Memory for pitch versus memory for loudness.

The decays of pitch traces and loudness traces in short-term auditory memory were compared in forced-choice discrimination experiments. The two stimuli presented on each trial were separated by a variable delay (D); they consisted of pure tones, series of resolved harmonics, or series of unresolved harmonics mixed with lowpass noise. A roving procedure was employed in order to minimize the influence of context coding. During an initial phase of each experiment, frequency and intensity discrimination thresholds [P(C) = 0.80] were measured with an adaptive staircase method while D was fixed at 0.5 s. The corresponding physical differences (in cents or dB) were then constantly presented at four values of D: 0.5, 2, 5, and 10 s. In the case of intensity discrimination, performance (d') markedly decreased when D increased from 0.5 to 2 s, but was not further reduced when D was longer. In the case of frequency discrimination, the decline of performance as a function of D was significantly less abrupt. This divergence suggests that pitch and loudness are processed in separate modules of auditory memory.

Pitch perception: a difference between right- and left-handed listeners.

Various results indicate that the perception of a complex tone's "virtual" pitch is generally lateralized in the right cerebral hemisphere. The primary aim of this work was to test the hypothesis that this is not the case for the "spectral" pitch percepts induced by complex tones. Forty right-handed and 18 left-handed listeners were monaurally presented with pairs of successive tones made up of n consecutive equal-amplitude harmonics of a missing fundamental (F0). n varied from two to four across subjects. In "test" conditions, the paired tones differed in F0 but the spectral components of the tone with the lower F0 were higher in frequency than the corresponding components of the other tone (except for one component, which was identical). The subjects had to say if, from one tone to the other, pitch rose or fell. From such judgements, one could infer that the pitch dominantly perceived in each tone was a virtual pitch (corresponding to F0) or a spectral pitch (i.e., the pitch of a single spectral component, or a perceptual quality corresponding to the centroid of the power spectrum). For n = 2, the results indicated that virtual pitch was less salient than spectral pitch; the opposite occurred for n = 3 and n = 4. The ear (left or right) to which the stimuli were presented had some influence on the judgements, in the expected direction. However, this influence was not a robust one. Unexpectedly, a reliable effect of the listeners' handedness was observed: for each value of n, the judgements indicating virtual pitch perception were less frequent in the left-handers than in the right-handers. Discrimination performances measured in "control" conditions showed that the handedness factor was not confounded with a factor of frequency discrimination ability.

Speech versus nonspeech in pitch memory.

The memory trace of the pitch sensation induced by a standard tone (S) can be strongly degraded by subsequently intervening sounds (I). Deutsch [Science 168, 1604-1605 (1970)] suggested that the degradation is much weaker when the I sounds are words than when they are tones. In Deutsch's study, however, the pitch relations between S and the I words were not controlled. The first experiment reported here was similar to that of Deutsch except that the speech and nonspeech stimuli used as I sounds were matched in pitch. The speech stimuli were monosyllabic words derived from recordings of a real voice, whereas the nonspeech stimuli were harmonic complex tones with a flat spectral profile. These two kinds of I sound were presented at a variable pitch distance (delta-pitch) from the S tone. In a same/different paradigm, S had to be compared with a tone presented 6 s later; this comparison tone could be either identical to S or shifted in pitch by +/- 75 cents. The nature of the I sounds (spoken words versus tones) affected discrimination performance, but markedly less than did delta-pitch. Performance was better when delta-pitch was large than when it was small, for the speech as well as nonspeech I sounds. In a second experiment, the S sounds and comparison sounds were spoken words instead of tones. The differences to be detected were restricted to shifts in fundamental frequency (and thus pitch), the other acoustic attributes of the words being left unchanged. Again, discrimination performance was positively related to delta-pitch. This time, the nature of the I sounds (words versus tones) had no significant effect. Overall, the results suggest that, in auditory short-term memory, the pitch of speech sounds is not stored differently from the pitch of nonspeech sounds.

Further evidence for an autonomous processing of pitch in auditory short-term memory.

In four related experiments, subjects had to discriminate between the presence or absence of a frequency difference between two pure tones separated by 4.3 s. The interference effects of other tones (I), inserted during the retention interval, were investigated. A previous study [C. Semal and L. Demany, J. Acoust. Soc. Am. 89, 2404-2410 (1991)] had shown that subjects' performance strongly depended on the pitch relations between the test tones and the I tones, but not on the spectral composition of the I tones. This suggested that the mnemonic system processing pitch is deaf to sharpness of timbre. In the present study, the I tones could differ or not from the test tones in intensity (by +/- 6 or 15 dB) or in amplitude envelope (periodic as well as aperiodic envelopes were used). It was found that such differences had very little effect on performance, suggesting that the mnemonic system processing pitch is deaf to loudness and to dynamic aspects of timbre. However, for I tones with a dense spectrum in the vicinity of the test tones' frequencies, widening the I tones' spectrum improved performance, probably because this spectral widening decreased the salience of the I tones' pitches.

