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Results for “Differential Threshold”

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PubMed1989

Matching forces: constant errors and differential thresholds.

A contralateral limb-matching procedure was used to study the perception of forces generated by the elbow flexor muscles. Subjects were required to generate forces ranging from 15 to 85% of their maximum voluntary contraction (MVC range: 169-482 N), and after achieving the target force to produce a force of the same perceived intensity with their contralateral arm. Under these conditions, subjects consistently overestimated the amplitude of the two lowest forces, and the most accurate matching of forces occurred in the middle of the response range (around 50% MVC). This pattern of constant errors could be explained in terms of an artifact of the starting position, which has been shown to influence the accuracy of judgements of stimulus magnitude. The Weber fraction for force calculated from the matching data was 0.07, which is within the range reported previously for weight. These thresholds are, however, considerably lower than those described for friction and the moment of inertia, the perception of which also involves the proprioceptive system.

Adult↗
PubMed1986

The interpretation of the differential threshold in the central visual field.

Computer assisted perimetry has revolutionised the investigation of the visual field. Experience of central field assessment with the Octopus Automated Perimeter shows that sensitivity recorded with target size 3 across all age groups can frequently be greater than the published normative values. Use of the latter values can therefore provide a serious underestimation of field loss. Inter-individual variation in sensitivity is found within and between age groups. The limitations associated with the use of the measurement error to define abnormality and the additional problems of hypernormal thresholds and resolution of the blind spot are discussed. It is suggested that methods should be developed to evaluate sensitivity on an intra-individual basis.

Adolescent↗
PubMed1983

Changes in differential threshold in patients with glaucoma during prolonged perimetry.

Patients with chronic open-angle glaucoma and others suspected of having glaucoma were subjected to continuous contrast threshold measurement by automatic and manual perimetric techniques. The results show that an increase of contrast threshold over time is a frequent finding in glaucoma patients and that this increment can be large, especially at points close to existing field defects. it is reproducible and independent of background illumination and can be demonstrated with both automatic and manual testing, but it is larger in the automatic than in the manual mode of testing. The results may have some important implications for visual field testing in glaucoma.

Differential Threshold↗
PubMed1985

Automated differential threshold perimetry for detecting glaucomatous visual field loss.

Because early glaucomatous visual field defects occur asymmetrically across the horizontal meridian, we analyzed data from automated perimetry by comparing sums of threshold values of corresponding groups of points in the superior and inferior hemispheres of the central 30 degrees tested by the Humphrey Field Analyzer. We developed patterns and criteria from 25 early glaucomatous and 36 normal control eyes to achieve optimal balance between sensitivity (96%) and specificity (86%). Application of these criteria to an independent group of 27 glaucomatous and 105 control eyes yielded a sensitivity of 88.9% and specificity of 85.7%. Minor modification of the criteria improved sensitivity and specificity to more than 90% for both patients and controls.

Adult↗
PubMed1997

Differential threshold of length and response criterion for inspecting irregular objects.

This research investigated human visual sensitivity and bias in inspecting irregular objects. A preliminary study was conducted using the method of constants to determine the threshold value for judgment of size. A factorial experiment was conducted using payoffs, rate of defective items, and detectability in the signal-detection theory as the factors. In total, eight experimental conditions were tested. 10 college students were recruited as subjects. Each subject was asked to compare 40 teapot shapes to a standard teapot shape under eight experimental conditions. Defective shapes were generated by lengthening the vertical dimension of a standard teapot shape by a factor of 1.01 and 1.04 for 'low' and 'high' detectability. The decision time and responses of 'identical' or 'different' were collected under all experimental conditions. Analysis indicates that the decision-making strategy used to inspect this irregular object was very close to maximizing the accuracy of decision-making by considering the rate of defective items. This result is different from most research findings in signal-detection theory in which responses of human beings are similar to degraded Bayes optimizers. The standard deviation of the signal distribution was about 1.30 and 1.41 times that of the noise distributions for 'low' and 'high' detectability.

Decision Making↗
PubMed1988

Differential threshold for long-term potentiation in the hippocampus of rats with inborn high or low learning capacity.

Threshold of stimulation frequency in the perforant path to induce long-term potentiation (LTP) in dentate gyrus was determined in hippocampal slices obtained from two different lines of rats inbred for 30 generations according to their performance in an avoidance escape test in a shuttle box. High-performance (HP) rats were defined as those giving at least 70% conditioned responses (CRs) and low-performance (LP) rats as those giving less than 15% CRs. LTP was defined as a 30% or more increase in the amplitude of the evoked population spike (PS), lasting at least 20 min. Stimulation frequency threshold was determined by stimulating with a train of pulses of 0.5 ms duration during 1 s. The same slice was stimulated with trains of increasing frequency from 5 to 400 Hz, each train separated by an interval of at least 20 min. HP rats showed a lower threshold (13 +/- 4 Hz) than LP rats (92 +/- 42 Hz) for the induction of LTP; there were no differences in the magnitude of LTP. The greater learning ability of HP rats may be related to the plasticity of hippocampal synaptic transmission.

Action Potentials↗
PubMed2002

Differential thresholds of local field potentials and unit discharges in rat auditory cortex.

Thresholds for responses to tone bursts in the primary auditory field of pentobarbital-anesthetized rat are significantly lower for local field potentials (5.60 dB+/-1.76 S.E.M.) than for multiple unit discharges (17.80 dB+/-3.17), recorded simultaneously from the same microelectrode. The characteristic frequencies (CFs) of local field potentials provide a good 'predictive' estimate of unit CFs at their higher thresholds. The findings are consistent with the view that local field potentials in the auditory cortex reflect summed synaptic potentials rather than cellular discharges.

Acoustic Stimulation↗