Biomedical subjects

R D Patterson

Publications and source records attributed to R D Patterson.

At least 19 recordsLinked to original sources

PubMed2006

Processing the acoustic effect of size in speech sounds.

The length of a vocal tract is reflected in the sound it is producing. The length of the vocal tract is correlated with body size and humans are very good at making size judgments based on the acoustic effect of vocal tract length only. Here we investigate the underlying mechanism for processing this main auditory cue to size information in the human brain. Sensory encoding of the acoustic effect of vocal tract length (VTL) depends on a time-stabilized spectral scaling mechanism that is independent of glottal pulse rate (GPR, or voice pitch); we provide evidence that a potential neural correlate for such a mechanism exists in the medial geniculate body (MGB). The perception of the acoustic effect of speaker size is influenced by GPR suggesting an interaction between VTL and GPR processing; such an interaction occurs only at the level of non-primary auditory cortex in planum temporale and anterior superior temporal gyrus. Our findings support a two-stage model for the processing of size information in speech based on an initial stage of sensory analysis as early as MGB, and a neural correlate of the perception of source size in non-primary auditory cortex.

Acoustic Stimulation↗

PubMed2003

Separating pitch chroma and pitch height in the human brain.

Musicians recognize pitch as having two dimensions. On the keyboard, these are illustrated by the octave and the cycle of notes within the octave. In perception, these dimensions are referred to as pitch height and pitch chroma, respectively. Pitch chroma provides a basis for presenting acoustic patterns (melodies) that do not depend on the particular sound source. In contrast, pitch height provides a basis for segregation of notes into streams to separate sound sources. This paper reports a functional magnetic resonance experiment designed to search for distinct mappings of these two types of pitch change in the human brain. The results show that chroma change is specifically represented anterior to primary auditory cortex, whereas height change is specifically represented posterior to primary auditory cortex. We propose that tracking of acoustic information streams occurs in anterior auditory areas, whereas the segregation of sound objects (a crucial aspect of auditory scene analysis) depends on posterior areas.

Acoustic Stimulation↗

PubMed2003

Using genetic algorithms to find the most effective stimulus for sensory neurons.

Genetic algorithms (GAs) can be used to find maxima in large search spaces in a relatively short period of time. We have used GAs in electrophysiological experiments to find the most effective stimulus (MES) for sensory neurons in the cochlear nucleus and inferior colliculus of anaesthetised guinea pigs. The MES is the stimulus that elicits the greatest number of spikes from a unit. We show that GAs provide an effective means of determining the best combination of up to four parameters for sinusoids with amplitude modulation. Using GAs, we have found tuning to modulation frequencies as a function of carrier frequency, sound level and temporal asymmetry. These results demonstrate the suitability of GAs in electrophysical experiments for estimating the position of the most effective stimulus in a specified parameter space.

Acoustic Stimulation↗

PubMed2003

Localization of primary auditory cortex in humans by magnetoencephalography.

Brief auditory stimuli activate the primary auditory cortex (PAC) earlier than any other cortical area so, within a certain latency range, the PAC is the only cortical source contributing to the auditory evoked field (AEF). Nevertheless, there is no AEF component specific to PAC that can be reliably detected in all individuals. The present study suggests that a peak in the first temporal derivative of the magnetic field at about 20 ms (dP20m) is a genuine correlate of PAC activity. AEFs in response to clicks presented to the right ear were recorded with a 37-channel axial gradiometer system positioned over the left hemisphere in nine normal-hearing subjects. More than 8500 stimuli were presented in each of two independent sessions at a rate of approximately 3/s. The dipole coordinates for the dP20m derived from the two sessions typically differed by only a few millimeters. Coregistration of the dipoles with structural magnetic resonance images suggests that dP20m arises from an area close to the retroinsular origin of Heschl's gyrus. Although the dP20m is simply the point of steepest slope on the well-known middle-latency peak, P30m or Pam, it would appear that dP20m and P30m do not have the same cortical origin. Evidence is provided that P30m receives major contributions from at least two distinct cortical areas, only one of which is PAC.

