiosurgery unit from 2009 to 2013 were retrospectively studied. All patients were immobilized by facemask and received 90 Gy point dose via a 4 mm cone from an average of 6 non-coplanar arcs to the affected trigeminal nerve. The in-room kV X-ray imaging system with 6-degree of freedom robotic couch was utilized for image-guided positioning corrections. During each frameless IGRS, translational shifts in lateral, longitudinal and vertical directions, as well as rotational shifts in pitch, roll and yaw were conducted at each couch angle. These 6-dimentional shifts and the average calculated distance derived from translational shifts were analyzed and correlated with clinical pain outcome. Clinical pain outcome was assessed by patient interviews according the 5-point Barrow Neurological Institute (BNI) pain scale. Student’s t test was used to detect significance between values. The absolute mean lateral, longitudinal and vertical translational were 0.46 ± 0.15, 0.36 ± 0.16 and 0.21 ± 0.08 mm, respectively. The absolute mean pitch, roll and yaw rotational shifts were 0.33 ± 0.24, 0.18 ± 0.09 and 0.27 ± 0.15 degrees, respectively. For patients with less than 2 points of pain relief, the absolute mean lateral, longitudinal and vertical translational shifts were 0.09 ± 0.01, 0.14 ± 0.01 and 0.09 ± 0.01 mm, respectively. The average calculated distance shift for patients with less than 2 points of pain relief was 0.23 ± 0.01 mm. The average absolute pitch, roll and yaw rotational shifts for these patients were 0.15 ± 0.01, 0.10 ± 0.00 and 0.09 ± 0.01 degrees, respectively. For patients with at least 2 points of pain relief, the average absolute lateral, longitudinal and vertical translational shifts were 0.12 ± 0.00, 0.16 ± 0.01 and 0.09 ± 0.00 mm, respectively. The average calculated distance shift for these patients was 0.26 ± 0.01 mm. The average absolute pitch, roll and yaw rotational shifts for these patients were 0.14 ± 0.01, 0.10 ± 0.00 and 0.13 ± 0.00 degrees, respectively. The two patient groups demonstrate no statistically significant difference in the translational or rotational intra-fractional shifts. Our analysis revealed no correlation between pain relief outcome and the amount of intra-fractional shift in all six dimensions during frameless IGRS. Our results indicate the less than 0.5 mm nominal mechanical deviation during frameless IGRS does not impact on TGN pain outcome.

Bioelectrical brain effects of one's own voice identification in pitch of voice auditory feedback.

Control of voice fundamental frequency (F0) relies in part on comparison of the intended F0 level and auditory feedback. This comparison impacts "sense of agency", or SoA, commonly defined as being the agent of one's own actions and plays a key role for self-awareness and social interactions. SoA is aberrant in several psychiatric disorders. Knowledge about brain activity reflecting SoA can be used in clinical practice for these disorders. It was shown that perception of voice feedback as one's own voice, reflecting the recognition of SoA, alters auditory sensory processing. Using a voice perturbation paradigm we contrasted vocal and bioelectrical brain responses to auditory stimuli that differed in magnitude: 100 and 400 cents. Results suggest the different magnitudes were perceived as a pitch error in self-vocalization (100 cents) or as a pitch shift generated externally (400 cents). Vocalizations and neural responses to changes in pitch of self-vocalization were defined as those made to small magnitude pitch-shifts (100 cents) and which did not show differential neural responses to upward versus downward changes in voice pitch auditory feedback. Vocal responses to large magnitude pitch shifts (400 cents) were smaller than those made to small pitch shifts, and neural responses differed according to upwards versus downward changes in pitch. Our results suggest that the presence of SoA for self-produced sounds may modify bioelectrical brain responses reflecting differences in auditory processing of the direction of a pitch shift. We suggest that this modification of bioelectrical response can be used as a biological index of SoA. Possible neuronal mechanisms of this modification of bioelectrical brain response are discussed.

