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PubMed1984

Forward and backward tactile recognition masking.

Forward and backward tactile recognition masking were investigated with a 15 by 15 array of tactile point-stimulators with the use of targets consisting of line segments differing in location and orientation and a random-dot embedding mask. Ss were paid graduate student volunteers (three males and one female). Durations of targets and masks were varied, and interstimulus intervals ranged from zero to 300 msec. Increases in target duration over mask duration decreased forward, but not backward masking. Small increases in mask duration over target duration increased both forward and backward masking. Further large increases in mask duration increased backward masking, but had no effect on forward masking. The results were interpreted as indicating that forward masking is predominantly influenced by peripheral processes, while backward masking is the result of a combination of peripheral and central processes, in agreement with similar findings in audition and vision.

Discrimination Learning↗
PubMed1986

Vibrotactile frequency recognition: forward and backward masking effects.

Forward and backward vibrotactile recognition masking was investigated in 4 subjects with 240-Hz and 160-Hz targets of 20 ms duration and four 200-Hz masks, using interstimulus intervals (ISIs) ranging from -500 to 500 ms. Two of the masks (short) were 20 ms and two (long) were 200 ms in duration. One of each set of masks was matched in subjective intensity to the targets, but the others were more intense. The range of ISIs over which masking was obtained was comparable to that found by Massaro (1970) with auditory stimuli. Both short masks produced more masking than either long mask except at short ISIs. Larger mask intensities increased masking only at very short ISIs, and longer mask durations increased backward but not forward masking.

Discrimination Learning↗
PubMed1996

The effect of introducing fibreoptic bronchoscopes on gas flow in laryngeal masks and tracheal tubes.

The laryngeal mask airway, reinforced laryngeal mask airway and tracheal tube were studied to determine (1) flow resistance during simulated inspiration and (2) the maximum size of fibreoptic scope which can be passed down the lumen at clinically useful ventilatory settings. In addition, the flow resistance imposed by the mask aperature bars was quantified. The laryngeal mask airway can accommodate a larger fibrescope than the corresponding sizes of reinforced laryngeal mask airway or tracheal tube. Mean (range) flow resistance was 2.3 (1.7-3.5) times higher with the reinforced laryngeal mask airway compared to the laryngeal mask airway, 2.1 (1.2-4.2) times higher with the tracheal tube compared with the laryngeal mask airway and 1.2 (0.7-1.8) times lower with the tracheal compared with the reinforced laryngeal mask airway. Removal of the mask aperture bars resulted in a mean decrease in flow resistance of 3.6%. Our data have shown that the laryngeal mask airway can accommodate a larger fibrescope than either the reinforced laryngeal mask airway or tracheal tube at clinically useful ventilatory settings and that the current recommendations for maximum size of fibrescope should be revised.

Airway Resistance↗
PubMed1992

Intensity and frequency resolution: masking of absolute identification and fixed and roving discrimination.

Auditory intensity and frequency resolution were studied in three paradigms under masking conditions. Absolute identifications of single stimuli (one-interval paradigm) and 2IFC judgments of fixed- and roving-level pairs of stimuli (two-interval paradigm) were obtained from the same experienced observers. Judgments were made under optimal (no mask) conditions, in the presence of a broadband noise mask (simultaneous mask), and when the stimulus(i) to be judged were either preceded (forward mask) or followed (backward mask) by a broadband noise mask. Substantial masking of intensity resolution was found in all mask conditions. Only a simultaneous mask affected frequency resolution. In the no mask condition, performance was best for fixed-level (or frequency) 2IFC discrimination, followed by roving-level (frequency) 2IFC, and finally absolute identification. These differences were maintained under masking for frequency resolution, but not for intensity resolution. The results are discussed in terms of the Braida and Durlach (1988) model of intensity resolution. A similar model is suggested for frequency resolution with differences suggested by the differences in neural coding of sound intensity and frequency.

Auditory Perception↗
PubMed1995

Additivity of masking in normally hearing and hearing-impaired subjects.

