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Results for “Differential Threshold”

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PubMed1983

[Characteristics of the coding of light stimulus intensity by visual cortex neurons during light adaptation in the cat].

Response of 70 neurons in area 17 of the visual cortex to optimal stimuli of different intensity in the receptive field under conditions of photopic adaptation were analyzed in unanesthetized cats. The reaction threshold, differential sensitivity, optimal intensity and the width of the brightness range were estimated. No intensity detectors were found in this area. 70% of neurons studied had inhibitory distortion in the range of their intensity functions. The neurons differed in their threshold reactions by 5-6 orders, in dynamic range--by 3-4 orders, and in differential sensitivity--by 2-3 orders. The visual cortex neurons with receptive fields in central and periphery parts of the visual field had different intensity functions.

Animals↗
PubMed1998

[The sensorineural component of hearing loss associated with cholesteatoma].

Patients with cholesteatoma often suffer neurosensorial hearing loss with variable bone conduction thresholds. Its origin is debated and has been attributed to the ototoxicity of topical drugs, immune reactions, effects of ototoxic antibiotics applied to the ear, etc. A selected series of 50 patients who underwent surgery for chronic ear disease due to cholesteatoma in our ENT department were studied to evaluate the possible origin of the bone conduction component of hearing loss. Different clinical, audiological, and surgical aspects were analyzed, including cholesteatoma site and extension, age, sex, evolution of the symptoms, pure tone audiometry data, middle ear involvement, the operation performed, and the occurrence of complications. Bone conduction thresholds were reported as pure tone differential thresholds (affected vs non-affected ear). A specific cholesteatoma-related neurosensorial hearing loss was observed that might lead to irreversible hearing loss. Neurosensorial involvement seems to be related mainly to the duration of symptoms, type of surgery, certain specific clinical aspects, and complications.

Adolescent↗
PubMed1984

Factors influencing velocity coding in the human visual system.

Differential velocity detection in the fovea was measured over a wide range of velocities (0.25-256 degrees/sec). Differential thresholds were minimum (about 6%) for intermediate velocities (4-32 degrees/sec). Velocity judgements were shown not to depend on duration judgments. The U-shaped curve relating differential velocity detection and velocity was preserved at different background levels and different contrasts. The physiological correlates of these observations are discussed.

Differential Threshold↗
PubMed1986

Induced desensitization.

Viewing of annuli modulated in color in a sawtooth fashion in time results in differential threshold elevations for the detection of color changes of inscribed disks. The elevations are of nearly the same magnitude as those resulting from viewing modulated disks. However, the differential effects on thresholds for complimentary colors are reversed. The differential effects, thus, are correlated with the variation in appearance of the test area.

Color Perception↗
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↗
PubMed2004

Velocity discrimination of auditory image moving in vertical plane.

This research investigated the ability of humans to discriminate changes in velocity of apparent movement of a sound source (as defined by the time required for the sound to traverse a 180 deg arc) in the median vertical plane. Apparent auditory movement was created by successive switching of the loudspeakers situated over the arc. The broadband noise with band width of 0.25-4 kHz (low-pass noise - LP) and of 4-12.5 kHz (high-pass noise - HP) was employed as stimuli. Discrimination thresholds were calculated for reference velocities of 58 and 115 deg/s under four stimuli types: movement of stepped movement of noise for low-pass noise and for high-pass noise and continuous motion for low-pass noise and for high-pass noise. The result showed that discrimination of the velocity depended on the signal frequency spectrum. The differential thresholds for the signals with low pass noise were significantly higher than those for signals with high pass noise (F(1;78) >> 3.96, p < 0.05). Magnitude of the absolute thresholds was the highest when the velocity was 115 deg/s for each of four types. It is interesting to note that the thresholds magnitude depended on the type of signal motion, that is on whether it was continuous or stepped.

Acoustic Stimulation↗
PubMed2000

Visual resolution in humans fluctuates over the 24h period.

