scholarly journals Suprathreshold contrast response in normal and anomalous trichromats

2019 ◽  
Author(s):  
Kenneth Knoblauch ◽  
Brennan Marsh-Armstrong ◽  
John S. Werner
Keyword(s):  
Maximum Likelihood ◽  
Low Frequency ◽  
Luminance Contrast ◽  
Contrast Gain ◽  
Detection Model ◽  
Response Range ◽  
The Difference ◽  
Contrast Response ◽  
Contrast Range ◽  
Perceptual Scale

AbstractMaximum Likelihood Difference Scaling was used to measure suprathreshold contrast response difference scales for low-frequency Gabor patterns modulated along luminance and L-M color directions in normal, protanomalous, and deuteranomalous observers. Based on a signal-detection model, perceptual scale values, parameterized as d′, were estimated by maximum likelihood. The difference scales were well fit by a Michaelis-Menten model, permitting estimates of response and contrast gain parameters for each subject. Anomalous observers showed no significant differences in response or contrast gain from normal observers for luminance contrast. For chromatic modulations, however, anomalous observers displayed higher contrast and lower response gain compared to normal observers. These effects cannot be explained by simple pigment shift models and support a compensation mechanism to optimize the mapping of the input contrast range to the neural response range. A linear relation between response and contrast gain suggests a neural trade-off between them.

Visual evoked potentials for red–green gratings reversing at different temporal frequencies: Asymmetries with respect to isoluminance

2005 ◽  
Vol 22 (6) ◽  
pp. 735-747 ◽  
Author(s):  
INGER RUDVIN ◽  
ARNE VALBERG
Keyword(s):  
Evoked Potentials ◽  
Visual Evoked Potentials ◽  
Sudden Change ◽  
Luminance Contrast ◽  
Rapid Phase ◽  
Response Characteristics ◽  
Reversal Frequency ◽  
Contrast Response ◽  
Contrast Range ◽  
Visual Evoked

Human visual evoked potentials (VEPs) were recorded for abrupt reversals of 2 cycles/deg (c/deg) square-wave gratings combining high red–green contrast with different levels of luminance contrast. Response characteristics—2nd harmonic amplitudes and peak latencies as a function of luminance contrast—were compared for four different reversal rates ranging from 6.25 Hz to 12.5 Hz. At every reversal frequency, the VEP amplitude and latency plots were nonsymmetrical with respect to isoluminance. The amplitude dropped to a minimum within a region of rapid phase change, always at a red–green luminance contrast for which the green color had the higher luminance, at about 40% or 50% Michelson luminance contrast. The rapid phase shift around this contrast suggested a sudden change in the relative impact of VEP generators with different latencies, possibly dominated by parvocellular or magnocellular input. The most prominent VEP waveform through most of the luminance contrast range, P110, is interpreted in terms of a parvo-mediated response that is attenuated with increasing reversal frequency. Contrast-dependent changes in the P110 amplitude appear to be responsible for the VEP asymmetries reported here.

Contrast gain control in the kitten's visual system

1985 ◽  
Vol 54 (3) ◽  
pp. 668-675 ◽  
Author(s):  
G. Sclar ◽  
I. Ohzawa ◽  
R. D. Freeman
Keyword(s):  
Gain Control ◽  
Sine Wave ◽  
Response Functions ◽  
Cortical Cells ◽  
Contrast Gain ◽  
Contrast Gain Control ◽  
Response Range ◽  
Adult Cats ◽  
Contrast Response ◽  
Different Levels

We have studied the effects of contrast adaptation on cortical cells from 4- and 6-wk-old kittens (49 and 47 cells, respectively) using sine-wave grating stimuli. We wished to know if the effects of adaptation to different contrast levels are more extensive than those in adult animals. Our experiments involved adapting cells to different contrasts (3.1, 12.5, and 50%) while concurrently measuring their contrast-response functions at each of these different levels. We found qualitatively that the effects of adaptation in the kitten are similar to those we have previously documented in adult animals (19). Contrast-response functions are laterally shifted along the log-contrast axis, effectively matching the response range of the cells to prevailing contrast levels. The degree to which this occurred varied from cell to cell. The average degree to which cells showed these effects, as assessed both qualitatively and quantitatively, was greater for kittens than for adult cats, and greater for 4-wk-old kittens than for those aged 6 wk. This suggests that susceptibility to adaptation varies as a function of age. Additional studies were undertaken with the intent of localizing these adaptive effects. First, lateral geniculate cells and fibers (n = 23) were studied with our standard protocol, and second, we investigated the degree to which the effects of adaptation of cortical cells transferred interocularly.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Analysis of Low-Frequency Mutations Associated with Drug Resistance to Raltegravir before Antiretroviral Treatment

