[MASKING AND MASKING NOISES. DATA ON SOME MASKING SOUNDS USED IN AUDIOMETRY].
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Audiometry↗
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Evaluating masking in a randomized, double-masked clinical trial in children with myopia.
PURPOSES: The purposes of this study were to evaluate the success of masking in the Correction of Myopia Evaluation Trial (COMET), a study designed as a randomized, double-masked clinical trial comparing the effect of progressive addition lenses (PALs) with single-vision lenses (SVLs) in slowing myopia progression among children and to investigate the impact of unmasking on the treatment effect. METHODS: The success of masking of children and parents was assessed by questionnaires administered after the clinical trial results were reported and before families were informed of their child's lens assignment. Children and parents who correctly guessed their assignment with absolute or "pretty sure" certainty were considered as unmasked. The role of children's age, gender, and ethnicity in unmasking was evaluated using logistic regression. The impact of unmasking on the treatment effect at 3 years was investigated using analysis of variance. The success of masking of the study optometrists was assessed by data collected at the child's follow-up visits. RESULTS: Overall 93% (436 of 469) of the COMET children responded to the questions about lens assignment and certainty. Thirty-seven percent (163 of 436) of children met the criteria for being unmasked with similar results from the parents. The majority (91%) of the 163 "unmasked" children reported that their glasses were the main reason for lens identification. Although children 10 to 11 years at baseline became unmasked more often than did children 6 to 9 years (44% vs. 31%, p = 0.01), there was no difference between boys and girls becoming unmasked (p = 0.2). The treatment effect did not differ between the masked and unmasked children (p = 0.69). The study optometrists became unmasked for five children over the course of 3-year follow up. CONCLUSIONS: Masking was successfully maintained for the study optometrists and the majority (63%) of COMET children. Although some children were able to identify their lens assignment, the primary study outcome was not affected by unmasking.
Child↗
The effect of a masked stimulus on the response to the masking stimulus.
Four experiments are reported in which the subjects had to respond to a target that masked a preceding prime via metacontrast masking. In one part of Experiment 1, the subjects discriminated the target's shape (square or diamond) by a motor-choice reaction, and in another part they had to respond with a simple reaction. The prime was neutral (circular) with respect to the target's shape. The data showed a facilitation effect. In both tasks the reaction time was reduced by the masked prime. However, the reduction was more pronounced with simple reaction than with choice reaction. In the other experiments, additional primes were used with the same angular shapes as the targets. In Experiments 2 and 3, after discriminating the target's shape by a choice reaction, the subjects had to judge the prime's shape in a signal-detection task. While neither the d' value for discriminating the angular primes from the circular ones (Exp. 2) nor the d' value for distinguishing between the angular primes (Exp. 3) was different from zero, the choice-reaction data showed a congruency effect. With a congruent prime (i.e., a prime that had the same shape as the target), the reaction times were reduced. With an incongruent prime, the reaction times grew. In Experiment 4 the errors were investigated. The facilitation effect was present in the RT, but not in the number of errors, whereas the congruency effect was present in the number, but not in the RT of errors. While the facilitation effect can be attributed either to an unspecific activation by the masked prime or to an influence of the prime on attentional processes, the congruency effect can be explained by the assumption that the masked prime directly activates the specific response, which corresponds to the prime's shape.
Fixation, Ocular↗
Preattentive processing, preparedness and phobias: effects of instruction on conditioned electrodermal responses to masked and non-masked fear-relevant stimuli.
We hypothesized that autonomic responses conditioned to fear-relevant stimuli, in contrast to responses conditioned to neutral stimuli, can be elicited after only an automatic, non-conscious analysis of the stimulus. Consequently, they may be expected to be insensitive to verbal instructions. Normal subjects were conditioned to either fear-relevant stimuli (snakes or spiders) or neutral stimuli (flowers or mushrooms) in a differential conditioning paradigm with shock as the unconditioned stimulus. In a subsequent extinction series, half of the subjects were shown the conditioned stimuli under masking conditions preventing their conscious recognition, whereas the other half were exposed to non-masked stimuli. Then half of the subjects in each of the masking conditions were verbally instructed that no more shocks would be delivered and then the extinction trials followed. Consistent with our hypothesis, differential responses to the fear-relevant CSs+ and CSs- remained unaffected by both masking and instruction, whereas differential responding to neutral stimuli was wiped out by the masking procedure and the verbal instruction.
