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D D Greenwood

Publications and source records attributed to D D Greenwood.

18 recordsLinked to original sources
PubMed1997

The Mel Scale's disqualifying bias and a consistency of pitch-difference equisections in 1956 with equal cochlear distances and equal frequency ratios.

In 1956, Stevens 'commissioned' an experiment to equisect a pitch difference between two tones. Results appear to reveal a methodological flaw that would invalidate the Mel Scale (Stevens and Volkmann, 1940). Stevens sought to distinguish sensory continua, e.g., loudness and pitch, on various criteria. He expected that the pitch continuum would not exhibit 'hysteresis'; i.e., that subjects dividing a pitch difference (delta f) into equal-appearing parts would not set dividing frequencies higher when listening to notes in ascending order than in descending order. Seven subjects equisected a pitch difference, between tones of 400 and 7000 Hz, into equal-seeming parts by adjusting the frequencies of three intermediate tones. All seven exhibited hysteresis, contrary to expectation. This outcome bears on other issues. Years prior, Stevens suggested that equal pitch differences might correspond to equal cochlear distances, but not to equal frequency ratios nor to equal musical intervals (Stevens and Davis, 1938; Stevens and Volkmann, 1940). In 1960 (reported now), both the 1940 Mel Scale and the equal pitch differences of 1956 were compared to equal cochlear distances, using a frequency-position function that fitted Békésy's cochlear map (Greenwood, 1961, 1990). When ascending and descending settings were combined to contra-pose biases, equal pitch differences did coincide with equal distances--which the Mel Scale did not. Further, the biased ascending-order data coincided with the Mel Scale, suggesting the Mel Scale was similarly biased. Thus, the combined-order equal pitch differences of 1956--but not the Mel Scale--are consistent with equal cochlear distances. However, since the map between 400 and 7000 Hz is nearly logarithmic, equal frequency ratios also approximate equal distances. Ironically, above 400 Hz, Békésy's map and Stevens' equal-distance hypothesis jointly imply that musical intervals will nearly agree with equal pitch differences, which Stevens thought he had disconfirmed. However, given Békésy's map, only near the cochlear apex will equal distances not approximate equal frequency ratios; and Pratt's (Pratt, 1928) bisections of delta fs greater than an octave indicated that equal pitch differences, on average, did agree with equal distances. However, they did so for only two of four subjects and coincided instead with equal frequency ratios for one musical subject. Historical distinctions suggest that between the parts of equisected delta fs subjective equivalence may be of two kinds--one linked to musical intervals, leading to equal frequency ratios; a second linked to 'tone-height' and 'distance', leading to deviations from equal frequency ratios near the apex, though not appreciably if equisected delta fs are less than an octave (or if perhaps subjects are musicians). Data of other kinds suggest that, if pure-tone pitch height were a function of place, the place could be the apical excitation-pattern edge, in any case not a maximum, which in neural data shifts and disappears with tone level.

Audiometry↗
PubMed1996

Comparing octaves, frequency ranges, and cochlear-map curvature across species.

Comparisons of the cochlear maps of various species might be more revealing if the form and parameter values of the functions fitted to the maps were taken into more explicit account. One empirical frequency-position function (Greenwood, 1961), the form of which fits several species, was recently reviewed (Greenwood, 1990). It was shown that mechanical and physiological data from human, cat, guinea pig, chinchilla, and monkey, are well fitted by an almost-exponential function. An exponential term, the argument of which is normalized position, x, on the cochlear partition (x = 0 at apex, 1 at base), is first reduced by a small term, k < or = 1, before the quantity, (exponential - k), is multiplied by a third parameter, A, to yield the frequency associated with a given position, x. Since the normalized coefficient, alpha, of the exponential's argument is about the same, 2.1, in several species, there are some very simple but noteworthy consequences. The quantity (exponential - k) is thus nearly the same function of x (if k is about equal and in any case as x nears 1) among those species, despite differences in cochlear lengths. Therefore among these species, differences in frequency range are related only to the multiplier, A. Moreover, the function's form implies that only the exponential term (and k) determine the proportion of cochlear length occupied by an octave. Thus, if the exponential's coefficient and k are equal for some species, corresponding octaves (highest, next highest, etc.) correspond in these species to equal percentages of cochlear length, independent of length and frequency range (and they must differ if the coefficient differs). Further, these percentages diminish nearer the apex if cochlear maps (log-frequency versus position) are apically curved (k > 0). But to determine the presence or absence of curvature, cochlear maps must include points from the apical 25% of the cochlea; if not, a simple exponential (k = 0) will probably suffice to fit data in the basal 75%. The apical curvature may have functional value and that some degree of it may be typical is consistent with models which show that curvature and tapering-viscosity effects combine to reduce apical reflections and standing waves, smoothing cochlear impedance (Puria and Allen, 1991a, b).