2010 ◽  
Vol 55 (3) ◽  
pp. 1114-1119 ◽  
Author(s):  
Jia Liu ◽  
Michael D. Miller ◽  
Robert M. Danovich ◽  
Nathan Vandergrift ◽  
Fangping Cai ◽  
...  
Keyword(s):  
Drug Resistance ◽  
Treatment Failure ◽  
Low Frequency ◽  
Hiv Treatment ◽  
Viral Population ◽  
Virologic Suppression ◽  
Resistance Mutations ◽  
The Difference ◽  
Allele Specific Sequencing ◽  
Hiv 1

ABSTRACTRaltegravir is highly efficacious in the treatment of HIV-1 infection. The prevalence and impact on virologic outcome of low-frequency resistant mutations among HIV-1-infected patients not previously treated with raltegravir have not been fully established. Samples from HIV treatment-experienced patients entering a clinical trial of raltegravir treatment were analyzed using a parallel allele-specific sequencing (PASS) assay that assessed six primary and six secondary integrase mutations. Patients who achieved and sustained virologic suppression (success patients,n= 36) and those who experienced virologic rebound (failure patients,n= 35) were compared. Patients who experienced treatment failure had twice as many raltegravir-associated resistance mutations prior to initiating treatment as those who achieved sustained virologic success, but the difference was not statistically significant. The frequency of nearly all detected resistance mutations was less than 1% of viral population, and the frequencies of mutations between the success and failure groups were similar. Expansion of pre-existing mutations (one primary and five secondary) was observed in 16 treatment failure patients in whom minority resistant mutations were detected at baseline, suggesting that they might play a role in the development of drug resistance. Two or more mutations were found in 13 patients (18.3%), but multiple mutations were not present in any single viral genome by linkage analysis. Our study demonstrates that low-frequency primary RAL-resistant mutations were uncommon, while minority secondary RAL-resistant mutations were more frequently detected in patients naïve to raltegravir. Additional studies in larger populations are warranted to fully understand the clinical implications of these mutations.

scholarly journals Meteorological conditions over Antarctic blue-ice areas and their influence on the local surface mass balance

2001 ◽  
Vol 47 (156) ◽  
pp. 37-50 ◽  
Author(s):  
Richard Bintanja ◽  
Carleen H. Reijmer
Keyword(s):  
Mass Balance ◽  
Low Frequency ◽  
Meteorological Conditions ◽  
Surface Mass Balance ◽  
Surface Mass ◽  
Wind Speeds ◽  
Dry Conditions ◽  
The Difference ◽  
Sublimation Rates ◽  
Different Characteristics

AbstractThis paper addresses the causes of the prevailing meteorological conditions observed over an Antarctic blue-ice area and their effect on the surface mass balance. Over blue-ice areas, net accumulation is zero and ablation occurs mainly through sublimation. Sublimation rates are much higher than over adjacent snowfields. The meteorological conditions favourable for high sublimation rates (warm, dry and gusty) are due to the specific orographic setting of this blue-ice area, with usually a steep upwind mountainous slope causing strong adiabatic heating. Diabatic warming due to radiation, and entrainment of warm air from aloft into the boundary layer augment the warming. The prevailing warm, dry conditions explain roughly 50% of the difference in sublimation, and the different characteristics of blue ice (mainly its lower albedo) the other 50%. Most of the annual sublimation (∼70%) takes place during the short summer (mainly in daytime), with winter ablation being restricted to occasional warm, dry föhn-like events. The additional moisture is effectively removed by entrainment and horizontal advection, which are maximum over the blue-ice area. Low-frequency turbulent motions induced by the upwind mountains enhance the vertical turbulent transports. Strong gusts and high peak wind speeds over blue-ice areas cause high potential snowdrift transports, which can easily remove the total precipitation, thereby maintaining zero accumulation.

