[Differential light threshold of the retina].
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Differential Threshold↗
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Neuropathies of the optic nerve and visual evoked potentials with special reference to color vision and differential light threshold measured with the computer perimeter OCTOPUS.
The contrast evoked potentials (VEPs) to different check sizes were recorded in about 200 cases of discrete optic neuropathies (ON) of different origin. Differential light threshold (DLT) was tested with the computer perimeter OCTOPUS. Saturated and desaturated tests were applied to evaluate the degree of acquired color vision deficiency. Delayed VEP responses are not confined to optic neuritis (RBN) alone and the different latency times obtained from other ON are confluent. The delay may be due to demyelination, to an increasing dominance of paramacular VEP subcomponents or to an increasing dominance of the upper half-field responses. Recording with smaller check sizes has the advantage that discrete dysfunctions in the visual field (VF) center are more easily detected: a correlation between amplitudes and visual acuity is best in strabismic amblyopias, is less expressed in maculopathies of the retina and weak in ON. The absence or reduction of amplitudes to smaller check sizes, however, is an important indication of a disorder in the VF center of ON in an early or recovered stage. Acquired color vision defects of the tritan-like type are more confined to discrete ON, whereas the red/green type is reserved to more severe ON. The DLT of the VF center is reduced in a different, significant and non significant extent in discrete optic neuropathies and the correlation between DLT and visual acuity is weak. A careful numerical analysis is needed in types of discrete ON where the central DLT lies within normal statistical limits: a side difference of the DLT between the affected and the normal fellow eye is always present. Evaluation of visual fatigue effects and of the relative sensitivity loss of VF center and VF periphery may provide further diagnostic information.
Adolescent↗
[Dynamics of the differential analyzer thresholds during activity].
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Acoustic Stimulation↗
Contingent negative variations and differential hearing thresholds.
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Acoustic Stimulation↗
Impaired short temporal interval discrimination in a dyslexic adult.
The ability to discriminate short temporal intervals was examined in a dyslexic adult (E.C.) and six matched controls. Listeners had to decide whether the second interval was shorter or longer than a standard (target) interval. Each interval was defined as the silent duration between two successive brief tones. Eight target intervals were used, ranging from 100 to 1,200 ms in duration. At each target interval, the differential threshold (DL) for duration was assessed, with the use of an adaptive psychophysical procedure. The results show that E.C.'s differential threshold values were much larger than those of controls. Moreover, the slope estimates covering the duration range from 100 to 800 ms indicated that in comparison to controls, E.C.'s differential threshold increased dramatically as the target duration increased. Thus her timing impairment becomes more pronounced with increasing duration. This timing deficit is consistent with other studies that have found temporal processing deficits associated with dyslexia.
Adaptation, Physiological↗
Monaural and binaural perception of approaching and withdrawing auditory images in humans.
Radial motion of the auditory image (approach or withdrawal) was modeled with the help of two loud-speakers placed at different distances from the listener in the anechoic chamber. The thresholds of sound duration for image motion and differential thresholds for its velocity at various azimuthal angles were studied. At azimuthal angles of 0 degrees, 30 degrees, 45 degrees, and 60 degrees, the threshold values of the stimulus durations were 150-200 ms. At an azimuthal angle of 90 degrees from the head midline, it increased by about 25-30% as compared to other angles. In the case of monaural listening to the signals by unilaterally deaf subjects, the threshold durations of the sound signals were two to three times higher as compared to healthy subjects. Differential thresholds for calculated velocity of the radial motion have been measured within the range 0.4-1.0 m/s, increasing with increase of the standard velocity from 3.4 to 6.9 m/s.
Adult↗
Unification of psychophysical phenomena: the complete form of Fechner's law.
