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PubMed1992

[Study of tinnitus masking by self-recording audiometer].

The tinnitus masking test, in which the minimum masking levels of tinnitus by various pure tones and band noises are measured and used to produce tinnitus masking curves, is one of the methods for evaluating the character of tinnitus. At present, the tinnitus masking test is usually performed using a pure tone audiometer. In this study, tinnitus masking curves were produced using a self-recording audiometer (Bekesy audiometer) in 22 cases of tinnitus, and the basic nature of the tinnitus masking curves from the self-recording audiometer was investigated and compared with those from a pure tone audiometer. The results showed no changes in the masking level, and the amplitudes of the tinnitus masking curves from the self-recording audiometer were observed to be at the tinnitus pitches. The amplitude of the tinnitus masking curve showed a negative correlation with tinnitus loudness as measured by the loudness balance test for tinnitus, that is, the amplitude tended to decrease as the tinnitus became louder. This suggests that the loudness of the masking tone influences the tinnitus masking phenomenon.

Audiometry, Pure-Tone↗
PubMed1978

Effects of using long breathing hoses upon mask pressure.

Effects of using oxygen breathing hoses from 0.9 to 8.2 m (3 to 27 ft) long and mask fit upon mask pressure during 0.75 to 12-s decompressions from 2,438 m (8,000 ft) to either 6,096, 10,668, or 15,240 m (20,000, 35,000 or 50,000 ft) were determined. Peak mask pressures and duration of high mask pressure were related to mask fit, mask and hose stretch compliance, pressure differential, decompression rate, and other factors, with mask pressure increasing with hose length. Peak mask pressures frequently exceeded 80 mm Hg, a high pressure associated with increased incidence of pulmonary damage. Cargo-type aircraft, however, have sufficiently large volumes so that they will not decompress rapidly enough to have high mask pressure, even with an 8.2-m long hose. Long breathing hoses should not be used in smaller aircraft since small cabin volume will result in rapid decompression rates and high mask pressure. Above a flight altitude of 2,438 m, oxygen should always be breathed if hoses longer than 2.9 m (9 ft) are used. This would help prevent hypoxia, associated with the need to deplete air in the hose before oxygen is breathed, should cabin pressure be lost at a high altitude. The fastest decompression rates compatible with preventing mask pressures from exceding 80 mm Hg during decompressions to different altitudes with different length breathing hoses are given.

Aerospace Medicine↗
PubMed2005

Forward and backward visual masking in unaffected siblings of schizophrenic patients.

BACKGROUND: Visual masking tasks assess the earliest stages of visual processing. This study examined visual masking performance for forward and backward masking tasks in siblings of schizophrenic patients and healthy comparison subjects. METHODS: A staircase method was used to ensure that unmasked target identification was equivalent across subjects to eliminate differences due to discrimination of simple perceptual inputs. Four computerized visual masking tasks were administered to 43 siblings of patients and 42 normal comparison subjects. The tasks included: 1) locating a target; 2) identifying a target with a high-energy mask; 3) identifying a target with a low-energy mask; and 4) a paracontrast/metacontrast procedure with nonoverlapping target and mask. RESULTS: Across masking conditions, there was a significant group by forward/backward interaction, meaning that siblings showed a larger difference from control subjects in backward versus forward masking. This group difference was more pronounced in the location condition. CONCLUSIONS: These results support the theory that visual masking procedures may be indicators of vulnerability to schizophrenia. The pattern of findings in this report (larger group differences on backward versus forward masking and on the location condition) suggests that the activity of transient visual channels may be particularly linked to vulnerability.

Adult↗
PubMed2004

Pupillary responses and attentional allocation problems on the backward masking task in schizophrenia.

