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Biomedical subjects

A G Samuel

Publications and source records attributed to A G Samuel.

At least 19 recordsLinked to original sources
PubMed1995

Lexical and sublexical feedback in auditory word recognition.

Currently, there are two qualitatively different model classes in the field of spoken language understanding. Autonomous models allow only bottom-up information flow, whereas interactive models allow higher level representations (e.g., lexical) to affect processing at lower levels (e.g., phonemic). Part 1 of the present study included a test of a prediction that differentiates the two model classes: Is phoneme monitoring faster for targets in real words than in pseudowords, even before the word could in principle be recognized? The results indicate that this lexical advantage does occur, in accord with the predictions of interactive models. In Part 2, speech compression and expansion were used to assess the sufficiency or necessity of bottom-up evidence and of processing time in accomplishing lexical access. The results of Parts 1 and 2 suggested that in addition to the lexical effects posited by current models, sublexical activation may also play an important role. Data are presented in Part 3 that support this interpretation. Collectively, the results in the current study support interactive models of lexical processing, but require additional sublexical processes as well.

Adult↗
PubMed1993

An empirical and meta-analytic evaluation of the phoneme identification task.

Recent studies that used Ganong's (1980) identification task have produced discrepant results. The present study sought to resolve these discrepancies by examining the influence of methodological factors on phoneme identification and differences in data analysis techniques. Three factors were examined across 2 experiments: position of target phoneme, phonetic contrast, and 2 task conditions in which stimulus quality (S/N ratio) or cognitive load varied. A meta-analysis was then performed on the results from all identification studies, including the present one, in an effort to obtain additional insight on factors that influence the task. The experiments and meta-analysis identified the importance of several methodological factors in affecting identification, most notably position of the target phoneme.

Adult↗
PubMed1991

Perceptual degradation due to signal alteration: implications for auditory pattern processing.

When a passage is alternately presented to the right and left ears over headphones, perceptual processing is disrupted under certain conditions: When the signal alternation rate is approximately 3-4 cps, intelligibility is greatly reduced. Experiment 1 demonstrated that contrary to previous theorizing, the effect is not mediated by the disruption of syllabic units. Experiment 2 explored the generality of the perceptual degradation by testing perception of simple piano melodies. The basic effect holds for these complex auditory patterns. The final experiment tested a source-effect explanation of the phenomenon by using 3 signal locations (right, middle, and left) rather than 2. The degree of disruption depends on the likelihood that sounds are assigned to different sources. Together, the experiments help to account for the strikingly selective breakdown in perceptual processing and speak to the issues of perceptual units, domain specificity, and auditory source assignment.

Attention↗
PubMed1991

A further examination of attentional effects in the phonemic restoration illusion.

Models of how listeners understand speech must specify the types of representations that are computed, the nature of the flow of information, and the control structures that modify performance. Three experiments are reported that focus on the control processes in speech perception. Subjects in the experiments tried to discriminate stimuli in which a phoneme had been replaced with white noise from stimuli in which white noise was merely superimposed on a phoneme. In the first two experiments, subjects practiced the discrimination for thousands of trials but did not improve, suggesting that they have poor access to low-level representations of the speech signal. In the third experiment, each (auditory) stimulus was preceded by a visual cue that could potentially be used to focus attention in order to enhance performance. Only subjects who received information about both the identity of the impending word and the identity of the critical phoneme showed enhanced discrimination. Other cues, including syllabic plus phonemic information, were ineffective. The results indicate that attentional control of processing is difficult but possible, and that lexical representations play a central role in the allocation of attention.

Adult↗
PubMed1990

The use of rhythm in attending to speech.

Three experiments examined attentional allocation during speech processing to determine whether listeners capitalize on the rhythmic nature of speech and attend more closely to stressed than to unstressed syllables. Ss performed a phoneme monitoring task in which the target phoneme occurred on a syllable that was either predicted to be stressed or unstressed by the context preceding the target word. Stimuli were digitally edited to eliminate the local acoustic correlates of stress. A sentential context and a context composed of word lists, in which all the words had the same stress pattern, were used. In both cases, the results suggest that attention may be preferentially allocated to stressed syllables during speech processing. However, a normal sentence context may not provide strong predictive cues to lexical stress, limiting the use of the attentional focus.

Adult↗
PubMed1990

The role of knowledge-based expectations in music perception: evidence from musical restoration.