Many of the laws and empirical observations of fundamental psychophysics can be unified with a single equation, which has been called the complete form of Fechner's law. It can be shown that this law embraces both of the commonly used forms: Stevens's and Fechner's laws. It assumes one or the other form with appropriate values of the parameters. However, the complete equation confers an advantage beyond simply containing the classical laws. It offers greater flexibility in the representation of experimental data. It is shown that psychophysical phenomena may be represented by any number of triplets of quantities: subjective magnitude of stimulus, subjective just noticeable difference (jnd), and differential threshold. Each of the preceding quantities are functions of the physical magnitude of the stimulus. The investigator has the license to choose two of these quantities in the form he or she thinks is best; the third quantity is determined by the choice of the first two. Thus, for example, different forms of the law of sensation and different forms of the mathematical function for differential threshold may coexist with equal validity.
Auditory Threshold↗
Handedness and psychophysics: weight and roughness.
A sample of 20 men (10 right-handed, 10 left-handed) was selected. Using the method of constant stimuli, the number of correct responses and the differential threshold for weight and roughness for both hands, were studied. The findings were: (1) In the weight test, the number of correct responses was greater and the differential threshold lower in the right-handed than in the left-handed subjects, and the preferred hand was superior to the nonpreferred hand for both groups; (2) In the roughness test, the number of correct responses was greater and the differential threshold lower for the nonpreferred hand. Implications of these findings with regard to our present knowledge of handedness organization are analyzed.
Adult↗
[INFLUENCE OF THE RATIO BETWEEN SURFACE AND BRIGHTNESS OF THE STIMULUS AND OF PUPIL DIAMETER ON THE DIFFERENTIAL RETINAL THRESHOLD EXAMINED WITH GOLDMANN'S PERIMETER IN MESOPIC CONDITIONS].
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Adolescent↗
Differential light threshold. Short- and long-term fluctuation in patients with glaucoma, normal controls, and patients with suspected glaucoma.
In the diagnosis and evaluation of progression of chronic open-angle glaucoma, a quantitative comparison of visual fields is important for which a knowledge of the spontaneous fluctuation of the visual field is essential. This study shows that in patients with glaucoma, the components of the short- and long-term fluctuation are substantially greater than in patients without the disease. Patients with suspected glaucoma show fluctuation in between, and all components of the fluctuation are greater in them than in normals and smaller than in patients with open-angle glaucoma.
Differential Threshold↗
Spatiotemporal boundaries of linear vection.
Thresholds for the perception of linear vection were measured. These thresholds allowed us to define the spatiotemporal contrast surface sensitivity and the spatiotemporal domain of the perception of rectilinear vection (a visually induced self-motion in a straight line). Moreover, a Weber's law was found, such that a mean relative differential threshold in angular velocity of about 41% is necessary to perceive curvilinear vection. This visually induced self-motion corresponds to the sensation of moving in a curved path. It is proposed that curvilinear vection is induced when the apparent velocity difference is detectable. The spatiotemporal domain of perception of rectilinear vection and its spatiotemporal contrast surface sensitivity are centered on low spatial frequencies. Concurrently, the values which correspond to the relative differential thresholds of curvilinear vection are low spatial frequencies. Accordingly, the peripheral ambient visual system seems to be involved in perceiving linear vection. It is argued further that the central ambient system might also be involved in the processing of linear vection.
Contrast Sensitivity↗
Unilateral and bilateral temperature comparisons in acallosal and split-brain subjects.
Therapeutic section of the corpus callosum in adult epileptic patients typically results in their incapacity to carry out interhemispheric comparisons of lateralized information. The fact that acallosal and early split-brain subjects display few of these symptoms when tested in the tactile modality has led to the suggestion that these patients may use ipsilateral projections of the somatosensory system more effectively. Compensation, however, is limited by the fact that the lemniscal pathway is strongly lateralized, especially for the distal parts of the body, where few ipsilaterally projecting fibres have been demonstrated. The pathway carrying temperature information has a larger ipsilateral component. Bilateral comparisons within the same hemisphere in subjects who are lacking the corpus callosum should be more common and the development of compensatory mechanisms in early-sectioned or acallosal subjects should be more likely. The objective of the present experiment was to evaluate differential thresholds for thermal stimuli applied on a number of regions either on the same side or on corresponding sites on opposite sides of the body. One subject callosotomized as an adult and one split-brain subject who underwent callosotomy in childhood, as well as three acallosal subjects, were compared to IQ-matched and normal-IQ control subjects. The fingers, forearm and trunk were tested. The comparison temperature was 30 degrees C and the other was varied in an ascending or descending fashion using a modified method of limits. Differential thresholds were similar for within- and between-side comparisons, and comparable to those of the IQ-matched subjects. The results indicate that comparisons involving temperature discrimination for stimuli applied to the two sides of the body do not require the integrity of the corpus callosum.