Acoustic Stimulation↗
PubMed1996

Mechanical and "temporal" filtering as codeterminants of the response by cat primary fibers to amplitude-modulated signals.

From previous studies it appears that at least two factors limit the upper frequency at which auditory-nerve (AN) fibers can entrain to the envelope of a sinusoidally amplitude-modulated (AM) tone. Cochlear mechanical filtering insures that, in the local motion driving a fiber tuned to the carrier, sidetone amplitudes decrease as sidetone displacement envelopes separate with modulation frequency (fm). Only if at least one side-tone's amplitude is large enough, relative to carrier's, will there be modulation of basilar motion at the point tuned to the carrier. In addition, processes within haircell and fiber limit the upper frequency at which they follow variations in amplitude. To assess change, along the cochlea, in the two factors' relative importance. AN modulation transfer functions (MTFs) [Joris and Yin, J. Acoust. Soc. Am. 91, 215-232 (1992)] were replotted versus distance in mm between sidetones and carrier, using an empirical frequency-place function [Greenwood, J. Acoust. Soc. Am. 87, 2592-2605 (990)]. MTF bandwidths, converted to mm changed little over the apical 40% of cochlea but decreased basally. Expressed in Hz, they increased from apex to base and reached an upper limit at a characteristic frequency (CF) of 20 kHz. This is consistent with the idea that at high CFs phase-locking constraints limit envelope-following before mechanical filtering does, while in apical regions spatial filtering reduces envelope amplitude variation, hence envelope following, before limits on phase locking do. Consistently, MTF bandwidths parallel tuning curve bandwidths in the apical cochlea, but are smaller near the base, where tuning curve bandwidths and spatial filtering appear constant.

Animals↗
PubMed1993

The intensitive DL of tones: dependence of signal/masker ratio on tone level and on spectrum of added noise.

In Greenwood [J. Acoust. Soc. Am. 33, 484-502 (1961a)] the ratio of masked signal threshold to masker level (S/M) decreased about 4 dB at a masker level of about 50 dB SL, the 'transition' level, when noise bands were subcritical but not when supercritical. Schlauch et al. [J. Acoust. Soc. Am. 71, S73 (1982)] report a related result. A pilot study [Greenwood, Harvard Psychoacoustic Lab. Status Report 37, 8-9 (1961)] in which pure tones masked identical tones in-phase showed a larger change in S/M. Detailed tone-tone growth-of-masking curves from over a dozen subjects in 1967-69, and in 1960, are reported here. A transition in slope, of variable abruptness, often begins to occur at about 50 dB SL, dropping S/M ratio by 6 to 8 dB or more [Rabinowitz et al., J. Acoust. Soc. Am. 35, 1053 (1976)]; the curves sometimes possess two segments, sometimes are simply convex. All have overall slopes less than 1.0, known also as the 'near miss'. Consistent with other results [Zwicker, Acustica 6, 365-396 (1956); Viemeister, J. Acoust. Soc. Am. 51, 1265-1296 (1972); Moore and Raab, J. Acoust. Soc. Am. 55, 1049-1060 (1974)], addition of low-level wide-band and high-pass noise was found to counteract the change in S/M, i.e., to raise the high-level section of the growth-of-masking curve. However, the ability of narrow 'band-pass' noise to exert this effect was greatest when added at a frequency ratio (band/masking-tone) of 1.3 to 1.5, which seems more closely to link the effects of added noise to the effects of increasing a masking band from sub- to supercritical width (above). Interpretation of the decrease in DL with level begins by noting that the 'transition' level correlates approximately with the level at which a primary unit population excited by a given pure tone begins rapidly to expand basally. Underlying this, the basalward shift of a tone's displacement envelope peak accelerates at about the same level [Rhode, J. Acoust. Soc. Am. 49, 1218-1231 (1971); Sellick et al., J. Acoust. Soc. Am. 72, 131-141 (1982)].(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed1991

Critical bandwidth and consonance in relation to cochlear frequency-position coordinates.

