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Biomedical subjects

R G Whittaker

Publications and source records attributed to R G Whittaker.

32 records · Page 2Linked to original sources
PubMed1980

Dichotic and monotic masking of CV's by CV second formants with different transition starting values.

Listeners were asked to identify ambiguous and unambiguous stop-vowel targets placed in monotic and dichotic competition with second formants (bleats) from voiced consonant-vowel (CV) syllables lying along a place-of-articulation continuum. Target performance varied with bleat-continuum position as well as bleat intensities. In cases where target errors occurred, either dichotically or monotically, they reflected predominantly the place cue of the bleat. This result, like that of previous studies, suggests the dominance of target or bleat reflects the relative "salience" of the two signals' cues. Differences were seen between monotic and dichotic conditions in the rate of change in performance with bleat intensity and continuum position. The rate of monotic performance change was a more precipitous (higher slope) function of these variables than was dichotic performance. This difference was interpreted as suggesting that monotic interference includes a peripheral masking component which is sensitive to the relative spectral energies of target and bleat. Dichotic effects, in contrast, seem to primarily reflect the operation of (central) processes which grant different perceptual weights to signals' cues depending on their intensity-dependent saliences. The observation that ambiguity, per se, of the targets (or the CV's from which the bleats were extracted) played little role in predicting results, was interpreted as reflecting a primarily prephonetic (i.e., auditory) locus for both monotic and dichotic interactions.

Humans↗
PubMed1979

Ear dominance in perception of dichotic chords: pure tones versus tone glides.

Pitch judgments for dichotic chords composed of two pure tones often show a bias in favor of the chord-component going to one ear. This "ear-advantage for pitch" (EAP) varies between subjects, but is very stable within subject and is thought to reflect differences in spectral "sensitivity" of the two auditory pathways. The present study explored this hypothesis by examining pitch judgments of complexes composed of tones dichotically paired with frequency-varying signals. The direction and strength of EAP was first established using pure tones, then rising tone glides were introduced into the channel going to thenondominant ear. Since a glide possesses less energy at a given frequency than a pure tone of equal duration, an increase in EAP was expected. An increase in EAP was consistently observed for only one subject; three subjects showed small, variable effects; and six subjects displayed a decrease in EAP. The results suggested that factors other than relative spectral sensitivity affect observed EAP.

Acoustic Stimulation↗
PubMed1975

Studies on monotreme proteins. VI. Amino acid sequence of the beta-chain of haemoglobin from the platypus, Ornithorhynchus anatinus.

The amino acid sequence of the 146 residues of the beta-chain of the major haemoglobin from the platypus has been determined. The soluble peptides derived from the chain by tryptic digestion were isolated by paper ionophoresis and chromatography. The amino acid sequences were determined by the dansyl-Edman procedure or by further digestion with other enzymes. The tryptic peptides were aligned by homology with other beta-globins. There were 14 changes in sequence compared with echidna beta-chain. The number of changes in sequence compared with human beta-chain is 34 which is less than the 39 changes between human and platypus alpha-chains. Generally there are more changes between beta-chains; there are only three other examples reported where there are more changes between alpha-chains than beta-chains, these are of echidna, rabbit and dog globins. By comparison with the 'contact sites' in horse haemoglobin there is one change in beta-haem contacts, three changes in beta1-alpha1 contacts and no changes in beta2-alpha1 contacts. The date of divergence of the monotremes from the other mammals was estimated at 132 +/- 33 million years, based on the number of amino acid differences between species and allowing for multiple mutations during the evolutionary period. This estimate differs widely from the estimate given by similar treatment of the alpha-chain sequences and the significance of this discrepancy to the validity of the method is discussed.

Amino Acid Sequence↗
PubMedDate not supplied

Hydrophobicity indices for amino acid residues as determined by high-performance liquid chromatography.

The retention times of compounds on reversed-phase high-performance liquid chromatography columns are determined by their overall hydrophobicity. This paper exploits this relationship to derive hydrophobicity indices for amino acid residues. Retention times of 20 Z-amino acids and their methyl, ethyl and benzyl esters were determined under standard conditions on reversed-phase high-performance liquid chromatography at pH 3.0 and pH 7.5. Retention times of derivatives of six of the amino acids were used to calculate amino acid residue hydrophobicity values relative to glycine and leucine by a computer-based iterative procedure that used splines to optimize the smoothness of fit. Using these derived curves, values for each derivative of the remaining 14 Z-amino acids were determined and averages calculated. The curves, generated independently for pH 3.0 and pH 7.5 were effectively identical and the determined hydrophobicity values (other than for charged residues) were also similar at the two pHs. The values obtained vary significantly from other published values. Comparisons with some of the more commonly used hydrophobicity/hydropathy tables are presented. The highest correlation was found with constants determined for water/octanol partitioning of N- and C-terminal protected amino acids.

Amino Acids↗
PubMedDate not supplied

A gentle method for linking Tris to amino acids and peptides.

A gentle method for the addition of Tris to the carboxyl group of amino acids or peptides for the purpose of altering their solubility and/or for providing sites for further derivatization is described. Under mild alkaline conditions and in high concentrations of aqueous dimethylformamide, the amino group of Tris cleaves simple esters of N-protected amino acids or peptides to form an amino acid-Tris linkage. The effects of pH, temperature and dimethylformamide concentration on the rate and the efficiency of the reaction of Tris with benzyloxycarbonyl-alanine methyl ester were examined and the general applicability of the method demonstrated on a range of amino acid and small peptide substrates. Side-chain protection was not required and the degree of racemization was found to be lower than with conventional chemical coupling.

Amino Acid Sequence↗