Adolescent↗
The effect of white-noise mask level on sinewave contrast detection thresholds and the critical-band-masking model.
It is known that visual noise added to sinusoidal gratings changes the typical U-shaped threshold curve which becomes flat in log-log scale for frequencies below 10c/deg when gratings are masked with white noise of high power spectral density level. These results have been explained using the critical-band-masking (CBM) model by supposing a visual filter-bank of constant relative bandwidth. However, some psychophysical and biological data support the idea of variable octave bandwidth. The CBM model has been used here to explain the progressive change of threshold curves with the noise mask level and to estimate the bandwidth of visual filters. Bayesian staircases were used in a 2IFC paradigm to measure contrast thresholds of horizontal sinusoidal gratings (0.25-8 c/deg) within a fixed Gaussian window and masked with one-dimensional, static, broadband white noise with each of five power density levels. Raw data showed that the contrast threshold curve progressively shifts upward and flattens out as the mask noise level increases. Theoretical thresholds from the CBM model were fitted simultaneously to the data at all five noise levels using visual filters with log-Gaussian gain functions. If we assume a fixed-channel detection model, the best fit was obtained when the octave bandwidth of visual filters decreases as a function of peak spatial frequency.
Bayes Theorem↗
Pollution with nitrous oxide using laryngeal mask or face mask.
BACKGROUND: As environmental pollution by nitrous oxide may influence the health of the personnel working in operating theatres, the incidence and magnitude of nitrous oxide (N2O) leakage, when using a face mask or a laryngeal mask airway (LMA) for controlled ventilation, were studied in 34 patients scheduled for elective cystoscopy. METHODS: A semi-closed gas delivery ventilation system with active scavenging was used. The N2O concentrations were measured every 8 s at a position 30 cm above the patient's mouth with a N2O gas monitor (GD 200, Simrad Optronics). RESULTS: When using a face mask, the leakage of N2O resulted in a N2O concentration of 157 (85-332) p.p.m. (parts per million) (median concentration and 25% and 75% percentiles). With the LMA, a lower median concentration of N2O of 60 (28-126) p.p.m. was found (P=0.04). With the face mask, a concentration above 100 p.p.m. was found during 51% of the exposure time compared to 24% of the time in the LMA group. CONCLUSION: Environmental pollution was less with the LMA than the face mask, but under the conditions of the study both modes of airway management were associated with levels of N2O peak concentrations in the breathing zone of anaesthetists that are deemed to be excessively high by the Danish National Institute for Occupational Safety.
Aged↗
Resistive load of laryngeal mask airway and ProSeal laryngeal mask airway in mechanically ventilated patients.
BACKGROUND: The ProSeal Laryngeal Mask Airway (PLMA) ventilation tube is narrower and shorter than the standard Laryngeal Mask Airway (LMA) and is without the vertical bars at the end of the tube. In this randomized, crossover study, PLMA and LMA resistances were compared. METHODS: Respiratory mechanics was calculated in 26 anesthetized, mechanically ventilated patients with both LMA and PLMA. The laryngeal mask positioning was fiberoptically evaluated. Differences in the respiratory mechanics of the LMA and the PLMA were attributed to the differences between the laryngeal masks. RESULTS: In the total study population the airway resistance was 1.5 +/- 2.6 hPa.l-1.s-1 (P = 0.005) higher with the PLMA than with the LMA. During the PLMA use, the peak expiratory flow reduced by 0.02 +/- 0.05 l min-1 (P = 0.046), the expiratory resistance increased by 0.6 +/- 1.3 hPa.l-1.s-1 (P = 0.022), and the time constant of respiratory system lengthened by 0.09 +/- 0.18 s (P = 0.023). These differences doubled when the LMA was better positioned than the PLMA, whereas they disappeared when the PLMA was positioned better than the LMA. CONCLUSIONS: The standard LMA offers a lower resistive load than the PLMA. Moreover, the fitting between the laryngeal masks and the larynx, as fiberoptically evaluated, plays a major role in determining the resistive properties of these devices.
Adult↗
[The importance of the laryngeal mask in the difficult intubation and early experience with the intubating laryngeal mask airway--ILMA--Fastrach].