The effects of combining two equally effective maskers were studied in normally hearing and elderly hearing-impaired subjects. The additivity of nonsimultaneous masking was investigated by measuring thresholds for a brief 4-kHz signal in the presence of a broadband-noise forward masker, a backward masker, and a combination of both. For the normally hearing subjects, combining two equally effective nonsimultaneous maskers resulted in up to a 15-dB greater increase in threshold than the 3 dB predicted by an energy-summation model ("excess masking"). However, the hearing-impaired subjects showed little or no excess masking. The difference between the two groups is consistent with a theory linking excess masking to the compressive transfer function measured on the basilar membrane (BM). In the hearing-impaired subjects the transfer function is more linear, accounting for the lack of excess masking. The additivity of simultaneous masking was investigated by measuring thresholds for a 100-ms 4-kHz signal in the presence of either a 400-ms broadband noise masker or a 400-ms sinusoidal masker at the same frequency as the signal, and then combining two equally effective maskers, a noise and a tone. The maximum amount of excess masking (3 to 4 dB) was similar across the two groups of subjects, consistent with an explanation based on the use of different detection cues for the tonal and noise maskers. It is argued that, while peripheral compression may underlie excess masking for pairs of nonsimultaneous maskers, it is unlikely that in simultaneous masking, where the maskers are close in frequency to the signal, the two maskers are compressed individually before their effects are combined. It is further suggested that BM nonlinearity may underlie the effects of the upward spread of masking and the nonlinear growth of forward masking, as well as accounting for the additivity of simultaneous masking when the masker frequencies are well below that of the signal.

Adult↗
PubMed1978

Functional characteristics of cochlear nucleus in behaving cat examined by acoustic masking of electrical stimuli.

1. Cats were trained, using an operant procedure, to detect and respond to electrical stimulation delivered in the vicinity of the cochlear nucleus. The electrical stimuli were presented both in silence and in synchrony with repeated noise bursts to determine whether detection thresholds for the electrical stimuli were elevated by the acoustic masking noise. 2. For stimulation sites centered within auditory structures (cochlear nucleus or acoustic nerve root), the acoustic maskers caused a consistent elevation of the electrical detection thresholds. For stimulation sites that were in or bordered on nonacoustic neural structures (e.g., vestibular), the acoustic maskers caused little or no elevation of electrical detection thresholds. 3. The magnitude of the acoustic masking effect was monotonically related to the intensity of the acoustic masker across the range of intensities tested. 4. The magnitude of the masking effect was strongly dependent on the relative timing of the stimulus pulse and the masker noise burst. Maximum masking occurred when the pulse just followed the onset of the neural activity in cochlear nucleus evoked by the masker burst. Less masking occurred when the electrical pulse occurred at the middle or end of the masker burst, and still less when the pulse occurred just prior to the onset (backward masking) or just after the offset (forward masking) of the masker burst. 5. The magnitude of the masking effect also depended on the frequency of the acoustic masker. For tone bursts, masking was maximal for each electrode at a particular frequency and declined monotonically for masker frequencies above or below the optimal frequency. 6. It is concluded that the masking of an electrical stimulus by an acoustic stimulus depends on a direct interaction between the neural responses evoked by the two stimuli, and that similar central, neural interactions may contribute to acoustic masking of acoustic stimuli. It is also concluded that the technique of masking an electrical stimulus by an acoustical stimulus is a precise and useful tool for the study of sensory-neural organization in intact behaving animals.

Animals↗
PubMed2002

Masking by fast gratings.

Perception of an oriented pattern is impaired in the presence of a superimposed orthogonal mask. This masking effect most likely arises in visual cortex, where neuronal responses are suppressed by masks having a broad range of orientations. Response suppression is commonly ascribed to lateral inhibition between cortical neurons. Recent physiological results, however, have cast doubt on this view: powerful suppression has been observed with masks drifting too rapidly to elicit much of a response in cortex. We show here that the same is true for perceptual masking. From contrast discrimination thresholds, we estimated the cortical response to drifting patterns of various frequencies, and found it greatly reduced above 15-20 Hz. In the same subjects, we measured the strength of masking by the same patterns and found it equally strong for masks drifting slowly (2.7 Hz) as for masks drifting rapidly (27-38 Hz). Fast gratings thus cause strong masking while eliciting weak cortical responses. Our results might be explained by inhibition from cortical neurons that respond to unusually high frequencies, and yet do not make their signals fully available for perceptual judgments. A more parsimonious explanation, however, is that masking does not involve lateral inhibition from cortex. Masking might operate in retina or thalamus, which respond to much higher frequencies than cortex. Masking might also be due to thalamic signals to cortex, perhaps through depression at thalamocortical synapses.

Contrast Sensitivity↗
PubMed1977

Visual masking by translation equivalents in bilinguals.

