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Particles are accelerated in cosmic sites probably under conditions very different from those at terrestrial particle accelerator laboratories. Nevertheless, specific experiments which explore plasma conditions and stimulate particle acceleration carry significant potential to illuminate some aspects of the cosmic particle acceleration process. Here we summarize our understanding of cosmic particle acceleration, as derived from observations of the properties of cosmic ray particles, and through astronomical signatures caused by these near their sources or throughout their journey in interstellar space. We discuss the candidate-source object variety, and what has been learned about their particle-acceleration characteristics. We conclude identifying open issues as they are discussed among astrophysicists. – The cosmic ray differential intensity spectrum across energies from 1010 eV to 1021 eV reveals a rather smooth power-law spectrum. Two kinks occur at the “knee” (≃1015 eV) and at the “ankle” (≃ 3×1018 eV). It is unclear if these kinks are related to boundaries between different dominating sources, or rather related to characteristics of cosmic-ray propagation. Currently we believe that galactic sources dominate up to 1017 eV or even above, and the extragalactic origin of cosmic rays at highest energies merges rather smoothly with galactic contributions throughout the 1015–1018 eV range. Pulsars and supernova remnants are among the prime candidates for galactic cosmic-ray production, while nuclei of active galaxies are considered best candidates to produce ultrahigh-energy cosmic rays of extragalactic origin. The acceleration processes are probably related to shocks formed when matter is ejected into surrounding space from energetic sources such as supernova explosions or matter accreting onto black holes. Details of shock acceleration are complex, as relativistic particles modify the structure of the shock, and simple approximations or perturbation calculations are unsatisfactory. This is where laboratory plasma experiments are expected to contribute, to enlighten the non-linear processes which occur under such conditions. [ABSTRACT FROM AUTHOR]

Tasks assessing perception of a phonemic contrast based on voice onset time (VOT) and a nonspeech analog of a VOT contrast using tone onset time (TOT) were administered to children (ages 7.5 to 15.9 years) identified as having reading disability (RD; n = 21), attention deficit/hyperactivity disorder (ADHD; n = 22), comorbid RD and ADHD (n = 26), or no impairment (NI; n = 26). Children with RD, whether they had been identified as having ADHD or not, exhibited reduced perceptual skills on both tasks as indicated by shallower slopes on category labeling functions and reduced accuracy even at the endpoints of the series where cues are most salient. Correlations between performance on the VOT task and measures of single word decoding and phonemic awareness were significant only in the groups without ADHD. These findings suggest that (a) children with RD have difficulty in processing speech and nonspeech stimuli containing similar auditory temporal cues, (b) phoneme perception is related to phonemic awareness and decoding skills, and (c) the potential presence of ADHD needs to be taken into account in studies of perception in children with RD., (Copyright 2001 Academic Press.)

This paper examines three auditory hypotheses concerning the location of category boundaries among vowel sounds. The first hypothesis claims that category boundaries tend to occur in a region corresponding to a 3-Bark separation between adjacent spectral peaks. According to the second hypothesis, vowel category boundaries are determined by the combined effects of the Bark distances between adjacent spectral peaks but that the weight of each of these effects is inversely related to the individual sizes of the Bark distances. In a series of perceptual experiments, each of these hypotheses was found to account for some category boundaries in American English but not others. The third hypothesis, which has received preliminary support from studies in our laboratory and elsewhere, claims that listeners partition the vowel space of individual talkers along lines corresponding to relatively simple linear functions of formant values when scaled in auditorily motivated units of frequency such as Bark., (Copyright 2000 S. Karger AG, Basel)

Among the world's languages, syllable inventories allowing only initial consonants predominate over those allowing both initial and final consonants. Final consonants may be disfavored because they are less easy to identify and/or more difficult to produce than initial consonants. In this study, two perceptual confusion experiments were conducted in which subjects identified naturally produced consonant-vowel-consonant syllables in different frame sentences. Results indicated that initial consonants were significantly more identifiable than final consonants across all conditions. Acoustic analyses of the test syllables indicated that the relative identifiability of initial and final consonants might be explained in terms of production differences as indicated by the greater acoustic distinctiveness of initial consonants.

