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Results for “Differential Threshold”

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PubMed1981

Psychophysical properties of displacement thresholds for moving targets.

Psychophysical movement displacement thresholds were determined for three stimulus parameters (line length, stimulus luminance, and duration of movement) at various locations in the visual field. Although some differences were noted, foveal and peripheral movement displacement threshold functions were generally similar when scaled and plotted on logarithmic coordinates. The findings were consistent with known physiological and anatomical properties of retina, and suggest that retinal mechanisms are an important determinant of motion displacement threshold.

Differential Threshold↗
PubMed2006

CT colonography with computer-aided polyp detection: volume and attenuation thresholds to reduce false-positive findings owing to the ileocecal valve.

PURPOSE: To retrospectively identify volume and average attenuation thresholds for differentiating between ileocecal valve (ICV) and polyp at computed tomographic (CT) colonography with computer-aided detection (CAD). MATERIALS AND METHODS: Informed consent (with consent for future retrospective research) and institutional review board (IRB) approval were obtained for the original prospective study. This retrospective study had IRB approval, as well, and was HIPAA-compliant. A total of 496 patients were selected from a larger screening population. CT colonographic images from 394 patients (227 men, 167 women; mean age, 58.0 years; range, 40-79 years) were used as a training set, and images from 102 patients (76 men, 26 women; mean age, 59.8 years; range, 46-79 years) were used as a test set. A series of 2742 volume and attenuation thresholds, for which segmented findings both larger in volume and lower in average attenuation were labeled as ICVs and remaining findings were labeled polyps, were applied to the training set to determine settings with 100% sensitivity for polyp detection and the highest specificity for ICV detection. The optimal settings were then applied to the test set. Significance was assessed with the Fisher exact test, and 95% confidence intervals (CIs) were computed for sensitivity and specificity. RESULTS: A total of 386 ICVs and 67 adenomatous polyps from the training set and 102 ICVs and 138 adenomatous polyps from the test set could be segmented with a three-dimensional segmentation algorithm. When supine and prone images were counted individually, 746 nonunique ICVs from the training set and 191 from the test set were segmentable. In the training set, a volume of 600 mm(3) and an attenuation of 36 HU provided 100% sensitivity (67 polyps; 95% CI: 93%, 100%) and the optimal 83% specificity (618 of 746 ICVs; 95% CI: 80%, 85%). When applied to the test set, this combination provided 97% sensitivity (134 of 138 polyps; 95% CI: 92%, 99%) and 84% specificity (160 of 191 ICVs; 95% CI: 78%, 89%). Differences in sensitivity and specificity in the detection of polyps between the sets were not significant. CONCLUSION: Volume and average CT attenuation thresholds can help differentiate most ICVs from true polyps.

Adult↗
PubMed1992

Non-differential underestimation may cause a threshold effect of exposure to appear as a dose-response relationship.

It is generally believed that non-differential misclassification will lead to a bias toward the null-value. However, using one graphical and one numerical example, we show that in situations where underestimation more than overestimation is the problem, non-differential misclassification may lead to a bias away from the null-value for intermediate categories of exposure variables. We show that a true threshold level for an exposure may, subsequently, appear as a dose-response relationship. Underestimation more than overestimation is likely to occur in studies in which self-reports are used to obtain data on activities which respondents voluntarily engage in and which are socially not acceptable or known to be potentially dangerous. Researchers should be aware that both a shown deleterious effect at a low level of exposure and a dose-response relationship may in fact be spurious and due to underestimation of exposure at higher levels.

Bias↗
PubMed1981

Detection and discrimination of moving gratings.

Two techniques are described which have been used to investigate mechanisms underlying the perception of velocity. The first, subthreshold summation establishes detection thresholds of two gratings of different spatial frequencies moving at the same velocity and also the detection thresholds of combinations of these gratings. The second technique employed a detection/discrimination procedure which establishes the discriminability of two different moving gratings at detection threshold. These experiments suggest that at low velocities the detection of 2 and 6 cycle/degree gratings is mediated by independent mechanisms, this independence being diminished at higher velocities. Gratings of 2 cycles/degree moving at different velocities are only discriminably different at detection threshold when widely separated in velocity.

Differential Threshold↗
PubMed2005

Parametric decomposition of optic flow by humans.

Ego motion and natural motions in the world generate complex optic flows in the retina. These optic flows, if produced by rigid surface patches, can be decomposed into four components, including rotation and expansion. We showed previously that humans can precisely estimate parameters of these components, such as the angular velocity of a rotational motion and the rate of expansion of a radial motion. However, natural optic flows mostly display motions containing a combination of more than one of these components. Here, we report that when a pure motion (e.g., rotation) is combined with its orthogonal component (e.g., expansion), no bias is found in the estimate of the component parameters. This suggests that the visual system can decompose complex motions. However, this decomposition is such that the presence of the orthogonal component increases the discrimination threshold for the original component. We propose a model for how the brain decomposes the optic flow into its elementary components. The model accounts for how errors in the estimate of local-velocity vectors affect the decomposition, producing the increase of discrimination thresholds.

