Catherine Semal

Learning to perceive pitch differences

This paper reports two experiments concerning the stimulus specificity of pitch discrimination learning. In experiment 1, listeners were initially trained, during ten sessions (about 11,000 trials), to discriminate a monaural pure tone of 3000 Hz from ipsilateral pure tones with slightly different frequencies. The resulting perceptual learning (improvement in discrimination thresholds) appeared to be frequency-specific since, in subsequent sessions, new learning was observed when the 3000-Hz standard tone was replaced by a standard tone of 1200 Hz, or 6500 Hz. By contrast, a subsequent presentation of the initial tones to the contralateral ear showed that the initial learning was not, or was only weakly, ear-specific. In experiment 2, training in pitch discrimination was initially provided using complex tones that consisted of harmonics 3-7 of a missing fundamental (near 100 Hz for some listeners, 500 Hz for others). Subsequently, the standard complex was replaced by a standard pure tone with a frequency which could be either equal to the standard complexs missing fundamental or remote from it. In the former case, the two standard stimuli were matched in pitch. However, this perceptual relationship did not appear to favor the transfer of learning. Therefore, the results indicated that pitch discrimination learning is, at least to some extent, timbre-specific, and cannot be viewed as a reduction of an internal noise which would affect directly the output of a neural device extracting pitch from both pure tones and complex tones including low-rank harmonics.

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.

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 Deutschs 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.

Individual differences in the sensitivity to pitch direction

It is commonly assumed that one can always assign a direction-upward or downward-to a percept of pitch change. The present study shows that this is true for some, but not all, listeners. Frequency difference limens (FDLs, in cents) for pure tones roved in frequency were measured in two conditions. In one condition, the task was to detect frequency changes; in the other condition, the task was to identify the direction of frequency changes. For three listeners, the identification FDL was about 1.5 times smaller than the detection FDL, as predicted (counterintuitively) by signal detection theory under the assumption that performance in the two conditions was limited by one and the same internal noise. For three other listeners, however, the identification FDL was much larger than the detection FDL. The latter listeners had relatively high detection FDLs. They had no difficulty in identifying the direction of just-detectable changes in intensity, or in the frequency of amplitude modulation. Their difficulty in perceiving the direction of small frequency/pitch changes showed up not only when the task required absolute judgments of direction, but also when the directions of two successive frequency changes had to be judged as identical or different.

The Role of Memory in Auditory Perception

Sound sources produce physical entities that, by definition, are extended in time. Moreover, whereas a visual stimulus lasting only 1 ms can provide very rich information, that is not the case for a 1-ms sound. Humans are indeed used to processing much longer acoustic entities. In view of this, it is natural to think that “memory” (in the broadest sense) must play a crucial role in the processing of information provided by sound sources. However, a stronger point can be made: It is reasonable to state that, at least in the auditory domain, “perception” and “memory” are so deeply interrelated that there is no definite boundary between them. Such a view is supported by numerous empirical facts and simple logical considerations. Consider, as a preliminary example, the perception of loudness. The loudness of a short sound, e.g., a burst of white noise, depends on its duration (Scharf 1978). Successive noise bursts equated in acoustic power and increasing in duration from, say, 5 ms to about 200 ms are perceived not only as longer and longer but also as louder and louder. Loudness is thus determined by a temporal integration of acoustic power. This temporal integration implies that a “percept” of loudness is in fact the content of an auditory memory. A commonsense notion is that memory is a consequence of perception and cannot be a cause of it. In the case of loudness, however, perception appears to be a consequence of memory. This is not a special case: Many other examples of such a relationship between perception and memory can be given. Consider, once more, the perception of white noise. A long sample of white noise, i.e., a completely random signal, is perceived as a static “shhhhh...” in which no event or feature is discernible. But if a 500-ms or 1-s excerpt of the same noise is taken at random and cyclically repeated, the new sound obtained is rapidly perceived as quite different. What is soon heard is a repeating sound pattern filled with perceptual events such as “clanks” and “rasping” (Guttman and Julesz 1963; Warren 1982, Chapter 3; Kaernbach 1993, 2004). It can be said that the perceptual events in question are a creation of memory, since they do not exist in the absence of repetitions. Kubovy and Howard (1976) provided another thought-provoking example. They constructed sequences of binaural “chords”

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 (jnds) 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 jnds are measured with long-duration tones. However, it was also found that the two effects are similar if the frequency jnds 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.

Auditory Change Detection: Simple Sounds Are Not Memorized Better Than Complex Sounds

Previous research has shown that the detectability of a local change in a visual image is essentially independent of the complexity of the image when the interstimulus interval (ISI) is very short, but is limited by a low-capacity memory system when the ISI exceeds 100 ms. In the study reported here, listeners made same/different judgments on pairs of successive “chords” (sums of pure tones with random frequencies). The change to be detected was always a frequency shift in one of the tones, and which tone would change was unpredictable. Performance worsened as the number of tones increased, but this effect was not larger for 2-s ISIs than for 0-ms ISIs. Similar results were obtained when a chord was followed by a single tone that had to be judged as higher or lower than the closest component of the chord. Overall, our data suggest that change detection is based on different mechanisms in audition and vision.

Fundamental differences in change detection between vision and audition.

We compared auditory change detection to visual change detection using closely matched stimuli and tasks in the two modalities. On each trial, participants were presented with a test stimulus consisting of ten elements: pure tones with various frequencies for audition, or dots with various spatial positions for vision. The test stimulus was preceded or followed by a probe stimulus consisting of a single element, and two change-detection tasks were performed. In the “present/absent” task, the probe either matched one randomly selected element of the test stimulus or none of them; participants reported present or absent. In the “direction-judgment” task, the probe was always slightly shifted relative to one randomly selected element of the test stimulus; participants reported the direction of the shift. Whereas visual performance was systematically better in the present/absent task than in the direction-judgment task, the opposite was true for auditory performance. Moreover, whereas visual performance was strongly dependent on selective attention and on the time interval separating the probe from the test stimulus, this was not the case for auditory performance. Our results show that small auditory changes can be detected automatically across relatively long temporal gaps, using an implicit memory system that seems to have no similar counterpart in the visual domain.

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.

Pitch perception and retention: Two cumulative benefits of selective attention

By presenting, before a “chord” of three pure tones with remote frequencies, a tone relatively close in frequency to one component (T1) of the chord, one can direct the listener’s attention onto T1 within the chord. In the first part of the present study, it was found that this increases the accuracy with which the pitch of T1 is perceived. The attentional cue improved the discrimination between the frequency of T1 and that of another tone (T2) presented immediately after the chord or very shortly (300 msec) after it. No improvement was found when T1 was presented alone instead of within a chord. A subsequent experiment, in which the chord and T2 were separated by either 300 msec or 4 sec, indicated that the attentional cue improved not only the perception, but also the memorization of the pitch of T1 (especially when T1 was the intermediate component of the chord). It is argued that the positive effect of attention on memory took place when the pitch percept was encoded into memory, rather than after the formation of the pitch memory trace.