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PubMed1983

Influence of diazepam and methylphenidate on identification of rapidly presented letter strings: diazepam enhances visual masking.

The effect of diazepam (0, 5, 10 mg) and methylphenidate (0, 5, 10 mg) on the identification of briefly displayed letter strings composing words was investigated. Each letter was presented for 70 ms. The interstimulus interval (ISI) between two successive letters was 10, 100 or 200 ms. The length of the words (WL) was three, five, seven or nine letters. The dependent variable was the number of correctly identified words. As predicted, strong visual masking effects, the strength of which was dependent on ISI and WL, appeared. In the 10 ms condition, diazepam at both doses, but not methylphenidate, further enhanced masking. It is suggested that the results reflect the effect of GABA on masking, and support certain psychological theories about the inhibitory neuronal pathways that are involved in masking. The human peripheral visual system is a promising model for the experimental assessment and integration of pharmacodynamic, neurophysiological and psychological observations.

Adult↗
PubMed1985

Masking of antigenic sites of fibronectin by glycosaminoglycans in ethanol-fixed embryonic tissue.

We studied the interaction between glycosaminoglycans (GAGs) and fibronectin in the basement membrane of the epiblast in the chicken blastoderm using testicular-hyaluronidase digestion of GAGs either on fixed tissue sections or in vivo after microinjection of the enzyme preparation prior to immunostaining for fibronectin. In the choice of fixatives, special attention was paid to their preservation of GAGs. The controls included alcian-blue staining of serial sections to test the efficiency of the digestion, and incubations in the presence of protease inhibitors to abolish contaminating proteolytic activity in the commercial hyaluronidase preparations. The results indicate that fixation in solutions which preserve GAGs, i.e. ethanolic solutions or aqueous solutions containing cetylpyridinium chloride, allows the immunocytochemical demonstration of fibronectin in the basement membrane of the epiblast at the level of the endophyllic crescent, but masks this glycoprotein at the epithelial-mesenchymal interface. As shown by both approaches, this masking of immunoreactivity is reversible. Moreover, the in vivo clearance of GAGs before fixation shows that the masking at the epithelial-mesenchymal interface is not an experimental peculiarity due to the use of a particular technique, but is the consequence of an interaction between GAGs and fibronectin in that particular area of the basement membrane that is used by mesoblast cells as a substrate for migration. The observation that fibronectin may be masked by GAGs in ethanol-fixed tissue--a commonly used fixation method--may require the re-evaluation of some negative results mentioned in the literature.

Animals↗
PubMed1999

Thresholds for masking responses to light in three strains of retinally degenerate mice.

Mutant mice with retinal degeneration (rd/rd) were given 1-h pulses of light of varying brightness at times of the night when they would normally be active. The mutant mice showed a significantly greater inhibition of locomotor activity to light (negative masking) than wildtype controls. Lack of impairment, or even enhancement of negative masking suggests that this response may depend on sparing in retinally degenerate mice of the same receptor type that mediates clock resetting, because synchronization of the circadian system is known to be unimpaired in these mutants. With very dim light pulses, mutants did not change their activity, but wildtypes actually became more active (positive masking). Positive and negative masking appear to depend on different sensory and central processes.

Animals↗
PubMed1999

Masking of locomotor activity in hamsters.

The inhibition of locomotion by light (masking) was investigated in Syrian hamsters. When 1-h pulses of light were presented in the early night, activity was strongly suppressed by irradiances of about 1 lx or greater. Ultradian light-dark cycles were used as another way to study masking. Hamsters were unable to entrain to 3.5:3.5-h light-dark cycles, thus permitting the masking and the entraining effects of light to be distinguished. Light had greater suppressive effects on activity in home cages than on activity in novel running wheels. Moreover, in home cages activity remained very low for about 30 min after lights were turned off. Post-pulse suppression of activity was not simply a consequence of reduced running, as shown by experiments in which running was temporarily prevented by locking the wheels. A phase response curve for masking was obtained by placing hamsters in novel wheels for 3-h periods at various times throughout their circadian cycles, and then superimposing a 30-min light pulse. The suppressive effect of light was maximal around the onset of activity, which normally coincides with dusk in hamsters. This may have adaptive value in limiting foraging to the hours of darkness.

