Biomedical subjects

M J Collins

Publications and source records attributed to M J Collins.

At least 55 records · Page 3Linked to original sources

PubMed1993

Measuring the strength of auditory fusion for synchronously and nonsynchronously fluctuating narrow-band noise pairs.

This experiment examines the "strength" of auditory fusion for narrow-band noise pairs. Each pair of noise bands consisted of a target band and a flanker band presented simultaneously. The temporal envelopes of the noise bands within a pair fluctuated either in synchrony (synchronous condition) or not in synchrony (nonsynchronous condition). Each noise-band pair was alternated rapidly with a noise band (captor band) presented alone. The duration of the silent period between a noise-band pair and a captor band [i.e., onset-to-onset interval (OTO)] was decreased by listeners until auditory fusion of the pair was disrupted by capturing the target band into a sequential-stream with the captor band. Results showed that listeners required significantly shorter OTOs to capture the target bands from the synchronous pairs than from the nonsynchronous pairs, suggesting that strength of auditory fusion was greater for the noise bands that fluctuated in synchrony than for those that did not. The results of this experiment are discussed relative to hypotheses based on auditory stream segregation to explain auditory phenomena such as comodulation detection difference, modulation detection interference, and comodulation masking release.

Acoustics↗

PubMed1993

A clinical and immunologic study of workers with trimellitic-anhydride-induced immunologic lung disease after transfer to low exposure jobs.

The objective of the study was to determine the clinical and immunologic status of trimellitic anhydride (TMA) workers who have had immunologic lung diseases and who have been moved to lower exposure jobs. Twenty-nine consecutive workers with TMA-induced immunologic lung diseases who had been moved to low exposure jobs for more than 1 yr were studied retrospectively. Pulmonary symptoms were obtained by physician-administered questionnaire. Immunologic studies were performed using radioimmunoassay. Spirometry and chest film were obtained. Workers with late asthma (LA) (n = 3), late respiratory systemic syndrome (LRSS) (n = 8), or both LRSS and asthma rhinitis (A/R) (n = 6) had improved symptoms, improved pulmonary functions, and lower total antibody against TM-HSA. Five of the 12 workers with A/R had improved symptoms, improved pulmonary functions, and lower IgE against TM-HSA, whereas seven continued to have moderate to severe symptoms, abnormal pulmonary functions, and elevated IgE against TM-HSA. There were no chest film findings in any group that were definitely attributed to TMA. Although TMA workers with LA or LRSS improve when moved to lower exposure jobs, only half of workers with A/R improve; elevated IgE against TM-HSA appears to be a marker for the subpopulation of workers with A/R that does not improve.

Adult↗

PubMed1992

Chromatic aberration and optical power of a diffractive bifocal contact lens.

Although diffractive contact lenses have been well documented in theory, no definitive experimental data have been reported which confirm that the near image is in fact created by diffraction rather than by refraction. We have tested the diffraction hypothesis for one type of diffractive contact lens (the Hydron Echelon bifocal) experimentally by measuring its longitudinal chromatic aberration in isolation and when worn on the eye. The basis of this test is that, according to theory, diffractive lenses should have chromatic aberration which is opposite in sign to that measured for the eye. Objective measurements of chromatic aberration were made with a focimeter when the lens was in a wet cell. Subjective measurements were made with a Badal optometer when the lens was worn on the eye. Four control experiments were conducted to provide baseline measurements of the eye's chromatic aberration, against which we compared the results obtained for the diffractive contact lens. The data were also compared with conventional measurements of refractive error obtained by standard subjective techniques and by an automated infrared refractor. Our results showed that the longitudinal chromatic aberration of the diffraction image of the Echelon bifocal lens was about one-half that obtained under the four control conditions: for the naked eye, for the nondiffraction image of the Echelon lens, or for either image of a refractive bifocal contact lens (CIBA Bisoft). These results are consistent with the theoretical prediction that the negative chromatic aberration of a diffractive contact lens should partially cancel the positive chromatic aberration of the human eye.(ABSTRACT TRUNCATED AT 250 WORDS)

Color Perception↗

PubMed1992

The effects of perceived motion on sound-source lateralization.

Lateralization of dichotic click pairs differing in time of onset was studied under conditions of angular acceleration, optokinetic stimulation, and gaze fixation. Data obtained from 20 subjects with normal hearing indicate poorer left-right judgment performance for small time differences, as well as shifts in subjective simultaneity, for all experimental conditions relative to control conditions. In addition, response times increased for the experimental conditions. The results suggest that real or apparent motion may affect an individual's ability to process one of the major cues for sound-source localization--binaural time difference--under conditions similar to those encountered in vehicular motion.