UNLABELLED: The conventional laryngeal mask airway ("Standard" laryngeal mask airway SLMA is of outstanding importance in the management of the difficult airway. The intubating laryngeal mask airway (ILMA, commercial name Fastrach) has become available recently. First results indicate that the excellent ventilation characteristics of SLMA are maintained, but in addition blind intubation is successful in more than 90% of patients with normal anatomy as well as with difficult intubation. PURPOSE: We present the use of ILMA, compare the potential of the two laryngeal mask types in difficult intubation by own results, present the results of a first symposium on the ILMA held at Jersey in December 1996, the role of the SLMA in difficult intubation as proposed by the American and the French Societies of Anaesthesiology, as well as an outlook on possible uses of the ILMA in the light of the available results. METHODS: The SLMA was prospectively used between 1992 and 1997 for 66 operations in 55 patients with difficult intubation (laryngoscopic view Cormack grade IV, n = 24; grade III, n = 35; grade < III, n = 7). 48 operations were performed after resection of a facial carcinoma, 14 on patients without carcinoma who could not be intubated conventionally, 5 on patients with periglottic pathology, and on 50 normals. The ILMA was used on 150 patients between 11/1996 and 11/1997, 106 had normal anatomy, 33 were difficult to intubate (Cormack grade IV, n = 12; grade III, n = 21), 24 had a reduced mouth opening of < or = 2.5 cm awake, 14 of these also were difficult to intubate. RESULTS: Ventilation was superior to a face mask (FM): (SLMA: ventilation not sufficient (SaO2 < 90% > 30 sec) with a FM in 22 operations compared to 5 with a SLMA; ILMA: ventilation not sufficient with a FM in 7 operations compared to 3 with an ILMA). Blind intubation through a SLMA had a success rate of 50% and 34% in 50 normals and in 32 operations with difficult intubation after a mean of 2.6 intubation attempts each. The success rate per intubation attempt for the SLMA was 22% in normals and 13% in difficult intubation. Through an ILMA, blind intubation was successful in 92% of normals, 5 of them with immobile spine, in 91% in patients with difficult intubation, and in 83% in patients with reduced mouth opening. The success rate per intubation attempt was 60% in normals, 46% in difficult intubation, and 46% in reduced mouth opening, with a success rate for the first intubation attempt of 57%. This compares favourably with results presented at the Jersey symposium in 554 patients. CONCLUSION: The ILMA maintains the superb ventilation potential of a SLMA in difficult intubation but doubles the success rate of blind intubation irrespective of anatomical difficulties, with a 50% success rate during the first intubation attempt. Possible uses of the ILMA may be in difficult intubation situations including immobile spine, in cannot ventilate--cannot intubate situations comparable to a SLMA with an improved chance of successful intubation, and perhaps as a device for ventilation and intubation for untrained people. The use of the ILMA can be trained during everyday practice. Expert assessment of successful endotracheal tube position is mandatory.
Facial Neoplasms↗
Cricoid pressure impedes placement of the laryngeal mask airway and subsequent tracheal intubation through the mask.
We have studied 40 patients to see if cricoid pressure affects the success rate of ventilation through, and the position of, the laryngeal mask and subsequent fiberscope-aided tracheal intubation. Adequate ventilation of the lungs was produced through the laryngeal mask in 19 of 20 patients in the control group, but in only 10 of 20 patients in the cricoid pressure group (P < 0.002). The laryngeal mask was positioned correctly in 16 patients in the control group, but in only two patients in the cricoid pressure group (P < 0.001). Tracheal intubation was accomplished in 19 patients in the control group, but in only three patients in the cricoid pressure group (P < 0.001). Release of cricoid pressure after placement of the laryngeal mask improved the view of the glottis, but tracheal intubation was still difficult because of laryngeal deviation. These results show that cricoid pressure impedes placement of the laryngeal mask and subsequent fiberscope-aided tracheal intubation.
Adult↗
The laryngeal mask airway reliably provides rescue ventilation in cases of unanticipated difficult tracheal intubation along with difficult mask ventilation.
