Harmonic Complex Tones Research Articles

The Origin of the Dominant: Schoenberg's ‘Strong Progression’ and the Realisation of Implied Virtual Pitches

ABSTRACTIn major‐minor tonality, V implies I, and rising fourths, falling thirds and rising seconds between successive chord roots are more common than falling fourths, rising thirds and falling seconds respectively. Possible explanations involve history (in two‐part medieval counterpoint, harmonic major sixths resolved to octaves – maintained in V–I); the rising leading note (V–I includes it, IV–I does not); acoustic speculation (in V–I, the third harmonic of resolves to the second); voice leading (in V7–I, a tritone resolves to a third by contrary step); melodic closure (a rising melodic leap implies subsequent falling steps, and melodies often end with –, harmonised V–I); root newness (chords ‘progress’ if the second chord's root is not part of the first); and tonal stability (V is less stable than IV, giving it a stronger ‘urge’ to resolve). An additional possibility combines the ‘virtual‐pitch’ theory of Ernst Terhardt with the ‘implication‐realisation’ theory of Leonard B. Meyer and Eugene Narmour. Major and minor triads imply subsidiary virtual pitches (missing fundamentals; see Rameau's ‘fundamental bass’) at third and fifth intervals below the root. These weakly perceived pitches are realised in the next chord if the root falls by a third or rises a fourth or major second, creating a feeling of forward progression – while also facilitating intonation for singers and melodic instrumentalists. The theory correctly predicts that successive harmonic complex (but not pure) tones an octave apart sound more similar if rising, and rising octaves are more common than falling in melody. It also explains why Classical modulations are asymmetrical in the opposite direction, major keys tending to modulate to V (not IV) and minor to III (not VI): accidental flats tend to be more perceptually salient or stable than sharps.

A psychoacoustic test on the effect of masking on annoyance to urban air mobility vehicle noise

Urban Air Mobility (UAM) vehicles have a large range of designs and configurations that lead to new noise characteristics and potentially different perceptual responses when compared to traditional aircraft. In addition, UAM vehicles are expected to operate around and within densely populated regions where the presence of ambient background noise is often present. Strategically, this can be leveraged to inform vehicle design and operations to partially or completely mask UAM noise, allowing for mitigation of negative responses and an increased number of allowed operations. A psychoacoustic test was conducted to investigate how masking effects can influence the annoyance response to a low frequency harmonic tone complex (80-320 Hz). To do this, five test subjects compared their annoyance response to the low frequency tonal noise with a higher frequency broadband noise (10 dB down bandwidth between 300 and 2000 Hz), with and without a masking noise present. Detection thresholds were also measured for both sounds to help fit a model to the data. Although the effect of masking on annoyance is complex, results indicate that for some individuals, masking leads to a lower annoyance than the sound level alone would predict.

Benefits of Harmonicity for Hearing in Noise Are Limited to Detection and Pitch-Related Discrimination Tasks.

Harmonic complex tones are easier to detect in noise than inharmonic complex tones, providing a potential perceptual advantage in complex auditory environments. Here, we explored whether the harmonic advantage extends to other auditory tasks that are important for navigating a noisy auditory environment, such as amplitude- and frequency-modulation detection. Sixty young normal-hearing listeners were tested, divided into two equal groups with and without musical training. Consistent with earlier studies, harmonic tones were easier to detect in noise than inharmonic tones, with a signal-to-noise ratio (SNR) advantage of about 2.5 dB, and the pitch discrimination of the harmonic tones was more accurate than that of inharmonic tones, even after differences in audibility were accounted for. In contrast, neither amplitude- nor frequency-modulation detection was superior with harmonic tones once differences in audibility were accounted for. Musical training was associated with better performance only in pitch-discrimination and frequency-modulation-detection tasks. The results confirm a detection and pitch-perception advantage for harmonic tones but reveal that the harmonic benefits do not extend to suprathreshold tasks that do not rely on extracting the fundamental frequency. A general theory is proposed that may account for the effects of both noise and memory on pitch-discrimination differences between harmonic and inharmonic tones.

Simulation of hearing loss can induce pitch shifts for complex tones.