The perceptual restoration of musical sounds was investigated in 5 experiments with Samuel's (1981a) discrimination methodology. Restoration in familiar melodies was compared to phonemic restoration in Experiment 1. In the remaining experiments, we examined the effect of expectations (generated by familiarity, predictability, and musical schemata) on musical restoration. We investigated restoration in melodies by comparing familiar and unfamiliar melodies (Experiment 2), as well as unfamiliar melodies varying in tonal and rhythmic predictability (Experiment 3). Expectations based on both familiarity and predictability were found to reduce restoration at the melodic level. Restoration at the submelodic level was investigated with scales and chords in Experiments 4 and 5. At this level, key-based expectations were found to increase restoration. Implications for music perception, as well as similarities between restoration in music and speech, are discussed.

Adult↗
PubMed1989

Insights from a failure of selective adaptation: syllable-initial and syllable-final consonants are different.

Selective adaptation with a syllable-initial consonant fails to affect perception of the same consonant in syllable-final position, and vice versa. One account of this well-replicated result invokes a cancellation explanation: with the place-of-articulation stimuli used, the pattern of formant transitions switches according to syllabic position, allowing putative phonetic-level effects to be opposed by putative acoustic-level effects. Three experiments tested the cancellation hypothesis by preempting the possibility of acoustic countereffects. In Experiment 1, the test syllables and adaptors were /r/-/l/CVs and VCs, which do not produce cancelling formant patterns across syllabic position. In Experiment 2, /b/-/d/ continua were used in a paired-contrast procedure, believed to be sensitive to phonetic, but not acoustic, identity. In Experiment 3, cross-ear adaptation, also believed to tap phonetic rather than acoustic processes, was used. All three experiments refuted the cancellation hypothesis. Instead, it appears that the perceptual process treats syllable-initial consonants and syllable-final ones as inherently different. These results provide support for the use of demisyllabic representations in speech perception.

Attention↗
PubMed1988

Central and peripheral representation of whispered and voiced speech.

Whispered speech is very different acoustically from normally voiced speech, yet listeners appear to have little trouble perceiving whispered speech. Two selective adaptation experiments explored the basis for the common perception of whispered and voiced speech, using two synthetic /ba/-/wa/ continua (one voiced, and one whispered). In the first experiment the endpoints of each series were used as adaptors, along with several nonspeech adaptors. Speech adaptors produced reliable labeling shifts of syllables matching in periodicity (i.e., whispered-whispered or voiced-voiced); somewhat smaller effects were found with mismatched periodicity. A periodic nonspeech tone with short rise time (the "pluck") produced adaptation effects like those for /ba/. These shifts occurred for whispered test syllables as well as voiced ones, indicating a common abstract level of representation for voiced and whispered stimuli. Experiment 2 replicated and extended Experiment 1, using same-ear and cross-ear adaptation conditions. There was perfect cross-ear transfer of the nonspeech adaptation effect, again implicating an abstract level of representation. The results support the existence of two levels of processing for complex acoustic signals. The commonality of whispered and voiced speech arises at the second, abstract level. Both this level, and the earlier, more directly acoustic level, are susceptible to adaptation effects.

Attention↗
PubMed1986

Attention within auditory word perception: insights from the phonemic restoration illusion.

Phonemic restoration is a powerful auditory illusion that arises when a phoneme is removed from a word and replaced with noise, resulting in a percept that sounds like the intact word with a spurious bit of noise. It is hypothesized that the configurational properties of the word impair attention to the individual phonemes and thereby induce perceptual restoration of the missing phoneme. If so, this impairment might be unlearned if listeners can process individual phonemes within a word selectively. Subjects received training with the potentially restorable stimuli (972 trials with feedback); in addition, the presence or absence of an attentional cue, contained in a visual prime preceding each trial, was varied between groups of subjects. Cuing the identity and location of the critical phoneme of each test word allowed subjects to attend to the critical phoneme, thereby inhibiting the illusion, but only when the prime also identified the test word itself. When the prime provided only the identity or location of the critical phoneme, or only the identity of the word, subjects performed identically to those subjects for whom the prime contained no information at all about the test word. Furthermore, training did not produce any generalized learning about the types of stimuli used. A limited interactive model of auditory word perception is discussed in which attention operates through the lexical level.

Attention↗
PubMed1986

Recency and suffix effects in serial recall of musical stimuli.