Activity Cycles↗
PubMed1983

Post-stimulation effects on the auditory brain stem response partial-masking and enhancement.

The auditory brain stem response (ABR) was recorded in human subjects using the stimulus configuration of a tone-on-tone forward-masking paradigm, but with all stimuli at suprathreshold levels. A masking stimulus preceded, by delta t msec, the probe stimulus which elicited the ABR. The latency vs. delta t functions for waves III and V were essentially parallel to each other and were interpreted in terms of a partial forward-masking effect, possibly originating in the cochlea. Likewise, the amplitude function for wave III showed varying degrees of decrement as a function of delta t that was also compatible with a partial forward-masking interpretation. In contrast, wave V showed an amplitude increment relative to the unmasked wave that was maximal for delta t values of 15 and 45 msec. The amplitude increment in wave V was termed enhancement and was interpreted as a central process governed by the timing of sound sequences.

Brain Stem↗
PubMed1981

Detection of immune deposits in glomeruli: the masking effect on antigenicity of formalin in the presence of proteins.

Formalin is known to mask the antigenicity of immune deposits in glomeruli but not of surface immunoglobulins of isolated lymphocytes. We have shown in mice with experimental passive anti-GBM glomerulonephritis that formalin masks the antigenicity of GBM-bound immunoglobulins only if the tissue is fixed before sectioning. The presence of a high concentration of normal bovine serum during fixation of cryostat sections masks the antigenicity of immune deposits, whereas formalin alone has no obvious effect. The same results were obtained with human immunoglobulins (IgG, IgM and IgA) bound to tissue sections. Protease treatment with pepsin and trypsin restored the ability of the immunoglobulins to be stained. The masking effect seems to be due to extensive cross-linking of environmental proteins which prevents fluorescent conjugates reaching their antigens. Methods for detecting immunoglobulins in tissues must, therefore, take into consideration the influence of fixatives not only on epitopes but also on the environment in which the antigenic determinants are localised.

Animals↗
PubMed1985

Sexually abused children: identifying masked presentations in a medical setting.

Sexual abuse of children frequently lies hidden while the victims receive medical care for other complaints. To identify clinical signals of latent abuse, we studied 50 children whose initial presentations masked the presence of sexual abuse and compared them with 31 overt cases identified by chief complaint. A broad variety of symptoms masked the abuse. While some, such as early adolescent pregnancy and genital symptomatology, might have suggested the diagnosis, unusual physical symptoms, psychosomatic, and behavioral disorders were as frequent. The masked group differed significantly from the more frequently studied overt group in that chronic history of sexual abuse was twice as common; school problems and psychosomatic disorders were three times as frequent; the alleged abuser was more often an immediate family member, usually the father; male victims were more likely to present in this disguised manner. Familiarity with typical masked presentations should aid earlier identification of these troubled children.

Adolescent↗
PubMed1996

Masking drug treatments in the Cardiac Arrhythmia Pilot Study (CAPS). FASHP for the CAPS Investigators.

The effectiveness of masking in the Cardiac Arrhythmia Suppression Study (CAPS) was assessed by surveying investigators and study coordinators. CAPS patients were assigned one of five treatments: encainide, flecainide, imipramine, moricizine, or placebo. Had all treatments appeared identical and equal numbers of patients been assigned to each, 20% of guesses of treatment assignment would be correct by chance alone. Since neither was possible in CAPS, higher rates of correct guessing were expected. Overall, respondents correctly identified treatment 39% of the time. Investigators identified the drug 30% of the time with rates of 20%, 24%, 37%, 20%, and 55% for the five treatment groups, respectively, whereas coordinators identified the treatments 47% of the time with scores of 42%, 45%, 50%, 40%, and 60%. Side effects and a suboptimal masking design detracted from masking; electrocardiographic changes did not imipramine, which caused characteristic side effects, was the most frequently identified active treatment. Scores were higher for investigators who had prior experience with the drugs, but scores did not improve over the course of the trial. Findings suggest that to improve masking all drugs should have been matched in appearance or persons evaluating treatments should not have been allowed to see the drugs.

Anti-Arrhythmia Agents↗
PubMed1991

Forward masking of the compound action potential: thresholds for the detection of the N1 peak.

