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Biomedical subjects

M Rodenburg

Publications and source records attributed to M Rodenburg.

At least 37 records · Page 2Linked to original sources
PubMed1981

Thresholds for the perception of rotation: variability, psychometric curves, and comparison with hearing thresholds.

Psychometric curves were determined for the perception of rotation about a vertical axis. If a logarithmic scale is used, an integrated Gaussian curve gives a reasonable description of the psychometric curve. This curve is characterized by two values: the 50% point, which is defined as the threshold, and the s.d. The s.d. of the vestibular psychometric curve is about 10 dB which is 4 times larger than the s.d. found for the auditory system. The distribution of vestibular thresholds in healthy subjects obtained by Clark and Stewart (1969) is plotted on a logarithmic acceleration scale; it can fitted by a Gaussian function. The s.d. of this function is 5.5 dB, a value which is similar to that found for auditory thresholds. From this it is concluded that the inter-individual variability of the detection threshold for the vestibular system is the same as the inter-individual variability of the detection for the auditory system.

Acoustic Stimulation↗
PubMed1981

The threshold of perception of angular acceleration as a function of duration.

The threshold for rotation about the yaw axis was determined for constant acceleration stimuli as a function of their duration in the range from 3 to 25 s. From the torsion-swing model the following theoretical equation can be derived: alpha thr = C/[1--exp(-ts/tau 1)], where alpha thr = acceleration amplitude at threshold, ts = duration of the acceleration, tau 1 = time constant, C = threshold for very long stimuli. According to this formula the Mulder product (i.e. the product of the threshold acceleration amplitude and the duration of the stimulus) is constant for durations up to 0.3 tau 1. The best fit of this theoretical function to the somatosensory data is found for tau 1 = 14.5 s, and C = 0.220/s2. The time within the Mulder product is constant (about 5 s) is doubtless due to the mechanics of the semicircular canals. For the oculogyral data a lower value of tau 1 is found. We do not have any explanation for this lower value.

Acceleration↗
PubMed1980

Statistical evaluation of nystagmus in cupulometry.

The literature on cupulometry shows inconsistent data as to (1) the magnitude of the time constant T1; (2) the inter-individual variation between subjects; (3) the difference between clockwise and counter-clockwise rotation, and (4) the linearity of the system. In our investigations, the nystagmus was measured after a start or a stop in angular velocity. All determinations were carried out six times for 5 subjects. The time constant T1 was calculated from the slope of the decay of the slow-phase eye velocity. Statistical evaluation of the results showed: a test-retest variability which is greater than the inter-individual variability; significant inter-individual differences between subjects; mean values of T1 for clockwise and counter-clockwise rotation of 13.2 (SD 1.4) and 12.8 (S.D. 1.7) sec, respectively; a significant difference of T1 between clockwise and counter-clockwise rotations for individual subjects at the 95% level; no relation between T1 and the amplitude of the step in angular velocity, and a linear increase of the maximum slow-phase eye velocity with the amplitude for velocities below 100 degrees/sec, whereas at higher velocities, saturation occurs.

Electronystagmography↗
PubMed1980

Significance of the SISI test and its relation to recruitment.

The aim of the present article is to reconsider critically some arguments currently used to support the significance of the SISI test. The first topic discussed is the possible relationship between a positive SISI result (i.e. a small difference limen for intensity) and the presence of recruitment. It is concluded that there is no relationship between these via the loudness function. The second topic concerns some statistical factors which have a bearing on the utility of the SISI test. It is argued that the significance of the SISI test may be largely determined by the prevalence rates of cochlear and retrocochlear disorders.

Humans↗
PubMed1979

Influence of the stimulus repetition rate on brain-stem-evoked responses in man.