Acoustic Stimulation↗

PubMed2003

Neuromagnetic evidence for a pitch processing center in Heschl's gyrus.

There have been several attempts to use the neuromagnetic response to the onset of a tonal sound (N100m) to study pitch processing in auditory cortex. Unfortunately, a large proportion of the N100m is simply a response to the onset of sound energy, independent of whether the sound produces a pitch. The current study describes a novel stimulus paradigm designed to circumvent the energy-onset response and thereby isolate the response of those neural elements specifically involved in pitch processing. The temporal resolution of magnetoencephalography enables us to show that the latency and amplitude of this pitch-onset response (POR) vary with the pitch and pitch strength of the tone. The spatial resolution is sufficient to show that its source lies somewhat anterior and inferior to that of the N100m, probably in the medial part of Heschl's gyrus.

Acoustic Stimulation↗

PubMed2001

The temporal representation of the delay of iterated rippled noise in the ventral cochlear nucleus of the guinea-pig.

1. We have examined the temporal discharge patterns of single units from the ventral cochlear nucleus (VCN) of anaesthetized guinea-pigs in response to iterated rippled noise (IRN). The pitch range evoked by the stimuli was from 32 to 1000 Hz. 2. Single units were classified into four groups using existing classification schemes: primary-like (PL), onset (O), sustained chopper (CS) and transient chopper (CT). For all unit types the delay of the IRN stimuli was well represented in the all-order interspike interval histograms (ISIHs). 3. A subset of the onset units (onset-chopper, OC) showed a clear preference for some delays of the IRN in their first-order interval statistics. We describe this delay preference as 'periodicity tuning'. The delay at which the pitch estimate was at its maximum was designated its best periodicity. The range of best periodicities for OC units was 3.75-13 ms (between 77 and 267 Hz). 4. The other unit types also showed enhancement of the first-order interval statistics at the delay of the IRN. The range of best periodicities was 1.4-8.8 ms (113-714 Hz) for the CT group, 2.25-10.8 ms (93-444 Hz) for the CS group and 0.5-4.6 ms (217-2000 Hz) for the PL group. 5. The correlation between the maximum interval enhancement observed in response to the IRN stimuli and the peak in the first-order ISIH in response to white noise was 0.81 for OC units, 0.72 for CS units, 0.44 for CT units and -0.15 for PL units. 6. These results demonstrate that all unit types in the VCN can enhance the representation of the delay of IRN using first-order interspike intervals (ISIs) over a range of periodicities. CS and OC units show the greatest range of best periodicities and they are well-suited to encode the delay of IRN in their first-order ISIs for a wide range of pitches.

Action Potentials↗

PubMed2001

The effects of temporal asymmetry on the detection and perception of short chirps.

There is an intriguing contrast between the physiological response to short frequency sweeps in the brainstem and the perception produced by these sounds. Dau et al. (2000) demonstrated that optimised chirps with increasing instantaneous frequency (up-chirps), designed to compensate for spatial dispersion along the cochlea, enhance wave V of the auditory brainstem response (ABR), by synchronising excitation of all frequency channels across the basilar membrane. Down-chirps, that is up-chirps reversed in time, increase cochlear phase delays and therefore result in a poor ABR wave V. In this study, a set of psychoacoustical experiments with up-chirps and down-chirps has been performed to investigate how these phase changes affect what we hear. The perceptual contrast is different from what was reported at the brainstem level. It is the down-chirp that sounds more compact, despite the poor synchronisation across channels and phase delays up to 20 ms. The perceived 'compactness' of a sound is apparently more determined by the fine structure of excitation within each peripheral channel than by between-channel phase differences. This suggests an additional temporal integration mechanism at a higher stage of auditory processing, which effectively removes phase differences between channels.

Acoustic Stimulation↗

PubMed2001

The responses of single units in the inferior colliculus of the guinea pig to damped and ramped sinusoids.