A two-interval forced-choice method was developed that provides a rapid and objective computerized measurement of the threshold for detection of the N1 peak of the compound action potential (CAP) recorded in response to a probe tone. The CAP was recorded at the round window of anesthetized chinchillas and several gerbils. An adaptive threshold-tracking procedure was verified by comparing measured thresholds to those obtained from neurometric functions, which plot the proportion of correct detections of the probe as a function of probe intensity. The adaptive procedure was applied in a forward masking paradigm to study the growth of masking of the CAP as a function of masker intensity. Results indicate that growth of masking of the CAP more closely corresponds to that observed psychophysically, than does forward masking observed in the response of a single neuron. Implications for neural encoding mechanisms are discussed.

Acoustic Stimulation↗
PubMed2006

Masking oligonucleotides improve sensitivity of mutation detection based on guanine quenching.

Guanine quenching of a fluorescence-labeled DNA probe is a powerful tool for detecting a mutation in a targeted site of a DNA strand. However, a different guanine adjacent to a targeted site can interfere with detection of a point mutation, resulting in unsatisfactory sensitivity. In the current study, we developed a simple method to improve sensitivity of the guanine quenching method using a masking DNA oligonucleotide. The simple addition of a masking DNA oligonucleotide was found to mask the interference of a different guanine in a target oligonucleotide on fluorescence and to enhance difference in the quenching ratio between wild-type and mutant oligonucleotides. Based on this strategy, we succeeded in discriminating various mutations from the wild-type YMDD motif of the hepatitis B virus DNA polymerase gene using guanine quenching with a masking oligonucleotide.

DNA Mutational Analysis↗
PubMed2006

Masked and unmasked electrophysiological repetition effects of famous faces.

We investigated immediate repetition effects of sequentially presented famous face pairs. The first face (F1) was presented masked or unmasked and preceded the second face (F2) with different SOAs (84 ms vs. 500 ms). Participants judged F2 with regard to either semantic category (actor vs. singer; indirect task) or perceptual match with F1 (same vs. different; direct task). Repetition shortened RT for unmasked but not for masked F1 conditions. In event-related brain potentials (ERPs), unmasked repetition effects were influenced by task and SOA and consisted a modulation of an occipitotemporal N170, an inferior temporal N250r (200-300 ms), a central-parietal N400 (300-500 ms), and a parietal P600 (500-800 ms). An early occipital negativity (onset approximately 100 ms) was present at the 84-ms SOA but diminished in the 500-ms SOA condition, probably reflecting a fast decaying iconic memory trace. Masked repetition effects in the indirect task were limited to a significant early (100-150 ms) prefrontal/lateral frontal and central-parietal modulation, and a strong trend for a reduced N170 amplitude. This suggests that masked repetition modulated early visual processing but did not influence processes beyond approximately 200 ms that reflect the access to facial representations and semantic information for people.

Adolescent↗
PubMed2005

Non-conscious modulation of cardiac defense by masked phobic pictures.

The present study investigated the modulation of cardiac defense by presenting emotional pictures under both effective and non-effective masking procedures. The aim was to test Ohman's model of pre-attentive processing of fear. Participants were 48 women volunteers with intense fear of spiders. The stimulus to elicit cardiac defense was a white noise of 105 dB, 500 ms duration and instantaneous risetime. Subjects had two trials of picture-noise presentation-one with a picture of a spider and one with a picture of a flower-, either under an effective masking procedure (30 ms duration) or a non-effective masking procedure (500 ms duration). Order of presentation was counterbalanced. Dependent variables were heart rate and subjective assessment of the noise. Results showed an increased cardiac response in the first trial and a less reduced cardiac response in the second trial when the noise was preceded by the phobic picture under both masking procedures. The response was accompanied by an increase in the subjective unpleasantness of the noise. These results provide support to Ohman's theoretical model.

Acoustic Stimulation↗
PubMed1997

Collection of three bacterial aerosols by respirator and surgical mask filters under varying conditions of flow and relative humidity.

