Dichotic Pitch Research Articles

Sensory and nonsensory influences on children’s performance of dichotic pitch perception tasks

Dichotic pitch perception reflects the auditory system's use of binaural cues to perceptually separate different sound sources and to determine the spatial location of sounds. Several studies were conducted to identify factors that influence children's dichotic pitch perception thresholds. An initial study of school children revealed an age-related improvement in thresholds for lateralizing dichotic pitch tones. In subsequent studies potential sensory and nonsensory limitations on young children's performance of dichotic pitch lateralization tasks were examined. A training study showed that with sufficient practice, young children lateralize dichotic pitch stimuli as well as adults, indicating an age difference in perceptual learning of the lateralization task. Changing the task requirements so that young children made a judgment about the pitch of dichotic pitch tones, rather than the spatial location of the tones, also resulted in significantly better thresholds. These findings indicate that nonsensory factors limit young children's performance of dichotic pitch tasks.

MEG responses to rippled noise and Huggins pitch reveal similar cortical representations

The onset of pitch within an ongoing noise signal evokes a particular brain activity, the pitch onset response (POR). Using whole-head MEG, PORs to iterated rippled noise (IRN) and Huggins pitch (HP), representing prototypical pitch-in-noise signals, were measured in twenty subjects during a pitch identification task (333 Hz, 400 Hz, randomized). HP and IRN yielded similar responses, lateralized to the left hemisphere and peaking about 180 ms after pitch onset. The initial phase (140 ms) showed stronger activations to 400 than to 333 Hz whereas later stages (200-300 ms) showed target vs nontarget effects. These results suggest, first, that different pitches converge into a common cortical representation and, second, that the POR encompasses various successive processing stages.

Object-related brain potentials associated with the perceptual segregation of a dichotically embedded pitch

The cortical mechanisms of perceptual segregation of concurrent sound sources were examined, based on binaural detection of interaural timing differences. Auditory event-related potentials were measured from 11 healthy subjects. Binaural stimuli were created by introducing a dichotic delay of 500-ms duration to a narrow frequency region within a broadband noise, and resulted in a perception of a centrally located noise and a right-lateralized pitch (dichotic pitch). In separate listening conditions, subjects actively discriminated and responded to randomly interleaved binaural and control stimuli, or ignored random stimuli while watching silent cartoons. In a third listening condition subjects ignored stimuli presented in homogenous blocks. For all listening conditions, the dichotic pitch stimulus elicited an object-related negativity (ORN) at a latency of about 150-250 ms after stimulus onset. When subjects were required to actively respond to stimuli, the ORN was followed by a P400 wave with a latency of about 320-420 ms. These results support and extend a two-stage model of auditory scene analysis in which acoustic streams are automatically parsed into component sound sources based on source-relevant cues, followed by a controlled process involving identification and generation of a behavioral response.

Psychophysical Indexes of Temporal Processing Abnormalities in Children With Developmental Dyslexia

Children with dyslexia and children progressing normally in reading performed several perceptual tasks to determine (a) the psychophysical measures that best differentiate children with dyslexia from children with average reading abilities; (b) the extent of temporal processing deficits in a single, well-defined group of children with dyslexia; and (c) the co-occurrence of visual and auditory temporal processing deficits in children with dyslexia. 4 of our 12 psychophysical tasks indicated differences in temporal processing ability between children with dyslexia and children with good reading skills. These included 2 auditory tasks (dichotic pitch perception and FM tone discrimination) and 2 visual tasks (global motion perception and contrast sensitivity). The battery of 12 tasks successfully classified 80% of the children into their respective reading-level groups. Within the group of children with dyslexia who had temporal processing deficits, most were affected in either audition or vision; few children were affected in both modalities. The observed deficits suggest that impaired temporal processing in dyslexia is most evident on tasks that require the ability to synthesize local, temporally modulated inputs into a global percept and the ability to extract the resultant global percept from a noisy environment.

