Biomedical subjects

A de Cheveigné

Publications and source records attributed to A de Cheveigné.

7 recordsLinked to original sources

PubMed2000

A model of the perceptual asymmetry between peaks and troughs of frequency modulation.

Pitch discrimination at peaks of frequency modulation is better than at troughs [L. Demany and K. I. McAnally, J. Acoust. Soc. Am. 96, 706-715 (1989)]. A similar asymmetry emerges within a time-domain pitch perception model based on autocorrelation. The model requires the following assumptions: (a) The neural discharge patterns must be temporally sharpened to a single narrow pulse per period (possibly by neural convergence within the cochlear nucleus). (b) Autocorrelation must be implemented as a cross correlation between the neural pulse train and a delayed pulse train convolved with a short kernel function. This kernel function must be asymmetric in time. (c) Pitch discrimination must rely on higher-order modes of the autocorrelation function. This particular implementation of the autocorrelation model produces modes that are sharper for peaks than for troughs, and thus accounts for the pitch discrimination asymmetry observed experimentally. As a by-product it can account for "hyperacute" discrimination observed at peaks of triangular modulation.

Humans↗

PubMed1999

Missing-data model of vowel identification.

Vowel identity correlates well with the shape of the transfer function of the vocal tract, in particular the position of the first two or three formant peaks. However, in voiced speech the transfer function is sampled at multiples of the fundamental frequency (F0), and the short-term spectrum contains peaks at those frequencies, rather than at formants. It is not clear how the auditory system estimates the original spectral envelope from the vowel waveform. Cochlear excitation patterns, for example, resolve harmonics in the low-frequency region and their shape varies strongly with F0. The problem cannot be cured by smoothing: lag-domain components of the spectral envelope are aliased and cause F0-dependent distortion. The problem is severe at high F0's where the spectral envelope is severely undersampled. This paper treats vowel identification as a process of pattern recognition with missing data. Matching is restricted to available data, and missing data are ignored using an F0-dependent weighting function that emphasizes regions near harmonics. The model is presented in two versions: a frequency-domain version based on short-term spectra, or tonotopic excitation patterns, and a time-domain version based on autocorrelation functions. It accounts for the relative F0-independency observed in vowel identification.

Humans↗

PubMed1999

Vowel-specific effects in concurrent vowel identification.

An experiment investigated the effects of amplitude ratio (-35 to 35 dB in 10-dB steps) and fundamental frequency difference (0%, 3%, 6%, and 12%) on the identification of pairs of concurrent synthetic vowels. Vowels as weak as -25 dB relative to their competitor were easier to identify in the presence of a fundamental frequency difference (delta F0). Vowels as weak as -35 dB were not. Identification was generally the same at delta F0 = 3%, 6%, and 12% for all amplitude ratios: unfavorable amplitude ratios could not be compensated by larger delta F0's. Data for each vowel pair and each amplitude ratio, at delta F0 = 0%, were compared to the spectral envelope of the stimulus at the same ratio, in order to determine which spectral cues determined identification. This information was then used to interpret the pattern of improvement with delta F0 for each vowel pair, to better understand mechanisms of F0-guided segregation. Identification of a vowel was possible in the presence of strong cues belonging to its competitor, as long as cues to its own formants F1 and F2 were prominent. delta F0 enhanced the prominence of a target vowel's cues, even when the spectrum of the target was up to 10 dB below that of its competitor at all frequencies. The results are incompatible with models of segregation based on harmonic enhancement, beats, or channel selection.

Adolescent↗

PubMed1999

Pitch shifts of mistuned partials: a time-domain model.