Temporal asymmetry can have a pronounced effect on the perception of a sinusoid. For instance, if a sinusoid is amplitude modulated by a decaying exponential that restarts every 50 ms, (a damped sinusoid) listeners report a two-component percept: a tonal component corresponding to the carrier and a drumming component corresponding to the envelope modulation period. When the amplitude modulation is reversed in time (a ramped sinusoid) the perception changes markedly; the tonal component increases while the drumming component decreases. The long-term Fourier energy spectra are identical for damped and ramped sinusoids with the same exponential half-life. Modelling studies suggest that this perceptual asymmetry must occur central to the peripheral stages of auditory processing (Patterson and Irino, 1998). To test this hypothesis, we have recorded the responses of single units in the inferior colliculus of the anaesthetised guinea pig. We divided single units into three groups: onset, on-sustained and sustained, based on their temporal adaptation properties to suprathreshold tone bursts at the unit's best frequency. The asymmetry observed in the neural responses of single units was quantified in two ways: a simple total spike count measure and a ratio of the tallest bin of the modulation period histogram to the total number of spikes. Responses were more diverse than those observed with similar stimuli in a previous study in the ventral cochlear nucleus (Pressnitzer et al., 2000). The main results were: (1) The shape of the responses of on-sustained units to ramped sinusoids resembled the shape of the responses to damped sinusoids. This is in contrast to the response shapes in the VCN, which were always similar to the stimulating sinusoid. (2) Units classified as onsets often responded only to the damped stimuli. (3) All units display significant asymmetry in discharge rate for at least one of the half-lives tested and 20% showed significant response asymmetry over all of the half-lives tested. (4) A summary population measure of temporal asymmetry based on total spike count reveals the same pattern of results as that obtained psychophysically using the same stimuli (Patterson, 1994a).

Acoustic Stimulation↗

PubMed2001

Encoding of the temporal regularity of sound in the human brainstem.

We measured the neural activity associated with the temporal structure of sound in the human auditory pathway from cochlear nucleus to cortex. The temporal structure includes regularities at the millisecond level and pitch sequences at the hundreds-of-milliseconds level. Functional magnetic resonance imaging (fMRI) of the whole brain with cardiac triggering allowed simultaneous observation of activity in the brainstem, thalamus and cerebrum. This work shows that the process of recoding temporal patterns into a more stable form begins as early as the cochlear nucleus and continues up to auditory cortex.

Acoustic Stimulation↗

PubMed2001

The lower limit of melodic pitch.

An objective melody task was used to determine the lower limit of melodic pitch (LLMP) for harmonic complex tones. The LLMP was defined operationally as the repetition rate below which listeners could no longer recognize that one of the notes in a four-note, chromatic melody had changed by a semitone. In the first experiment, the stimuli were broadband tones with all their components in cosine phase, and the LLMP was found to be around 30 Hz. In the second experiment, the tones were filtered into bands about 1 kHz in width to determine the influence of frequency region on the LLMP. The results showed that whenever there was energy present below 800 Hz, the LLMP was still around 30 Hz. When the energy was limited to higher-frequency regions, however, the LLMP increased progressively, up to 270 Hz when the energy was restricted to the region above 3.2 kHz. In the third experiment, the phase relationship between spectral components was altered to determine whether the shape of the waveform affects the LLMP. When the envelope peak factor was reduced using the Schroeder phase relationship, the LLMP was not affected. When a secondary peak was introduced into the envelope of the stimuli by alternating the phase of successive components between two fixed values, there was a substantial reduction in the LLMP, for stimuli containing low-frequency energy. A computational auditory model that extracts pitch information with autocorrelation can reproduce all of the observed effects, provided the contribution of longer time intervals is progressively reduced by a linear weighting function that limits the mechanism to time intervals of less than about 33 ms.

Adult↗

PubMed2001

A compressive gammachirp auditory filter for both physiological and psychophysical data.