A variety of respirator filters and surgical masks were challenged with three aerosolized bacteria: Mycobacterium abscessus (M.a.) (a rod), Staphylococcus epidermidis (S.e.) (a sphere), and Bacillus subtilis (B.s.) (a rod). Tests were conducted at two flow rates (45 and 85 l./min) and two humidity levels (30 and 70%). Aerosols were measured with a total-particle, direct-reading, spectrometer and a viable particle cascade impactor. Measurements up- and downstream of the filter or mask were used in determining aerosol penetration; respirator or surgical mask fit was not evaluated. Bioaerosol penetration measured with two aerosol sampling instruments was found to correlate. Additionally, bioaerosol test parameters were evaluated with respect to their effect on penetration. Increasing flow resulted in increased penetration of all organisms while an increase in relative humidity did not exert a consistent effect on all organisms. Of the respirators approved by the National Institute for Occupational Safety and Health (NIOSH), filter efficiency was as expected with dust/mist respirators having the lowest and HEPA filters the highest efficiency. Surgical masks were the least efficient of all filters tested; these are not certified by NIOSH. Bioaerosol penetration was compared to that of a polystyrene latex sphere (PSL) aerosol. Penetration of the test aerosols was predicted on the basis of particle aerodynamic diameter and was expected to be in this order: PSL > M.a. > S.e. = B.s. The PSL aerosol was the most penetrating, as predicted. However, results showed that B.s. was more penetrating than S.e. The aerodynamic diameter may not be the best parameter for predicting aerosol penetration of non-spherical particles in these filters.

Aerosols↗
PubMed1998

Assessment of triethylamine and diethylamine emission from military gas mask canisters.

A study was undertaken to evaluate the suitability of four types of amine modified charcoal filter canisters (cartridge) for use with gas masks (respirators) by measuring emissions of triethylamine (TEA) and diethylamine (DEA). Sampling and analysis methods for TEA and DEA were validated and optimized to ensure accurate measurement at low levels. A total of 88 air samples were taken by the validated methods to measure concentrations of TEA and DEA emitted from gas mask canisters during simulated use in an environmental chamber. Samples were collected on a mannequin equipped with a breather pump and also on human volunteers. Very low levels of TEA and moderately low levels of DEA emissions were measured during the simulations. The C7 (KOH-TEA-BPL/ASC3T) gas mask canister giving the lowest emission has been selected for use by the Canadian Forces. The potential health hazard from TEA and DEA for soldiers using the gas masks, under normal conditions, based on estimated use of one to two days per month, for a maximum of 4 hours/day for a normal working lifetime, was considered to be minimal and acceptable.

Canada↗
PubMed2003

Masked bilateral superior oblique palsy.

BACKGROUND: A diagnosis of masked bilateral superior oblique palsy (MBSOP) is established when signs of SOP appear in the normal eye of a patient after strabismus surgery for SOP in the contralateral eye. Despite the absence of signs of bilaterality before surgery, a palsy will develop in the previously unaffected eye in 10% or more of the patients undergoing surgery. This paper examines the clinical profiles and results of surgical management of 14 patients with MBSOP. METHODS: We retrospectively analysed the records of all 14 patients with the clinical criteria for MBSOP in the clinical strabismus database of patients treated by the second author between 1979 and 2001. We extracted the history and data from the pre- and postoperative ophthalmic and orthoptic examinations, recorded the surgical procedures and tabulated the postoperative results. The surgical outcome was considered successful if normal head posture was restored, diplopia was eliminated in functional positions of gaze, and ocular alignment was improved to within 5 prism dioptres (PD) of orthotropia. RESULTS: All 14 patients had presented with seemingly unilateral SOP. The average primary-position hypertropia preoperatively was 17 (range 4-30) PD. The mean excyclotorsion was 5 degrees (n = 12). Most patients (93%) had a head tilt, mild V pattern, moderate inferior oblique overaction and mild superior oblique underaction. Initial surgery consisted of ipsilateral inferior oblique weakening with or without contralateral inferior rectus recession. The average primary-position hypertropia after the first operation (n = 14) was 8 (range 0-15) PD. In the previously masked eye inferior oblique overaction averaged +1.8 and superior oblique underaction -1.1. The average interval from initial surgery to involvement of the contralateral side was 14.9 (range 0.2-52) weeks. The average primary-position hypertropia after the second operation (n = 10) was 1.6 (range 0-10) PD; follow-up averaged 15 (range 0-120) months. Postoperative alignment was excellent (within 6 PD of orthotropia) and binocular vision restored in 9 of the 10 patients. INTERPRETATION: Masked superior oblique palsy is difficult to detect before surgical correction of the initially manifest palsy. However, the possibility of an occult contralateral palsy should be considered in all patients undergoing surgery for unilateral SOP. Patients should be informed preoperatively of the possibility of this outcome. When the masked palsy becomes evident, a successful surgical outcome can usually be expected.