In order to record brain-stem-evoked responses as fast as possible, the influence of the stimulus repetition rate was investigated. The repetition frequency was varied from 2.5 to 80 Hz. The amplitudes of N2-N4 diminish uniformly with increasing stimulus rate. The repetition rate has little or no influence on the amplitude of N5; however, increasing the repetition frequency about 10 Hz causes an increase in the latencies of N2-N5. It seems that the decrease in the amplitude of N2-N4 and the increase in the latencies of N2-N5 are of cochlear origin, since the amplitude and the latency of the cochlear responses are influenced in the same way by the repetition rate as the above-mentioned brain stem responses.

Adult↗
PubMed1977

The health of the very aged.

Little information is available on the health status of persons 85 years or over. Recent United States data indicate that 20% of individuals 85 years of age or over reside in nursing and personal care homes and that among these institutional residents 31% are bedfast, 11% are chairfast and 71% manifest evidence of senility. An investigation into the health of persons 85 years of age or over in two Ontario counties revealed that 39% resided in long-stay institutions, and that one of the main differences between old people living independently in the community and those in institutions was the higher proportion of the latter needing help with the activities of daily living and showing mental disorientation. Of those individuals 85 years of age or over in institutions for 1 year, 26% acknowledged often feeling depressed and 18% acknowledged often wishing they were dead, but these tendencies were not more frequent in those 85 years of age or over than in those 65 to 84 years of age. These findings have implications for service and research needs and attitudes towards death.

Affect↗
PubMed1977

Psychophysical determination of the phase characteristic of the vestibular system of man for sinusoidal oscillation in yaw.

UNLABELLED: The phase characteristic of the vestibular system of man was determined for sinusoidal oscillation in yaw in the frequency range from 0.0025 to 0.4 Hz. Three different sets of experimental conditions were used: (1) a dark room with a fixation light; stimulus: sinusoidal rotation; (2) a dark room without a fixation light; stimulus: sinusoidal rotation + noise, and (3) a dark room without a fixation light; stimulus; sinusoidal rotation. RESULTS: the sensation leads the velocity by about 90 degrees at 0.005 Hz. The phase lead decreased for higher frequencies becoming nearly zero at 0.05 Hz and remaining constant in the frequency range 0.05 to 0.4 Hz. A phase lag was not found. At very low frequencies (less than 0.005 Hz), the phase lead was more than 90 degrees. The results can be described in terms of a second-order model with time constants Tau1 = 20 sec and Tau2 = 0.013 sec and an adaptation term with a time constant of Taau = 0.40 sec.

Humans↗
PubMed1976

Elderly applicants to long-term care institutions. I. Their characteristics, health problems and state of mind.

As part of a study of long-term institutional care of the elderly, this report presents a comparison of the characteristics, health problems, and state of mind of 193 elderly applicants for such care (Group A) with those of 141 elderly persons living independently in the community (Group I). Group A members were older, living with a spouse less often, and had low incomes. They showed much more cerebrovascular disease, incontinence, recent loss of independence in the activities of daily living, dementia, recent hospitalization, loneliness, and depression. They had had much less recent involvement in social and recreational activities, although most had not been socially isolated. They had received more extensive help from relatives and friends, and it seemed unlikely that additional help from these sources would keep many more of these elderly persons out of institutions. Community agencies and services had been used by a relatively low proportion of Group A, and hardly at all by Group I.

Activities of Daily Living↗
PubMed1976

Elderly applicants to long-term care institutions. II. The application process; placement and care needs.

As part of a study of long-term institutional care of the elderly, this report presents salient data concerning 193 elderly applicants. Physicians play an important role in decisions to apply for such care. More than half of the applicants and about 80% of their family members approved of the proposed move. The number applying to homes for the aged vs. other institutions seemed much greater than appropriate; many of these applicants appeared more elibible for placement in foster homes and specialized facilities for the demented, or for remaining in their own homes. About a fifth of the applicants could have continued living independently if they had received a reasonable amount of community assistance. Action implications include: 1) expansion and more informed use of community services, 2) more programs of supervised foster homes for the elderly, 3) construction of specialized institutions for the demented, and 4) a greater effort by institutions to satisfy the desire of many new residents to be involved there in useful tasks.

Aged↗