A gammachirp auditory filter was developed by Irino and Patterson [J. Acoust. Soc. Am. 101, 412-419 (1997)] to provide a level-dependent version of the linear, gammatone auditory filter, with which to explain the level-dependent changes in cochlear filtering observed in psychophysical masking experiments. In this 'analytical' gammachirp filter, the chirp varied with level and there was no explicit representation of the change in filter gain or compression with level. Subsequently, Carney et al. [J. Acoust. Soc. Am. 105, 2384-2391 (1999)] reviewed Carney and Yin's [J. Neurophysiol. 60, 1653-1677 (1988)] reverse-correlation (revcor) data and showed that the frequency glide of the chirp does not vary with level in their data. In this article, the architecture of the analytical gammachirp is reviewed with respect to cochlear physiology and a new form of gammachirp filter is described in which the magnitude response, the gain, and the compression vary with level but the chirp does not. This new 'compressive' gammachirp filter is used to fit the level-dependent revcor data reported by Carney et al. (1999) and the level-dependent masking data reported by Rosen and Baker [Hear. Res. 73, 231-243 (1994)].

Auditory Perception↗

PubMed2001

Asymmetry of masking between noise and iterated rippled noise: evidence for time-interval processing in the auditory system.

This study describes the masking asymmetry between noise and iterated rippled noise (IRN) as a function of spectral region and the IRN delay. Masking asymmetry refers to the fact that noise masks IRN much more effectively than IRN masks noise, even when the stimuli occupy the same spectral region. Detection thresholds for IRN masked by noise and for noise masked by IRN were measured with an adaptive two-alternative, forced choice (2AFC) procedure with signal level as the adaptive parameter. Masker level was randomly varied within a 10-dB range in order to reduce the salience of loudness as a cue for detection. The stimuli were filtered into frequency bands, 2.2-kHz wide, with lower cutoff frequencies ranging from 0.8 to 6.4 kHz. IRN was generated with 16 iterations and with varying delays. The reciprocal of the delay was 16, 32, 64, or 128 Hz. When the reciprocal of the IRN delay was within the pitch range, i.e., above 30 Hz, there was a substantial masking asymmetry between IRN and noise for all filter cutoff frequencies; threshold for IRN masked by noise was about 10 dB larger than threshold for noise masked by IRN. For the 16-Hz IRN, the masking asymmetry decreased progressively with increasing filter cutoff frequency, from about 9 dB for the lowest cutoff frequency to less than 1 dB for the highest cutoff frequency. This suggests that masking asymmetry may be determined by different cues for delays within and below the pitch range. The fact that masking asymmetry exists for conditions that combine very long IRN delays with very high filter cutoff frequencies means that it is unlikely that models based on the excitation patterns of the stimuli would be successful in explaining the threshold data. A range of time-domain models of auditory processing that focus on the time intervals in phase-locked neural activity patterns is reviewed. Most of these models were successful in accounting for the basic masking asymmetry between IRN and noise for conditions within the pitch range, and one of the models produced an exceptionally good fit to the data.

Adult↗

PubMed2000

Frontal processing and auditory perception.

Disordered processing of the pattern in sound over time has been observed in a number of clinical disorders, including developmental dyslexia. This study addresses the brain mechanisms required for the perception of such a pattern. We report the systematic evaluation of temporal perception in a patient with a single intact right auditory cortex and a large right frontal lobe lesion. A striking dissociated deficit was demonstrated in the perception of temporal pattern at the level of tens or hundreds of milliseconds. This proves that, contrary to common belief, mechanisms in the pathway up to and including the primary auditory cortex are not sufficient for the normal perception of temporal pattern. This work suggests a need for frontal processing for the normal perception of auditory pattern.

Adult↗

PubMed2000

The responses of single units in the ventral cochlear nucleus of the guinea pig to damped and ramped sinusoids.