Earedness: Left-eared and right-eared listeners

The Huggins pitch (HP) stimulus known as HP- is created with a broadband background noise having an interaural phase difference of zero, together with a narrow boundary region wherein the interaural phase varies with frequency. At the spectral center of the boundary region the interaural phase is 180 deg. Therefore, HP- is symmetrical with respect to the two ears. Despite the symmetry, most listeners hear the HP image strongly lateralized to one side of the head. Some hear it on the right; others hear it on the left. Two surveys, involving 51 listeners, found that these perceptions do not change when the headphones are reversed. Extensive experiments with five listeners found that the lateralization directions were usually insensitive to variations in the frequency of the boundary region (more than two octaves). The left or right preference was strong enough that listeners chose alias locations (differing from a more central location by 360 deg) on the preferred side when various frequency-independent interaural delays and phase shifts were added to the HP stimulus. The experiments suggest that given ambiguous stimuli, listeners exhibit earedness—a preference similar to, but not as strong as, handedness. [Work supported by the NIDCD Grant DC 00181.]

Lateralization of the Huggins pitch

The lateralization of the Huggins pitch (HP) was measured using a direct estimation method. The background noise was initially N0 or Nπ, and then the laterality of the entire stimulus was varied with a frequency-independent interaural delay, ranging from −1 to +1 ms. Two versions of the HP boundary region were used, stepped phase and linear phase. When presented in isolation, without the broadband background, the stepped boundary can be lateralized on its own but the linear boundary cannot. Nevertheless, the lateralizations of both forms of HP were found to be almost identical functions both of the interaural delay and of the boundary frequency over a two-octave range. In a third experiment, the same listeners lateralized sine tones in quiet as a function of interaural delay. Good agreement was found between lateralizations of the HP and of the corresponding sine tones. The lateralization judgments depended on the boundary frequency according to the expected hyperbolic law except when the frequency-independent delay was zero. For the latter case, the dependence on boundary frequency was much slower than hyperbolic. [Work supported by the NIDCD grant DC 00181.]

Binaural models and the strength of dichotic pitches.

Modern physiologically based models of the binaural system incorporate internal delay lines in the pathways from left and right peripheries to central processing nuclei. Different binaural models for the formation of dichotic pitch employ these delay lines in different ways. Consequently, the different models make different predictions for the relative strengths of dichotic pitches made with particular phase conditions. The differences are magnified for dichotic pitches at low frequencies where especially long delay lines may be required. Data from four low-frequency pitch strength experiments on pure-tone-like dichotic pitches (two on Huggins pitch and two on binaural coherence edge pitch) are consistent with models of the equalization-cancellation type and not consistent with the central activity pattern model.

Ear advantage and consonance of dichotic pitch intervals in absolute-pitch possessors

Left–right asymmetry in the central processing of musical consonance was investigated by dichotic listening tasks. Two piano tones paired at various pitch intervals (1–11 semitones) were presented one note in each ear to twenty absolute-pitch possessors. As a result, a weak overall trend for left ear advantage (LEA) was found, as is characteristic of trained musicians. Second, pitches of dissonant intervals were more difficult to identify than those of consonant intervals. Finally, the LEA was greater with dissonant intervals than with consonant intervals. As the tones were dichotically presented, the results indicated that the central auditory system could distinguish between consonant and dissonant intervals without initial processing of pitch–pitch relations in the cochlea.

Neural activity associated with binaural processes for the perceptual segregation of pitch.

We measured late cortical potentials in a psychophysical procedure for binaural unmasking of a dichotically-embedded pitch. Late-latency auditory evoked potentials were measured from 128 recording channels in 13 healthy subjects. Control stimuli consisted of 500 ms segments of broadband acoustic noise presented identically to both ears via earphones, evoking a perception of noise localized in the centre of the head. Dichotic pitch stimuli were created by introducing a dichotic delay to a narrow frequency region of the same noise segments, and resulted in a perception of both the centrally-located noise and a right-lateralized pitch. Both stimuli evoked late auditory event-related potentials (ERPs) characterized by a P1-N1-P2 complex of waves between 60 and 180 ms after stimulus onset. ERPs associated with the control and dichotic pitch stimuli showed no amplitude differences for the P1 and N1 waves. ERPs to dichotic pitch stimuli became significantly more negative beginning at a latency around 150 ms, an effect that was maximal between 210 and 280 ms. Topographic mapping showed that this late negativity was lateralized to the left hemisphere. The late negative wave elicited by the dichotic pitch stimulus reflects neural processing that is dependent upon binaural fusion within the auditory system. The dichotic pitch paradigm may provide a useful tool for the electrophysiological assessment and study of the temporal processing capabilities of the auditory system. This paradigm may also be useful for the study of binaural mechanisms for the perceptual segregation of concurrent sound sources.