Early visual information processing impairment has consistently been found on the backward masking task in patients with schizophrenia, but the nature of this impairment remains unclear. Pupillometry was used to measure attentional allocation during visual backward masking task performance in patients with schizophrenia (n=16) and nonpsychiatric controls (n=16). The extent of pupil dilation recorded during a cognitive task reflects the processing load placed on the nervous system by the task. Schizophrenia patients detected significantly fewer targets than controls only when the stimulus onset asynchrony (SOA) between targets and masks reached 317 ms. For both groups, peak pupil dilation responses were also significantly larger in the 317 ms SOA condition relative to a no-mask condition, suggesting that the processing load of the 317 SOA masking condition was greater than the no-mask condition. In addition, a principal components analysis of pupillary response waveforms identified time-related factors that appeared to differentially index attentional allocation to targets vs. masks. Patients with schizophrenia showed less dilation than controls on a middle factor that appeared to index attentional allocation to targets, but patients showed greater dilation than controls on a late factor that appeared to index attentional allocation to masks. That is, controls attended more to targets than to masks, but patients attended more to masks than to targets. These findings suggest that masking impairments at SOA intervals greater than 100-200 ms may be due abnormalities in attentional allocation mechanisms.

Attention↗
PubMed2004

Paracontrast and metacontrast in schizophrenia: clarifying the mechanism for visual masking deficits.

Schizophrenic patients consistently demonstrate performance deficits on visual masking procedures. Visual masking can occur through two distinctly different mechanisms: interruption and integration. One highly effective way to limit the masking mechanism to interruption is to use a mask that surrounds, but does not spatially overlap, the target. These procedures are called paracontrast and metacontrast (for forward and backward masking, respectively). Despite their clear advantages for interpretation, paracontrast and metacontrast have not been used previously in schizophrenia. In the present study, we examined the reliability of the paracontrast and metacontrast procedures by administering these tasks to 103 schizophrenic patients and 49 normal control subjects. In addition, we compared the results to those from a low-energy masking condition, which is an alternative way to limit masking to interruption. Patients showed deficits on both the paracontrast and metacontrast procedures. The deficits in paracontrast and metacontrast were comparable to those seen previously with low-energy masking. These results suggest that the paracontrast/metacontrast procedure and the procedure using a low-energy mask are roughly equally sensitive to deficits in early visual processing among schizophrenic patients. These results bolster previous conclusions that schizophrenic patients show deficits on visual masking tasks even when masking on those tasks occurs entirely through the interruption mechanism.

Adolescent↗
PubMed2005

Prevalence, persistence, and clinical significance of masked hypertension in youth.

Masked hypertension, an elevated daytime ambulatory blood pressure in the presence of a normal office blood pressure, confers an increased cardiovascular risk to adults. We investigated the prevalence, persistence, and clinical significance of masked hypertension in children and adolescents. We enrolled 592 youths (6 to 18 years old). Youths with masked hypertension (n=34) and a random sample of the normotensive participants (n=200) were followed-up. In a nested case-control study, we compared echocardiographic left ventricular mass among cases with persistent masked hypertension and normotensive controls. At baseline, mean age was 10.2 years; 535 youths were normotensive on office and daytime ambulatory blood pressure measurement (90.4%), and 45 had masked hypertension (7.6%). Compared with normotensive controls, participants with masked hypertension had a higher ambulatory pulse rate, were more obese, and were 2.5-times more likely to have a parental history of hypertension. Among 34 patients with masked hypertension (median follow-up 37 months), 18 became normotensive, 13 had persistent masked hypertension, and 3 had sustained hypertension. Patients with persistent masked hypertension (n=17) or who progressed from masked to sustained hypertension (n=3) had a higher left ventricular mass index (34.9 versus 29.6 g/m2.7; P=0.023) and a higher percentage with left ventricular mass index above the 95th percentile (30% versus 0%; P=0.014) than normotensive controls. In children and adolescents, masked hypertension is a precursor of sustained hypertension and left ventricular hypertrophy. This condition warrants follow-up and, once it becomes persistent, is an indication for blood pressure-lowering treatment.

Adolescent↗
PubMed1997

Backward masking performance in unaffected siblings of schizophrenic patients. Evidence for a vulnerability indicator.