Human listeners hear an asymmetry in the perception of damped and ramped sinusoids; the partial loudness of the envelope component is greater than the partial loudness of the carrier component for damped sinusoids. Here we show that an asymmetry also occurs in the physiological responses of most units in the ventral cochlear nucleus to these same sounds. The activity elicited by damped sinusoids is mainly restricted to the beginning of each envelope period, which is not the case for ramped sinusoids. This can be quantified by computing the ratio of the tallest bin of the modulation period histogram to the total number of spikes (the peak-to-total ratio, p/t). Damped sinusoids produce a higher p/t than ramped sinusoids, which demonstrates physiological temporal asymmetry. It is also the case that ramped sinusoids typically elicit more spikes than damped sinusoids. The physiological asymmetry occurs where the perceptual asymmetry is present. It is maximal at modulation half-lives of 4 and 16 ms, greatly reduced at 1 ms and absent at 64 ms. Different unit types exhibit differing degrees of temporal asymmetry. Onset units produce the greatest p/t asymmetry, primary-like units produce the least asymmetry and chopper units are in-between. With regard to total spike count, the maximal asymmetry occurs with chopper units. If primary-like units are assumed to reflect the activity in primary auditory nerve fibres, then there is enhancement of temporal asymmetry in the ventral cochlear nucleus by both onset and chopper units.

Acoustic Stimulation↗

PubMed2000

The lower limit of pitch as determined by rate discrimination.

This paper is concerned with the lower limit of pitch for complex, harmonic sounds, like the notes produced by low-pitched musical instruments. The lower limit of pitch is investigated by measuring rate discrimination thresholds for harmonic tones filtered into 1.2-kHz-wide bands with a lower cutoff frequency, F(c), ranging from 0.2 to 6.4 kHz. When F(c) is below 1 kHz and the harmonics are in cosine phase, rate discrimination threshold exhibits a rapid, tenfold decrease as the repetition rate is increased from 16 to 64 Hz, and over this range, the perceptual quality of the stimuli changes from flutter to pitch. When F(c) is increased above 1 kHz, the slope of the transition from high to low thresholds becomes shallower and occurs at progressively higher rates. A quantitative comparison of the cosine-phase thresholds with subjective estimates of the existence region of pitch from the literature shows that the transition in rate discrimination occurs at approximately the same rate as the lower limit of pitch. The rate discrimination experiment was then repeated with alternating-phase harmonic tones whose envelopes repeat at twice the repetition rate of the waveform. In this case, when F(c) is below 1 kHz, the transition in rate discrimination is shifted downward by almost an octave relative to the transition in the cosine-phase thresholds. The results support the hypothesis that in the low-frequency region, the pitch limit is determined by a temporal mechanism, which analyzes time intervals between peaks in the neural activity pattern. It seems that temporal processing of pitch is limited to time intervals less than 33 ms, corresponding to a pitch limit of about 30 Hz.

Adult↗

PubMed2000

The perceptual tone/noise ratio of merged iterated rippled noises.

Iterated rippled noise (IRN) is constructed by delaying a random noise by d ms, adding it back to the same noise, and repeating the process iteratively. When two IRNs with the same power but slightly different delays are added together, the perceptual tone/noise ratio of the "merged" IRN is markedly reduced with respect to that of either of the component IRNs. In this paper, the reduction in the perceptual tone/noise ratio is measured for IRNs in which one of the delays is always 16 ms and the other is either 16 +/- 0.1 ms or 16 +/- 1.1 ms. The component IRNs have the same number of iterations, and the number varies across conditions from 4 to 256. The perceptual tone/noise ratio is measured using a discrimination matching procedure developed for single IRNs; each merged IRN is compared with a range of "standard" stimuli having varying proportions of a complex tone and a broadband noise [Patterson et al., J. Acoust. Soc. Am. 100, 3286-3294 (1996)]. For single IRNs, the function relating the signal-to-noise ratio of the matching standard to the number of iterations in the IRN was found to be essentially straight. This relationship was explained in terms of the height of the first peak in the autocorrelation of the stimulus wave, or by the first peak in the summary autocorrelogram produced by a time-domain auditory model. For the merged IRNs in the current experiment, the matching-point functions are found to have pronounced downward curvature, in addition to being well below the function for single IRNs. To account for the reduction in the perceptual tone/noise ratio of merged IRNs, the autocorrelation model was extended to include a simple rule for combining adjacent peaks in the autocorrelation function of the wave, and the autocorrelogram model was revised to improve the simulation of the "loss of phase locking" at higher frequencies in the autocorrelogram.