Auditory presentation of verbal items leads to larger recency effects in recall than visual presentation. This enhanced recency can be eliminated if a stimulus suffix (an irrelevant sound) follows the last item. Four experiments tested the hypothesis that recency and suffix effects in serial recall result from a speech-specific process. It was demonstrated that serial recall of musical notes played on a piano exhibited substantial recency effects. These recency effects were reduced when the list items were followed by either a piano chord or the word start. However, a white-noise suffix had no effect on recency. This pattern of data is consistent with current work on auditory perception and places constraints on theories of recency and suffix effects.

Adolescent↗
PubMed1984

More adaptation of speech by nonspeech.

Three experiments tested Samuel and Newport's (1979) hypothesis that the perceptual system sorts its input on the basis of its spectral quality (periodic vs. aperiodic). In Experiment 1, repeated presentation of a shaped white-noise segment (aperiodic) produced a labeling shift on a /ja-za/ continuum (primarily aperiodic); two periodic adaptors produced no effect, supporting Samuel and Newport's hypothesis. The second experiment replicated these results and showed that the nonspeech adaptor produced almost as much adaptation as the test series' endpoint /za). In addition, using several mixtures of periodic and aperiodic adaptors indicated that the aperiodic component dominates adaptation effects for /ja-za/. A final experiment, using a similarity rating task, confirmed that subjects group /za/ with unvoiced fricatives rather than with other voiced consonants. The results thus indicate that the perceptual system is sensitive to whether the input is primarily periodic or aperiodic, regardless of whether it is speech or nonspeech.

Adaptation, Physiological↗
PubMed1984

Which syllable does an intervocalic stop belong to? A selective adaptation study.

Three selective adaptation experiments were conducted to investigate whether intervocalic stops are perceived as the end of the preceding syllable or as the beginning of the following one. The pattern of adaptation effects (and just as importantly, noneffects) indicated that intervocalic stop consonants are perceptually more like syllable-initial than syllable-final ones. From this it might be concluded that the perceptual system breaks down a vowel-consonant-vowel (VCV) utterance into a V-CV sequence. However, the similarity of an intervocalic stop to a syllable-initial one is quite limited; the consonant in a VCV is apparently treated as essentially different from consonants in either VC or CV utterances. These results clarify, and perhaps complicate, the role of the syllable in models of the speech perception process.

Adaptation, Physiological↗
PubMed1983

Perception of intervocalic stop consonants: the contributions of closure duration and formant transitions.

Acoustic analyses of vowel-consonant-vowel (VCV) utterances indicate that they generally include formant transitions from the first vowel into a period of closure (VC transitions), and transitions out of the closure into the second vowel (CV transitions). Three experiments investigated the perceptual importance of the VC transitions, the CV transitions, and the closure period in identification of medial stop consonants varying in place of articulation. Experiment 1 compared identification of members of synthetic VC and CV continua with those from VCV series made by concatenating corresponding VC and CV stimuli using various closure durations. Experiment 2 examined identification of VCV stimuli constructed with only VC, only CV, or both VC and CV transitions; again closure duration was systematically varied. Experiment 3 correlated CV and VC identification with identification of VCV stimuli. Neither closure duration nor formant transition structure (i.e., only VC, only CV, or both) had an independent effect on identification. Instead, the formant structure and closure duration together strongly affected stop identification. When both VC and CV transitions were present, the CV transitions contributed somewhat more to identification of medial stops with short closures, than the VC transitions did. With longer closure durations, neither set of transitions appeared to determine perceived place of articulation in any simple way. Overall, the data indicate that the perception of a medial consonant is more than simply a (weighted) sum of its parts.

Humans↗
PubMed1982

Length effects in word perception: we is better than i but worse than you or them.

Under tachistoscopic viewing conditions letters are better reported if they are presented as part of a word than if they are presented in isolation. Several recent theories attribute this word advantage to the influence of lexical representations. The present study replicated Wheeler's finding that the words I and A do not have the same advantage as other words, despite their lexical status. This result holds even under conditions designed to influence subjects to process I and A as words. The poor performance on these single-letter words was shown to be a manifestation of a more general length effect: Recognition of briefly presented words improves with increasing length (up to three or four letters). The perceptual advantage for longer words was not found for closely matched strings of unrelated letters. The strength and robustness of the word-length effect suggest that theories of the word advantage must include mechanisms that are length dependent.

Adolescent↗
PubMed1982

Phonetic prototypes.

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Adaptation, Physiological↗