Most studies on pitch shift provoked by hearing loss have been conducted using pure tones. However, many sounds encountered in everyday life are harmonic complex tones. In the present study, psychoacoustic experiments using complex tones were performed on healthy participants, and the possible mechanisms that cause pitch shift due to hearing loss are discussed. Two experiments were performed in this study. In experiment 1, two tones were presented, and the participants were asked to select the tone that was higher in pitch. Partials with frequencies less than 250, 500, 750, or 1,000 Hz were eliminated from the harmonic complex tones and used as test tones to simulate low-tone hearing loss. Each tone pair was constructed such that the tone with a lower fundamental frequency (F0) was higher in terms of the frequency of the lowest partial. Furthermore, partials whose frequencies were greater than 1,300 or 1,600 Hz were also eliminated from these test tones to simulate high-tone hearing loss or modified sounds that patients may hear in everyday life. When a tone with a lower F0 was perceived as higher in pitch, it was considered a pitch shift from the expected tone. In experiment 2, tonal sequences were constructed to create a passage of the song "Lightly Row." Similar to experiment 1, partials of harmonic complex tones were eliminated from the tones. After listening to these tonal sequences, the participants were asked if the sequences sounded correct based on the melody or off-key. The results showed that pitch shifts and the melody sound off-key when lower partials are eliminated from complex tones, especially when a greater number of high-frequency components are eliminated. Considering that these experiments were performed on healthy participants, the results suggest that the pitch shifts from the expected tone when patients with hearing loss hear certain complex tones, regardless of the underlying etiology of the hearing loss.

Mechanisms of masking by Schroeder-phase harmonic tone complexes in the budgerigar (Melopsittacus undulatus)

Schroeder-phase harmonic tone complexes can have a flat temporal envelope and rising or falling instantaneous-frequency sweeps within F0 periods, depending on the phase-scaling parameter C. Human tone-detection thresholds in a concurrent Schroeder masker are 10-15 dB lower for positive C values (rising frequency sweeps) compared to negative (falling sweeps), potentially due to cochlear mechanics, though this hypothesis remains controversial. Birds provide an interesting model for studies of Schroeder masking because many species produce vocalizations containing frequency sweeps. Prior behavioral studies in birds suggest less behavioral threshold difference between maskers with opposite C values than in humans, but focused on low masker F0s and did not explore neural mechanisms. We performed behavioral Schroeder-masking experiments in budgerigars (Melopsittacus undulatus) using a wide range of masker F0 and C values. Signal frequency was 2800 Hz. Neural recordings from the midbrain characterized encoding of behavioral stimuli in awake animals. Behavioral thresholds increased with increasing masker F0 and showed minimal difference between opposite C values, consistent with prior budgerigar studies. Midbrain recordings showed prominent temporal and rate-based encoding of Schroeder F0, and in many cases, marked asymmetry in Schroeder responses between C polarities. Neural thresholds for Schroeder-masked tone detection were often based on a response decrement compared to the masker alone, consistent with prominent modulation tuning in midbrain neurons, and were generally similar between opposite C values. The results highlight the likely importance of envelope cues in Schroeder masking and show that differences in supra-threshold Schroeder responses do not necessarily result in neural threshold differences.

The effect of rhythm on selective listening in multiple-source environments for young and older adults

Understanding continuous speech with competing background sounds is challenging, particularly for older adults. One stimulus property that may aid listeners understanding of to-be-attended (target) material is temporal regularity (rhythm). In the context of speech-in-noise understanding, McAuley and colleagues recently showed a target rhythm effect whereby recognition of target speech was better when natural speech rhythm of a target talker was intact than when it was temporally altered. The current study replicates the target rhythm effect using a synthetic vowel sequence paradigm in young adults (Experiment 1) and then uses this paradigm to investigate potential age-related changes in the effect of rhythm on recognition (Experiment 2). Listeners identified the last three vowels of temporally regular (isochronous) and irregular (anisochronous) synthetic vowel sequences in quiet and with a competing background sequence of vowel-like harmonic tone complexes presented at various tempos. The results replicated the target rhythm effect whereby temporal regularity in the vowel sequences improved identification accuracy of young listeners compared to irregular vowel sequences. The magnitude of the effect was not found to be influenced by background tempo, but faster background tempos led to greater vowel identification accuracy independent of regularity. Older listeners also demonstrated a target rhythm effect but received less benefit from the temporal regularity of the target sequences than did young listeners. This study highlights the importance of rhythm for understanding age-related differences in selective listening in complex environments and provides a novel paradigm for investigating effects of rhythm on perception.

Sensitivity to Frequency Modulation is Limited Centrally.