Auditory Perception↗

PubMed2000

Temporal dynamics of pitch strength in regular-interval noises: effect of listening region and an auditory model.

Recently, it was demonstrated that the pitch strength of a stimulus denoted "AABB" differed from rippled noise (RN) despite the fact that their long-term spectra and autocorrelation functions are identical (Wiegrebe et al., 1998). Rippled noise is generated by adding a delayed copy of Gaussian noise back to itself; AABB is generated by concatenating equal-duration, Gaussian-noise segments where every segment is repeated once. It was shown that a simple model based on a two-stage integration process separated by a nonlinear transformation explains the pitch-strength differences quantitatively. Here, we investigate how the spectral listening region influences pitch-strength differences between RN and AABB. Bandpass filtering the two stimuli with a constant bandwidth of 1 kHz revealed a systematic effect of center frequency. For relatively high pitches (corresponding to delays, d, of 4 or 5.6 ms, pitch strength differences between AABB and RN were absent when the pass band was between 0 and 1 kHz. When the pass band was between 3.5 and 4.5 kHz, pitch-strength differences were substantial. For lower pitches (d equal to or longer than 8 ms), AABB had a substantially greater pitch strength independent of the filter center frequency. The model presented in Wiegrebe et al. (1998) cannot capture these effects of center frequency. Here, it is demonstrated that it is possible to simulate the RN-AABB pitch-strength differences, and the effect of listening region, with a computer model of the auditory periphery. It is shown that, in an auditory model, pitch-strength differences are introduced by the nonlinear transformation possibly associated with half-wave rectification or mechanoelectrical transduction. In this experimental context, however, the nonlinearity has perceptual relevance only when the differences in short-term fluctuations of AABB and RN are preserved in auditory-filter outputs. The current experiments relate the purely functional model introduced in the preceding paper to basic properties of the peripheral auditory system. The implication for neural time constants of pitch processing is discussed.

Adult↗

PubMed1999

The role of envelope modulation in spectrally unresolved iterated rippled noise.

Iterated rippled noise (IRN) produces a pitch corresponding to the IRN delay. The pitch persists even when the sound is high-pass filtered at 12 times the reciprocal of the IRN delay, i.e., in the absence of resolved spectral peaks. Typically, when a sound produces a pitch in the absence of spectral cues, the pitch is explained in terms of periodic envelope modulation, for example, the pitch of a high-pass filtered cosine-phase harmonic complex, or the pitch of sinusoidally amplitude-modulated noise (SAMN). This study presents experiments designed to search for periodic modulation in IRN. The occurrence and significance of modulation is investigated in the envelope of the stimulus waveform as well as in the IRN envelope as represented after narrow-band filtering similar to that occurring in peripheral auditory filters. The results indicate that the envelope of band-pass filtered IRN reveals modulation but that the order of modulation (corresponding to the number of envelope maxima recurring every period) increases with increasing filter bandwidth. The occurrence of first-order modulation, like that of SAMN, is indirectly demonstrated for spectrally unresolved IRN in the lower unresolved frequency range between the 10th and 20th spectral peaks. The significance of recurring transients sometimes visible in the IRN waveform with respect to their contribution to the IRN pitch was assessed by replacing portions of the IRN period with random noise. The results of this experiment indicate that this 'waveform modulation' is not essential for the IRN pitch perception. The presence of temporal pitch in the absence of first-order modulation is demonstrated in two experiments involving the detection of phase delays and f0 differences for spectrally separated, narrow bands of harmonic complexes and IRNs.

Acoustic Stimulation↗