Dynamics of Ferroelectric and Nematic Liquid Crystals Confined in Porous Matrices

1994 ◽  
Vol 366 ◽  
Author(s):  
Fouad M. Aliev
Keyword(s):  
Liquid Crystals ◽  
Heterogeneous Media ◽  
Volume Fraction ◽  
Low Frequency ◽  
Pore Wall ◽  
Polar Molecules ◽  
Average Pore ◽  
Surface Polarization ◽  
The Difference ◽  
Frequency Relaxation

ABSTRACTWe performed dielectric spectroscopy measurements to study dynamics of collective modes of ferroelectric (FLC) and molecular motion of nematic (NLC) liquid crystals with polar molecules confined in silica macroporous and microporous glasses with average pore sizes of 1000 Å (volume fraction of pores 40%) and 100 Å (27%) respectively. For FLC the Goldstone and the soft modes are found in macropores. The rotational viscosity associated with the soft mode is about 10 times higher in pores than in the bulk. These modes are not detected in micropores although low frequency relaxation is present. The last one probably is not connected with the nature of liquid crystal but is associated with surface polarization effects typical for two component heterogeneous media. The difference between the dynamics of orientational motion of the polar molecules of NLC in confined geometries and in the bulk is qualitatively determined by the total energy Fs of the interaction between molecules and the surface of the pore wall, which is found Fs ≈ 102erg/cm2.

High-frequency seismic noise as a function of depth

1991 ◽  
Vol 81 (4) ◽  
pp. 1101-1114
Author(s):  
Jerry A. Carter ◽  
Noel Barstow ◽  
Paul W. Pomeroy ◽  
Eric P. Chael ◽  
Patrick J. Leahy
Keyword(s):  
New York ◽  
High Frequency ◽  
Seismic Noise ◽  
Low Frequency ◽  
Time Variability ◽  
Orthogonal Components ◽  
The Difference ◽  
Frequency Coherence ◽  
Cultural Noise ◽  
Natural Wind

Abstract Evidence is presented supporting the view that high-frequency seismic noise decreases with increased depth. Noise amplitudes are higher near the free surface where surface-wave noise, cultural noise, and natural (wind-induced) noise predominate. Data were gathered at a hard-rock site in the northwestern Adirondack lowlands of northern New York. Between 15- and 40-Hz noise levels at this site are more than 10 dB less at 945-m depth than they are at the surface, and from 40 to 100 Hz the difference is more than 20 dB. In addition, time variability of the spectra is shown to be greater at the surface than at either 335- or 945-m depths. Part of the difference between the surface and subsurface noise variability may be related to wind-induced noise. Coherency measurements between orthogonal components of motion show high-frequency seismic noise is more highly organized at the surface than it is at depth. Coherency measurements between the same component of motion at different vertical offsets show a strong low-frequency coherence at least up to 945-m vertical offsets. As the vertical offset decreases, the frequency band of high coherence increases.

Low frequency of BCL-2/JH translocation in peripheral blood lymphocytes of healthy Japanese individuals

Blood ◽  
2001 ◽  
Vol 98 (2) ◽  
pp. 486-488 ◽  
Author(s):  
Masaki Yasukawa ◽  
Shiro Bando ◽  
Gottfried Dölken ◽  
Eiji Sada ◽  
Yoshihiro Yakushijin ◽  
...  
Keyword(s):  
Follicular Lymphoma ◽  
Peripheral Blood ◽  
Low Frequency ◽  
Peripheral Blood Lymphocytes ◽  
Blood Lymphocytes ◽  
Japanese Adults ◽  
Japanese General Population ◽  
The Difference ◽  
Follicular Lymphomas ◽  
Immunoglobulin Heavy Chain Genes

The incidence of follicular lymphoma differs significantly between white and Japanese individuals. Translocation between theBCL-2 and immunoglobulin heavy chain genes is detected in 85% to 90% of all follicular lymphomas in whites. Recently,BCL-2/JH translocation was detected in peripheral blood lymphocytes from more than 50% of healthy white individuals. To clarify the reason for the difference in incidence of follicular lymphoma between whites and Japanese, the frequency ofBCL-2/JH translocation in peripheral blood lymphocytes of healthy Japanese individuals was compared with that of German individuals. The prevalence of BCL-2/JHtranslocation in Japanese adults appeared to be significantly lower than that in German adults. The present data suggest that the low frequency of BCL-2/JH translocation in the Japanese general population may be one of the major reasons for the difference in incidence of follicular lymphoma between whites and Japanese.

