Individual differences in the processing of speech and nonspeech sounds by normal-hearing listeners.

While a large portion of the variance among listeners in speech recognition is associated with the audibility of components of the speech waveform, it is not possible to predict individual differences in the accuracy of speech processing strictly from the audiogram. This has suggested that some of the variance may be associated with individual differences in spectral or temporal resolving power, or acuity. Psychoacoustic measures of spectral-temporal acuity with nonspeech stimuli have been shown, however, to correlate only weakly (or not at all) with speech processing. In a replication and extension of an earlier study [Watson et al., J. Acoust. Soc. Am. Suppl. 1 71. S73 (1982)] 93 normal-hearing college students were tested on speech perception tasks (nonsense syllables, words, and sentences in a noise background) and on six spectral-temporal discrimination tasks using simple and complex nonspeech sounds. Factor analysis showed that the abilities that explain performance on the nonspeech tasks are quite distinct from those that account for performance on the speech tasks. Performance was significantly correlated among speech tasks and among nonspeech tasks. Either, (a) auditory spectral-temporal acuity for nonspeech sounds is orthogonal to speech processing abilities, or (b) the appropriate tasks or types of nonspeech stimuli that challenge the abilities required for speech recognition have yet to be identified.

Distinctiveness and serial position effects in tonal sequences.

The proportion-of-the-total-duration rule (Kidd & Watson, 1992) states that the detectability of a change in a component of a tonal sequence can be predicted by the proportional duration of the changed component relative to the length of the sequence as a whole. A similar viewpoint relies on temporal distinctiveness to account for primacy, recency, and other serial position effects in memory (Murdock, 1960; Neath, 1993a, 1993b). Such distinctiveness models predict that an item will be remembered if it is more distinctive along some dimension relative to possible competitors. Three experiments explored the relation between distinctiveness and proportional duration by examining the effects of the proportion of the total duration of a tone in a sequence, serial position, and interstimulus interval (ISI) on the detection of a change in one component of a tonal sequence. Experiment 1 replicated the basic effect with relatively untrained subjects and a fixed frequency difference. Experiment 2 showed that distinctiveness holds for tonal sequences and a same/different task. Experiment 3 combined the two to show that proportional duration, ISI, and position of the changed tone all contribute to discrimination performance. The present research combines theories that have been proposed in the psychophysics and memory fields and suggests that a comprehensive principle based on relative distinctiveness may be able to account for both perceptual and memory effects.

Manipulations of irrelevant information: suffix effects with articulatory suppression and irrelevant speech.

Numerous studies have demonstrated impaired recall when the to-be-remembered information is accompanied or followed by irrelevant information. However, no current theory of immediate memory explains all three common methods of manipulating irrelevant information: requiring concurrent articulation, presenting irrelevant speech, and adding a stimulus suffix. Five experiments combined these manipulations to determine how they interact and which theoretical framework most accurately and completely accounts for the data. In Experiments 1 and 2, a list of auditory items was followed by an irrelevant speech sound (the suffix) while subjects engaged in articulatory suppression. Although articulatory suppression reduced overall recall compared to a control condition, comparable suffix effects were seen in both conditions. Experiments 3 and 4 found reliable suffix effects when list presentation was accompanied by irrelevant speech. Experiment 5 found a suffix effect even when the irrelevant speech was composed of a set of different items. Implications for working memory, precategorical acoustic store, the changing-state hypothesis, and the feature model are discussed.

Familiarity and pronounceability of nouns and names.

Ratings of familiarity and pronounceability were obtained from a random sample of 199 surnames (selected from over 80,000 entries in the Purdue University phone book) and 199 nouns (from the Kucera-Francis, 1967, word database). The distributions of ratings for nouns versus names are substantially different: Nouns were rated as more familiar and easier to pronounce than surnames. Frequency and familiarity were more closely related in the proper name pool than the word pool, although both correlations were modest. Ratings of familiarity and pronounceability were highly related for both groups. A production experiment showed that rated pronounceability was highly related to the time taken to produce a name. These data confirm the common belief that there are differences in the statistical and distributional properties of words as compared to proper names. The value of using frequency and the ratings of familiarity and pronounceability for predicting variations in actual pronunciations of words and names are discussed.

The perception of speech gestures.

Two experiments examined the effects of temporal overlap of speech gestures on the perception of stop consonant clusters. Sequences of stop consonant gestures that exhibit temporal overlap extreme enough to potentially eliminate the acoustic evidence of (at least) one of the consonants were obtained from x-ray microbeam data. Subjects were given a consonant monitoring task using stimuli containing stop sequences as well as those containing single stops. Results showed that (1) the initial consonant in the stop sequences was detected significantly less often than in the single stops; (2) bilabial gestures were considerably more effective at obscuring a preceding alveolar than the reverse; and (3) the detection rate correlated with an index of overlap between lip and tongue tip gestures. Experiment 2 employed stimuli that were truncated during the closure for the critical stop or stop sequence, so as to eliminate any information occurring in the acoustic signal at the stop release. This experiment showed that removing release information decreased detectability of the consonants generally. However, consistent with the observed gestural patterns, removing the release did not decrease detection of the alveolar stop when it was the first consonant of a sequence, indicating that there was no information about the alveolar stop present in acoustic realization of the second stop release. These experiments show that certain gestural patterns actually produced by English speakers may not be completely recoverable by listeners, and further, that it is possible to relate recoverability to particular metric properties of the gestural pattern.

Irrelevant speech eliminates the word length effect.