A recent paper (Greenwood, 1990) has reviewed some of the data in the literature on the frequency-position coordinates of the cochlear partition in a number of species and the degree to which they are fitted by empirical functions developed in 1961 (Greenwood, 1961b, 1974b). Continued confirmation by physiological data makes this frequency-position function more independent of non-physiological data and provides a more secure means of testing possible relations of psychoacoustic data to cochlear coordinates. The present paper reviews various sets of critical band, or similar, data in humans and other species and finds that a considerable body of bandwidth estimates correspond to equal distances along the cochlear partition (on this assumption), confirming also to an exponential function of distance. As shown in 1961, such a function would imply that the same set of bandwidths is also a linear function of frequency. Some of the early critical bandwidth, and also 'consonant interval', estimates in man correspond to equal distances on the cochlear partition to a degree not generally recognized. Thus above about 300 to 500 Hz most of the critical band data (of Zwicker and Gässler collated by Zwicker et al., 1957), correspond quite well to equal distances on the Békésy-Skarstein cochlear map fitted by the frequency-position function, as opposed to the values published in the critical band table or curve (which do not do so above 3 kHz). Consonant interval data tend to correspond closely to equal distances, from below 100 Hz to about 3 kHz. Certain post-1961 'critical band' (ERB) estimates collated by Moore and Glasberg (1983) and extended by Moore et al. (1990) and Shailer et al. (1990) also correspond quite closely to constant distances calculated by the 1961 function. So too do some, but not all, of the frequency intervals shown by Plomp (1964) and Plomp and Mimpen (1968) to be required to resolve the components of a harmonic complex. Some critical bandwidth data from animal studies may also correspond approximately to equal distances. This survey of old and new results, plotted on a rational distance scale, may assist in explaining what potential mix of factors operates to determine the estimated bandwidths when the values differ across experiments or in different frequency ranges. The correspondence, in the preponderance of cases, of critical bandwidth to a constant distance may facilitate an understanding of the operational definitions of critical bandwidth in different experiments and of the common underlying mechanisms.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1991

Critical bandwidth and consonance: their operational definitions in relation to cochlear nonlinearity and combination tones.

A recent paper (Greenwood, 1990) reviewed cochlear coordinates in several species in relation to empirical frequency-position functions (Greenwood, 1961b, 1974b), one of which well fits the Békésy-Skarstein human cochlear map (Békésy, 1960; Kringlebotn et al, 1979). This increased the independence of the human function from the psychoacoustic data originally used to construct it and encouraged a second assessment of the relations of similar psychoacoustically significant bandwidths to distance and position on the cochlear map. The companion paper (Greenwood, 1991, this issue), found that, among such bandwidths, 'classical' critical bandwidth, and also 'constant interval', estimates in man correspond to equal distances to a closer extent than generally recognized, and over large parts of the frequency range they conform also to an exponential function of distance, as do most of the ERB estimates. This correspondence to almost constant and similar distances facilitates, and forms a part of, an explanation of the operational definitions of critical bandwidth in different experiments. The present account recapitulates the basic explanation of critical bandwidth and consonance offered in Greenwood (1971, 1972b, 1973b, 1974b) and Greenwood et al. (1976): by adding schematic details to the earlier account of critical bandwidth measurements in pure tone masking (the masker-notch interval), two-tone masking, narrow-band masking, and two-tone dissonance-consonance judgements and by outlining its applicability to AM and Quasi-FM detection and to two-band (nominally notched-noise) masking experiments. The measured bandwidths derive from approximately uniform dimensions of traveling wave envelopes in the peak region and from the effects of the resulting spatial pattern of nonlinear interference among primary components. In this account, critical bandwidth in man corresponds to a distance of about 1 or 1.25 mm, depending upon the direction the interval projects from the stimulus frequency to which it is referenced. It is identified with the apical segment of the traveling wave displacement envelope, which in guinea pig and squirrel monkey appears to be about 2/3rds and 3/4ths of a millimeter, respectively and would be about 1.25 mm in man if these distances were scaled (Greenwood, 1962) among these three species (Greenwood, 1974b, 1977a). When reflected also in the basal direction, the upper end of the frequency interval, at a 1.065 mm distance, makes a total two-critical-band distance, which corresponds with the region of nonlinear input-output functions that extends in both directions from the envelope peak and hence also with the frequency-dispersive region of accelerated phase accumulation (Greenwood, 1974b, 1977a).(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed1990

A cochlear frequency-position function for several species--29 years later.