Masking thresholds for common words as a function of the relationship between target and mask were assessed using French-English bilingual subjects. Five target-mask combinations were employed. Two control conditions involved unrelated pairs presented in either the same or both languages. The experimental conditions employed masks that were subordinate to the target, e.g., animal-horse, masks that were thr translation equivalents of the targets, and masks which were homophones of the target. Homophones were superior masks compared to same-language, unrelated masks which were in turn superior to subordinately related masks. Translation equivalents were less effective masks than different-language, unrelated masks but were similar to subordinate same-language masks. The results suggest that the relationship between the representations of translation equivalents is similar to that between same-language superordinate and subordinate words.

Adult↗
PubMed2005

Disposable surgical face masks: a systematic review.

UNLABELLED: 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. Surgical face masks have recently been advocated as a protective barrier between the surgical team and the patient, but the role of the surgical face mask as an effective measure in preventing surgical wound infections is questionable. The aim of the systematic review is to identify and review all randomised controlled trials evaluating disposable surgical face masks worn by the surgical team during clean surgery to prevent postoperative surgical wound infection. 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 Association of Operating Room Nurses were contacted for details of unpublished and ongoing studies. Randomised controlled trials (RCTs) and quasi-randomised controlled trials comparing the use of disposable surgical masks with the use of no mask were included. 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. REVIEWERS' 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.

Antisepsis↗
PubMed1979

Two-tone masking and auditory critical bandwidths.

Two-tone masking of 1,000-Hz signals was investigated in 5 normally-hearing listerners. The results indicate a consistent increase in critical bandwidth with level of the two masking tones (approximately 3%/dB). Irregularities in the individual two-tone masking functions led to further investigations with a single listener. For subcritical frequency separations between masking tones, -10 dB/decade masking slopes were demonstrated along with large dips or notches in the two-tone masking functions. Both the -10 dB/decade masking slopes and the large notches were replicated in detail when only the lower-frequency tones of the two-tone masking pairs were employed as maskers. Separate masking bands were then introduced that eliminated the -10 dB/decade masking slope and the large notch. It is concluded that the two-tone masking experiment is really a single-tone experiment, and that the detection of beats, roughness, and combination tones determines the form of single-tone and two-tone masking functions. If critical bnadwidth estimates are to be obtained from these experiments, it is most appropriate to refer to those estimates as "critical bandwidths for tonal interaction".

Acoustic Stimulation↗
PubMed1981

Backward, simultaneous, and forward masking as a function of signal delay and frequency.

Backward, simultaneous, and forward masking were investigated in 7 normal-hearing adults using a 1-kc/s sinusoid masker of 250 msec duration and 60 db SPL. 10-msec sinusoidal signals (probes) were varied in frequency (.4, .8, .9, .95, 1.05, 1.1, 1.2, 1.6 kc/s) and temporal location, delta t, prior to (-250, -150, -40, -20, -10, -2 msec re: masker onset), during (2, 10, 20, 40, 125, 250 msec re: masker onset), or following (2, 10, 20, 40, 125, 250 msec re: masker offset). The double random staircase psychophysical method (Cornsweet, 1962) was used in all conditions. Monotic thresholds were obtained for the backward and forward masking conditions. Dichotic and monotic thresholds were collected for the simultaneous condition. Results showed: (a) Backward masking. The greatest masking (up to 25 db) occurred between 0.0 and -40 msec when the signal probe was within +/- .2 cps of the masker. There was a linear decrease in masking as a function of delta t; masking effects extended to 250 msec. (b) Forward masking. The data revealed no masking beyond 125 msec delta t, an asymmetry in the masking pattern, relatively large threshold shifts (up to 33 db) when delta t was less than 40 msec and the signal was approximately +/- .2 kc/s within the masker. (c) Simultaneous masking. Overshoot occurred at onset and offset for both dichotic and monotic conditions; onset overshoot was larger in both conditions. The data revealed more forward masking than backward masking at equivalent absolute delta t values. Data were discussed in terms of cochlear vibration patterns and hypothesized central mechanisms.

Adult↗
PubMedDate not supplied

Attributes of tinnitus and the acceptance of masking.