Modulations in both amplitude and frequency are prevalent in natural sounds and are critical in defining their properties. Humans are exquisitely sensitive to frequency modulation (FM) at the slow modulation rates and low carrier frequencies that are common in speech and music. This enhanced sensitivity to slow-rate and low-frequency FM has been widely believed to reflect precise, stimulus-driven phase locking to temporal fine structure in the auditory nerve. At faster modulation rates and/or higher carrier frequencies, FM is instead thought to be coded by coarser frequency-to-place mapping, where FM is converted to amplitude modulation (AM) via cochlear filtering. Here, we show that patterns of human FM perception that have classically been explained by limits in peripheral temporal coding are instead better accounted for by constraints in the central processing of fundamental frequency (F0) or pitch. We measured FM detection in male and female humans using harmonic complex tones with an F0 within the range of musical pitch but with resolved harmonic components that were all above the putative limits of temporal phase locking (>8 kHz). Listeners were more sensitive to slow than fast FM rates, even though all components were beyond the limits of phase locking. In contrast, AM sensitivity remained better at faster than slower rates, regardless of carrier frequency. These findings demonstrate that classic trends in human FM sensitivity, previously attributed to auditory nerve phase locking, may instead reflect the constraints of a unitary code that operates at a more central level of processing.SIGNIFICANCE STATEMENT Natural sounds involve dynamic frequency and amplitude fluctuations. Humans are particularly sensitive to frequency modulation (FM) at slow rates and low carrier frequencies, which are prevalent in speech and music. This sensitivity has been ascribed to encoding of stimulus temporal fine structure (TFS) via phase-locked auditory nerve activity. To test this long-standing theory, we measured FM sensitivity using complex tones with a low F0 but only high-frequency harmonics beyond the limits of phase locking. Dissociating the F0 from TFS showed that FM sensitivity is limited not by peripheral encoding of TFS but rather by central processing of F0, or pitch. The results suggest a unitary code for FM detection limited by more central constraints.

In search of the missing resolved harmonics: Neural and behavioral studies of pitch discrimination

The pitch of harmonic complex tones (HCT) plays important roles in speech and music perception and in the perceptual organization of sound. Human listeners rely primarily on the spectral pattern of harmonics individually resolved by the frequency analysis in the cochlea to derive a pitch percept. Yet, evidence for a robust neural representation of resolved harmonics in animal models has been elusive, and some species appear to rely on temporal envelope cues rather than on resolved harmonics to discriminate pitch. We performed both behavioral experiments on pitch discrimination by rabbits and single-unit recordings from the auditory nerve (AN) and inferior colliculus (IC) using HCTs with equal-amplitude harmonics in which the fundamental frequency (F0) was varied over a wide range. We found that rabbits can discriminate the pitch of HCT using the spectral pattern of resolved harmonics for F0s within the range of conspecific vocalizations. Correspondingly, many IC neurons contribute to a rate-place code for the frequencies of resolved harmonics for F0s >500 Hz, and this code is more robust to variations in stimulus level than that found in the AN. A remaining challenge is to identify the neural mechanisms underlying enhanced rate-place coding in IC. [Work supported by NIH-NIDCD DC002258.]

Investigating the neural correlates of the emergence of pitch using harmonic and inharmonic stimuli

The emergence of a pitch percept, referred to as the pitch onset response (POR), has predominantly been studied using transitions from noise to regular interval noise (RIN), click trains and more recently, harmonic complex tones. The POR is typically an asymmetrical change response which shows a larger response for stimuli that go from having no salient pitch to a salient pitch but not vice versa. However, the spectro-temporal differences between the pitch inducing stimulus and noise make it difficult to disentangle whether the response reflects a change in regularity or a true difference in pitch salience. The aim of this experiment is to use spectrally similar stimuli that differ in pitch salience (harmonic versus inharmonic tones) without changes in temporal regularity. We recorded EEG responses in normal-hearing participants to investigate the cortical correlates of pitch emergence in humans. We used the noise to RIN transitions as a baseline measure to replicate the asymmetry in the POR. We also used transitions from harmonic to inharmonic stimuli and vice versa to investigate if the POR asymmetry would hold for stimuli with minimal spectro-temporal differences. Results from this study will help us further understand the parameters affecting this response.

Temporal hierarchy of cortical responses reflects core-belt-parabelt organization of auditory cortex in musicians.

