[Differential threshold of the intensity of band noise in different forms of hearing disorders].
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Audiometry↗
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Light differential threshold studies of reattached retina and macula.
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Adolescent↗
Encoding and decoding of auditory signals in relation to human speech and its application to human cochlear implants.
A description of the optimal electrode and stimulus configuration, based on mathematical model simulation of (1) the mechanical conduction and (2) the mechanoelectrical transduction of the middle and inner ear, will be presented. It is assumed that a sensorineurally deaf patient, whose auditory nerve is at least partially intact, will be able to hear and understand, when an activation pattern in specific groups of remaining fibers of the hearing nerve can be reproduced in a manner equivalent to normal hearing. The placement of 2 bipolar concentric electrodes in the modiolus of the basal and middle cochlear turn in a deaf patient has provided the opportunity for testing of electrical hearing thresholds, differential thresholds, and electrode impedance changes over a 5-month period, with direct access to the electrodes through a skin window. The stimulator was housed in a pocket case to provide easy use in a daily environment. Bipolar pulses of 0.02-1.0 ms were triggered either by zero crossings or by a speech envelope controlled oscillator. It was found that loudness should be encoded by pulse amplitude or duration rather than by pulse repetition rate, since the charge per pulse was the primary variable of loudness sensation. The periodicity hearing allowed for electrical differential thresholds equivalent to or lower than the acoustical ones in normal persons in the 80- to 150-Hz region. For the optimal coding of speech, a multichannel system of 4-10 electrodes each for different nerve fiber groups will be necessary.
Cochlear Implants↗
[Thresholds of differentiation of image size and orientation in albino rats].
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Animals↗
Covariates of the long-term fluctuation of the differential light threshold.
The scatter of the differential light threshold has a short-term and a long-term component. Although these components are significantly positively correlated, the relationship is not strong enough to accurately predict in an individual patient the long-term fluctuation from the short-term fluctuation. The reversible variation of the retinal sensitivity with time is statistically related to the temporal variation of the short-term scatter, to the variation in reaction time, and probably to the variation in the intraocular pressure.
Differential Threshold↗
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↗
Color-prediction discrepancies and differential chromaticity thresholds with photopigment bleaching.
The differential chromaticity thresholds of three color stimuli have been determined from metameric matches carried out during the cone-plateau period after photopigment bleaching. The results are compared with some recently published ones [E. Hita, L. Jiménez del Barco, and J. Romero, J. Opt. Soc. Am. A 3, 1203 (1986)] obtained under similar experimental conditions but without prior photopigment bleaching. The possible effects of rod intrusion on color-prediction discrepancies are discussed in the light of both sets of results. Under our experimental conditions, with foveal fields of 3 deg, luminance within the low photopic level, and sets of primary colors produced by filters of differing spectral bandwidth, the rod intrusion effect can be ruled out as a possible cause of color-prediction discrepancies, although it does appear to produce variations in the sizes of the discrimination ellipses and in their orientation.
Acclimatization↗
[On the absolute limit imposed by quantitative fluctuations of the differential luminance threshold].
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Differential Threshold↗
Differential motion thresholds to sinusoidal gratings at two eccentricities.
Differential motion thresholds were measured at eccentricities of 9 degrees and 16.6 degrees using computer-generated sinusoidal gratings. Three spatial frequencies (0.51, 0.25, and 0.13 cycles/deg) were examined at reference velocities of 2, 4, 8, 16, 32, and 48 deg/sec. Minimum differential velocity thresholds were between 20 and 30% of the reference velocities for the three spatial frequencies at both eccentricities. Increasing eccentricity produced an increase in the velocity at which minimum velocity discrimination occurred. Temporal frequency tuning was between 4 and 8 Hz, regardless of eccentricity.
Acceleration↗
[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↗
Increase of the short-term fluctuation of the differential light threshold around a physiologic scotoma.
Because determination of the differential light threshold of a visual field is a psychophysiologic test, the results can be subject to variation. This scatter measured during a single examination is usually called the short-term fluctuation. Increases of the short-term fluctuation were thought to occur primarily in abnormal visual fields; however, we found an increase of the short-term fluctuation in normal visual fields when the measurements were made at the border of a physiologic scotoma, such as the blind spot. These results suggest that an increase of the short-term fluctuation may be mainly related to measurements done with any static perimeter at the border of a depression of the island of vision.
Adult↗
Two-pulse monocular and binocular interactions at the differential luminance threshold.
Interaction between two pulses at the differential luminance threshold was studied for stimuli pairs presented to the same eye or to opposite eyes with an interocular delay. With monocular stimuli, the results replicated the earlier observations by Ikeda (1965) and Rashbass (1970) indicating linear interaction followed by rectification occurring at about 50-60 msec into the integration epoch. Binocular results were different, in accord with observations made in the contrast domain by Green and Blake (1981). Binocular stimuli of opposite polarity showed no cancellation. Binocular facilitation at threshold was found when either the stimuli of the same sign (+ + or - -) occurred with little interocular delay (stimulus onset asynchrony, SOA less than 15 msec), or the stimuli of the opposite sign (+ - or - +) were presented with an interocular delay between 15 and 100 msec SOA; the latter effect was at maximum with flashes 50 msec in duration presented with 50 msec interocular SOA. These results imply that binocular interaction takes place between rectified internal effects of luminance pulses. From the two-channel binocular model of Cogan (1987), binocular facilitation is attributed to the "fused" response derived from multiplicative excitation between same-sign (half-wave rectified), internal pulse responses. The absence of cancellation between simultaneous opposite-sign dichoptic stimuli is attributed to the "either-eye" binocular process dealing with full-wave rectified internal pulse responses to transient stimuli.