Dichotic pitch and the missing fundamental

A dichotic pitch can be heard by introducing interaural phase shifts in one or more low-frequency spectral regions of an otherwise diotic noise. The present study examined the perceived pitch associated with phase disparities in spectral regions corresponding to harmonics of a low-frequency fundamental. Of particular interest was whether the pitch of the complex was related to the frequency region of the harmonics or whether it was associated with the missing fundamental. Discrimination thresholds for this dichotic virtual pitch were estimated in a 3AFC paradigm, where listeners were asked to identify the interval with the lower virtual pitch. After modest training, listeners were able to perform this task well even when a randomized subset of harmonics above F0 were presented on each trial, a manipulation designed to make spectral region an unreliable cue. In another manipulation, frequency regions of the phase disparity were chosen such that although the frequency increased, the missing fundamental decreased (or vice versa). In these cases listeners reported that the perceived pitch shifted according to the change in F0, not according to the spectral region of the harmonics. Results were consistent with the interpretation that the perceived pitch correspond to the missing fundamental.

On the lateralization of the Huggins pitch

The central activity pattern (CAP) model of Raatgever and Bilsen [J. Acoust. Soc. Am. 80, 429–441 (1986)] correctly predicts that Huggins pitch (HP+) is lateralized in the center whereas HP− is lateralized to the left or the right. Experiments show that some listeners (left-eared listeners) always hear the pitch sensation on the left and others always hear it on the right. Still others can hear it on one side or the other. The CAP model also predicts that the laterality of HP− should follow a hyperbolic function of the boundary frequency. To test this prediction, laterality was measured in careful laterality estimation experiments, wherein HP− was combined with a set of interaural time differences (ITDs). Although laterality estimates followed predictions for finite (ITDs), on those trials where the ITD was zero the hyperbolic law was violated for five out of five listeners. Instead, the laterality of HP− was very insensitive to the boundary frequency over the range tested, 200 to 1000 Hz. A search for a satisfactory variation on the CAP model continues. [Work supported by the NIDCD under Grants Nos. DC00181 and DC00100.]

Melody recognition using three types of dichotic-pitch stimulus.

The recognition of 10 different 16-note melodies, constructed using either dichotic-pitch stimuli or diotic pure-tone stimuli, was measured. The dichotic pitches were created by placing a frequency-dependent transition in the interaural phase of a noise burst. Three different configurations for the transition were used in order to give Huggins pitch, binaural-edge pitch, and binaural-coherence-edge pitch. Forty-nine inexperienced listeners participated. The melodies evoked by the dichotic stimuli were consistently identified well in the first block of trials, indicating that the sensation of dichotic pitch was relatively immediate and did not require prolonged listening experience. There were only small improvements across blocks of trials. The mean scores were 97% (pure tones), 93% (Huggins pitch), 89% (binaural-edge pitch), and 77% (binaural-coherence-edge pitch). All pairwise differences were statistically significant, indicating that Huggins pitch was the most salient of the dichotic pitches and binaural-coherence-edge pitch was weakest. To account for these differences in salience, a simulation of lateral inhibition was applied to the recovered spectrum generated by the modified equalization cancellation model [J. F. Culling, A. Q. Summerfield, and D. H. Marshall, J. Acoust. Soc. Am. 103, 3509-3526 (1998)]. The height of the peak in the resulting "edge-enhanced" recovered spectrum reflected the relative strength of the different dichotic pitches.