UNLABELLED: In 1995, our department of anesthesiology established an airway team to assist in treating unanticipated difficult endotracheal intubations and an airway quality improvement (QI) form to document the use of emergency airway techniques in airway crises (laryngeal mask airway [LMA], flexible fiberoptic bronchoscopy, retrograde intubation [RI], transtracheal jet ventilation [TTJV], and cricothyrotomy). Over a 2-yr period, team members and staff anesthesiologists completed airway QI forms to document the smallest peripheral SpO2 during an airway crisis, the number of direct laryngoscopies (DL) performed before using an emergency airway technique, and the emergency airway technique that succeeded in rescue ventilation. Team members agreed to use the LMA as the first emergency airway technique to treat the difficult ventilation/difficult intubation scenario. A SpO2 value < or =90% during mask ventilation defined difficult ventilation. Inability to perform tracheal intubation by DL defined difficult intubation. An increase in the SpO2 value >90% defined rescue ventilation. Review of airway QI forms from October 1, 1995 until October 1, 1997 revealed 25 cases of difficult ventilation/difficult intubation. Before airway rescue, the median SpO2 was 80% (range 50%-90%), and there were four median attempts at DL (range one to nine). The LMA had a success rate of 94% (95% confidence interval [CI] 77-100). Flexible fiberoptic bronchoscopy, TTJV, RI, and surgical cricothyrotomy had success rates of 50% (95% CI 0-100), 33% (95% CI 0-100), 100% (95% CI 37-100), and 100% (95% CI 37-100), respectively. LMA insertion as the first alternative airway technique was useful in dealing with unanticipated instances of simultaneous difficulty with mask ventilation and tracheal intubation. IMPLICATIONS: Twenty-five cases of simultaneous difficulty with mask ventilation and tracheal intubation occurred after the induction of general anesthesia during the study period. The laryngeal mask was used in 17 cases, and it provided rescue ventilation without complication in 94% of these cases (95% confidence interval 77-100).
Anesthesia↗
Masking the face: recognition of emotional facial expressions as a function of the parameters of backward masking.
Four experiments are reported investigating recognition of emotional expressions in very briefly presented facial stimulus. The faces were backwardly masked by neutral facial displays and recognition of facial expressions was analyzed as a function of the manipulation of different parameters in the masking procedure. The main conclusion was that stimulus onset asynchrony between target and mask proved to be the principal factor influencing recognition of the masked expressions. In general, confident recognitions of facial expressions required about 100-150 msec, with shorter time for happy than for angry expressions. The manipulation of the duration of both the target and the mask, by itself, had only minimal effects.
Adolescent↗
Transient masking and the temporal course of simultaneous tone-on-tone masking.
Previous studies have shown that threshold for a signal in tone-on-tone simultaneous masking is sometimes lower when the masker is continuous than when it is gated. Threshold may also decline as signal onset is delayed relative to the onset of a longer duration masker, though it may increase again near masker offset. In the present study, the level of a 1250-Hz sinusoidal masker was found which would just mask a 20-ms, 1000-Hz sinusoid presented at 10-dB sensation level (SL). Masker duration was 20 or 400 ms; in the latter case, the signal was presented in one of three temporal positions within the masker. The level of the 1250-Hz masker necessary to mask the signal was reduced, sometimes by as much as 20-25 dB, by a 20-ms, 500-Hz sinusoid (transient masker) presented at the times when the signal might occur, but at a level 30 dB below that at which it would mask the 10-dB SL signal. This suggests that, in the earlier studies, at least some of the elevation in threshold in the presence of a short-duration masker or at the beginning (or end) of a longer duration masker may have been due to the transient responses to the masker affecting detection of the signal, but not necessarily masking the signal in terms of excitation in the signal "channel."
Acoustic Stimulation↗
Speech masking. I. Simultaneous and nonsimultaneous masking within stop /d/ and flap closures.
This article reports on investigations of the relative roles of simultaneous and nonsimultaneous masking on detection thresholds using natural speech utterances. Thresholds were obtained for 15-ms probe tones placed in the stop or flap closures of /ada/ and /idi/. Threshold elevations due to simultaneous and nonsimultaneous masking could be explained by the dynamics of neighboring speech spectra. Nonsimultaneous effects were related to spectra at least 30 ms around the probe tone. Although simultaneous masking is usually stronger than nonsimultaneous masking, the relative amplitude of adjacent speech segments in natural speech is sufficiently high near formant regions to cause noticeable effects of nonsimultaneous masking.
Adult↗
Minimal upward spread of masking: correlations with speech and auditory brainstem response masked thresholds.
Much less than predicted upward spread of masking, termed undermasking, was previously noted in three elderly listeners, who are the focus of this report. Three aspects of undermasking were studied: Reliability, facilitation of speech recognition in noise, and correlation with physiological measurements. The masker was a 90-dB-SPL 1-kHz low-pass-filtered noise. Reliability of undermasking was assessed from serial measurements made over an approximately 2-year interval. Masked speech thresholds were measured with an adaptive procedure for two types of stimuli: spondaic words and the California Consonant Test. Subjects with undermasking had substantially lower masked speech thresholds than either audiometrically matched elderly subjects or young, normal-hearing subjects. It appears that undermasking is a stable characteristic that provides the listener with exceptionally good communication abilities in noise. Finally, a strong positive correlation was observed between the masked auditory brainstem response (wave V) threshold and the masked behavioral threshold, suggesting that the mechanism producing undermasking is in the auditory periphery.