Event-related magnetic fields (ERFs) were recorded from the left hemisphere in nine normal volunteers in response to four consonant-vowel (CV) syllables varying in voice-onset time (VOT). CVs with VOT values of 0 and +20 ms were perceived as /ga/ and those with VOT values of +40 and +60 ms as /ka/. Results showed: (1) a displacement of the N1m peak equivalent current dipole toward more medial locations; and (2) an abrupt reduction in peak magnetic flux strength, as VOT values increased from +20 to +40 ms. No systematic differences were noted between the 0 and +20 ms stimuli or between the +40 and +60 ms CVs. The findings are in agreement with the results of multiunit invasive recordings in non-human primates regarding the spatial and temporal pattern of neuronal population responses in the human auditory cortex which could serve as neural cues for the perception of voicing contrasts., (Copyright 1998 Elsevier Science B.V.)

Traunmüller (1981) suggested that the tonotopic distance between the first formant (F1) and the fundamental frequency (F0) is a major determinant of perceived vowel height. In the present study, subjects identified a vowel-height continuum ranging in formant pattern from /I/to/epsilon/, at five F0 values. Increasing F0 led to an increased probability of /I/responses (i.e., the phoneme boundary shifted toward the /epsilon/ end of the continuum). Various conditions of filtering out the lower harmonics of the stimuli caused only marginal shifts of the phoneme boundary. The experiments provide evidence against interpretations of Traunmüller's (1981) results that claim that vowel height is determined by the distance between F1 and the lowest harmonic that is present in the basilar membrane excitation pattern.

Purpose: The purpose of this investigation was to evaluate complete denture patients at pretreatment and postinsertion, 6 months and 18 months after denture delivery in order to develop an explanatory model of successful denture therapy to better understand patient acceptance of complete dentures., Materials and Methods: Sixty complete-denture patients treated at a dental student clinic were followed through denture therapy and for 18 months thereafter. Subjects were examined and completed pretreatment questionnaires and posttreatment interviews. Three outcome measures of denture success were tested, and factors considered substantive in achieving a successful denture outcome were examined using multivariate analyses., Results: At post-insertion, 76.7% of subjects were satisfied with their dentures, 74.6% said their expectations were met, and 66.7% said they adjusted easily to their new dentures; reports at 6 and 18 months were similarly high. Logistic regression findings suggest that psychological and interpersonal factors are more important determinants of denture satisfaction than anatomic or clinical factors., Conclusions: Subject characteristics including age, gender, race, income level, education, marital status, and maxillary and mandibular anatomy were not significantly associated with denture success as defined by the three outcome measures used in this study. Although these variables may represent important co-factors in the patient's acceptance of dental services and may affect the way a patient perceives dental care outcomes, statistically significant relationships were not found within our sample. Psychosocial variables, such as pretreatment expectations, satisfaction with the dental care received, and mental health showed a stronger relationship to a successful outcome.

In a study of vowel height perception using front vowels, Hoemeke and Diehl [J. Acoust. Soc. Am. 96, 661-674 (1994)] found that F1 - F0 distance was the best predictor of perceived vowel height for the phonological distinction [+/- high], while for two other vowel height distinctions F1 alone was the best predictor. Further, the [+/- high] identification function was defined by a sharp boundary located at 3- to 3.5-Bark F1 - F0 distance. One hypothesis offered was that F1 - F0 distance had cue value for the [+/- high] distinction because of an underlying quantal region on the F1 - F0 distance dimension. However, the results are also predicted if it is supposed that F1 - F0 distance is a cue for vowel height only for pure height distinctions. The present study further tested these possibilities, using back vowels. The results allowed us to reject both as general explanations of vowel height perception. However, the results were consistent with a third possible explanation, namely, that phonetic quality is determined by the tonotopic distances between any adjacent spectral peaks (e.g., F3 - F2, F2 - F1, and F1 - F0), with greater perceptual weight accorded to smaller distances.