BACKGROUND: Visual masking is a procedure that is used to assess the earliest components of visual processing. In backward masking, the identification of an initial stimulus (the target) is disrupted by a later stimulus (the mask). The masking function can be divided into an early component (e.g., up to about 60 ms) that reflects the involvement of sensory-perceptual processes, and a later component that reflects susceptibility to attentional disengagement as the mask diverts processing away from the representation of the target. Schizophrenic patients show anomalies on both masking components. It is not known whether backward masking deficits reflect enduring genetic vulnerability to schizophrenia. METHODS: We assessed 32 unaffected siblings of schizophrenic patients and 52 normal control subjects on the early and late components of 4 masking conditions. The conditions differentially involved the sustained and transient visual pathways. RESULTS: The unaffected siblings showed poorer overall performance than control subjects on the masking procedures. More specifically, siblings showed anomalies on the early, sensory-perceptual component, but not on the later, attentional disengagement component. CONCLUSIONS: The backward masking performance deficits that have been observed in schizophrenic patients appear to reflect enduring vulnerability to the disorder rather than only the symptoms of the illness. This vulnerability appears to be associated with early, sensory-perceptual processes.

Adolescent↗
PubMed2002

Disposable surgical face masks for preventing surgical wound infection in clean surgery.

BACKGROUND: Surgical face masks were originally developed to contain and filter droplets of microorganisms expelled from the mouth and nasopharynx of healthcare workers during surgery, thereby providing protection for the patient. However there are several ways in which surgical face masks could potentially contribute to contamination of the surgical wound. OBJECTIVES: To identify and review all randomised controlled trials evaluating disposable surgical face masks worn by the surgical team during clean surgery to prevent post-operative surgical wound infection. SEARCH STRATEGY: All relevant publications about disposable surgical face masks were sought through the Specialised Trials Register of the Cochrane Wounds Group (March 2001). Manufacturers and distributors of disposable surgical masks as well as professional organisations including the National Association of Theatre Nurses and the American Operating Room Nurses Association were contacted for details of unpublished and ongoing studies. SELECTION CRITERIA: Randomised controlled trials (RCTs) and quasi-randomised controlled trials comparing the use of disposable surgical masks with the use of no mask were included. DATA COLLECTION AND ANALYSIS: Data were extracted independently by AL and PE. MAIN RESULTS: Two randomised controlled trials were included involving a total of 1453 patients. In a small trial there was a trend towards masks being associated with fewer infections, whereas in a large trial there was no difference in infection rates between the masked and unmasked group. Neither trial accounted for cluster randomisation in the analysis. REVIEWER'S CONCLUSIONS: From the limited results it is unclear whether wearing surgical face masks results in any harm or benefit to the patient undergoing clean surgery.

Disposable Equipment↗
PubMed2002

Development of a computerized assessment for visual masking.

Visual masking provides a highly informative means of assessing the earliest stages of visual processing. This procedure is frequently used in psychopathology research, most commonly in the study of schizophrenia. Deficits in visual masking tasks appear to reflect vulnerability factors in schizophrenia, as opposed to the symptoms of the illness. Visual masking procedures are typically conducted on a tachistoscope, which limits standardization across sites, as well as the number of variables that can be examined in a testing session. Although visual masking can be administered on a computer, most methods used so far have had poor temporal resolution and yielded a limited range of variables. We describe the development of a computerized visual masking battery. This battery includes a staircase procedure to establish an individual's threshold for target detection, and a relatively dense sampling of masking intervals. It includes both forward and backward masking trials for three different masking conditions that have been used previously in experimental psychopathology (target location, target identification with high-energy mask, and target identification with low-energy mask).

Adult↗
PubMed1984

Selective color effects in dichoptic masking.

Dichoptic masking was investigated under conditions designed to isolate, in turn, achromatic and chromatic pathways in the visual system. Red, green, and blue tests and masks were used in various combinations. For the achromatic condition, achieved with a 3 min, 10 msec test flash and a 3 deg masking flash and with both eyes light adapted, there is essentially no dichoptic masking. With a 50 min test flash and conditions otherwise the same, a small amount of chromatically nonselective dichoptic masking occurs which is attributed to interaction between fairly remote contours, a form of weak pattern masking. For the chromatic condition, achieved with a 1 deg test flash delivered for 200 msec with both eyes light adapted, a small, nonselective masking effect, also attributed to weak pattern masking, occurs for most color combinations. The only chromatically-selective effect observed occurs for blue tests seen with blue masks. For this condition, dichoptic thresholds reach a maximum at modest photopic luminances of the mask and then decline.

Adaptation, Ocular↗
PubMed1994

Stereo matching precedes dichoptic masking.