Detection of inharmonicity in dichotic pure-tone dyads.

Thresholds for the detection of quasi-sinusoidal frequency ratio fluctuations were measured with stimuli consisting of dichotic dyads of simultaneous pure tones. The two component tones of each dyad were slowly modulated in frequency, in such a way that the ratio of their instantaneous frequencies oscillated (or not) around some standard frequency ratio (SFR). As in a previous study [Demany and Semal (1988) J. Acoust. Soc. Am. 83, 687-695], it was found that smaller oscillations could be detected when the SFR was precisely an octave (2/1) than when it was slightly smaller or larger (2/1 +/- 50 or 100 cents). Similar 'harmonicity effects' were obtained here for SFRs in the vicinity of a fifth (3/2), a twelfth (3/1), or a double octave (4/1). However, these harmonicity effects were generally less pronounced than those observed in the vicinity of an octave. Each of our four subjects provided evidence for a central sensitivity to the octave harmonicity, but the same consistency could not be found with respect to other kinds of harmonicity.

Dissociation of pitch from timbre in auditory short-term memory.

In three experiments, untrained listeners made same/different judgments on pairs of pure or complex tones with periods that eventually differed by +/- 4%. On each trial, the two test tones were separated by 4.3 s, during which other tones (I) were heard but had to be ignored. The period (p) of the first test tone was randomly selected between 1/600 and 1/300 s. The period of each I tone was randomly selected among four possible values, close to p (+/- 3% or 6% apart) in some conditions, and remote from p in other conditions. In addition, from condition to condition, the spectral content of the I tones was varied independently of their periods: The I tones could have the same harmonic content as the test tones, or a very different harmonic content. Subjects' performances were much better when the periods of the I tones were remote from p than when they were close to p, as expected from previous findings by D. Deutsch [e.g., Science 175, 1020-1022 (1972)]. But, more importantly, the relation between the spectral contents of the I tones and the test tones had, by itself, practically no effect on performance. Thus performance was affected by the pitches of the I tones, but not by their timbres. These results suggest that pitch is processed independently of timbre in auditory short-term memory.

Harmonic and melodic octave templates.

For normal-hearing adult listeners, two simultaneous pure tones with a frequency ratio close to 2/1 may perceptually fuse into a single sound, which shows that such listeners are sensitive to "octave harmony." Many adult listeners are also able to consistently adjust two successive pure tones "one octave apart," which shows that they possess melodic octave templates. According to Terhardt [J. Acoust. Soc. Am. 55, 1061-1069 (1974)], melodic octave templates and the perception of octave harmony originate from a common learning process taking place in early life. In the two experiments reported here, subjects performed repeated octave adjustments for pairs of simultaneous and successive tone bursts. Both tones were presented monaurally, at 45 or 65 dB SPL. The frequency of the lower tone (fref) was an independent variable, while the frequency of the higher tone was adjustable within a 500-cent range. In some conditions, when the two tones were presented simultaneously, they were sinusoidally frequency modulated in a coherent manner, at a rate of 2 or 4 Hz; the aim of this frequency modulation was to force the subjects to adopt a synthetic listening strategy, i.e., to base their adjustments on perceived harmony. For fref values ranging from 270-2000 Hz, subjects performed consistent adjustments when the tones were presented successively: fref had little effect on the adjustments' variability. However, in the same frequency range, the variability of the harmonic adjustments markedly increased with fref; for the highest fref values, it was much greater than the variability of the melodic adjustments. The results suggest that, in adult listeners, the perception of octave harmony disappears at frequencies for which melodic octaves are still accurately perceived.

The effect of vibrato on the recognition of masked vowels.

Five experiments on the identifiability of synthetic vowels masked by wideband sounds are reported. In each experiment, identification thresholds (signal/masker ratios, in decibels) were measured for two versions of four vowels: a vibrated version, in which FO varied sinusoidally around 100 Hz; and a steady version, in which F0 was fixed at 100 Hz. The first three experiments were performed on naive subjects. Experiment 1 showed that for maskers consisting of bursts of pink noise, vibrato had no effect on thresholds. In Experiment 2, where the maskers were periodic pulse trains with an F0 randomly varied between 120 and 140 Hz from trial to trial, vibrato slightly improved thresholds when the sound pressure level of the maskers was 40 dB, but had no effect for 65-dB maskers. In Experiment 3, vibrated rather than steady pulse trains were used as maskers; when these maskers were at 40 dB, the vibrated versions of the vowels were slightly less identifiable than their steady versions; but, as in Experiment 2, vibrato had no effect when the maskers were at 65 dB. Experiment 4 showed that the unmasking effect of vibrato found in Experiment 2 disappeared in subjects trained in the identification task. Finally, Experiment 5 indicated that in trained listeners, vibrato had no influence on identification performance even when the maskers and the vowels had synchronous onsets and offsets. We conclude that vibrating a vowel masked by a wideband sound can affect its identification threshold, but only for tonal maskers and in untrained listeners. This effect of vibrato should probably be considered as a Gestalt phenomenon originating from central auditory mechanisms.