On the relation between pitch and level

Pitch is the perceptual dimension along which musical notes are ordered from low to high. It is often described as the perceptual correlate of the periodicity of the sound's waveform. Previous reports have shown that pitch can depend slightly on sound level. We wanted to verify that these observations reflect genuine changes in perceived pitch, and were not due to procedural factors or confusion between dimensions of pitch and level. We first conducted a systematic pitch matching task and confirmed that the pitch of low frequency pure tones, but not complex tones, decreases by an amount equivalent to a change in frequency of more than half a semitone when level increases. We then showed that the structure of pitch shifts is anti-symmetric and transitive, as expected for changes in pitch. We also observed shifts in the same direction (although smaller) in an interval matching task. Finally, we observed that musicians are more precise in pitch matching tasks than non-musicians but show the same average shifts with level. These combined experiments confirm that the pitch of low frequency pure tones depends weakly but systematically on level. These observations pose a challenge to current theories of pitch.

Interindividual variability in auditory scene analysis revealed by confidence judgements.

Because musicians are trained to discern sounds within complex acoustic scenes, such as an orchestra playing, it has been hypothesized that musicianship improves general auditory scene analysis abilities. Here, we compared musicians and non-musicians in a behavioural paradigm using ambiguous stimuli, combining performance, reaction times and confidence measures. We used 'Shepard tones', for which listeners may report either an upward or a downward pitch shift for the same ambiguous tone pair. Musicians and non-musicians performed similarly on the pitch-shift direction task. In particular, both groups were at chance for the ambiguous case. However, groups differed in their reaction times and judgements of confidence. Musicians responded to the ambiguous case with long reaction times and low confidence, whereas non-musicians responded with fast reaction times and maximal confidence. In a subsequent experiment, non-musicians displayed reduced confidence for the ambiguous case when pure-tone components of the Shepard complex were made easier to discern. The results suggest an effect of musical training on scene analysis: we speculate that musicians were more likely to discern components within complex auditory scenes, perhaps because of enhanced attentional resolution, and thus discovered the ambiguity. For untrained listeners, stimulus ambiguity was not available to perceptual awareness.This article is part of the themed issue 'Auditory and visual scene analysis'.

Pitch ranking with different virtual channel configurations in electrical hearing

Monopolar Virtual Channels (MPVCs) use current steering to increase the number of spectral channels provided to cochlear implant users beyond the physical number of electrodes. The current spread created with a current steered channel is similar to the spread found for monopolar stimulation, and this spread may be one of the bottlenecks for improved performance with an increased number of channels. Quadrupolar Virtual Channels (QPVCs) use current focusing in combination with steering in an attempt to increase the number of channels while reducing channel interaction. However, due to the potentially asymmetric current field generated by QPVCs, there may be distortions in the place pitch representation using this mode. A Virtual Tripole (VTP) is introduced as a current focused virtual channel with a relatively symmetrical electric field distribution. In this study, we looked at pitch ranking in cochlear implant users with QPVC, VTP, and MPVC configurations to determine if place pitch shifts similarly across the cochlea or if any of the stimulation modes shift non-monotonically. Results suggest that MPVC and VTP stimulation provide a consistent monotonic shift across cochlear positions while the place shift provided by QPVCs was more variable. The use of VTP stimulation would be recommended instead of QPVC for a speech processing strategy.

The Effects of Pitch Shifts on Delay-Induced Changes in Vocal Sequencing in a Songbird.

Like human speech, vocal behavior in songbirds depends critically on auditory feedback. In both humans and songbirds, vocal skills are acquired by a process of imitation whereby current vocal production is compared to an acoustic target. Similarly, performance in adulthood relies strongly on auditory feedback, and online manipulations of auditory signals can dramatically alter acoustic production even after vocalizations have been well learned. Artificially delaying auditory feedback can disrupt both speech and birdsong, and internal delays in auditory feedback have been hypothesized as a cause of vocal dysfluency in persons who stutter. Furthermore, in both song and speech, online shifts of the pitch (fundamental frequency) of auditory feedback lead to compensatory changes in vocal pitch for small perturbations, but larger pitch shifts produce smaller changes in vocal output. Intriguingly, large pitch shifts can partially restore normal speech in some dysfluent speakers, suggesting that the effects of auditory feedback delays might be ameliorated by online pitch manipulations. Although birdsong provides a promising model system for understanding speech production, the interactions between sensory feedback delays and pitch shifts have not yet been assessed in songbirds. To investigate this, we asked whether the addition of a pitch shift modulates delay-induced changes in Bengalese finch song, hypothesizing that pitch shifts would reduce the effects of feedback delays. Compared with the effects of delays alone, combined delays and pitch shifts resulted in a significant reduction in behavioral changes in one type of sequencing (branch points) but not another (distribution of repeated syllables).

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.