Human auditory cortex (AC) organization resembles the core-belt-parabelt organization in nonhuman primates. Previous studies assessed mostly spatial characteristics; however, temporal aspects were little considered so far. We employed co-registration of functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG) in musicians with and without absolute pitch (AP) to achieve spatial and temporal segregation of human auditory responses. First, individual fMRI activations induced by complex harmonic tones were consistently identified in four distinct regions-of-interest within AC, namely in medial Heschl's gyrus (HG), lateral HG, anterior superior temporal gyrus (STG), and planum temporale (PT). Second, we analyzed the temporal dynamics of individual MEG responses at the location of corresponding fMRI activations. In the AP group, the auditory evoked P2 onset occurred ~25ms earlier in the right as compared with the left PT and ~15ms earlier in the right as compared with the left anterior STG. This effect was consistent at the individual level and correlated with AP proficiency. Based on the combined application of MEG and fMRI measurements, we were able for the first time to demonstrate a characteristic temporal hierarchy ("chronotopy") of human auditory regions in relation to specific auditory abilities, reflecting the prediction for serial processing from nonhuman studies.

Fast processing models effects of reflections on binaural unmasking

Sound reflections and late reverberation alter energetic and binaural cues of a target source, thereby affecting its detection in noise. Two experiments investigated detection of harmonic complex tones, centered around 500 Hz, in noise, in a virtual room with different modifications of simulated room impulse responses (RIRs). Stimuli were auralized using the Simulated Open Field Environment’s (SOFE’s) loudspeakers in anechoic space. The target was presented from the front (0°) or 60° azimuth, while an anechoic noise masker was simultaneously presented at 0°. In the first experiment, early reflections were progressively added to the RIR and detection thresholds of the reverberant target were measured. For a frontal sound source, detection thresholds decreased while adding early reflections within the first 45 ms, whereas for a lateral sound source, thresholds remained constant. In the second experiment, early reflections were removed while late reflections were kept along with the direct sound. Results for a target at 0° show that even reflections as late as 150 ms reduce detection thresholds compared to only the direct sound. A binaural model with a sluggishness component following the computation of binaural unmasking in short windows predicts measured and literature results better than when large windows are used.

Factors underlying masking release by voice-gender differences and spatial separation cues in multi-talker listening environments in listeners with and without hearing loss.

Voice-gender differences and spatial separation are important cues for auditory object segregation. The goal of this study was to investigate the relationship of voice-gender difference benefit to the breadth of binaural pitch fusion, the perceptual integration of dichotic stimuli that evoke different pitches across ears, and the relationship of spatial separation benefit to localization acuity, the ability to identify the direction of a sound source. Twelve bilateral hearing aid (HA) users (age from 30 to 75 years) and eleven normal hearing (NH) listeners (age from 36 to 67 years) were tested in the following three experiments. First, speech-on-speech masking performance was measured as the threshold target-to-masker ratio (TMR) needed to understand a target talker in the presence of either same- or different-gender masker talkers. These target-masker gender combinations were tested with two spatial configurations (maskers co-located or 60° symmetrically spatially separated from the target) in both monaural and binaural listening conditions. Second, binaural pitch fusion range measurements were conducted using harmonic tone complexes around a 200-Hz fundamental frequency. Third, absolute localization acuity was measured using broadband (125-8000 Hz) noise and one-third octave noise bands centered at 500 and 3000 Hz. Voice-gender differences between target and maskers improved TMR thresholds for both listener groups in the binaural condition as well as both monaural (left ear and right ear) conditions, with greater benefit in co-located than spatially separated conditions. Voice-gender difference benefit was correlated with the breadth of binaural pitch fusion in the binaural condition, but not the monaural conditions, ruling out a role of monaural abilities in the relationship between binaural fusion and voice-gender difference benefits. Spatial separation benefit was not significantly correlated with absolute localization acuity. In addition, greater spatial separation benefit was observed in NH listeners than in bilateral HA users, indicating a decreased ability of HA users to benefit from spatial release from masking (SRM). These findings suggest that sharp binaural pitch fusion may be important for maximal speech perception in multi-talker environments for both NH listeners and bilateral HA users.

Role of perceptual integration in pitch discrimination at high frequenciesa).

At very high frequencies, fundamental-frequency difference limens (F0DLs) for five-component harmonic complex tones can be better than predicted by optimal integration of information, assuming performance is limited by noise at the peripheral level, but are in line with predictions based on more central sources of noise. This study investigates whether there is a minimum number of harmonic components needed for such super-optimal integration effects and if harmonic range or inharmonicity affects this super-optimal integration. Results show super-optimal integration, even with two harmonic components and for most combinations of consecutive harmonic, but not inharmonic, components.

