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Biomedical subjects

D L Johnson

Publications and source records attributed to D L Johnson.

At least 307 records · Page 17Linked to original sources
PubMed1980

Identification of the minimum noise level capable of producing an asymptotic temporary threshold shift.

The present study was designed to identify the minimum noise level capable of producing an asymptotic temporary threshold shift (ATTS). It was estimated that at some level below 85 dBA, probably 70-80 dBA, there existed an exposure level at which no ATTS would occur. It is assumed that if a long-duration noise does not produce temporary changes in hearing levels, then it would not produce permanent changes either. This level would then define an exposure condition below which personnel could be exposed for indefinite periods of time without adverse auditory effects. Subjects were exposed to continuous pink noise for 24 h at levels of 65, 70, 75, 80, and 85 dBA. TTS growth and recovery was measured at specific intervals throughout each condition. Results demonstrate that at the most sensitive frequency (4000 Hz), at ATTS threshold level would be predicted in the region of 75-80 dBA.

Adult↗
PubMed1979

Locus of control and behavior in treatment groups.

Studied the Rotter Locus of Control scale for effective prediction of behavior in small groups. Subjects were 205 male VA Hospital patients participating in self-directed groups who completed the AGCT, Psychological and Somatic Symptom Scales, and Rotter's I-E measure of locus of control. Group behavior was measured through sociometry and a Group Member Evaluation form. Three hypotheses were not supported: (a) Persons scoring high in the direction of internal control (internals) will be more likely to act to influence their social environment; (b) internals will be more active than externals in gathering and processing information in group discussions, and (c) internals will be more self-directed and less susceptible to being influenced by others. Two hypotheses were supported: (a) externals will express more somatic and psychological complaints than internals, and (b) externals will be perceived as behaving more defensively than internals. In contrast, intelligence was correlated with a large number of group process measures. Locus of control and intelligence measures predict different kinds of behavior in groups.

Adjustment Disorders↗
PubMed1979

Intervals between multiple ovulations in PMSG-treated and untreated ewes and the relationship between ovulation and oestrus.

The timing of ovulations in 42 PMSG-treated ewes was determined by repeated endoscopy. The first ovulation occurred at a median time of 23 . 6 +/- 0 . 5 (s.e.m.) h after the onset of oestrus. The median interval between first and second ovulations was less than 1 h, and that between first and last ovulations was approximately 6 h. In 59 untreated ewes, probit regression analysis was applied to the number of ovulations which were found by endoscopy to have occurred by 23, 25 and 27 h after the onset of oestrus. The median time of first ovulation was 25 . 5 +/- 0 . 5 h after the onset of oestrus, this interval being similar in single- and twin-ovulating ewes. The median interval between twin ovulations was 1 . 2 +/- 0 . 6 h. Ovulation occurred after the end of oestrus in at least 75% of ewes.

Animals↗
PubMed1979

Noise dosimeter measurements in the Air Force.

Personal noise dosimeter monitoring devices, operating on the Air Force rule of 4 dB per doubling time and 84 dB(A) criterion level, have been used for the past year in determining the occupational noise exposures of Air Force personnel working in hazardously noisy jobs. The research conducted by the Aerospace Medical Research Laboratory has resulted to date in 418 8-h occupational noise exposure measurements being collected on 120 different individuals. The 8-h occupational noise levels ranged from 66-111 dB(A) with the median level at 84.5 dB(A). In addition, noise dosimeters have been used at Air Force bases across the country in an experimental effort to see how well their use would fit in with existing Air Force hearing conservation programs. A total of 567 noise data measurements have been received from various bases. The base response data noise exposures ranged from 60-101 dB(A) with a median level of 80.1 dB(A). Along with the 8-h occupational noise exposure study, 16 individuals wore an equal energy noise dosimeter for 24-h or more to determine their nonoccupational noise exposure. A total of 73 separate 24-h measurements were taken. The median daily A-weighted average sound level was 77 dB(A). This is only 2 dB higher than the median of 75 dB(A) found for the typical American by previous studies. Some of the merits of noise dosimeters, as well as some of the problems involved in setting up ongoing noise monitoring programs, are discussed.

Adolescent↗
PubMed1978

Vital root retention in humans: a preliminary report.

With increasing experience in the technique, it has become apparent that more generous contouring of the retained root after amputation is desirable. The effect is to produce a more rounded ridge instead of the "boxy" one that would result from mere horizontal sectioning of the crown structure. The surgical sectioning of vital teeth, followed by anequate mucoperiosteal eversion suturing, has proved to be successful. Periodontal evaluation of each tooth seems to be paramount to success or failure. Accurate impression-making and postsurgical treatment including soft acrylic resin relines and removal of pressure spots appear to be next in importance. Age of the patient, condition of the clinical crowns, and length of surgical procedures did not seem to affect normal healing in the patients involved in the project.

Adult↗
PubMed1978

The typical noise: first step in the development of a short procedure for estimating performance of hearing protectors.

An exact measurement of the effectiveness of a hearing protector requires the determination of how well it works in the specific noise in which it is to be worn. As a practical matter, though, people do not generally remain in a single noise spectrum throughout a working career or even throughout a working day, so it does not matter so much that most measurers are not likely to be equipped to perform spectrum analyses. Other techniques for judging earplugs and earmuffs are obviously necessary. Previous research has tried to find the average attenuation given by a particular device in several (or many) noises, or it has tried to deal with the attenuation given in noises given with particular C-minus-A values. In this paper, a procedure is developed for compressing these multiple-spectra calculations into a single-spectrum computation that proves to be at least as accurate as the more complex methods.