Mistuning one partial of a complex harmonic tone makes that partial easier to hear as a tone separate from the complex. At the same time, two pitch shifts may be observed. First, the low pitch of the complex is shifted in the direction of the mistuning, as if it were "pulled" by the partial. Second, the mistuning of the partial is perceptually exaggerated, as if the pitch of the partial were "pushed" away from the harmonic series defined by the complex. This paper shows how the latter effect can emerge within a hypothetical neural circuit. The circuit involves a gating neuron fed by three pathways, one direct and excitatory and the other two delayed and inhibitory. The neuron responds to any excitatory input spike unless it is accompanied by an inhibitory input spike on either delayed input, thus acting as a kind of "anticoincidence counter." The first delay is fixed and tuned to the period of the background harmonic complex. Its purpose is to weaken correlates of in-tune components and allow the mistuned partial to stand out. The second delay is variable and used to estimate the period of the mistuned partial, by searching for a minimum output as a function of delay. With an appropriate choice of parameters, the estimate is subject to shifts that are of the same sign as the mistuning and that peak at about 4% mistuning and decrease beyond, as observed experimentally.

Hair Cells, Auditory↗

PubMed1999

Waveform interactions and the segregation of concurrent vowels.

Two experiments investigated the effects of small values of fundamental frequency difference (delta F0) on the identification of concurrent vowels. As delta F0's get smaller, mechanisms that exploit them must necessarily fail, and the pattern of breakdown may tell which mechanisms are used by the auditory system. Small delta F0's also present a methodological difficulty. If the stimulus is shorter than the beat period, its spectrum depends on which part of the beat pattern is sampled. A different starting phase might produce a different experimental outcome, and the experiment may lack generality. The first experiment explored the effects of delta F0's as small as 0.4%. The smallest delta F0 conditions were synthesized with several starting phases obtained by gating successive segments of the beat pattern. An improvement in identification was demonstrated for delta F0's as small as 0.4% for all segments. Differences between segments (or starting phase) were also observed, but when averaged over vowel pairs they were of small magnitude compared to delta F0 effects. The nature of delta F0-induced waveform interactions and the factors that affect them are discussed in detail in a tutorial section, and the hypothesis that the improvement in identification is the result of such interactions (beat hypothesis) is examined. It is unlikely that this hypothesis can account for the effects observed. The reduced benefit of delta F0 for identification at smaller delta F0's more likely reflects the breakdown of the same F0-guided segregation mechanism that operates at larger delta F0's.

Biomechanical Phenomena↗

PubMed1998

Cancellation model of pitch perception.

A model of pitch perception is presented involving an array of delay lines and inhibitory gating neurons. In response to a periodic sound, a minimum appears in the pattern of outputs of the inhibitory neurons at a lag equal to the period of the sound. The position of this minimum is the cue to pitch. The model is similar to the autocorrelation model of pitch, multiplication being replaced by an operation similar to subtraction, and maxima by minima. The two models account for a wide class of pitch phenomena in very much the same way. The principal goal of this paper is to demonstrate this fact. Several features of the cancellation model may be to its advantage: it is closely related to the operation of harmonic cancellation that can account for segregation of concurrent harmonic stimuli, it can be generalized to explain the perception of multiple pitches, and it shows a greater degree of sensitivity to phase than autocorrelation, which may allow it to explain certain phenomena that autocorrelation cannot account for.

Humans↗

PubMed1995

Identification of concurrent harmonic and inharmonic vowels: a test of the theory of harmonic cancellation and enhancement.

The improvement of identification accuracy of concurrent vowels with differences in fundamental frequency (delta F0) is usually attributed to mechanisms that exploit harmonic structure. To decide whether identification is aided primarily by selecting the target vowel on the basis of its harmonic structure ("harmonic enhancement") or removing the interfering vowel on the basis of its harmonic structure ("harmonic cancellation"), pairs of synthetic vowels, each of which was either harmonic or inharmonic, were presented to listeners for identification. Responses for each vowel were scored according to the vowel's harmonicity and that of the vowel that accompanied it. For a given target, identification was better by about 3% for a harmonic ground unless the target was also harmonic with the same F0. This supports the cancellation hypothesis. Identification was worse for harmonic than for inharmonic targets by 3%-8%. This does not support the enhancement hypothesis. When both vowels were harmonic, identification was better by about 6% when the F0's differed by 1/2 semitone, consistent with previous experiments. Results are interpreted in terms of harmonic enhancement and harmonic cancellation, and alternative explanations such as waveform interaction are considered.

Adult↗