Stereo matching can intervene to prevent dichoptic masking. In a dichoptic masking paradigm we measured the contrast threshold for a bar target, presented to one eye, as a function of the contrast of an identical masking bar, presented at retinal correspondence in the other eye. Confirming previous studies of dichoptic masking with sinusoidal gratings, the test bar thresholds rose proportionally with increasing masking contrast. This threshold elevation was almost nullified when an extra bar was presented to the eye seeing the test stimulus. Release from masking occurred when the disparity between the masking bar and extra bar was < 20 min arc over a range of contrast levels (8-45%), and for bars containing either broad spatial frequency spectra or bars with only high spatial frequencies (peak = 12 c/deg). The latter result rules out an explanation for the release from masking based on contrast discrimination in low spatial frequency channels. The extra bar was effective in releasing the test bar from masking as long as the extra bar's contrast was greater than about one-fifth the contrast of the mask, a result that suggests that there is a contrast threshold for stereo matching. We interpret our findings to indicate that a stage of stereo matching occurs prior to the neural site limiting dichoptic contrast discrimination.

Contrast Sensitivity↗
PubMed1982

The phase angle of addition in temporal masking for diotic and dichotic listening conditions.

The phase angle, alpha, between a tonal signal and a tonal masker was varied from 0 degrees to 135 degrees in simultaneous masking, forward masking, and pulsation-threshold paradigms. In all conditions the frequency of the signal and masker was 500 Hz. For forward masking both diotic (MOSO) and dichotic (MOS pi) listening conditions were investigated. Only the dichotic case was studied using the pulsation threshold method. In simultaneous masking, thresholds varied as a function of alpha in both diotic and dichotic conditions. Thresholds in the diotic conditions were consistently different from those in the dichotic conditions -- i.e., there were masking-level differences (MLDs) at most values of alpha tested. In forward masking and pulsation-threshold, however, thresholds were independent of alpha in the dichotic conditions; and thresholds were independent of alpha in the diotic, forward masking conditions. Nevertheless, for forward masking the dichotic thresholds remained below the diotic thresholds, yielding MLDs of 3-6 dB. Thus, in nonsimultaneous masking, there is a clear effect of the interaural signal phase, but not of the masker-signal phase relationship, on signal detectability. These results imply that masker-signal phase information is either not preserved or not used by subjects in nonsimultaneous tone-on-tone masking experiments.

Auditory Perception↗
PubMed1985

Forward masking of the auditory nerve neurophonic (ANN) and the frequency following response (FFR).

The forward masking behavior of two averaged neurophonic responses was examined in cats. The auditory nerve neurophonic (ANN) was recorded with bipolar electrodes placed on the auditory nerve as it exits the internal meatus. The frequency following response (FFR) was recorded using scalp electrodes placed at the vertex and below the stimulated ear. Masking functions (response amplitude vs masker level) for frequencies both above and below the probe frequency were recorded. From these masking functions, 30% iso-depression contours (forward masking tuning curves, FMTCs) were constructed. The time course of the recovery from forward masking was also examined. It was found that the forward masking behavior of these neurophonics have many similarities to the behavior of other responses recorded using psychophysical and physiological methods. However, forward masking of the ANN and FFR has a number of unusual features. First, the best masking frequency (BMF), which in most forward masking studies is equal to the probe frequency, can be off-set from the probe frequency by as much as an octave. Second, the masker level at BMF can be as much as 30 dB below the probe level. Third, the magnitude of both of these off-sets is a function of the probe level. Fourth, low level neurophonic response could be enhanced by some forward 'maskers'. The features of neurophonic forward masking are discussed and a model of the neurophonics is suggested. This model is based on the spatial distribution of phase and amplitude in the phase-locked activity in the auditory nerve and it can qualitatively account for many of the properties of the neurophonics.

Animals↗
PubMed1995

Masking and pitch shift of tone bursts and clicks by low-frequency tones.