Extra Force From Asynchronous Stimulation of Cat Soleus Muscle Results From Minimizing the Stretch of the Common Elastic Elements

2006 ◽  
Vol 96 (3) ◽  
pp. 1401-1405 ◽  
Author(s):  
Thomas G. Sandercock
Keyword(s):  
Low Frequency ◽  
Muscle Length ◽  
Test Frequency ◽  
The Common ◽  
Tension Curve ◽  
Ventral Roots ◽  
The Difference ◽  
Dynamic Stretch ◽  
Elastic Elements ◽  
Stimulation Of

Rack and Westbury showed that low-frequency asynchronous stimulation of a muscle produces greater force compared with synchronous stimulation. This study tested the hypothesis that the difference results from the dynamic stretch of the common elastic elements. In eight anesthetized cats, the soleus was attached to a servomechanism to control muscle length and record force. The ventral roots were divided into four bundles so each innervated approximately 1/4 of the soleus. The elasticity shared by each part of the muscle was estimated and the servomechanism programmed to compensate for its stretch. At each test frequency (5, 7.5, and 10 Hz), the muscle was stimulated by asynchronous stimulation, synchronous stimulation, summation of force with each part stimulated individually, and summation with each part stimulated individually and the servomechanism mimicking tendon stretch during asynchronous stimulation. Muscle length was isometric except for the last protocol. The observed differences were small. The greatest difference occurred during stimulation at 5 Hz with muscle length on the ascending limb of the length-tension curve. Here, the average forces, normalized by asynchronous force, were asynchronous, 100%; synchronous, 73%; summation, 110%; and summation with stretch compensation, 98%. The results support the hypothesis and suggest that the common elasticity can be used to predict force gains from asynchronous stimulation.

Low Frequency of Adenylate Kinase Release into Cerebrospinal Fluid during Balanced, Normotensive Anaesthesia and a Non-Orthognathic Surgical Procedure

1997 ◽  
Vol 25 (2) ◽  
pp. 92-97 ◽  
Author(s):  
M Enlund ◽  
O Mentell ◽  
L Edmark ◽  
G Ronquist
Keyword(s):  
Cerebrospinal Fluid ◽  
Adenylate Kinase ◽  
Orthognathic Surgery ◽  
Cell Injury ◽  
Low Frequency ◽  
Brain Cell ◽  
Contributing Factors ◽  
Oscillating Saw ◽  
The Difference ◽  
Increased Activity

Activity of strictly intracellular enzymes in the cerebrospinal fluid (CSF) may indicate leakage from dysfunctional brain cells. Increased activity of adenylate kinase (AK) in the CSF is indicative of brain cell injury arising from several sources, among them orthognathic surgery. The mechanism in the latter case is obscure, but the use of an oscillating saw which generates vibrations, and the site of surgery close to the brain may be contributing factors. Anaesthesia may also play a role. In the present study, CSF-AK activity was measured after hysterectomy and was compared with activity after orthognathic surgery in two other studies. Four of 19 patients (21%) in the present study expressed pathological activity, compared with 34 of 47 (72%) orthognathic patients in the two other studies. No firm conclusion may be drawn from historical comparisons, and the difference in activity seen between the two types of surgery might not necessarily be the result of surgical factors. Until this is investigated further, however, we conclude that there may be a difference in postoperative CSF-AK activity between orthognathic and lower abdominal surgery.

scholarly journals The Importance of Service Attributes between Low-cost and Full-service Carrier Customers: A case of Airline Type Hybridisation

2021 ◽  
Vol 10 (10(6)) ◽  
pp. 1741-1757
Author(s):  
Nkululeko Funyane
Keyword(s):  
Factor Analysis ◽  
Maximum Likelihood ◽  
Exploratory Factor Analysis ◽  
Low Cost ◽  
Latent Factors ◽  
Significant Difference ◽  
The Difference

This study sought to assess if the importance attached by customers to the airline service attributes differed across low-cost and full-service airline models. A Mann-Whitney U Test was used to assess the difference between the two models. However, before subjecting the data to differential tests, an exploratory factor analysis (maximum likelihood) was performed on the fifty-five items of service attributes, reducing them into forty-two items retained into ten latent factors (airline service attributes). The results of the revealed a significant difference in the importance attached to staff competence, courtesy and responsiveness only. Such findings suggest that the positioning of airlines into binary (FSC - LCC) models could be a waste of effort and resources since airlines seem to be converging.

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