Humans↗
Spatial summation of the differential light threshold as a function of visual field location and age.
Static differential light thresholds were measured as a function of stimulus size (Goldmann sizes I-V) along four visual field meridia (75, 165, 255 and 345 degrees) with the Humphrey Field Analyzer 640. Data were obtained for both young (n = 10, age 23.6 +/- 2.9 years) and elderly (n = 10, age 72.0 +/- 5.2 years) normal subjects. The resulting peripheral spatial summation curves could be equated to the foveal data simply by a change in size scale, which increased linearly with eccentricity. E2 values, expressing the eccentricity at which stimulus size must double for performance to remain comparable to the fovea, were in the order of 3-9 degrees. Whilst the rate of scale change is approximately the same for both young and elderly observers, differences in performance can be explained by a combination of lower sensitivity and a bias in sensitivity towards larger stimulus sizes with increasing age.
Adult↗
Differential light threshold in automated static perimetry. Factors influencing short-term fluctuation.
The scatter of the differential light threshold observed during a single visual field test is called the short-term fluctuation. A number of factors that may influence the magnitude of the short-term fluctuation were studied. The main factor was the level of the differential light sensitivity itself, followed by the rate of false responses in the catch trials. The pupil size was only notable in patients with glaucoma, while age as well as the mean reaction time did not appear to be notable. The short-term fluctuation is not dependent on the location in the visual field up to 27 degrees of eccentricity degrees tested in normal subjects and patients suspected of having glaucoma, but there is a slight tendency in patients with glaucoma for a larger short-term fluctuation in the upper half of the visual field.
Differential Threshold↗
Short-term effect of intraocular pressure variation on differential light threshold and colour vision.
Laser trabeculoplasty was performed in one eye in each of 38 patients with uncontrolled chronic open-angle glaucoma (37 patients) or low-tension glaucoma (1). Topical therapy was stopped for 1 week before the procedure and for 1 week before reassessment 6 weeks later. Differential light threshold values were determined with an automatic perimeter four times throughout the study, and colour vision was tested twice. The patients were followed for 3 months. The rise and subsequent drop in intraocular pressure were not found to be correlated with differential light threshold or colour error scores.
Color Perception↗
Repression of Dpp targets in the Drosophila wing by Brinker.
Patterning along developing body axes is regulated by gradients of transcription factors, which activate or repress different genes above distinct thresholds. Understanding differential threshold responses requires knowledge of how these factors regulate transcription. In the Drosophila wing, expression of genes such as omb and sal along the anteroposterior axis is restricted by lateral-to-medial gradients of the transcriptional repressor Brinker (Brk). omb is less sensitive to repression by Brk than sal and is consequently expressed more laterally. Contrary to previous suggestions, we show that Brk cannot repress simply by competing with activators, but requires specific repression domains along with its DNA-binding domain. Brk possesses at least three repression domains, but these are not equivalent; one, 3R, is sufficient to repress omb but not sal. Thus, although sal and omb show quantitative differences in their response to Brk, there are qualitative differences in the mechanisms that Brk uses to repress them.
Amino Acid Sequence↗
[Age-specific structural features of the nasal septum in children].
Hearing was studied in 20 and 34 patients with subclinical and initial renal failure (RF), respectively. RF was secondary to chronic glomerulonephritis, chronic pyelonephritis, renal polycystosis (29, 24 and 1 patients, respectively). Hearing function was assessed at tonal threshold, suprathreshold and speech audiometry, ultrasound investigations. It was found that one third of the patients had bilateral symmetric hearing disorder of neurosensory hypoacusis type. The affection was not severe but involved both peripheral and central compartments of the acoustic analyzer. High-frequency sound sensitivity suffered most of all. There was a rise in hearing thresholds by air and bone conductivity at frequencies 12-18 kHz. This rise was the only marker of affected acoustic analyzer in 39% of the examinees. 12% of the patients demonstrated elevated hearing thresholds combined with elevated ultrasound thresholds, low differential threshold of sound intensity and abnormal threshold adaptation.
Adolescent↗
Differential color thresholds from metameric matches: experimental results concerning failures of colorimetric additivity.
The differential chromaticity thresholds obtained by varying degrees of metamerism have been evaluated for five target chromaticities. Differences have been found between the chromaticities predicted by the CIE-1931 standard observer and those actually observed under our experimental conditions, with foveal fields of 3 degrees, luminance within the low photopic level, and sets of primary colors produced by filters of differing spectral bandwidths. Failures of colorimetric additivity under these experimental conditions are discussed. The results have also been analyzed by using other sets of color-matching functions, i.e., Judd's proposed modification at short wavelengths and also the supplementary standard observer, CIE-1964.
Color↗