Adolescent↗
Fluctuation of the differential light threshold at the border of absolute scotomas. Comparison between glaucomatous visual field defects and blind spots.
The outcome of repeated measurements of the differential light sensitivity fluctuates slightly. This fluctuation can be markedly increased in glaucoma patients but has also been described at the border of the blind spot of healthy subjects. The question arises, therefore, whether in glaucoma this increase may be due to the fact that many test locations may touch the border of (detected or undetected) scotomas. This study compares the behavior of the threshold at the border of glaucomatous defects and blind spots. The threshold was measured with program F8 of the Octopus 201 (Interzeag, Inc, Schlieren, Switzerland) automated static perimeter. The results revealed that the borders of glaucomatous defects are less steep than those of blind spots, the fluctuation is largest just at the border of the scotomas in both groups, and that the fluctuation is significantly larger at the edge of glaucomatous defects than at the edge of blind spots of normal subjects.
Glaucoma, Open-Angle↗
Dual-energy CT in the diagnosis and quantification of fatty liver: limited clinical value in comparison to ultrasound scan and single-energy CT, with special reference to iron overload.
BACKGROUND/AIMS: It has been suggested that dual-energy CT could differentiate irregular fatty liver from other hypodense lesions. We compared dual-energy CT to ultrasound scan and single-energy CT in the diagnosis and quantification of fatty liver, with special reference to iron overload. METHODS: Twenty-seven patients were included according to ultrasound: fatty liver (n=16) and normal liver (n=11). Single and dual-energy CT were performed. Attenuation measurements of hepatic lobes and control tissues were taken at 140 kV and 80 kV CT-guided liver biopsy was done in fatty liver patients, the degree of infiltration was estimated, and the histologic iron overload determined (iron overload, n=11; iron-free, n=5). RESULTS: The mean changes in attenuation for the right hepatic lobe were: normal liver: -0.8 (ns); iron overloaded fatty liver: 1.5 (ns); and iron-free fatty liver: 7.7 (p<0.0053). A spleen-liver attenuation differential threshold of 12H (140 kV, single-energy CT) and a right hepatic lobe 140 kV to 80 kV attenuation differential threshold of 9 H (dual-energy CT) were specific for fatty liver. Histology confirmed all cases of fatty liver diagnosed by ultrasound, independently of iron overload. Ultrasound did not differentiate cases of irregular from diffuse fatty liver detected on CT. Iron overload produced a masking effect in CT, decreasing its sensitivity: fatty liver was diagnosed in 67% of cases by single-energy CT and in 20% by dual-energy CT. Degree of fatty infiltration correlated with single-energy CT. CONCLUSIONS: Ultrasound diagnosed fatty liver best. Single-energy CT quantifies fatty infiltration, and best differentiates the irregular from the diffuse forms. Dual-energy CT is limited by poor sensitivity, especially in iron overload.
Adult↗
Psychophysical characteristics of the auditory image movement perception during dichotic stimulation.
Dichotic stimulation with binaurally presented click trains at time-varying interaural differences of stimulation caused a pronounced sensation of fused image (FI) movement in man. Threshold click rate in the trains needed for the FI movement sensation during variations of interaural time differences of stimulation equalled 7.6 Hz and during variations of interaural intensity differences it equalled 9.6 Hz. When FI movement velocity ranged from about 20 to 120 degrees/s with changing interaural intensity of stimulation, differential threshold for FI movement velocity increased from 2 to 12 degrees/s. Relative differential thresholds of the perception of FI movement velocity were essentially independent of the velocity. Subjective scales of FI movement velocity perception could be basically approximated by linear relations y = AX, y = A(X-X0). The scale slopes appeared to be significantly different during fractionation and multiplication procedures.