The present experiment was designed to assess daily fluctuations of visual discriminability, a function reflecting the resolution power of the visual sensitivity by measure of a differential threshold. Sixteen subjects underwent a visual discrimination threshold task (using the constant method) in a protocol allowing one point every 2h over the 24h period. The results show that the visual discrimination threshold is low in the morning and increases progressively over the day, reaching a first peak at 22:00. During the night, the same pattern occurs, with low threshold levels at the beginning of the night and high levels at the end. This profile is quite different from that of detection threshold variations, suggesting that the two visual functions are under the control of different underlying mechanisms. Two interpretations could account for this discrepancy. The first relates to different oscillators in the eye for detection and discrimination. The second refers to a possible linkage of visual discriminability with the sleep-wake cycle since threshold measures were systematically low (i.e., high resolution power) after long sleep periods.

Adult↗
PubMed1990

Double pattern of relationship between skin temperature, thermoregulation and sensory nerve conduction.

Electroneurographic and thermographic investigations were done in 32 persons. Sensory nerve conduction velocity, amplitude of sensory nerve potential, subjective and objective sensory thresholds were determined during stimulation of each finger. The maximal and minimal skin temperatures for each finger were evaluated from thermograms taken from the dorsal and palmar surface of the hand before and after standard cooling test. The measurements were done in a thermostabilised room at 19-21 degrees C effective ambient temperature. The second degree correlations between the electroneurographic and thermographic parameters were calculated. The statistical analysis revealed the presence of a double correlation pattern depending on the homoiothermic or poikilothermic thermoregulatory ability of the finger. The differentiation threshold criterion for the poikilo- and homoiothermic group assignment was the minimal rest temperature of the finger equal to 28 degrees C. The correlations in the poikilothermic fingers were very strong and much stronger than in the homoiothermic fingers. Correlations with temperatures were strong both at rest as well as after cooling. Correlations for the sensory nerve potential amplitude likewise for the objective and subjective thresholds were stronger than for the conduction velocity. Sensory nerve potential amplitude increases and subjective and objective thresholds decrease with finger temperature. The obtained results suggest that sensory nerve conduction is related not only to the actual tissue temperature but also to local thermoregulatory ability.

Adult↗
PubMed1999

An evaluation of acrylic complete dentures using the discrimination of elastic bodies or viscous fluids.

The discrimination test on elastic bodies and viscous fluids was carried out for 16 young dentists and 13 denture patients, because it is considered that dentures affect the ability to discriminate food. The materials used in this test were six thermoplastic polyurethane elastomers with compressive elastic moduli from 11.8 to 62.0 MPa and six silicone impression pastes with coefficients of viscosity from 1.77 x 10(-2) to 23.0 x 10(-2) MPa x s. The subjects (dentists and patients) discriminated the materials based on differences in elastic moduli or coefficients of viscosity by chewing the materials for 10 s. From these experiments, it became clear that the ability to discriminate between elastic bodies or viscous fluids upon chewing, of subjects who use complete-dentures in combination with their own teeth and either an upper or lower complete-denture (S/D) or who have a set of complete-dentures in both jaws (D/D) decreased considerably, compared with that of subjects who have their own teeth in upper and lower jaws (S/S). The ratios of S/D and D/D against S/S were 0.5 and 0.3, respectively. This indicates that with an increase in the area occupied by dentures in the oral cavity, the value of the differential threshold increased markedly and made food discrimination more difficult. In addition, discriminating viscous fluids was 2.4 to 3.1 times more difficult compared with the discrimination of elastic bodies, independent of denture placement.

Acrylic Resins↗
PubMedDate not supplied

[Mechanism of time perception by animals].

The study of changes in the precision of evaluating different time intervals by animals (monkeys, rabbits) showed that the value of error in time evaluation delta and the value of confidential interval of time evaluation delta, characterizing differential thresholds of time perception, depend on the duration of signal interval, which is in maximal conformity with Weber's law. The revealed dependence is considered as a sign of the increase with time of the intensity of excitatory process, used by the nervous system as a substratum for time counting. Assumed nature of neurodynamic processes underlying this relation is discussed.

Animals↗