Various characteristics of tinnitus were surveyed to determine whether they were associated with the acceptance of masking, which is used as a relief procedure for tinnitus. The characteristics considered were duration, loudness match, minimum masking level, and residual inhibition. Data for the characteristics of tinnitus were obtained from the Tinnitus Data Registry at the Oregon Hearing Research Center, which contains information on 784 tinnitus patients. The acceptance of masking was determined by each individual patient based on actual tests with wearable masking units. Variations in the individual characteristics listed above were not found to be significantly associated with the acceptance of masking and thus should not be used a priori to deny patients the opportunity for possible relief of their tinnitus. A masking indicator was found to be significantly (P = .03) associated with the acceptance of masking. This masking indicator is obtained by subtracting the loudness match of the tinnitus from the minimum masking level. When the masking indicator was 10 dB or less, the acceptance of masking was in excess of 50%. The data presented may help to dispel some current misconceptions about the masking of tinnitus.

Consumer Behavior↗
PubMed1985

Proteins that mask the nuclear binding sites of the avian oviduct progesterone receptor.

The binding of a steroid receptor to specific nuclear sites (i.e., nuclear acceptor sites) represents the immediate event preceding the steroid regulation of gene transcription. How the same steroid receptor regulates different genes in different tissues is unknown. Since a major fraction of the nuclear acceptor sites for a variety of steroid receptors has been reported to be masked in the chromatins of a variety of tissues, the differential expression of the nuclear acceptor sites may explain this regulation of different genes. In the avian oviduct, the removal of a subfraction of chromosomal non-histone proteins, termed CP-2, results in the unmasking of the nuclear acceptor sites for the progesterone receptor (PR). Further, the extent of masking of these nuclear acceptor sites for PR has been reported to vary during cytodifferentiation of the avian oviduct. This paper describes a method for the reconstitution of the masking of PR nuclear acceptor sites in the avian oviduct chromatin using a partially purified chromosomal protein fraction (CP-2b). The reannealling of the CP-2b fraction to unmasked avian oviduct chromatin (termed nucleoacidic protein or NAP) results in the "remasking" of about the same number of nuclear acceptor sites for PR as found in intact chromatin. Because some of the PR acceptor sites on the NAP cannot be remasked, these sites either must be protected from masking or not be recognized by the masking proteins. The masking activity apparently involves only protein(s) because the unmasking of acceptor sites can be achieved with protease but not ribonuclease activities and because the dissociated masking activity is destroyed only by proteases. The masking appears to be reversible because the reconstituted masked sites can again be unmasked. Preliminary purification and characterization of the masking activity in fraction CP-2b by molecular sieve chromatography indicate a heterogeneity of size with the activity eluting in a molecular weight range of from 60 000 to greater than 150 000. Whether the masking proteins prevent the binding of the progesterone receptor by directly binding the acceptor sites or by binding neighboring domains to condense the chromatin is unknown. It is speculated that the masking of acceptor sites may be responsible in part for determining the tissue-specific gene expression induced by steroids and/or may play a role in the unresponsiveness of certain human tumors containing steroid receptors.

Animals↗
PubMed1987

The effect of temperature and humidity levels in a protective mask on user acceptability during exercise.

Subjective and physiological responses were obtained from six subjects wearing a ventilated face mask while exercising (3.8 met) for 15 min on a bicycle ergometer. Different combinations of ambient air temperatures (7 degrees, 16 degrees, 25 degrees C) and mask air temperatures (22 degrees, 27 degrees, 33 degrees C) were studied together with two different air humidities inside the mask (61% and 86% RH). Control experiments were performed without the mask at the same ambient temperatures. Skin temperatures, heart rates and skin wettedness were monitored during exercise. The subject's acceptance of the mask and thermal environment, thermal sensation, sensations of discomfort, sweating and skin wettedness, and their judgment of the work of breathing were assessed at the end of the 15 min exercise period. The acceptance of both the ambient thermal environment and of the thermal microclimate in the mask primarily was determined by the ambient air temperature, but it was influenced by the air temperature and humidity inside the mask. At ambient temperatures of 7 degrees C and 25 degrees C, the acceptance of the thermal work conditions decreased. In the warm environment a mask air temperature less than or equal to 27 degrees C was 100% acceptable and increased the acceptance of thermal environment. In the cool environment, a mask air temperature greater than or equal to 27 degrees C was 100% acceptable. The humidity content of the mask air was only important when the mask air was warm. Warm humid air significantly decreased acceptance of the mask conditions.

Adult↗
PubMed1981

Tinnitus masking:unresolved problems.