A low-frequency paradox in binaural pitch

Binaural pitches, such as the Huggins pitch and binaural coherence edge pitch (BICEP), can be approached in terms of a model network of binaural neurons that are tuned in frequency and in interaural delay [e.g., Raatgever and Bilsen, J. Acoust. Soc. Am. 80, 429–441 (1986)]. The basic rule of binaural combination resembles addition. Binaural pitches appear as peaks or edge features in the frequency-delay plane. The characteristic frequency of a feature determines the pitch, and the internal delay of the feature determines the lateralization of the pitch image. Because delay lines become sparser with increasing delay, the model predicts that binaural pitches of very low frequency should be more difficult to hear the more they are lateralized. However, our Huggins pitch and BICEP discrimination and detection experiments show that the reverse is true. These experiments favor a model in which the basic rule of binaural combination resembles subtraction. However, the predictions of the subtractive model disagree with the observed lateralization. Furthermore, the low-frequency discrimination and detection experiments do not agree with a model in which additive and subtractive binaural combinations are alternative options. This is the low-frequency paradox. [Work supported by NIDCD.]

The lateralization of simple dichotic pitches

A "simple" dichotic pitch arises when a single narrow band possesses a different interaural configuration from a surrounding broadband noise whose interaural configuration is uniform and correlated. Such pitches were created by interaurally decorrelating a narrow band (experiment 1) or by giving a narrow band a different interaural time difference from the noise (experiment 2). Using an adaptive forced-choice procedure, listeners adjusted the interaural intensity difference of "pointers" to match their lateralization to that of the dichotic pitches. The primary determinants of lateralization were the interaural configuration of the broadband noise (experiment 1), the center frequency of the narrow band (experiment 1), and its interaural configuration (experiment 2). The ability of two computational models to predict these results was evaluated. A version of the central-spectrum model [J. Raatgever and F. A. Bilsen, J. Acoust. Soc. Am. 80, 429-441 (1986)] incorporating realistic frequency selectivity accounted for the main results of experiment 1 but not experiment 2. A new "reconstruction-comparison" model accounted for the main results of both experiments. To accommodate the variables shown to influence lateralization, this model segregates evidence of the dichotic pitch from the noise, reconstructs the cross-correlogram of the noise, and compares it with the cross-correlogram of the original stimulus.

On the dichotic pitch of simultaneously presented interaurally delayed white noises. Implications for binaural theory.

A dichotic pitch known as Fourcin Pitch (FP) is perceived when two independent interaurally delayed white noises are presented simultaneously. Experiments in the past mainly dealt with stimulus situations where one interaural delay was smaller than 4 ms and the other was in the range 0-10 ms. Here, experiments are reported showing a novel pitch percept that occurs when one noise is interaurally delayed at the left ear and the other noise is about equally delayed at the right ear, for delays in the range of 4-10 ms. It is shown that, for both the previously reported FP and the novel pitch, the Central Spectrum (CS) theory [Raatgever and Bilsen, J. Acoust. Soc. Am. 80, 429-441 (1986)] provides a correct prediction of both the pitch value and the lateral position of the pitch image, where other current theories partly or completely fail. Further experiments indicate that the lateralized position of the pitch image is essentially not influenced by an interaural intensity difference (IID). This is also predicted by the CS model and leads to the generalized conclusion that interaural time and intensity differences are processed separately in the auditory system until, at least, the level where the dichotic pitch is generated.

Binaural coherence edge pitch—Manipulations and models

Binaural coherence edge pitch (BICEP) is a dichotic broadband noise pitch effect. The stimulus is made by summing spectrally dense sine components with random phases. The interaural phase angle is a constant (e.g., 0 or π) for components with frequencies below (or above) a chosen edge frequency, and it is a random variable for the remaining components. Pitch-matching experiments show that the BICEP exists for coherence edge frequencies between 300 and 1000 Hz. It is matched by a pure tone frequency shifted from the edge frequency by 5% to 10%. The matching frequency falls on the incoherent side of the edge. The BICEP persists if the noise to one of the ears is delayed (<3 ms). Some BICEP exists even when the component amplitudes are entirely independent in the two ears, so long as the phase coherence conditions of the stimulus are maintained. The existence of the BICEP is a challenge for current models of dichotic pitch, though the pitch shift is consistent with the equalization-cancellation model as previously applied to dichotic pitch effects by M. A. Klein and W. M. Hartmann [J. Acoust. Soc. Am. 70, 51–61 (1981)]. [Work supported by the NIDCD of the NIH and by the NSF REU Program.]

