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P Howell

Publications and source records attributed to P Howell.

At least 19 recordsLinked to original sources
PubMed1992

Acoustic analysis and perception of vowels in children's and teenagers' stuttered speech.

The syllable repetitions of 24 child and eight teenage stutterers were investigated to assess whether the vowels neutralize and, if so, what causes this. In both groups of speakers, the vowel in CV syllable repetitions and the following fluent vowel were excised from conversational speech samples. Acoustic analyses showed the formant frequencies of vowels in syllable repetitions to be appropriate for the intended vowel and the duration of the dysfluent vowels to be shorter than those of the fluent vowels for both groups of speakers. The intensity of the fluent vowels was greater than that of the dysfluent vowels for the teenagers but not the children: For both age groups, excitation waveforms obtained by inverse filtering showed that the excitation spectra associated with dysfluent vowels fell off more rapidly with frequency than did those associated with the fluent vowels. The fundamental frequency of the children's dysfluent speech was higher than their fluent speech while there was no difference in the teenager's speech. The relationship between the intensities of the glottal volume velocities was the same as that of the speech waveforms. Perceptual tests were also conducted to assess whether duration and the differences found in the source excitation would make children's vowels sound neutral. The experiments show that in children neither vowel duration nor fundamental frequency differences cause the vowels to be perceived as neutral. The results suggest that the low intensity and characteristics of the source of excitation which cause vowels to sound neutral may only occur in late childhood. Furthermore, monitoring stuttered speech for the emergence of neutral vowels may be a way of indexing the progress of the disorder.

Adolescent↗
PubMed1991

The use of prosody in highlighting alterations in repairs from unrestricted speech.

A speaker has several ways in which he or she may highlight the fact that an error or imprecision of speech has been made and subsequently altered. The three principal ones are by signalling through the structure of the speech that surrounds the error (the repair-syntax), by the use of prosody, and through the semantic content. The role of prosody in the correction process is investigated in the current studies. Analysis of the prosody of a number of errors and their alterations drawn from unrestricted speech are reported. The analysis shows that pauses occur at the moment of interruption and that an increase in stress occurs at the start of the alteration. Pauses could indicate the moment of interruption, and stress could highlight what has been altered. Two sets of perceptual experiments were carried out to assess whether these cues are salient for listeners who hear constructions containing an error and its alteration. Two paradigms were employed in each set of experiments: (1) direct judgement about the comprehensibility of sentences containing errors and alterations, and (2) repeating a message that had an error and alteration without the error. The effects of stress and pauses on (Experiments 1A and 1B) or pauses around (Experiment 2A and 2B) the alterations were assessed. In the first set of experiments it was shown that pauses and stress help listeners process repairs. When a word is spoken in error, the speaker may repeat a section of speech immediately preceding the alteration and/or a section immediately following that word. Inclusion of these repeated sections allows assessment of whether pauses signal where the interruption occurred. The second experiment shows that the placing of the pause before the retrace, rather than at other locations, indicates to listeners where the repair starts.

Adult↗
PubMed1990

Comparison of four local extradural anaesthetic solutions for elective caesarean section.

We have examined a combination of two local anaesthetics to see if the resultant solution is superior to the agents individually. This study shows that a mixture of bupivacaine and lignocaine provided an excellent alternative to bupivacaine alone, and was superior to 2% lignocaine with adrenaline for elective Caesarean section. By reducing the dose of bupivacaine used, the combination may reduce the risk of cardiotoxicity.

Adult↗
PubMed1990

Comparison of false-positive reactions in direct-binding anti-HIV ELISA using cell lysate or recombinant antigens.

In a 2-year study of false-positive anti-HIV-1 tests in blood donors at Manchester and Lancaster Blood Banks, the reactions associated with a HIV-infected cell lysate antigen were compared with those using recombinant-antigen-based tests. In year 1 (cell lysate test) at Manchester BTS 0.21% of 119.178 donations were repeatedly reactive, compared with 0.53% of 119,004 donations in year 2 (recombinant antigen). Reactive sera were tested at Manchester PHL by three different immunoassays. Referred specimens were classified as anti-HIV positive (95-100% reactive in all the assays), equivocal or negative (negative results in all three immunoassays). Two donors were confirmed to be anti-HIV positive over the 2-year period. Most sera were negative by confirmatory immunoassays in years 1 and 2. In year 1, a study of 60 referred sera with sex- and age-matched controls showed high correlation between a reactive anti-HIV-1 screening test and indeterminate anti-HIV-1 patterns on Western blot showing reactions with HIV gag-coded proteins. In year 2, less than 10% of referred sera were reactive by Western blot, and there was no correlation between a reactive screening anti-HIV test, the strength of signal in the test or a reactive Western blot. Follow-up showed that donors whose sera were reactive in years 1 and 2 by the anti-HIV-1 screening test formed almost two different populations. Four donors with equivocal anti-HIV-1 confirmatory tests had anti-HIV 'envelope' reactions.(ABSTRACT TRUNCATED AT 250 WORDS)

Blotting, Western↗
PubMed1990

Correlation of monocyte-monolayer assay results, number of erythrocyte-bound IgG molecules, and IgG subclass composition in the study of red cell alloantibodies other than D.

Comparisons have been made between the serological and immunological characteristics of 42 blood group alloantibodies (other than D) covering twelve systems using a monocyte-monolayer assay (MMA), a radiometric antiglobulin test for antibody binding and IgG subclass determinations. The results of the MMA correlated well with the level of IgG molecules bound on incompatible cells, and the highest levels in both cases were associated with the presence of the IgG3 subclass. However, limited clinical data shows that, while in general the MMA clearly identifies the clinically significant antibodies, the correlation with the degree of clinical outcome is less well defined, and in some instances other factors may be operating to ameliorate the in vivo effect of the antibody.