Detection thresholds for sinusoidal frequency modulation.

An adaptive forced-choice procedure was used to measure, in four normal-hearing subjects, detection thresholds for sinusoidal frequency modulation as a function of carrier frequency (fc, from 250 to 4000 Hz) and modulation frequency (fmod. from 1 to 64 Hz). The results show that, for a wide range of fmod values, fc and fmod have almost independent effects on the thresholds when the thresholds are expressed as just-noticeable frequency swings and plotted on a log scale. In two subjects, the effect of fc on the thresholds was compared to the effect of standard frequency on the frequency just noticeable differences (jnd's) of successive and steady tones. In agreement with previous data [H. Fastl, J. Acoust. Soc. Am. 63, 275-277 (1978)], it was found that the two effects are significantly different if the frequency jnd's are measured with long-duration tones. However, it was also found that the two effects are similar if the frequency jnd's are measured with 25-ms tones. These results support the idea that, at least for low fmod values, the detection of continuous and periodic frequency modulations is mediated by a pitch-sampling process using a temporal window of about 25 ms.

Dichotic fusion of two tones one octave apart: evidence for internal octave templates.

Stimuli consisting of two simultaneous and sinusoidally frequency-modulated pure tones were dichotically presented to four listeners. Two component tones of each stimulus were approximately an octave apart. They were both modulated at 2 Hz, and the frequency swing resulting from each modulation corresponded to one tenth of the carrier frequency. The listeners' task was to detect phase differences between the modulation waveforms of the two simultaneous tones: With an adaptive 2IFC procedure, just-noticeable values of phi, the phase angle of the modulation waveforms, were measured as a function of the interval formed by the carrier frequencies (one octave, i.e., 1200 cents, +/- 0, 25, 50, or 100 cents). When the carrier frequencies were not too high, just-noticeable values of phi often varied nonmonotonically with the interval, showing a minimum at or near 1200 cents. An additional experiment indicated that most, if not all, of these octave effects were not due to some form of beat detection. As a whole, the results reported here provide evidence for the existence of internal octave templates. Such templates might play an important role in the perceptual segregation of simultaneous harmonic signals, as well as in pitch perception.

Early development in mice: II. Sensory motor behavior and genetic analysis.

The genetic and environmental bases for differences in rate of development were investigated in 2 inbred strains of mice: C57BL/6By (B) and BALB/cBy (C). Twelve motor responses, aside from individual weight, were used to measure these differences. The Recombinant Inbred Strains method was chosen to perform the genetic analysis. Overdominance is shown to be present in 2 variables alone (eye opening, weight at 10 and 20 days). In most cases, each of the response reflexes was found to be associated with several genes (locomotion, hind limb, crossed extensor, righting, vibrissae placing, bar holding). Differences across strains are associated with one segregating unit for rate of disappearance of the rooting response. This unit is mapped on the part of the 4th chromosome including the loci b and H-21. The strain distribution pattern differs for each sensory motor response, consequently no one general genetic factor of development can be advanced. Maternal effects were found for 4 variables (grasping, fore limb placing, eye opening and weight). For two responses, the F1 pups developing the fastest were reared by mothers from the slowest developing parental strain. As regards this latter finding, the authors hypothesize that mothers differ as to the quality of the environment they furnish to their young and pups differ in their ability to benefit from these environments.

Differences in patterns of pup care in mice. V--Pup ultrasonic emissions and pup care behavior.

Newborn mice, like all newborn rodents, are able to emit high frequency signals, in particular when they are put out of the nest. Moreover, it is known that in this situation retrieving behaviors are induced in the foster mother, which are likely to reveal stable differences across inbred strains of mice. The question that arises is whether these differences are causally linked to differences in the pup rate of signalling and/or to the capacity of the females of these strains to perceive them. To provide insights into this question, the behavior of 8 inbred strains of mice was observed: A/J, BALB/c, CBA/H, C57BL/6, C57Br, DBA, NZB and XLII. Pup ultrasonic calls of each of these strains, emitted in the same conditions as a retrieving test, were recorded and tabulated. Auditory sensitivities of females belonging to these strains were determined by auditory evoked potentials recorded in the inferior colliculus. These two variables were analysed in relation to scores of females of these strains on three variables of a retrieving test. Results show that the presence of other factors than auditory cues must be taken into account to describe differences across strains in retrieving performances. This conclusion has been confirmed by results obtained using cross-fostering procedure. Female mice unable to utilize ultrasonic information may use other sensory channels. Furthermore, female mice capable of perceiving ultrasounds may also be able to use different sensory modalities in different situations.