Brain↗
PubMed1999

Effects of a hair cell transcription factor, Brn-3.1, gene deletion on homozygous and heterozygous mouse cochleas in adulthood and aging.

The transcription factor Brn-3.1, is expressed in the inner ear hair cells throughout life and is necessary for the development of these cells. Mutant mice in which the Brn-3.1 encoding region has been deleted have no identifiable hair cells, greatly reduced numbers of spiral ganglion cells and are deaf. A mutation in the human homologue of this gene has been shown to be related to adult onset, sensorineural hearing loss (Vahava et al., 1998). The question whether haploinsufficiency in the mutant Brn-3.1 mouse with a mixed C57BL6/129Sv genetic background could affect the adult or aged cochlea was tested, therefore, by measuring the auditory brainstem responses and examining the cochlea's histologically at 2, 18 and 24 months of age. The heterozygotes had a comparable hearing to the wild-type animals and similar patterns of cochlear degeneration. Both groups showed an about 30 dB hearing loss beginning at 18 months of age, outer hair cell degeneration and loss of spiral ganglion neurons in the basal turn. There appeared to be no effect of Brn-3.1 haploinsufficiency on the mouse cochlea, implying that one intact copy of the gene is sufficient to maintain a normal cochlea.

Aging↗
PubMed2007

Influence of chronic middle ear diseases on gustatory function: an electrogustometric study.

OBJECTIVE: We aimed to quantitatively determine whether middle ear inflammation associated with unilateral chronic otitis media (COM), cholesteatoma, or otosclerosis affects gustatory function. STUDY DESIGN: Prospective study. SETTING: University Hospital, Department of Otolaryngology. PATIENTS: Forty-two patients had unilateral COM (22 men, 20 women; mean age, 54.2 yr), 57 had unilateral cholesteatoma (35 men, 22 women; mean age, 42.1 yr), and 19 had unilateral otosclerosis (10 men, 9 women; mean age, 49.3 yr). MAIN OUTCOME MEASURES: Patients underwent taste testing using electrogustometry (EGM) and sensation thresholds were compared in the affected and unaffected ears among groups and between affected and unaffected ears in each group. RESULTS: Patients with COM and cholesteatoma exhibited an increase in taste threshold in the affected ears compared to the unaffected ears (p < 0.05), whereas otosclerosis patients did not. The extent of the increase of the sensation thresholds in the affected ears was very similar between patients with COM and those with cholesteatoma (p = 0.548). CONCLUSION: Our EGM study showed that cholesteatoma and chronic middle ear inflammation affected gustatory function to a similar degree.

Adult↗
PubMed1994

Functional expression of human D3 dopamine receptors in differentiated neuroblastoma x glioma NG108-15 cells.

This study describes the depression of calcium currents caused by activation of human D3 dopamine receptors which have been stably expressed in the neuroblastoma x glioma NG108-15 cell line. Transfected cells, which had been differentiated with prostaglandin E1 and isobutylmethylxanthine, exclusively expressed D3 receptor mRNA, which was demonstrated by reverse transcription polymerase chain reaction techniques. Transfected cells had high affinity binding sites for iodosulpiride, with a Kd of 0.8 nM and receptor density of 240 fmol mg-1 protein. Calcium currents were recorded using nystatin-perforated patch clamp techniques. In contrast to untransfected cells that had been differentiated, high-threshold calcium currents in differentiated hD3-NG108-15 cells were depressed by application of dopamine and quinpirole. These responses were abolished by the dopamine receptor antagonist S-(-)-sulpiride (1 microM), demonstrating that they were caused by the activation of the transfected dopamine receptors. Coupling of human D3 receptors to calcium currents was sensitive to the action of pertussis toxin, suggesting the involvement of G-proteins of the Gi and/or G(o) subtype. These results demonstrate that human D3 receptors represent a functional class of dopamine receptor.

Brain Neoplasms↗
PubMed2001

Binaural processing model based on contralateral inhibition. III. Dependence on temporal parameters.

This paper and two accompanying papers [Breebaart et al., J. Acoust. Soc. Am. 110, 1074-1088 (2001); 110, 1089-1104 (2001)] describe a computational model for the signal processing of the binaural auditory system. The model consists of several stages of monaural and binaural preprocessing combined with an optimal detector. Simulations of binaural masking experiments were performed as a function of temporal stimulus parameters and compared to psychophysical data adapted from literature. For this purpose, the model was used as an artificial observer in a three-interval, forced-choice procedure. All model parameters were kept constant for all simulations. Model predictions were obtained as a function of the interaural correlation of a masking noise and as a function of both masker and signal duration. Furthermore, maskers with a time-varying interaural correlation were used. Predictions were also obtained for stimuli with time-varying interaural time or intensity differences. Finally, binaural forward-masking conditions were simulated. The results show that the combination of a temporal integrator followed by an optimal detector in the time domain can account for all conditions that were tested, except for those using periodically varying interaural time differences (ITDs) and those measuring interaural correlation just-noticeable differences (jnd's) as a function of bandwidth.

Auditory Threshold↗