The word length effect refers to the observation that memory is better for short than for long words. The irrelevant speech effect refers to the finding that memory is better when items are presented against a quiet background than against one with irrelevant speech. According to Baddeley's (1986, 1994) working memory, these variables should not interact: The word length effect arises from rehearsal by the articulatory control process, whereas irrelevant speech reduces recall through interference in the phonological store. Four experiments demonstrate that, like articulatory suppression, irrelevant speech eliminates the word length effect for both visual and auditory items. These results (1) provide further evidence against the ability of working memory to explain the word length and irrelevant speech effects and (2) confirm a specific prediction of Nairne's (1990) feature model.

The relation between discriminability and memory for vowels, consonants, and silent-center vowels.

People remember lists of vowel-contrasting syllables better than lists that vary only in stop consonant identity. Most views suggest that this difference is due to the structure of immediate memory and the greater discriminability of vowels compared with consonants. In all of these views, there is a presumed systematic relationship between discriminability and recall so that the more discriminable an item, the better that item should be recalled. The 11 experiments reported here measured the relative discriminability of and compared serial recall for (1) intact syllables that varied only in the medial vowel, (2) intact syllables that varied only in the initial consonant, and (3) syllables with the center vowel replaced by silence (so-called silent-center vowels). When item discriminability, as measured by identification, was equated for consonant-contrasting and silent-center lists, serial recall performance was also equal. However, even when the vowels were less discriminable than the consonants or silent-center vowels, serial recall performance for the vowels was still better. These results are problematic for theories based on acoustic discriminability but can be explained parsimoniously by Nairne's (1990) feature model.

Auditory recency in immediate memory.

Six experiments investigated the locus of the recency effect in immediate serial recall. Previous research has shown much larger recency for speech as compared to non-speech sounds. We compared two hypotheses: (1) speech sounds are processed differently from non-speech sounds (e.g. Liberman & Mattingly, 1985); and (2) speech sounds are more familiar and more discriminable than non-speech sounds (e.g. Nairne, 1988, 1990). In Experiments 1 and 2 we determined that merely varying the label given to the sets of stimuli (speech or non-speech) had no effect on recency or overall recall. We varied the familiarity of the stimuli by using highly trained musicians as subjects (Experiments 3 and 4) and by instructing subjects to attend to an unpracticed dimension of speech (Experiment 6). Discriminability was manipulated by varying the acoustic complexity of the stimuli (Experiments 3, 5, and 6) or the pitch distance between the stimuli (Experiment 4). Although manipulations of discriminability and familiarity affected overall level of recall greatly, in no case did discriminability or familiarity alone significantly enhance recency. What seems to make a difference in the occurrence of convincing recency is whether the items being remembered are undegraded speech sounds.

Effects of notexin on neuromuscular transmission in the guinea pig vas deferens.

The effects of notexin on neuromuscular transmission in the isolated vas deferens of the guinea pig have been investigated using intracellular recording techniques. The toxin had no effect on the resting membrane potential, the amplitude or frequency of spontaneous excitatory junctional potentials or on the time constant of the decay of the evoked excitatory junctional potential in the smooth muscle cells. The amplitude of the evoked excitatory junctional potential was selectively reduced in the presence of notexin. The reduction in amplitude lasted for 20-30 min. Recovery occurred despite the continued presence of the toxin. Once recovery had been achieved the preparation remained insensitive to further exposure to the toxin. Although the amplitude of excitatory junctional potentials recovered in the continued presence of notexin, facilitation remained depressed. Action potentials, when generated, were indistinguishable from those in control tissues. It is concluded that notexin is a presynaptic inhibitor of transmission in the guinea pig vas deferens.

Effect of refrigerated storage on cefaclor in Mueller-Hinton agar.

Cefaclor is less stable than most cephalosporins in media at 35 degrees C. We demonstrated that the activity of cefaclor in Mueller-Hinton agar diminishes continuously at 4 degrees C, resulting in a loss of two-thirds of the activity within 21 days. We recommend that agar dilution plates for this cephalosporin be prepared on the day of their use.

Some properties of the excitatory junction potentials recorded from saphenous arteries of rabbits.

1. Excitatory junction potentials (e.j.p.s) were recorded from smooth muscle cells of the saphenous arteries of young rabbits. 2. The amplitudes of e.j.p.s recorded from different preparations, in response to a single maximal stimulus, were small and variable (5--14 mV). They decayed exponentially with a time constant of about 200 msec. 3. At frequencies greater than 1 Hz the shape of those e.j.p.s which exceeded 12--15 mV in amplitude was changed. The early part of the e.j.p.s became faster in time course. 4. Trains of up to five stimuli, at frequencies greater than 4 Hz, caused summation of e.j.p.s; 'active responses' were superimposed on this depolarization. Peak amplitude of the response to repetitive stimulation was 50 mV. 5. In normal solution, contraction appeared to be associated with a change in the configuration of e.j.p.s. 6. No action potentials resembling those recorded from most visceral smooth muscles were observed in normal solutions although these could be evoked in the presence of TEA (2.5--10 mM). 7. The method of Abe & Tomita (1968) was used to determine the values of the length constant (lambda) and time constant (tau) of the smooth muscle of intact arteries. The value of lambda (0.6 mm) was about half that found for circular strips cut from larger arteries. 8. The time constant of decay of single e.j.p.s of less than 12 mV in amplitude was indistinguishable from the membrane time constant. 9. Noradrenaline caused contraction of the artery in the absence of a change in membrane potential. 10. It is tentatively suggested that there may be two different populations of receptors in this smooth muscle membrane.