Acoustic Stimulation↗
When the target becomes the mask: using apparent motion to isolate the object-level component of object substitution masking.
J. T. Enns and V. Di Lollo (1997) discovered a new form of visual masking that they labeled object substitution masking (OSM). OSM occurs when 4 dots, presented around a target, trail in the display after target offset. The present study showed that the physical presence of the masking dots after target offset is not necessary for OSM. Instead, the continued presence of a changing high-level representation associated with the target suffices to yield OSM. Apparent motion was used to define such representation. In these experiments, the initial display offset and was followed by a 2nd display where masks appeared at new locations. Only when the spatiotemporal properties of the stimuli on the 2nd display supported the perception of the target moving and turning into the mask was OSM observed.
Analysis of Variance↗
A study on the microbial filtration efficiency of surgical face masks--with special reference to the non-woven fabric mask.
With the experimental apparatus designed and made available by Nicholes, we evaluated the bacterial filtration efficienty (B.F.E.) of the non-woven fabric and cotton cloth masks. The apparatus was supplied by Nicholes (U.S. Military Specification 36954 C mask, surgical, disposable). The study presented here was performed as a round robin test with Nicholes. By using this apparatus, comparison was made as to the B.F.E. of the six different kinds of surgical face mask before and after prolonged use. The result was obtained that the disposable mask made of glass fiber mat combined with non-woven fabric proved to be the highest in performance with a B.F.E. of 98.1-99.4%. It is useful both in preventing hospital infection and in general clinical practice. The B.F.E. of the conventional cotton cloth masks is not only lower but variable over a wide range of 43.1-93.6%.
Aerosols↗
[Auditory masking patterns in forward, backward, and simultaneous-masking situations (author's transl)].
To investigate the temporal course of the frequency characteristics of the response elicited in the auditory system, pure-tone masking patterns were obtained at several time positions relative to the onset or the offset of the masker. The simultaneous masking patterns obtained suggest that the shape of the response distribution remained almost unchanged during the masker, although they are less informative compared to the other conditions because of interaction effects between the masker and the probe. The forward masking data illustrate the decay course of the distribution and are believed to give more reliable informations as to the frequency selectivity of the auditory system. The backward masking data, however, fail to give any tenable suggestions. The phenomenon of the shift in the maximum-masking-frequency was observed in all conditions and its underlying mechanisms were discussed.
Adult↗
Yeast transcriptional regulator Leu3p. Self-masking, specificity of masking, and evidence for regulation by the intracellular level of Leu3p.
Recent work suggests that the masking of the activation domain (AD) of yeast transactivator Leu3p, observed in the absence of the metabolic signal alpha-isopropylmalate, is an intramolecular event. Much of the evidence came from the construction and analysis of a mutant form of Leu3p (Leu3-dd) whose AD is permanently masked (Wang, D., Hu, Y., Zheng, F., Zhou, K., and Kohlhaw, G. B. (1997) J. Biol. Chem. 272, 19383-19392). In a modified two-hybrid experiment, the ADs of both wild type Leu3p and Leu3-dd were shown to interact with the remainder of the Leu3 protein, in an alpha-isopropylmalate-dependent manner. The finding that masking and unmasking proceed apparently normally when full-length Leu3p is expressed in mammalian cells is also consistent with the notion of intramolecular masking. Here we report on the identification of nine missense mutations (all of them suppressors of the Leu3-dd phenotype) that cause permanent unmasking of Leu3p. The nine mutations map to three short segments located within a 140-residue-long region of the C-terminal part of the middle region of Leu3p. These segments may be part of a spatial trap for the AD. We also performed "domain swaps" between Leu3p and Cha4p, a serine/threonine-responsive activator that, like Leu3p, belongs to the family of Zn(II)2Cys6 proteins. We show that AD masking and response to the appropriate metabolic signal only occur when a given AD remains attached to its own middle region; middle region swapping results in constitutively active proteins. Finally, we show that the extent to which Leu3p regulates reporter gene expression depends on the intracellular concentration of Leu3p. The possible physiological significance of this observation is discussed in light of the known regulation of Leu3p by Gcn4p.
Amino Acid Substitution↗