Acceleration↗

PubMed1992

Tolerance to spherical aberration induced by rigid contact lenses.

We have investigated the effects of spherical aberration (SA) on visual performance by fitting subjects with rigid lenses of varying front surface asphericity. Three pairs of lenses were worn by each subject with front surface asphericities of Q = 0 (conventional spherical surface), Q = -0.26 (similar to the average corneal asphericity) and Q = -0.51. The calculated average change in spherical aberration induced by each pair of contact lenses in photopic conditions was +0.02 D (Q = 0), -0.49 D (Q = -0.26) and -0.94 D (Q = -0.51). In mesopic conditions these same lenses induced an average change in spherical aberration of +0.01 D (Q = 0), -1.18 D (Q = -0.26) and -2.16 D (Q = -0.51). In this double-blind study, 12 adapted, low to moderate myopic rigid lens wearers wore each pair of lenses for one week and noted visual performance. With each pair of lenses we also measured the subject's visual acuity with high and low contrast logMAR charts. All measurements were conducted using the right eye at distance in photopic and mesopic conditions. When forced to select the lenses they would accept as compensation for participation in the study, most subjects (9 out of 12) chose the Q = 0 lenses, 3 subjects those the Q = -0.26 lenses and none of the subjects chose the Q = -0.51 lenses. Visual performance measures showed little difference between the Q = 0 and Q = -0.26 lenses. However, the Q = -0.51 lenses significantly reduced visual acuity in mesopic conditions with the low contrast acuity chart.

Contact Lenses↗

PubMed1992

Regional variations in binocular summation across the visual field.

Binocular summation for a contrast detection task was measured as a function of eccentricity and target size along the horizontal and vertical meridians for ten young normal subjects. Binocular summation at the fovea was of the order of 1.4 for all target sizes, although there was some intersubject variation. Binocular summation was highest along the vertical meridian. With increasing eccentricity from the fovea, binocular summation for target size I (0.108 degrees projected diameter) decreased, remained relatively constant for target size III (0.431 degrees projected diameter) and increased with increasing eccentricity from the fovea for target size V (1.724 degrees projected diameter). For target sizes I and III, binocular summation was present only when interocular differences in sensitivity were under 5 dB, for target size V this relationship did not hold. Influences such as stimulation of corresponding retinal points and cortical representation are considered.

Adult↗

PubMed1991

Resolution of the four hemes of cytochrome c554 from Nitrosomonas europaea by redox potentiometry and optical spectroscopy.

The electrochemical behavior of tetraheme cytochrome c554 from Nitrosomonas europaea has been studied by thin-layer spectroelectrochemistry, cyclic voltammetry, differential pulse voltammetry, and alternating current voltammetry. Three redox couples were detected. Midpoint potentials for the high-m intermediate-, and low-potential couples are +47, -147, and -276 mV, respectively, from the spectroelectrochemical measurements and +50, -120, and -225 mV, respectively, from the voltammetry measurements. A coulometric titration shows that two electrons are taken up by the high-potential couple and one each is taken up by the intermediate- and low-potential couples. Results from the spectroelectrochemical titration at carefully chosen wavelengths indicate that the intermediate- and low-potential couples obey simple Nernstian behavior. The electrochemical behavior of the high-potential couple is apparently not truly Nernstian but is most consistent with two sites exhibiting slight positive cooperativity. Spectral changes associated with the three couples reveal distinctive features in the reduced-minus-oxidized difference spectra. The difference spectrum of the high-potential pair of hemes suggest a mixture of a high-spin heme and a low-spin heme with maxima at 424 and 432 nm. The difference spectrum of the intermediate-potential heme is low spin with a split Soret with maxima at 414 and 424 nm. The difference spectrum of the low-potential heme also shows a split Soret with maxima at 418 and 432 nm.

Cytochrome c Group↗

PubMed1991

Autoradiographic localization of [125I]endothelin binding sites in human blood vessels and coronary tissue: functional correlates.