Adolescent↗
PubMed1999

Randomized, double-masked comparison of oxytocin dosage in induction and augmentation of labor.

OBJECTIVE: To test the hypothesis that high-dose oxytocin, when used in a masked fashion, would result in shorter labors and less need for cesarean delivery. METHODS: We conducted randomized, double-masked trials of high-dose compared with low-dose oxytocin for augmentation and induction of labor. Patients were randomly assigned to receive oxytocin by either a low-dose protocol (1.5 mU/minute initially, increased by 1.5 mU/minute every 30 minutes) or a high-dose protocol (4.5 mU/minute initially, increased by 4.5 mU/minute every 30 minutes). Oxytocin solutions were prepared by a central pharmacy and infusion volumes (mL/hour) were identical, thus ensuring double masking. RESULTS: A total of 1307 patients were randomized (induction, 816; augmentation, 491). In the group receiving oxytocin for induction, high-dose oxytocin was associated with a significant shortening of labor (oxytocin to complete dilatation: 9.7+/-0.3 compared with 7.8+/-0.2 hours, P<.001; oxytocin to delivery: 10.5+/-0.3 compared with 8.5+/-0.3 hours, P<.001). The cesarean delivery rate with low-dose oxytocin was 15.0%, compared with 11.3% with high-dose oxytocin (P = .17). For nulliparous women undergoing induction, cesarean delivery rates were as follows: Total 17.3% (low dose) compared with 11.7% (high dose), P = .15; cephalopelvic disproportion 11.9% (low dose) compared with 5.9% (high dose), P = .06. When used for augmentation, high-dose oxytocin again was associated with a significant shortening of labor without a significant difference in cesarean birth rates. No differences in neonatal outcomes were noted between the groups for either augmentation or induction. CONCLUSION: When used in a double-masked fashion, high-dose oxytocin is associated with significantly shorter labors without any demonstrable adverse fetal or neonatal effects.

Adult↗
PubMed1999

A method of masking oxytocin infusion rates.

BACKGROUND: Controversy exists as to the optimum infusion rate of oxytocin during labor. A system is described to mask infusion rates, and this may help eliminate bias in the study of oxytocin infusion. METHOD: The hardware consists of a commercially available infusion pump that has the capability to receive and send computer messages and a laptop computer. The pump and a programmed computer are attached to a portable stand for bedside use. The display on the pump may be masked while the computer displays the level for any one of three actual rates. EXPERIENCE: Masked and unmasked simulations were performed without human subjects, followed by unmasked bedside testing in 45 patients. The simulation and bedside testing confirmed the system had the ability to maintain designated flow rates in all manner of increases, decreases, stoppages, and restarts. CONCLUSION: This system is a computer-controlled infusion pump with the ability to mask infusion rates. This may allow investigators to compare oxytocin infusion rates objectively in the induction and augmentation of labor.

Female↗
PubMed2003

Continual smoking of mentholated cigarettes may mask the early warning symptoms of respiratory disease.

BACKGROUND: Continual use of cold preparations including those containing menthol for relief from congestion, cough, or difficulty in breathing can mask the early warning symptoms of respiratory dysfunction. These products usually carry a warning label on the packaging that indicates that they are not for continuous use and may mask the early warning symptoms of a more serious condition. Menthol can be delivered in many dosage forms including the smoke of a mentholated cigarette. METHODS: Literature searches were done for the NLM databases (e.g., MEDLINE from 1966, TOXLINE, OLDMEDLINE (1958-1965), CANCERLIT), plus tobacco industry documents and hardcopy indices. The evidence was evaluated with application to mentholated cigarette smoking. RESULTS: A logical progression is presented to attempt to demonstrate that the continuous smoking of mentholated cigarettes may also mask the early warning symptoms of respiratory distress. The early warning symptoms caused by chronic irritation of the respiratory tract may be reduced in severity when the menthol found in a mentholated cigarette is continually delivered to the tract. CONCLUSION: This masking of the symptoms of an underlying respiratory disease can lead to delays in seeking medical attention resulting in a poor prognosis, additional suffering, and eventual death.

Black or African American↗