With care to provide properly chosen masking sounds, masking can help in 60-80% of clinically significant tinnitus cases. There is no universal masker; instead, an individual evaluation of each patient's tinnitus must be performed in order to match the masking sounds to the patient's audiogram and the spectral characteristics of the tinnitus. Successful long-term masking can usually be achieved in patients for whom (1) hearing impairment is not excessive. (2) the tinnitus frequency, FT, can be reliably located, and (3) the tinnitus can be completely masked by a band of noise at or near FT at a low sensation level. Such patients often experience residual inhibition (temporary suppression of tinnitus upon cessation of masking) which may accumulate with sustained use of masking, in some cases becoming permanent. Long-term masking is difficult or impossible for patients whose hearing is so impaired they cannot hear the masker, or those for whom the masking sounds must be presented at unacceptably loud levels to obtain adequate coverage of the tinnitus. There is a great need for additional work to determine what factors influence the effectiveness of masking, in order to improve our ability to provide appropriate masking stimuli even for the difficult cases.

Humans↗
PubMed1994

A test of an interruption/temporal-uncertainty theory of auditory backward recognition masking of target duration.

The present study examined auditory backward masking in a task requiring subjects to label a target sound as having a long or short duration. Perception of target duration was influenced by the interaction of the effects of (1) the similarity of the target/mask duration, (2) the acoustic similarity of the target and mask (tone vs. white noise), and (3) the interstimulus interval (ISI) between the target and mask. Specifically, relative to the long duration (100 ms) mask, the short duration (40 ms) mask helped performance for the target having a similar short duration (55 ms) but hurt performance for the target having a dissimilar long duration (85 ms). This effect of the similarity of target/mask duration was greater for acoustically similar targets and masks than for acoustically dissimilar targets and masks, and particularly so at the intermediate (45, 105, 165, 205 ms) ISIs. These results can be explained within the framework of Massaro and Idson's (1976) two-stage model by assuming that masking of perceived auditory duration is the result of two processes: (a) the mask's interruption of target processing in a peripheral auditory processing stage, and (b) a confusion of which item is the target vs. the mask, due to temporal uncertainty in the transfer of the target and mask into a central auditory processing stage.

Auditory Perception↗
PubMed1983

Spatial/temporal interactions: backward and forward metacontrast masking with sine-wave gratings.

A metacontrast masking paradigm is presented in which the detectability of a sine-wave target is measured in the presence of a spatially-flanking sine-wave mask. The onset of the mask either precedes (forward masking) or follows (backward masking) the onset of the target. Target detectability is measured as a function of stimulus onset asynchrony (SOA) for stimuli varying in spatial frequency and contrast. For low spatial-frequency targets, target detectability varies as a U-shaped function of SOA both in forward and backward masking. For high spatial frequency targets, U-shaped masking is observed only in backward masking. The magnitude of the masking effect at each SOA of maximal masking (SOAmax) depends on the spatial-frequency similarity of target and mask. SOAmax does not vary with contrast, but does vary with spatial frequency. These data are considered within the context of a model positing inhibitory interactions between the responses of fast- and slow-responding spatial-frequency selective channels, where the latency to channel response increases with spatial frequency.

Female↗
PubMed1987

Direction specific masking and the analysis of motion in two dimensions.

We measured the effects of moving two-component cosine grating masks on the detectability of a moving spatially localized test pattern with a 1.0 octave spatial frequency bandwidth. Masking was used to distinguish between two-component patterns with fluid motion (blobs) and those with rigid motion (plaids). The two gratings which made up the two-dimensional masking patterns were always of the same spatial frequency and contrast, but moved in different directions. We find that plaid masks consistently produced threshold elevations that are 2.0-4.0 times greater than are produced by a single component mask at twice the contrast. Furthermore, this effect is nearly independent of the angle between the two mask components. For fluid motion, however, masking is determined by the mask component whose direction of motion is closest to that of the test. The results obtained with moving two-dimensional patterns demonstrate that, for blobs, the motion of the pattern as a whole has no effect on the degree of masking, whereas, for plaids, the signals arising from the two components interact in a nonlinear manner, thus producing a substantial enhancement of masking, which is clearly related to the coherent motion of the entire pattern. These data shed light on the properties of higher order motion units (possibly in MT cortex) that respond to the direction of two-dimensional pattern motion, suggesting that they combine, in a nonlinear manner, the outputs of units which respond independently to the direction of each mask component.

Form Perception↗