Previous research has suggested that the direction of short-duration fundamental frequency (F0) perturbations following consonants helps to signal consonant [+voice]/[-voice] (abbreviated as [voice]) status. It has been proposed that the [voice] cue corresponds to the direction and extent of F0 perturbations relative to the overall intonation contour. A competing view, the low-frequency hypothesis, suggests that F0 participates in a more general way whereby low-frequency energy near the consonant contributes to [+voice] judgments. Listeners identified multiple stimulus series, each varying in voice onset time and ranging from /aga/ to /aka/. The series differed in overall intonation contour as well as in the direction of F0 perturbation relative to that contour. Consistent with one version of the low-frequency hypothesis, the F0 value at voicing onset, rather than the relative direction of the F0 perturbation, was the best predictor of [voice] judgments.

Perceived vowel height has been reported to vary inversely with the distance (in Bark) between the first formant frequency (F1) and the fundamental frequency (F0) [H. Traunmüller, J. Acoust. Soc. Am. 69, 1465-1475 (1981)]. Syrdal and Gopal [J. Acoust. Soc. Am. 79, 1086-1100 (1986)] observed that naturally produced [+high] and [-high] vowels tend to divide at a critical F1-F0 distance of 3-3.5 Bark, corresponding to the bandwidth of the "center of gravity" effect [L. Chistovich and V. Lublinskaja, Hear. Res. 1, 185-195 (1979)]. In the present study, listeners identified three sets of synthetic vowels varying orthogonally in F1 and F0 and ranging from /i/-/I/, /I/-/epsilon/, and /epsilon/-/ae/. For the /I/-/epsilon/ set, which corresponds to the [+high]/[-high] distinction, there was a relatively sharp identification boundary located at an F1-F0 distance of 3-3.5 Bark. However, for the /epsilon/-/ae/ and /i/-/I/ sets, which occupied regions where the F1-F0 distance was always greater than or always less than 3 Bark, vowel labeling varied more gradually as a function of F1-F0 distance. Also, F1-F0 distance was a better predictor of labeling performance than F1 alone only for the /I/-/epsilon/ set. Possible sources of the F1-F0 distance cue for vowel height are discussed.

Across and within languages voiced sibilants tend to be disfavored relative to voiceless ones. This paper explores the claim that voicing more adversely affects the distinctive acoustic properties of sibilants than those of nonsibilants. One prediction associated with this claim is that voicing differentially lowers the amplitude of frication noise for sibilants and non-sibilants so that amplitude differences between the two classes are reduced. Acoustic measurements confirm this prediction. A second prediction is that voicing has a greater negative effect on the identification of sibilants than nonsibilants. Perceptual results from this and previous studies are somewhat variable, but averaged data support this prediction. The findings suggest that voiced sibilants are disfavored in part for perceptual reasons.

Assimilation of nasals to the place of articulation of following consonants is a common and natural process among the world's languages. Recent phonological theory attributes this naturalness to the postulated geometry of articulatory features and the notion of spreading (McCarthy, 1988). Others view assimilation as a result of perception (Ohala, 1990), or as perceptually tolerated articulatory simplification (Kohler, 1990). Kohler notes that certain consonant classes (such as nasals and stops) are more likely than other classes (such as fricatives) to undergo place assimilation to a following consonant. To explain this pattern, he proposes that assimilation tends not to occur when the members of a consonant class are relatively distinctive perceptually, such that their articulatory reduction would be particularly salient. This explanation, of course, presupposes that the stops and nasals which undergo place assimilation are less distinctive than fricatives, which tend not to assimilate. We report experimental results that confirm Kohler's perceptual assumption: In the context of a following word initial stop, fricatives were less confusable than nasals or unreleased stops. We conclude, in agreement with Ohala and Kohler, that perceptual factors are likely to shape phonological assimilation rules.