On mistuning detection and beat perception for harmonic complex tones at low and very high frequencies.

This study assessed the detection of mistuning of a single harmonic in complex tones (CTs) containing either low-frequency harmonics or very high-frequency harmonics, for which phase locking to the temporal fine structure is weak or absent. CTs had F0s of either 280 or 1400 Hz and contained harmonics 6-10, the 8th of which could be mistuned. Harmonics were presented either diotically or dichotically (odd and even harmonics to different ears). In the diotic condition, mistuning-detection thresholds were very low for both F0s and consistent with detection of temporal interactions (beats) produced by peripheral interactions of components. In the dichotic condition, for which the components in each ear were more widely spaced and beats were not reported, the mistuned component was perceptually segregated from the complex for the low F0, but subjects reported no "popping out" for the high F0 and performance was close to chance. This is consistent with the idea that phase locking is required for perceptual segregation to occur. For diotic presentation, the perceived beat rate corresponded to the amount of mistuning (in Hz). It is argued that the beat percept cannot be explained solely by interactions between the mistuned component and its two closest harmonic neighbours.

Pitch discrimination is better for synthetic timbre than natural musical instrument timbres despite familiarity.

Pitch discrimination is better for complex tones than pure tones, but how pitch discrimination differs between natural and artificial sounds is not fully understood. This study compared pitch discrimination thresholds for flat-spectrum harmonic complex tones with those for natural sounds played by musical instruments of three different timbres (violin, trumpet, and flute). To investigate whether natural familiarity with sounds of particular timbres affects pitch discrimination thresholds, this study recruited non-musicians and musicians who were trained on one of the three instruments. We found that flautists and trumpeters could discriminate smaller differences in pitch for artificial flat-spectrum tones, despite their unfamiliar timbre, than for sounds played by musical instruments, which are regularly heard in everyday life (particularly by musicians who play those instruments). Furthermore, thresholds were no better for the instrument a musician was trained to play than for other instruments, suggesting that even extensive experience listening to and producing sounds of particular timbres does not reliably improve pitch discrimination thresholds for those timbres. The results show that timbre familiarity provides minimal improvements to auditory acuity, and physical acoustics (e.g., the presence of equal-amplitude harmonics) determine pitch discrimination thresholds more than does experience with natural sounds and timbre-specific training.

Neural processing and perception of Schroeder-phase harmonic tone complexes in the gerbil: Relating single-unit neurophysiology to behavior.

Schroeder-phase harmonic tone complexes have been used in physiological and psychophysical studies in several species to gain insight into cochlear function. Each pitch period of the Schroeder stimulus contains a linear frequency sweep; the duty cycle, sweep velocity, and direction are controlled by parameters of the phase spectrum. Here, responses to a range of Schroeder-phase harmonic tone complexes were studied both behaviorally and in neural recordings from the auditory nerve and inferior colliculus of Mongolian gerbils. Gerbils were able to discriminate Schroeder-phase harmonic tone complexes based on sweep direction, duty cycle, and/or velocity for fundamental frequencies up to 200 Hz. Temporal representation in neural responses based on the van Rossum spike-distance metric, with time constants of either 1ms or related to the stimulus' period, was compared with average discharge rates. Neural responses and behavioral performance were both expressed in terms of sensitivity, d', to allow direct comparisons. Our results suggest that in the auditory nerve, stimulus fine structure is represented by spike timing, whereas envelope is represented by rate. In the inferior colliculus, both temporal fine structure and envelope appear to be represented best by rate. However, correlations between neural d' values and behavioral sensitivity for sweep direction were strongest for both temporal metrics, for both auditory nerve and inferior colliculus. Furthermore, the high sensitivity observed in the inferior colliculus neural rate-based discrimination suggests that these neurons integrate across multiple inputs arising from the auditory periphery.