From experiments in animals and investigations in humans it is known that the normally phase-dependent masking of a short stimulus by a low-frequency continuous tone does not occur in the case of endolymphatic hydrops. The recording of the masked threshold of short tone stimuli in a loud tone of 30 Hz is to be evaluated for the clinical diagnostics of Ménière's disease. To this purpose, the main parameters of the measurements (type, frequency, duration of the stimulus, and intensity of the masker) and their effect of phase-dependent masking and pitch-shift are investigated. Stimuli above 2 kHz are masked less than those of lower frequencies. Wide-band stimuli are less useful, since only the low-frequency component of their spectrum is masked. The tone stimuli should be short (1 - 2 ms) in order to make the measurement of the phase dependence more accurate. With increasing masker level the masking at phase 0 degree corresponds to the increase in level, at phase 270 degrees the amount is twice as much. The pitch shift which is perceived in low-tone masking depends on the phase of the stimulus, and on the levels of the stimulus and the masking tone. The use of brain stem recordings in the investigation of phase-dependent low tone masking is problematic since well-synchronizing stimuli with high frequency spectral components are masked poorly.

Acoustic Stimulation↗
PubMed2005

Aerosol delivery in respiratory syncytial virus bronchiolitis: hood or face mask?

OBJECTIVES: To compare the utility of the hood versus the face mask for delivery of inhaled medications to infants hospitalized with viral bronchiolitis. STUDY DESIGN: Randomized, double-blinded, controlled trial; 49 hospitalized infants with viral bronchiolitis, age 2.75 +/- 2.2 months (mean +/- SD), were grouped to either the hood (n = 25) or the mask (n = 24). Each subject received inhalation treatments with the use of both devices. Half of the Hood Group received the active drug treatment (1.5 mg epinephrine in 4 mL saline [3%]) via hood followed immediately by placebo treatment (normal saline) via mask, whereas the other half received the opposite order. Half of the Mask Group received the active drug treatment via mask followed immediately by placebo treatment via hood, whereas the other half received the opposite order. Therapy was repeated 3 times daily until discharge. Outcome measures included clinical scores and parental preference. RESULTS: Percent improvement in clinical severity scores after inhalation was significant in both groups on days 1, 2, and 3 after admission (Hood Group: 15%, 15.4%, and 16.4%, respectively; Mask Group: 17.5%, 12.1%, and 12.7%, respectively; P < .001). No significant difference in clinical scores improvement between groups was observed. Eighty percent (39/49) of parents favored the hood over the mask; 18% (9/49) preferred the mask and 2% (1/49) were indifferent. CONCLUSIONS: In infants hospitalized with viral bronchiolitis and in whom aerosol treatment is considered, aerosol delivery by hood is as effective as by mask. However, according to parents, the tolerability of the hood is significantly better than that of a mask.

Aerosols↗
PubMed2004

Laryngeal mask airway in neonatal resuscitation: a survey of current practice and perceived role by anaesthesiologists and paediatricians.

OBJECTIVES: To survey current practice and to compare the opinion of paediatricians and anaesthesiologists regarding laryngeal mask airway (LMA) in neonatal resuscitation. DESIGN: A structured postal questionnaire on the use of the laryngeal mask airway in neonatal resuscitation was sent to the heads of department of the paediatric and anaesthesiology services. SETTING: Forty-three hospitals in the Veneto Region, Italy. RESULTS: During the year 2000, 1526 out of 33708 (4.5%) neonates in our region needed resuscitation. Of these cases, 101 (6.6%) were ventilated using the LMA. Laryngeal mask airway availability was significantly greater in the anaesthesiology department compared to the paediatric department (90% versus 50%; P = 0.002). However, 52% of anaesthesiologists and 72% of paediatricians had never used the laryngeal mask airway in their practice. The laryngeal mask airway was considered as an essential device more frequently by the anaesthesiologists than by the paediatricians (27% versus 5%; P = 0.015); both groups considered the laryngeal mask airway particularly useful in specific situations. Interestingly, while 16% of the paediatricians described the laryngeal mask airway as having no value, none of the anaesthesiologists did (P = 0.002). Staff competence was considered low by 70% of anaesthesiology heads of department compared with 90% of their pediatric colleagues. In both specialties, use of the laryngeal mask airway was limited to medical staff. With regard to training, 35% of anaesthesiologists and 22.5% of paediatricians had attended a course on laryngeal mask airway use. CONCLUSIONS: Laryngeal mask airway availability and perceived value were higher amongst anaesthesiologists than their paediatric colleagues. However, educational level, competence and utilization rates of the LMA in neonatal resuscitation were low in both groups.