There is some disagreement in the literature about the relative contribution of formant transition duration and amplitude rise time in signalling the contrast between stops and glides. In this study, listeners identified sets of /ba/ and /wa/ stimuli in which transition duration and rise time varied orthogonally. Both variables affected labelling performance in the expected direction (i.e. the proportion of /b/ responses increased with shorter transition durations and shorter rise times). However, transition duration served as the primary cue to the stop/glide distinction, whereas rise time played a secondary, contrast-enhancing role. A qualitatively similar pattern of results was obtained when listeners made abrupt-onset/gradual-onset judgements of single sine-wave stimuli that modelled the rise times, frequency trajectories, and durations of the first formant in the /ba/-/wa/ stimuli. The similarities between the speech and non-speech conditions suggest that significant auditory commonalities underlie performance in the two cases.

Fowler [J. Acoust. Soc. Am. 88, 1236-1249 (1990)] makes a set of claims on the basis of which she denies the general interpretability of experiments that compare the perception of speech sounds to the perception of acoustically analogous nonspeech sound. She also challenges a specific auditory hypothesis offered by Diehl and Walsh [J. Acoust. Soc. Am. 85, 2154-2164 (1989)] to explain the stimulus-length effect in the perception of stops and glides. It will be argued that her conclusions are unwarranted.

Phonologists have often held that phonetic 'substance' is more or less unrelated to phonological 'form'. This view rests on assumptions about the phonetic domain that are highly questionable on empirical grounds. Evidence is reviewed suggesting that very few phonetic properties of vowels fail to serve the linguistic function of preserving and enhancing distinctiveness. Accordingly, much of what has been considered to be purely phonetic is also phonological in character: that is to say, the domains of phonetics and phonology overlap significantly. Finally, several well-known criticisms of the program of phonetic explanation in phonology are discussed and rejected.

During presentation of a randomized list of nonadjacent associative pairs, Ss heard a cue after each word designating the task to be performed. All Ss performed two tasks. In the identical condition, Ss performed the same task on both members of an associative pair. In the nonidentical condition, Ss never performed the same task on pair members. Semantic tasks led to greater recall than did nonsemantic tasks. Also, percentage of clustering was greater when the second member of a recalled cluster had been used in a semantic task rather than a nonsemantic one. Identical and nonidentical conditions did not differ in the measure of recall. When the two tasks were a combination of one semantic and one nonsemantic task, the identical condition showed a greater percentage of clustering than the nonidentical condition. However, when the two tasks were both semantic, no difference in clustering was obtained.

To investigate possible auditory factors in the perception of stops and glides (e.g., /b/ vs /w/), a two-category labeling performance was compared on several series of /ba/-/wa/ stimuli and on corresponding nonspeech stimulus series that modeled the first-formant trajectories and amplitude rise times of the speech items. In most respects, performance on the speech and nonspeech stimuli was closely parallel. Transition duration proved to be an effective cue for both the stop/glide distinction and the nonspeech distinction between abrupt and gradual onsets, and the category boundaries along the transition-duration dimension did not differ significantly in the two cases. When the stop/glide distinction was signaled by variation in transition duration, there was a reliable stimulus-length effect: A longer vowel shifted the category boundary toward greater transition durations. A similar effect was observed for the corresponding nonspeech stimuli. Variation in rise time had only a small effect in signaling both the stop/glide distinction and the nonspeech distinction between abrupt and gradual onsets. There was, however, one discrepancy between the speech and nonspeech performance. When the stop/glide distinction was cued by rise-time variation, there was a stimulus-length effect, but no such effect occurred for the corresponding nonspeech stimuli. On balance, the results suggest that there are significant auditory commonalities between the perception of stops and glides and the perception of acoustically analogous nonspeech stimuli.

Recent studies have shown that vowels tend to be identified more accurately in consonantal context than in isolation. This contextual advantage is often explained perceptually, e.g., by assuming that the formant transitions associated with the consonants convey significant vowel information. In two experiments with stylized synthetic speech patterns, we were unable to replicate the contextual advantage. These negative results were probably due to certain unnatural stimulus characteristics. In another experiment we used natural speech stimuli to assess whether nonperceptual factors associated with the identification task contribute to the contextual advantage. Subjects responded to the test items either by (a) circling written CVC syllables, (b) circling written isolated vowels, or (c) vocally mimicking the items (a task that we assume imposes minimal memory load on subjects). Of these response conditions, only the first yielded an advantage for vowels in context, suggesting that the effect depends on two factors: Stimulus-response compatibility and memory load.