Antibody Specificity↗
PubMed1990

Analysis of periodic and aperiodic components during fluent and dysfluent phases of child and adult stutterers' speech.

The syllable repetitions of 6 child and 6 adult stutterers were investigated to establish whether dysfluent speech had a higher noise-to-signal ratio than fluent speech and whether this differed between children and adults. As predicted, the stuttered speech had a higher noise level for both age groups. During dysfluencies, the level of the noise components in the children's speech was higher than in the adults.

Adult↗
PubMed1990

An electrical network model of inertially induced bone-conducted sound.

A model for the description of inertially induced bone-conducted sound has been developed and a discussion of the appropriate techniques for its representation as an electrical network is described. Predictions are made for the sound pressure produced in the meatus in the cases of normal ears and pathological ears resulting from vibration applied to the skull. Evidence from this modelling suggests that the technique may provide improved discriminability over conventional immitance measurements for some types of pathology.

Acoustics↗
PubMed1989

Serological and immunological characteristics of maternal anti-Rh(D) antibodies in predicting the severity of haemolytic disease of the newborn.

A number of factors were analyzed for their predictive value in indicating the severity of haemolytic disease of the newborn (HDN) in 72 infants. The factors investigated were: maternal antibody titre in the indirect antiglobulin test, the number of antibody molecules on sensitized standard red cells evaluated by a radiometric antiglobulin test, the IgG subclass specificity and the reactivity in monocyte-monolayer assay (MMA) and in the rosette assays with lymphocytes and granulocytes from healthy individuals. The results of the MMA correlate much better with the severity of HDN than the antibody titre. In clinically unaffected infants the reactivity in the MMA never exceeded 20%, while in the severe/very severe group it was always greater than 20% (in 95% of very severe cases even above 50%). The number of IgG-bound molecules was also shown to closely correlate with the clinical severity and there was a much greater proportion of severe/very severe cases exhibiting combined IgG1 and IgG3 specificity. Of all the evaluations performed the rosette assays with lymphocytes and granulocytes were found to be less useful in predicting the severity of HDN.

Erythroblastosis, Fetal↗
PubMed1989

Jaw movement and bone-conduction in normal listeners and a unilateral hemi-mandibulectomee.

Relative movement between the mandible and skull may compress the auditory meatus and produce an excess sound in the ear canal. To test this, measurements of sound pressure in the ear canal, and movement of the upper and lower jaw are reported on normal subjects and a unilateral hemi-mandibulectomee. On the side the unilateral hemi-mandibulectomee has a jaw and in the subjects with normal jaws, the data confirm that mandible-movement relative to the skull produces sound in the ear canal. The excess sound in the ear canal when the jaw is free to move independently of the skull can be predicted from the relative movement between them.

Bone Conduction↗
PubMed1988

The contribution of the excitatory source to the perception of neutral vowels in stuttered speech.

The vowel in part-word repetitions in stuttered speech often sounds neutralized. In the present article, measurements of the excitatory source made during such episodes of dysfluency are reported. These measurements show that, compared with fluent utterances, the glottal volume velocities are lower in amplitude and shorter in duration and that the energy occurs more towards the low-frequency end of the spectrum. In a first perceptual experiment, the effects of varying the amplitude and duration of the glottal source were assessed. The glottal volume velocity recordings of the /ae/ vowels used in the analyses were employed as driving sources for an articulatory synthesizer so that judgments about the vowel quality could be made. With dysfluent glottal sources (either as spoken or by editing a fluent source so that it was low in amplitude and brief), the vowels sounded more neutralized than with fluent glottal sources (as spoken or by editing a dysfluent source to increase its amplitude and lengthen it). In a second perceptual experiment, synthetic glottal volume velocities were used to verify these findings and to assess the influence of the low-frequency emphasis in the dysfluent speech. This experiment showed that spectral bias and duration both cause stuttered vowels to sound neutralized.

Adult↗
PubMed1988

Assessment of sound in the ear canal caused by movement of the jaw relative to the skull.

To assess whether or not the reduction of threshold to bone-conducted sound on occlusion of the ears (the occlusion effect) is due to compression of the auditory meatus by the jaw, measurements of movement of the skull and mandible and sound in the ear canal are reported from four subjects. The change in bone-conducted sound in the ear canal was also measured when the mandible was moved out and in (presenting more or less of the mandible to compress the auditory meatus) and when vibration was applied directly to the mandible. Sound pressure increased when the jaw was moved out and when vibration was applied to the mandible.

Air Pressure↗
PubMed1986

Segmentation and speech perception in relation to reading skill: a developmental analysis.

The present paper examines the processing of speech by dyslexic readers and compares their performance with that of age-matched (CA) and reading-ability-matched (RA) controls. In Experiment 1, subjects repeated single-syllable stimuli (words and nonwords) presented either in a favorable signal-to-noise ratio or with noise masking. Noise affected all subjects to the same extent. Dyslexic children performed as well as controls when repeating high-frequency words, but they had difficulty relative to CA-controls with low-frequency words and relative to both CA- and RA-controls when repeating nonwords. In Experiments 2 and 3, subjects made auditory lexical decisions about the stimuli presented in Experiment 1. Dyslexics performed less well than CA-controls, gaining similar scores to RA-controls. Thus, their difficulty in repeating low-frequency words could be reinterpreted as a difficulty with nonword repetition. Taken together, these results suggest that dyslexics have difficulty with the nonlexical procedures (including phoneme segmentation) involved in verbal repetition. One consequence is that they take longer to consolidate "new" words; verbal memory and reading processes are also compromised.

Child↗