Accurate cochlear frequency-position functions based on physiological data would facilitate the interpretation of physiological and psychoacoustic data within and across species. Such functions might aid in developing cochlear models, and cochlear coordinates could provide potentially useful spectral transforms of speech and other acoustic signals. In 1961, an almost-exponential function was developed (Greenwood, 1961b, 1974) by integrating an exponential function fitted to a subset of frequency resolution-integration estimates (critical bandwidths). The resulting frequency-position function was found to fit cochlear observations on human cadaver ears quite well and, with changes of constants, those on elephant, cow, guinea pig, rat, mouse, and chicken (Békésy, 1960), as well as in vivo (behavioral-anatomical) data on cats (Schucknecht, 1953). Since 1961, new mechanical and other physiological data have appeared on the human, cat, guinea pig, chinchilla, monkey, and gerbil. It is shown here that the newer extended data on human cadaver ears and from living animal preparations are quite well fit by the same basic function. The function essentially requires only empirical adjustment of a single parameter to set an upper frequency limit, while a "slope" parameter can be left constant if cochlear partition length is normalized to 1 or scaled if distance is specified in physical units. Constancy of slope and form in dead and living ears and across species increases the probability that the function fitting human cadaver data may apply as well to the living human ear. This prospect increases the function's value in plotting auditory data and in modeling concerned with speech and other bioacoustic signals, since it fits the available physiological data well and, consequently (if those data are correct), remains independent of, and an appropriate means to examine, psychoacoustic data and assumptions.

Acoustic Stimulation↗
PubMed1986

What is "synchrony suppression"?

Synchrony of discharge of auditory neurons to two-tone stimuli and "synchrony suppression" have been analyzed by examining the implications of the definition of vector strength. Synchrony suppression, defined as the reduction in the vector strength for one component when a second is introduced, occurs by definition when partial ("half-wave") rectification occurs in an otherwise linear system. It does so with the usual shifts (on the abscissa) of empirical vector strength curves, disproving any necessity for compressive or other nonlinearities. Synchrony suppression is sometimes defined incompatibly as the shift in dB of a vector strength curve--said to be the magnitude of suppression. That this conception is incorrect is shown by the identification of partial rectification with vector strength reduction and curve shift, but it can be shown to be a logical fallacy as well. The vector strength definition was also applied to the complex waveform obtained at the output of an instantaneous amplitude compressive nonlinearity. The shifts of vector strength growth and decay curves (at their crossover points) necessarily equal those in the linear case for any compressive nonlinearity that compresses equal inputs equally. But such a compressive nonlinearity is not without noticeable effects on vector strengths. If the input levels lie in the range leading to compressed outputs, differences in the relative input levels will be accentuated in the relative output levels in the period histogram. Compression thus contributes to greater differences in the vector strengths, for unequal input levels, than in the linear case. More visible effects on vector strength curves result from waveform distortion, which reduces vector strength saturation and crossover values and causes them to recede at higher input levels.

Auditory Perception↗
PubMedDate not supplied

Cochlear nonlinearity and gain control as determinants of the response of primary auditory neurons to harmonic complexes.

Earlier papers reported a calculational "model" (Greenwood, 1985, 1986a, b, c), composed of an initial compressive nonlinearity accompanied by a nonlinear gain control and "rectification", to demonstrate in principle certain "two-tone suppression" effects seen in primary fiber response. This paper presents simulations of primary fiber response to more complex stimuli. When harmonic stimuli of Horst et al. (1985a, b; 1986a, b) are used, the calculated spectra closely agree with the empirical spectra they report, from fibers with both low or high spontaneous activity. Thus, the simulated nonlinear motion of the cochlear partition reflects a sufficient degree of compressive distortion and an appropriate form to calculate spectra closely matching the empirical spectra in respect to the pattern of intermodulation products and the main "enhancement" and cancellation effects. Comparison of spectra of full and truncated waveforms assess added effects of "rectification". The gain control, as for simpler stimuli, leads to appropriate growth and saturation of Fourier coefficients and average firing rate. The implication that the measured transverse motion of the cochlear partition could provide sufficient distortion to account for the main features of the histograms has a two-part corollary: that the mechanism which produces severe overall saturation does not add much compressive distortion to the waveform passed radially to IHC and primary fibers, and that the IHC is kept operating chiefly in an approximately linear part of its range, by a prior gain control that is, perforce, cochlear and mechanical. Further consequences, for IHC synapses and fiber types, stem from the sufficiency of negatively biased waveform centerlines in generating simulated period histograms and spectra which match those of at least some primary fibers characterized by low spontaneous activity.

Acoustic Stimulation↗