Japanese quail (Coturnix coturnix) learned a category for syllable-initial [d] followed by a dozen different vowels. After learning to categorize syllables consisting of [d], [b], or [g] followed by four different vowels, quail correctly categorized syllables in which the same consonants preceded eight novel vowels. Acoustic analysis of the categorized syllables revealed no single feature or pattern of features that could support generalization, suggesting that the quail adopted a more complex mapping of stimuli into categories. These results challenge theories of speech sound classification that posit uniquely human capacities.

It is generally believed that selective adaptation effects in speech perception are due to a reduction in sensitivity of auditory feature detectors. Recent evidence suggest that these effects may derive instead from contrast. In a further test of the contrast hypothesis, we conducted two experiments each involving both adaptation and contrast sessions with matching stimulus sets. During the adaptation sessions of Experiment 1, subjects identified two series of velar stimuli varying in voice onset time, [ga]-[kha] and [gi]-[khi], before and after adaptation with of the following stimuli: [ga], [kha], [gi], and [khi]. In the contrast session, subjects identified either of two ambiguous test items (drawn from near the phonetic boundaries of the [ga]-[kha] and the [gi]-[khi] series) following a single presentation of [ga], [kha], [gi], or [khi]. For both the adaptation and contrast sessions, (a) the [--a] test items were more greatly affected (in a contrast direction) by the [--a] than by the [--i] adaptor/context stimuli, and (b) the [--i] test items were not differentially affected by the [--1] and [--i] adaptor/context stimuli. An analogous design was used in Experiment 2, except that the stimulus sets varied in pitch rather than vowel quality. For both the adaptation and contrast sessions, the test items were not differentially affected by the pitch of the adaptor/context stimulus. These parallel results provide further evidence that adaptation effects are actually a form of contrast.

Changes in the identification of speech sounds following selective adaptation are usually attributed to a reduction in sensitivity of auditory feature detectors. An alternative explanation of these effects is based on the notion of response contrast. In several experiments, subjects identified the initial segment of synthetic consonant-vowel syllables as either the voiced stop [b] or the voiceless stop [ph]. Each test syllable had a value of voice onset time (VOT) that placed it near the English voiced-voiceless boundary. When the test syllables were preceded by a single clear [b] (VOT = -100 msec), subjects tended to identify them as [ph], whereas when they were preceded by an unambiguous [ph] (VOT = 100 msec), the syllables were predominantly labeled [b]. This contrast effect occurred even when the contextual stimuli were velar and the test stimuli were bilabial, which suggests a featural rather than a phonemic basis for the effect. To discount the possibility that these might be instances of single-trial sensory adaptation, we conducted a similar experiment in which the contextual stimuli followed the test items. Reliable contrast effects were still obtained. In view of these results, it appears likely that response contrast accounts for at least some component of the adaptation effects reported in the literature.

Although there is evidence that selective adaptation and contrast effects in speech perception are produced by the same mechanisms, Sawusch and Jusczyk (1981) reported a dissociation between the effects and concluded that adaptation and contrast occur at separate processing levels. They found that an ambiguous test stimulus was more likely to be labeled b following adaptation with [pha] and more likely to be labeled p following adaptation with [ba] or [spa] (the latter consisting of [ba] preceded by [s] noise). In the contrast session, where a single context stimulus occurred with a single test item, the [ba] and [pha] contexts had contrastive effects similar to those of the [ba] and [pha] adaptors, but the [spa] context produced an increase in b responses to the test stimulus, an effect opposite to that of the [spa] adaptor. One interpretation of this difference is that the rapid presentation of the [spa] adaptor gave rise to "streaming," whereby the [s] was perceptually segregated from the [ba]. In our experiment, we essentially replicated the results of Sawusch and Jusczyk (1981), using procedures similar to theirs. Next, we increased the interadaptor interval to remove the likelihood of stream segregation and found that the adaptation and contrast effects converged.