Biomedical subjects

T L Johnson

Publications and source records attributed to T L Johnson.

At least 91 records · Page 5Linked to original sources

PubMed1983

Dynamic specification of coarticulated vowels.

An adequate theory of vowel perception must account for perceptual constancy over variations in the acoustic structure of coarticulated vowels contributed by speakers, speaking rate, and consonantal context. We modified recorded consonant-vowel-consonant syllables electronically to investigate the perceptual efficacy of three types of acoustic information for vowel identification: (1) static spectral "targets," (2) duration of syllabic nuclei, and (3) formant transitions into and out of the vowel nucleus. Vowels in /b/-vowel-/b/ syllables spoken by one adult male (experiment 1) and by two females and two males (experiment 2) served as the corpus, and seven modified syllable conditions were generated in which different parts of the digitized waveforms of the syllables were deleted and the temporal relationships of the remaining parts were manipulated. Results of identification tests by untrained listeners indicated that dynamic spectral information, contained in initial and final transitions taken together, was sufficient for accurate identification of vowels even when vowel nuclei were attenuated to silence. Furthermore, the dynamic spectral information appeared to be efficacious even when durational parameters specifying intrinsic vowel length were eliminated.

Female↗

PubMed1982

Interaction of formamidines with the platelet 5-hydroxytryptamine uptake system.

1. The activity of the insecticide/acaricide N'-(4-chloro-o-tolyl)-N,N-dimethylformamidine (chlordimeform), its two formamidine metabolites, N'-(4-chloro-o-tolyl)-N-methylformamidine (demethylchlordimeform) and N'(4-chloro-o-tolyl) formamidine (didemethylchlordimeform), and 116 other formamidines and related compounds as inhibitors of rat platelet 5-hydroxytryptamine (5-HT) uptake was studied. Though several formamidines were more active than chlordimeform (pI50 3.9), none was as potent as imipramine. Didemethylchlordimeform (pI50 4.4) was the most potent formamidine examined. 2. Inhibition of 5-HT uptake by chlordimeform was mixed. Moreover, chlordimeform inhibition of 5-HT uptake by reserpinized platelets was not significantly different from uptake by non-reserpinized platelets. 3. Chlordimeform and its two formamidine metabolites caused release of platelet 5-HT, and their potency as releasers paralleled their activity as uptake inhibitors. 4. Electron microscopy indicated that chlordimeform treatment changed platelet shape and size but apparently did not alter physical integrity of the membrane. 5. It was suggested that platelet 5-HT storage vesicles were the most probable site of formamidine action.

Amidines↗

PubMed1982

Perceptual constancy of vowels in rapid speech.

In three experiments, we investigated the role of extrasyllabic speech context in the identification of /t/-vowel-/t/ syllables spoken at normal and rapid rates of articulation. Syllables spoken at the normal rate were identified with at least 95% accuracy regardless of the context in which they were presented. However, in experiment I, intrinsically long vowels in rapidly articulated syllables were identified with greater accuracy when the syllables were presented in rapid-rate sentence context than when they were presented in isolation or in normal-rate sentence context. Experiment II revealed that part of the performance deficit for excised isolated rapid syllables was attributable to sequential order effects among test items, and to listeners' assumptions about whether the test syllables were or were not produced in isolation. In experiment III, test syllables were presented in the context of extracted portions of the rapid carrier sentences to determine the locus of the extrasyllabic information for vowel identity. The presence of the stressed syllable which immediately followed the test syllables in the carrier sentence was especially important for accurate identification of intrinsically long vowels in rapidly articulated syllables. Results are discussed in terms of intrinsic timing theories of speech production.

Cues↗

PubMed1981

Inhibition of rat platelet 5-hydroxytryptamine uptake by chlordimeform.

Chlordimeform, a formamidine insecticide and acaricide, and two of its toxic N-demethyl metabolites inhibited rat blood platelet 5-hydroxytryptamine (5-HT) uptake. A direct relationship existed between formamidine uptake inhibitory potency and N-demethylation. Didemethylchlordimeform, the most potent formamidine inhibitor of 5-HT uptake examined, had a pI50 of 4.2. However, it was appreciably less active than the classical inhibitor imipramine, which yielded 86.4% inhibition of 5-HT uptake at a concentration of 1.10(-5) M.

Amidines↗

PubMed1981