The distribution of endothelin-1 (ET-1) receptors on human vascular tissue has been studied. High- and low-resolution autoradiography was used to determine the distribution of [125]ET binding sites in human blood vessels and ventricular myocardium. Dense, displaceable [125I]ET binding was associated with cardiac myocytes and the smooth muscle layer of all vessels were examined. There was also dense binding to vasa vasora. There was increased [125I]ET binding to atheromatous coronary arteries and vein graft, which was associated with the tunica media and vasa vasora or regions of neovascularization. Vasoconstrictor and positive inotropic activity of ET-1 has been established in vitro. The vasoconstrictor effect of ET-1 is likely to be mediated via the binding sites identified on vascular smooth muscle. The striking perivascular [125I]ET-1 binding suggests that ET-1 may also have constrictor activity on vasa vasora. There is experimental evidence that ET-1 has mitogenic activity on vascular smooth muscle cells in culture. The increased binding to both smooth muscle and regions of neovascularization in atheromatous vessels suggests that ET-1 may play a role in atherosclerosis.

Adolescent↗

PubMed1991

Task variables and visual discomfort associated with the use of VDT's.

We investigated task variables that may influence the incidence of visual discomfort amongst subjects who routinely spent a proportion of their day working with visual display terminals (VDT's). A diary was kept by subjects over five consecutive working days, in which they recorded visual symptoms, the visual tasks undertaken, the amount of time spent on workbreaks, work pressure, work interest, and personal moderating factors which may have influenced the symptoms recorded. The symptoms recorded by subjects were then treated as dependent variables in multiple regression analyses with the diary findings (task-related factors) as independent variables. The incidence of some types of symptoms was significantly associated with specific categories of work tasks, personal moderating influences, work pressure, work interest, time of day, and day of week.

Adult↗

PubMed1991

Discrimination of formant transition onset frequency: psychoacoustic cues at short, moderate, and long durations.

Two experiments determined the just noticeable difference (jnd) in onset frequency for speech formant transitions followed by a 1800-Hz steady state. Influences of transition duration (30, 45, 60, and 120 ms), transition-onset region (above or below 1800 Hz), and the rate of transition were examined. An overall improvement in discrimination with duration was observed suggesting better frequency resolution and, consequently, better use of pitch/timbre cues with longer transitions. In addition, falling transitions (with onsets above 1800 Hz) were better discriminated than rising, and changing onset to produce increments in transition rate-of-change in frequency yielded smaller jnd's than changing onset to produce decrements. The shortest transitions displayed additional rate-related effects. This last observation may be due to differences in the degree of dispersion of activity in the cochlea when high-rate transitions are effectively treated as non-time-varying, wideband events. The other results may reflect mechanisms that extract the temporal envelopes of signals: Envelope slope and magnitude differences are proposed to provide discriminative cues that supplement or supplant weaker spectrally based pitch/timbre cues for transitions in the short-to-moderate duration range. It is speculated that these cues may also support some speech perceptual decisions.

Attention↗

PubMed1990

Clinician interpersonal communication skills and contact lens wearers' motivation, satisfaction, and compliance.

The relation between the practitioner and patient may have important effects upon the safety and success of contact lens wear. In this study we investigated the interrelations among clinicians' interpersonal communication skills and patients' motivation, satisfaction, and compliance with care and maintenance instructions. These variables were measured through questionnaires and interviews. Significant associations were found among many aspects of the clinicians' interpersonal skills and aspects of the patients' motivation and satisfaction. These findings are consistent with those from other health care settings and indicate that the quality of the contact lens practitioner's interpersonal skills can substantially influence patient outcomes and perceptions.

Adult↗

PubMed1990

The time course of acoustic/phonemic cue integration in the sensorineurally hearing-impaired listener.

There is limited documentation available on how sensorineurally hearing-impaired listeners use the various sources of phonemic information that are known to be distributed across time in the speech waveform. In this investigation, a group of normally hearing listeners and a group of sensorineurally hearing-impaired listeners (with and without the benefit of amplification) identified various consonant and vowel productions that had been systematically varied in duration. The consonants (presented in a /haCa/ environment) and the vowels (presented in a /bVd/ environment) were truncated in steps to eliminate various segments from the end of the stimulus. The results indicated that normally hearing listeners could extract more phonemic information, especially cues to consonant place, from the earlier occurring portions of the stimulus waveforms than could the hearing-impaired listeners. The use of amplification partially decreased the performance differences between the normally hearing listeners and the unaided hearing-impaired listeners. The results are relevant to current models of normal speech perception that emphasize the need for the listener to make phonemic identifications as quickly as possible.

Adult↗

PubMed1989

Peripheral visual acuity with monovision and other contact lens corrections for presbyopia.