Acoustic Stimulation↗
Duration discrimination of empty and filled intervals marked by auditory and visual signals.
Experiments 1 and 2 compared, with a single-stimulus procedure, the discrimination of filled and empty intervals in both auditory and visual modalities. In Experiment 1, in which intervals were about 250 msec, the discrimination was superior with empty intervals in both modalities. In Experiment 2, with intervals lasting about 50 msec, empty intervals showed superior performance with visual signals only. In Experiment 3, for the auditory modality at 250 msec, the discrimination was easier with empty intervals than with filled intervals with both the forced-choice (FC) and the single stimulus (SS) modes of presentation, and the discrimination was easier with the FC than with the SS method. Experiment 4, however, showed that at 50 and 250 msec, with a FC-adaptive procedure, there were no differences between filled and empty intervals in the auditory mode; the differences observed with the visual mode in Experiments 1 and 2 remained significant. Finally, Experiment 5 compared differential thresholds for four marker-type conditions, filled and empty intervals in the auditory and visual modes, for durations ranging from .125 to 4 sec. The results showed (1) that the differential threshold differences among marker types are important for short durations but decrease with longer durations, and (2) that a generalized Weber's law generally holds for these conditions. The results as a whole are discussed in terms of timing mechanisms.
Acoustic Stimulation↗
Breathing reserve at the lactate threshold to differentiate a pulmonary mechanical from cardiovascular limit to exercise.
STUDY OBJECTIVES: Criteria used to define the respective roles of pulmonary mechanics and cardiovascular disease in limiting exercise performance are usually obtained at peak exercise, but are dependent on maximal patient effort. To differentiate heart from lung disease during a less effort-dependent domain of exercise, the predictive value of the breathing reserve index (BRI=minute ventilation [VE]/maximal voluntary ventilation [MVV]) at the lactate threshold (LT) was evaluated. DESIGN: Thirty-two patients with COPD and a pulmonary mechanical limit (PML) to exercise defined by classic criteria at maximum oxygen uptake (VO2max) were compared with 29 patients with a cardiovascular limit (CVL) and 12 normal control subjects. Expired gases and VE were measured breath by breath using a commercially available metabolic cart (Model 2001; MedGraphics Corp; St. Paul, Minn). Arterial blood gases, pH, and lactate were sampled each minute during exercise, and cardiac output (Q) was measured by first-pass radionuclide ventriculography (System 77; Baird Corp; Bedford, Mass) at rest and peak exercise. RESULTS: For all patients, the BRI at lactate threshold (BRILT) correlated with the BRI at VO2max (BRIMAX) (r=0.85, p<0.0001). The BRILT was higher for PML (0.73+/-0.03, mean+/-SEM) vs CVL (0.27+/-0.02, p<0.0001), and vs control subjects (0.24+/-0.03, p<0.0001). A BRILT > or = 0.42 predicted a PML at maximum exercise, with a sensitivity of 96.9%, a specificity of 95.1%, a positive predictive value of 93.9%, and a negative predictive value of 97.5%. CONCLUSIONS: The BRILT, a variable measured during the submaximal realm of exercise, can distinguish a PML from CVL.
Cardiac Output↗
The visual field in chronic simple glaucoma and ocular hypertension; its character, progress, relationship to the level of intraocular pressure and response to treatment.
Nine hundred and twenty-nine patients with chronic simple glaucoma or ocular hypertension were followed for one to thirteen years using the King's College Hospital glaucoma data base. The 30 degree visual field was divided into twelve clinical zones. The field sensitivity and its change as measured by the mean differential threshold both in these zones and overall was followed to determine the pattern and progress of field loss in eyes diagnosed initially as chronic simple glaucoma or ocular hypertension. The findings were related to other similar analyses in which the mean differential threshold in chronic glaucoma was found to correlate significantly with the initial intraocular pressure and its progress with the mean follow-up intraocular pressure under treatment. Inferences were drawn regarding the nature of chronic simple glaucoma and ocular hypertension and their management.
Adult↗