Measuring harmonic benefit in musicians and non-musicians in several tasks

Prior work has demonstrated that harmonic tones are easier to detect in noise and yield better F0 discrimination in noise than inharmonic tones. These effects, referred to as harmonic benefit, appear to be approximately the same size in musicians and non-musicians, despite musicians’ overall better pitch discrimination. The present study aimed to replicate these findings and extend them to include measurements of harmonic benefit in other tasks. Non-musicians and musicians were compared in four tasks: detection in noise, F0 discrimination, FM detection, and AM detection. The stimuli in each task were either harmonic or inharmonic complex tones and were presented in threshold-equalizing noise at a range of signal-to-noise ratios. We found that harmonic benefit for F0 discrimination was large and remained large even after accounting for differences in the detectability of harmonic and inahrmonic tones. In contrast, harmonic benefit was small for FM and AM detection and could mostly be accounted for by differences in detectability. In contrast to prior studies, we found that musicians showed a larger harmonic benefit than non-musicians. These results provide insight into how musical training may specialize the auditory system for processing of harmonicity and pitch. [Work supported by NIH grants F31 DC019247 and R01 DC005216.]

Pitch-timbre interactions as measured in discrimination and the frequency-following response

Perceptual interactions between pitch and timbre have been demonstrated repeatedly using discrimination tasks in psychoacoustics. The current study investigates whether the pitch-timbre interaction is reflected in neural signatures of pitch encoding in the brainstem. Listeners discriminated the pitch of harmonic tone complexes with low- or high-spectral centroids (SC) in a yes/no task. Fundamental frequency (F0) varied by one just noticeable difference (JND), while SC could be varied by two- or five- JNDs. Discrimination performance increased when both F0 and SC were higher as opposed to when one was higher, and one was lower. This suggests that higher SCs bias listeners toward “higher pitch” responses, replicating previous studies. Frequency-following responses (FFR) were obtained in response to the same stimuli from the same listeners. The recorded FFR signals were analyzed using autocorrelation functions, to evaluate the coding of periodicity, and the Fourier spectra, as an indicator of the encoded F0. The encoding of pitch-relevant information was similar for all stimuli, regardless of SC. Contrary to bias observed in pitch discrimination performance imposed by SC, the lack of a significant influence of SC in the FFR measurements suggests that the pitch-timbre interaction was not observed at the level of the brainstem.

Mechanisms of masking by Schroeder-phase harmonic tone complexes in the budgerigar

Schroeder-phase harmonic tone complexes have a flattened temporal envelope and either rising or falling instantaneous frequency glides within F0periods, depending on the polarity of the phase relationship between harmonics. Human detection thresholds for a pure-tone target added to a Schroeder masker can be 10–15 dB lower for the negative Schroeder (upward gliding) compared to positive (downward gliding), possibly due to human cochlear mechanics though this hypothesis remains controversial. In contrast, several avian species show minimal behavioral masking differences between Schroeder polarities for F0s of 50 and 100 Hz. To gain further insight into the mechanisms of Schroeder masking, we performed operant-conditioning experiments in budgerigars, a parakeet species, including F0s up to 400 Hz that are potentially better matched to avian cochlear mechanics. Awake neurophysiological recordings at the midbrain processing level characterized neural encoding of behavioral test stimuli. Behavioral Schroeder masking thresholds decreased with increasing F0 and showed minimal difference between Schroeder polarities even at high F0s. Neural recordings showed prominent temporal and rate-based encoding of F0 periodicity and, in some neurons, marked response asymmetries between Schroeder polarities. These results suggest that neural response asymmetries between Schroeder polarities need not produce large behavioral masking differences for pure-tone targets.

The effect of competitor rhythmic structure when recalling vowels in a complex listening environment

Research has shown that the rhythmic structure of speech is relevant to listening outcomes in complex environments. Several studies have shown that an intact, natural target rhythm facilitates listeners’ perception of auditory signals. However, less is known about the effect of competitor signal rhythmic structure on target recognition. The current study uses a synthetic vowel identification paradigm to investigate the influence of the rhythmic structure of to-be-ignored competing signals on listeners’ ability to identify speech information in a target signal. Listeners were tasked with identifying the last three vowels of target sequences of varying length presented alongside competing sequences consisting of either vowel-like harmonic tone complexes or similar vowels. The inter-onset-intervals in these sequences were manipulated to create conditions where the internal rhythm of the sequences was either isochronous or irregular. Competitor rhythm was found to be a significant factor for target recognition only with the vowel-sequence competitors. Isochronous target vowel recognition was better for vowel-sequence competitors with an irregular rhythm than with a regular (isochronous) rhythm. The results of this study highlight (1) the relevance of the rhythmic structure in selective listening tasks and (2) the importance of target and competitor similarity in determining the influence of competitor rhythm.