Anesthesiology↗
PubMed1993

A prototype erodible mask delivery system for the excimer laser.

PURPOSE: The authors developed an erodible mask delivery system for the argon-fluoride 193-nm excimer laser, which offers the possibility of correcting hyperopia and astigmatism as well as myopia. METHOD: Masks were made of polymethylmethacrylate on a quartz window, with intended corrections for myopia and hyperopia of 2.5 and 5 diopters (D). Ablations using the mask and control ablations using an expanding diaphragm were performed in 30 eyes of 15 pigmented rabbits with an Excimed UV200 laser (Summit Technology, Inc, Waltham, MA). The rabbits were followed for 134 days with regular biomicroscopy and retinoscopic examination by two observers. RESULTS: Ablations with the mask to correct myopia were successful and produced stable corrections, although the higher-power mask produced undercorrections. Hyperopic masks produced paradoxic myopic corrections, possibly due to the lack of a transition zone at the edge of the mask. Corneas ablated with the mask had less sub-epithelial haze than those ablated with the diaphragm at all examinations. Results of histopathologic examination showed epithelial hyperplasia over the ablation zone in all eyes. Dichlorotriazinyl aminofluorescein collagen staining showed subepithelial new collagen in all eyes, but there was no relation between the depth of ablation at any point on the cornea and the amount of new collagen deposited there. CONCLUSIONS: Myopic ablations are feasible with the erodible mask, although additional calibration is needed. Hyperopic ablations were unsuccessful with the current design. Corneas ablated with the mask may be clearer than corneas ablated with the diaphragm, possibly due to a smoother ablated surface. Regression of effect after laser ablation in the rabbit model is likely due more to epithelial hyperplasia than to stromal remodeling.

Animals↗
PubMed2001

Comparison of setup accuracy of three different thermoplastic masks for the treatment of brain and head and neck tumors.

PURPOSE: Setup accuracy is an important factor influencing the definition of the planning target volume (PTV). The purpose of this study was to compare the setup accuracy of three different thermoplastic masks used for immobilization of patients with brain or head and neck tumors. MATERIALS AND METHODS: Thirty patients with brain or head and neck tumors were consecutively assigned to one of three different thermoplastic masks (Posifix): head mask with three fixation points (3 FP, ten patients), head and shoulder mask with four fixation points (4 FP, ten patients), head and shoulder mask with five fixation points (5 FP, four fixations plus an additional one on the top of head, ten patients). Once a week, during the session with a 6 MV linac (Elekta), orthogonal (antero-posterior and lateral) portal images were acquired for three fictitious isocenters placed during the simulation at the level of the head, the neck and the shoulders. Portal images and digitized simulator films were compared using the PIPS pro software, and displacements in antero-posterior (A-P), cranio-caudal (C-C) and medio-lateral (M-L) directions were calculated. From these displacements, 2D or 3D errors were also calculated. RESULTS: A total of 915 portal images were obtained, of which 98% could be analyzed. For the whole population, total displacements reached a standard deviation (SD) of 2.2 mm at the level of the head and the neck. Systematic and random displacements were in the same order of magnitude and reached a SD of 1.8 mm. Patient setup was slightly worse at the shoulder level with a total displacement of 2.8 mm (1 SD) for both the C-C and the M-L directions. There again, the systematic and the random components were in the same order of magnitude below 2.4 mm (+/-SD). For isocenters in the head and in the neck, there was no substantial difference in the setup deviation between the three masks. The setup reproducibility was found to be significantly worse (P=0.01) at the level of the shoulders with the 3 FP mask. For the 2D random error, 1 SD of 2.3 mm was observed compared to 0.8 and 1.2 mm for the 4 and 5 FP masks, respectively. Lastly, 90% of the 3D total deviations were below 4.5 mm for the head and the neck. In the shoulder region, 90% of the 2D total deviations were below 5.5 mm. CONCLUSION: Thermoplastic masks provide an accurate patient immobilization. At the shoulder level, setup variations are reduced when 4 or 5 FP masks are used. These data could be used for the assessment of margins for the PTV.

Algorithms↗