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Results for “Differential Threshold”

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At least 19 recordsLinked to original sources
PubMed1992

Differential thresholds for limb movement measured using adaptive techniques.

Differential thresholds for limb movement were measured in 10 subjects, using the transformed up-down procedure. Subjects were required to indicate which of two random displacement perturbations delivered to their forearms had the larger standard deviation (SD). The SD of the reference signal was fixed for each experimental condition at one of seven values ranging from 0.05 to 3.2 mm. THe SD of the other signal varied depending on the subject's response. Using this procedure, the differential threshold for limb movement was calculated to be 8%, which is very similar to the thresholds estimated previously for changes in limb position (9%) and force (7%). The sensitivity of the human proprioceptive system to changes in limb displacement was much greater than anticipated, with subjects being able to resolve a 5-microns difference between two perturbations delivered to their arms.

Adult↗
PubMed1978

[New methods in the objective audiometry for the proof of simulation and for the determination of the differential thresholds for frequency and intensity (author's transl)].

The "late acoustically evoked potentials" (50 to 300 msec) can be recorded in different stages of vigilance and awareness; therefore their significance as a correlate of conscious central perception is doubtful. The "very late DC-potentials" (300 msec and more) reflect conscious central perception because of their cognitively determinated features and can be used for the proof of simulation. Their application in ERA comprises the determination of the hearing threshold, the "objective speech audiometry" and the determination of the differential thresholds. The "objective frequency decrement test" gives additional informations about the degree and the specifity of a hearing loss. The objective proof of the differential threshold for intensity demonstrates the insufficient significance of the SISI test.

Audiometry↗
PubMed1992

Effects of laser-induced retinal lesions on perimetric thresholds.

Differential light sensitivity and high-pass resolution thresholds were studied before and after pan-retinal photocoagulation in subjects with proliferative diabetic retinopathy. The photocoagulated retinal area was measured and the relative change in ganglion cell separation was estimated. The change in differential light thresholds after treatment, when expressed in decibels, appeared to be linearly related to the calculated change in ganglion cell separation. At present, this empirical finding lacks a theoretical explanation. For high-pass resolution, theory predicts a direct proportionality between the change in ganglion cell separation and resolution threshold. This relationship was confirmed, supporting the claim that high-pass resolution directly reflects the number of functional retino-cortical neural channels.

Adult↗
PubMed1992

[The clinical significance of following up the differential light threshold in glaucoma].

The correlation of the differential light threshold changes in the Bjerrum area to the glaucomatous visual field defects that followed was studied prospectively by the Humphrey Field Analyzer. Of 42 early glaucomatous eyes without field defects, 24 developed reproducible glaucomatous field defects in 2.5 years of follow-up. The agreement in location between the field defects and the meridian of highest light threshold elevation was remarkable (87.0%), and a mean 5 dB decline in local light sensitivity predicted ensuing field defect development. Thus, the discovery of glaucomatous field defects with automated Humphrey perimetry could be 1-2 years earlier than with Goldmann perimetry.

Adult↗
PubMed1976

[The capacity to destinguish changes in the intensity as a function of volume and frequency (author's transl)].

Békésy audiometry equipment was used for investigations carried out in 15 test persons to study the intensity differentiation threshold. We tried to find the degree of intensity required to recognize given dB changes in the intensity. The results achieved very well coincide with those established by other authors. It was possible to statistically prove the volume dependence of the intensity differentiation threshold, it was, however, not possible to establish any frequency dependence. The relations of our result with the SISI test are under discussion.

Audiometry↗
PubMed1979

Evaluation of color discrimination in the white region.

Reference and test stimuli were produced on two separate color television screens to evaluate the color discrimination ability of the human eye for near-white colors. Each test stimulus had a luminance approximately equal to that of the reference, but was slightly different in chromaticity, e.g., [deltax] less than 0.01, [deltay] less than 0.01. The evaluation involved 20 persons observing 26 sets of color stimuli of 16-cd/m2 luminance, and 21 persons observing sets of color stimuli of 253 cd/m2. Observers were requested to categorize the color differences they perceived on a six-level rating scale. The results indicate that the differential thresholds for color difference of near-whites are between 4 and 8 CD (Color Difference), except in the bluish region.

Color Perception↗
PubMedDate not supplied

[Functional state of the human hearing analyzer exposed to +Gx acceleration].

The functional state of the acoustic analyzer of man was investigated during an exposure to +Gx acceleration of 4-14 g applied at an angle of 78 degrees to the long axis of the body. During an exposure to 8-10 g the hearing state began to deteriorate. This included an increase in the tonic thresholds of hearing sensitivity with respect to the aerial and bone conduction, and an increase in the differential thresholds of hearing with respect to the strength and pitch. With an increase of the acceleration value these changes grew, reaching maximum at 14 g. It is suggested that possible mechanisms of changes in the hearing sensitivity are associated with disorders in the systems of sound conveyance and perception.

Acceleration↗
PubMed1977

[The importance of the "contingent negative variation" (CNV) for audiometry (author's transl)].