We have conducted two experiments to investigate the effect of monovision and other contact lens corrections for presbyopia upon peripheral visual acuity. In the first study, we measured binocular peripheral visual acuity using Landolt rings with seven subjects wearing a monovision correction. The Landolt rings were presented at eccentricities of 10, 20, 40, and 70 degrees on each side of the subject, with near additions of +1.50 D, +2.50 D, and no addition. We found no significant effect of monovision correction on peripheral visual acuity. In the second experiment we measured the peripheral visual acuity of 11 presbyopic subjects wearing distance contact lenses with lookover spectacles, soft progressive bifocal contact lenses, soft concentric bifocal contact lenses, monovision contact lenses, modified monovision contact lenses, and hard bifocal contact lenses using Koenig bar targets. There were no significant differences in peripheral visual acuity between any of the contact lens corrections for presbyopia.

Adolescent↗

PubMed1989

Contrast sensitivity with contact lens corrections for presbyopia.

We measured contrast sensitivity at three distances (330 mm, 660 mm and 4 m) with six contact lens and two multifocal spectacle corrections for presbyopia. The two spectacle corrections were D-segment bifocals and trifocals and the contact lens corrections were distance contact lens with lookover spectacles, soft progressive bifocals, soft concentric bifocals, monovision, modified monovision, and hard crescent segment bifocals. The spectacle corrections in general gave better results for the contrast sensitivity function (CSF), than did the contact lens corrections. Distance contact lenses with lookover spectacles performed best of the contact lens corrections used. However, the differences in CSF between the various contact lens corrections were small and not statistically significant.

Adolescent↗

PubMed1989

Peripheral visual acuity and age.

We measured the peripheral visual acuity of a group of eleven older subjects (mean age 54.2 years) and a group of seventeen young subjects (mean age 22.1 years). Peripheral visual acuity was measured using Konig bars with critical detail subtending 2.4 and 4.8 minutes of arc. The older group showed a substantial reduction of peripheral visual acuity.

Adult↗

PubMed1988

Reverberation, masking, filtering, and level effects on speech recognition performance.

The purpose of this investigation was to describe the interactive effects of four signal modifications typically encountered in everyday communication settings. These modifications included reverberation, masking, filtering, and fluctuation in speech intensity. The relationship between recognition performance and spectral changes to the speech signal due to the presence of these signal alterations was also studied. The interactive effects of these modifications were evaluated by obtaining indices of nonsense syllable recognition ability from normally hearing listeners for systematically varied combinations of the four signal parameters. The results of this study were in agreement with previous studies concerned with the effect of these variables in isolation on speech recognition ability. When present in combination, the direction of each variable's effect on recognition performance is maintained; however, the magnitude of the effect increases. The results of this investigation are reasonably accounted for a spectral theory of speech recognition.

Adult↗

PubMed1987

Effect of mouse hepatitis virus infection on combination therapy of P388 leukemia with cyclophosphamide and pyrimidinones.

At least three marked differences were noted in the results compared from two parallel experiments using identical protocols with virus-free mice and mouse hepatitis virus (MHV) infected mice inoculated with P388 leukemia. First, the therapeutic effect of cyclophosphamide (CY), a cytotoxic antitumor drug, was apparently augmented in MHV-infected mice. A 162% increase of life span (ILS) was obtained in MHV-infected mice compared to a 100% ILS in uninfected mice. Second, the experimental error in terms of the range of animal survival time was much larger with MHV-infected mice than with uninfected mice. In MHV-infected mice, the therapeutic effect of the combination treatment with CY and pyrimidinone was not statistically different from that of the treatment with CY alone. In uninfected mice, the effects of the combination therapy at all doses of pyrimidinone were statistically more effective than that of CY treatment alone.

Animals↗

PubMed1986

Patient compliance and its influence on contact lens wearing problems.

One hundred consecutively presenting patients, fifty from each of two contact lens clinics, were questioned about the procedures encountered in care and maintenance of their contact lenses and asked to demonstrate their use of those procedures. Their clinic records were then analyzed for the occurrence of signs and symptoms that were related potentially to noncompliance with instructions and procedures, and that could not be otherwise explained. Only 26% of patients were fully complaint. Noncompliance with instructions was related strongly to the occurrence of signs and symptoms indicative of potential wearing problems. Improvements in the level of patient compliance with instructions is likely to bring about increased patient success with contact lens wearing.

Contact Lenses↗