Cortical mechanisms of central pitch processing revealed by dichotic pitch stimuli

Cortical mechanisms of central pitch processing revealed by dichotic pitch stimuli

Cerebral correlates of hemispheric lateralization during a pitch discrimination task: an ERP study in dichotic situation

Objective: Electrophysiological correlates of perceptual asymmetry for dichotic pitch discrimination were investigated in 12 right-handed volunteers, whose dichotic listening performances attested the classical ‘right ear advantage’ in a verbal discrimination task.Methods: Event related potentials (ERPs), elicited by dichotic and binaural pairs of tones applied in a classical oddball paradigm including right ear targets, left ear targets and binaural targets (5% occurrence each) were recorded from medial and lateral scalp locations. Latencies and baseline to peak amplitudes were measured for P1, N1, P2, N2 and P3 components.Results: ERPs recorded in response to dichotic (compared with binaural) target pairs, exhibited delayed latencies for N2 and P3, correlated with prolonged RTs, probably linked to greater difficulty in identification of the target. They also displayed enhanced N1 and P2 voltages, which may reflect the simultaneous activation of two different populations of neurons in the auditory cortical areas. We observed specific lateralization effects for pitch discrimination with a left ear advantage on latency of early components.Conclusion: Together with amplitude asymmetries in the N2 component, the findings bring strong electrophysiological support to Kimura's structural model for dichotic perceptions with a right hemisphere prevalence in a pitch discrimination task.

The profile of interaural decorrelation across frequency: A binaural representation of pitch and timbre

Tones can be detected in noise at lower signal-to-noise ratios (SNRs) when they possess different interaural timing to the noise. One account, equalization-cancellation (E-C), suggests that the left- and right-ear signals are adjusted in time and amplitude to maximize their similarity, and are then cancelled by subtraction. At low SNRs, E-C improves the SNR of the tone by cancelling the noise. E-C is also a method for measuring interaural decorrelation, because the remainder after subtraction is a measure of the extent to which the tone reduces the interaural correlation of the noise. Applying E-C independently in each frequency channel reveals the profile of interaural decorrelation across frequency induced by a complex signal in noise. The profile is a place representation akin to an excitation pattern. It has three properties. (i) It displays the spectrum of speech at low SNRs. (ii) Listeners can integrate it perceptually with the conventional profile of spectral amplitude. (iii) Its spectral structure is compatible with a subset of the dichotic pitches phenomena in which tonal percepts are induced by introducing interaural phase changes into broadband noises. Finally, the profile can be recast in a form compatible with temporal accounts of pitch and timbre based on autocorrelation.

The existence region of Huggins' pitch

Huggins' pitch (HP) can be heard when listening to white noise which is diotic at all frequencies except for a narrow band over which the interaural phase of the noise changes progressively through 360°. The detectability ( d′) of HP was measured for 11 center frequencies between 100 Hz and 3200 Hz in half-octave steps. The listeners' task was to discriminate HP stimuli from diotic noises in a single-interval, YES/NO task. Detectability was simultaneously compared with that of pure tones presented interaurally out of phase and masked by diotic white noise (NoSπ). The levels of the tones were set so that they would fall below masked threshold monaurally at the higher frequencies tested. All four listeners showed similar patterns of detectability at high frequencies for both the Huggins-pitch stimuli and the masked tones. The results showed that HP can be detected at higher frequencies than previously reported; all four listeners could detect both the tones and HP to some extent at 2256 Hz and one listener could also detect HP at 3200 Hz. The results demonstrate that both HP and NoSπ stimuli show a sharp drop in detectability at around 1500 Hz, but remain detectable at higher frequencies.