Previous proofs of "central processes" in hearing were based on the determination of the late "auditory evoked potentials" (AEP's: 50--300 ms) in EEG. The appearance of AEP's in different sleep stages raises the question, if the AEP actually conscious hearing. Since the discovery of the "Contingent Negative Variation" (CNV), as a potential depending on conscious and cognitive factors, an appropriate "instrument" is available to solve this problem. Using the CNV-technique three proofs of central auditory perception are described and discussed: a) "The objective proof of the perception of pure-tones", useful for threshold determination, test in the case of simulation and central hearing disorders. b) "The objective proof of the perception of stimulus-changes", useful for exact determination of differential thresholds for frequencies or intensities. c) "The objective speech audiometry", proof of speech comprehension, useful in case of aphasia and simulation.

Auditory Perception↗
PubMed1975

[Audiological observations of a patient with auditory agnosia].

A case is reported in which a patient was become unable to identify all kinds of auditory material, including speech, despite only subnormal audiometric thresholds (i.e. "auditory agnosia"). The following audiological disorders were shown: some fragility in the perception of brief sound stimuli, difficulties to apprehending prolonged series of stimuli (rhythms), defective sound localization, an increase in the homolateral and in the contralateral effects of masking sounds. On the other hand, differential thresholds for frequency and for intensity, as well as fusion thresholds, were little affected, or unaffected. A complete dissociation appeared between the auditory evoked potentials and the audiometric thresholds; a year after the first examination, and the following years, the auditory potentials were largely reduced, or even have elapsed for one ear, while the audiometric thresholds seem to remain nearly the same.

Agnosia↗
PubMed1992

Can people hear the pitch change on a variable-pitch pulse oximeter?

The introduction of the variable-pitch feature on pulse oximeters in 1983 by the Nellcor Corporation (Hayward, CA) allowed users to rapidly detect changes in oxygen saturation by listening for changes in the pitch of the tones emitted by the pulse oximeter. A few individuals have reported that they have been unable to detect a change in pitch when oxygen saturation changes. To these individuals, the variable-pitch feature of these pulse oximeters has not been beneficial. Using the pitches from one manufacturer of oximeters, we created a computer program to simulate the pitches that accompanied various oxygen saturations. The pitches were recorded onto a tape player and played for 75 volunteer subjects unfamiliar with the pitches of a variable-pitch pulse oximeter. Of our sample, 67% were able to detect a single change in pitch corresponding to a 1% fall in oxygen saturation, and 11% of the population could not detect a change in pitch until there was a change in pitch with every beat. We suggested four alternative designs that may prove beneficial to this group of individuals.

Acoustic Stimulation↗
PubMed1976

Metabolism of testosterone by the epididymis and ventral prostate of rat and its inhibition by cyproterone acetate.

The metabolism of 3H-testosterone by the epididymis and accessory organs of adult male rats exposed continuously to microdoses of cyproterone acetate from subcutaneous capsules were studied. The major metabolite of 3H-testosterone in the epididymis, vas deferens and ventral prostate of control rat was dihydrotestosterone while the formation of androstanediol by these tissues was low. The highest percentage of DHT was formed by the ventral prostate and cauda epididymis. In rats exposed to cyproterone acetate for four months, the conversion of testosterone to DHT was inhibited in all the tissues but maximally in the ventral prostate and cauda epididymis. In these rats, the secretory function of the ventral prostate was normal while that of the epididymis was markedly decreased. These data are discussed based on the differential thresholds of androgens required to regulate the functions of the accessory organs.

Animals↗
PubMed1976

Studies on the physiology and biochemistry of mammalian epididymis: effect of flutamide, a nonsteroidal antiandrogen, on the epididymis of the rat.

The effect of flutamide (Sch 13521; 4'-nitro-3'-trifluoromethylisobutyranilide), a nonsteroidal antiandrogen, on male rat genital organs was studied. Administered at a dose of 25 mg/kg body weight daily for 30 days, flutamide caused a significant increase in the weight of the testis but had no effect on spermatogenesis and Leydig cell morphology. The secretory activity of the epididymis, as evidenced by the level of glycerylphosphoryl-choline and sialic acid, either remained unaffected or was stimulated. There was a significant decrease in seminal vesicle and ventral prostate weight and in the fructose content of the coagulating gland. The anti-androgen at the dose used did not affect the fertility of the rats. The significance of these findings is viewed in relation to the hypothesis of a differential threshold requirement of androgen for the epididymis and the accessory sex glands. The potentiality of antiandrogens as extragonadal antifertility agents in the male is discussed.

Anilides↗
PubMed1977

Direct excitatory interactions between spinal motoneurones of the cat.

1. Ninety-seven spinal motoneurones were identified by their antidromic invasion following stimulation of the muscle nerve and submitted to a series of four tests to reveal a possible direct excitation between motoneurones. 2. Threshold differentiation, refractoriness, hyperpolarization and collision revealed antidromically induced depolarizations in fourteen of the ninety-seven tested motoneurones. 3. The parameters of the antidromically induced depolarizations indicate a short latency, a low amplitude and independence with regard to the membrane polarization. 4. It is concluded that the antidromically induced depolarizations reached the impaled motoneurone via a route other than its own axon. 5. The mechanism may involve either electrotonic interactions between neighbouring motoneurones or excitatory recurrent collaterals between synergist motoneurones.

Action Potentials↗