Ear Protective Devices↗
PubMed1978

Longitudinal study of hearing in children: baseline data concerning auditory thresholds, noise exposure, and biological factors.

Serial auditory thresholds are being recorded at six-month intervals from 224 children and youths aged 4--18 years. The data from the first year show girls have lower threshold levels than boys, especially from 12--17 years, and, in both sexes, those aged 12--17 years have lower thresholds than those aged 6--11 years. Median total noise exposure scores tend to be higher in boys than girls, especially after 10 years of age, but these scores are not significantly correlated with auditory thresholds levels. The incidence of exposure to events associated with noise increases markedly in teenage boys and is related to auditory threshold levels. There are no significant associations between auditory thresholds levels and responses to general health questions or attained stature, but there are associations with meatal abnormalities. There is suggestive evidence, particularly in girls, that rapid maturation is associated with lower threshold levels, especially at lower frequencies.

Adolescent↗
PubMed1978

Effects of infrasound on cognitive performance.

The cognitive performance of 40 subjects was measured during exposure to infrasound and noise in three experiments. In the first experiment, 12 subjects were exposed for 15 min to each of four experimental conditions while performing a Serial Search Task. The conditions were: 65 dB ambient noise (AN), a low-frequency background noise (BN) at 110 dB, a 7-Hz tone at 125 dB + AN, and the 125 dB tone + BN. The second experiment was the same as the first except a Complex Counting Task was used and the exposure duration was increased from 15 min to 30 min. In the third experiment, the Complex Counting Task was used and the subjects were exposed for 15 min to each of the following four conditions: BN, 125 dB at 7 Hz plus BN, 132 dB at 7 Hz plus BN, and 142 dB at 7 Hz plus BN. No decrements in performance were obtained in any of the three experiments, and there were no subjective reports of dizziness or disorientation as suggested in some of the previous literature. The authors conclude that adverse effects of infrasound have been exaggerated and the current levels of infrasound components as produced by modern jet aircraft are not considered in themselves a practical problem.

Acoustic Stimulation↗
PubMed1977

Description of the measurement of an individual's continuous sound exposure during a 31-day period.

A dosimeter based on the equal energy rule with range from 55 to 110 dB was used to monitor continuously the noise exposure of one subject. The subject, who is the second author of this report, works in a relatively quiet laboratory area. The daily A-weighted average sound level was measured for each 24-h period [L(eq(24))] beginning at approximately 8:00 a.m. During the day the noise exposure associated with specific activities was noted. The 31-day average sound level was 76 dB while the daily L(eq)(24)) values varied from a low of 59 dB to a high of 83 dB. The type of activity that contributed most of the subject's total sound dose was night-time parties at private homes or nightclubs. Five such parties accounted for 42% of his total sound dose. One exposure at an automobile hobby shop and three outings at a bowling alley contributed another 27% to the total sound dose. If these outside recreational activities had been avoided, the 31-day average sound level would have been reduced to 71 dB. The problems involved in monitoring a 24-h noise exposure as well as future plans for more elaborate studies are discussed.

Environmental Exposure↗
PubMed1977

Social class, birth order, and newborn experience.

Early home experiences of a group of 32 2-week old infants, equally divided according to social class, birth order, and sex, were studied. Naturalistic observations were taken on 2 consecutive days for a total of 6 hours. Compared with later-borns, firstborns received significantly more caretaker interaction on all variables studied. Compared with lower-SES infants, those from higher-SES homes received significantly more direct verbal interaction although the 2 groups did not differ on total periods of other types of caretaking interaction. The findings are consistent with birth order and social class differences reported in home environments of older infants and children.

Birth Order↗
PubMed1977

Asymptotic behavior of temporary threshold shift and recovery from 24- and 48-hour noise exposures.

Temporary hearing loss (TTS) from long-duration noise exposure reaches an asymptote between 8 and 16 h and does not increase further during continued exposure for durations of at least 48 h. Potential auditory hazards of long-duration exposures are examined in terms of growth and recovery patterns of TTS. TTS growth and recovery patterns were compared during 24- and 48-h exposures of humans to continuous pink noise at a level of 85 dB A-weighted. Results indicate similar patterns of acquisition and relatively equal amounts of TTS for the two exposure durations. However, recovery of preexposure hearing at 4000 Hz following termination of the 48-h noise exposure differed somewhat from that which followed the 24-h exposure. The implications of these findings for long missions in noisy environments are discussed.

Adult↗
PubMed1976

Review of the effects of infrasound on man.

Claims that infrasound adversely affects human performance, makes people "drunk," and directly elicits nystagmus, have not been clearly demonstrated in any experimental study. The effects obtained at low intensity levels of 105 to 120 dB, if they can be substantiated at all, have been exaggerated. Recent well-designed studies conducted at higher intensity levels have found no adverse effects of infrasound on reaction time or human equilibrium. The levels at which infrasound becomes a hazard to man are still unknown. However, the hazardous levels are certain to be much higher than have been suggested in some of the literature. The preliminary exposure limits which were proposed several years ago for use in the U.S.A. are still considered safe and adequate based on present knowledge. Caution is necessary in future research because artifacts produced by faulty experimental procedures can suggest genuine psychological or physiological effects.

Humans↗