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PubMed1981

Tone-on-tone masking in subjects with normal hearing and with sensorineural hearing loss.

Quiet and masked thresholds were obtained from 5 subjects with normal hearing and 31 subjects with sensorineural hearing loss. Maskers were pure tones varying in frequency and intensity. The hearing-impaired subjects showed an abnormal spread of masking when masking was measured in terms of masked threshold. The abnormal spread of masking seems to be related to both the hearing threshold of the masker and the quiet threshold of the test signal. The notch due to detection of combination tones found on the high-frequency slope of masked audiograms of normal subjects (obscuring the actual extent to which the signal is masked) tends to accentuate the apparent abnormal upward spread of masking in the hearing-impaired subjects. The abnormal spread in the latter case is real, but comparison with the normal case must take the notch into account.

Acoustic Stimulation↗

PubMed1982

Detection and recognition masking-level differences for the individual CID W-1 spondaic words.

The detection and recognition masking-level differences for the 36 individual CID W-1 spondaic words (Technisonic Studios) were established on 36 listeners with normal hearing. The masking for two conditions, SoNo and S pi No, was accomplished with 70-dB-SPL speech-spectrum noise. The word lists were administered in 2-dB decrements with the 36 words presented at each signal-to-noise ratio, which ranged from 9 dB to -19 dB for SoNo and from 3 dB to -25 dB for S pi No. The detection and recognition thresholds determined for each spondaic word under both masking conditions are presented. Additionally, the slopes of the psychometric functions for each word under both conditions are given. The mean masking-level difference (SoNo-S pi No) for the detection-response task was 9.4 dB (SD = .7 dB). The mean masking-level difference for the recognition task was 7.2 dB (SD = 1.4 dB). The recognition masking-level differences for the individual spondaic words ranged from 4.4 dB (stairway) to 10.0 dB (oatmeal). A list of 10 words that had the largest masking-level differences for recognition is suggested to enhance the clinical utility of the masking-level difference for speech.

Auditory Threshold↗

PubMed1999

Development of adult-like performance in backward, simultaneous, and forward masking.

Some researchers have argued that specific language impairment (SLI) is associated with deficits in processing certain temporal aspects of auditory stimuli. One recent study (Wright et al., 1997) suggests that backward masking in particular poses a problem for children with SLI, as compared to simultaneous or forward masking. Interpretation of this finding is complicated by the fact that very little is known about the development of normal, adult-like performance in these masking paradigms. The study reported here examined performance for children 5-11 years old on forward, simultaneous, and backward masking and compared their performance to that of adults. The data show a trend for improvement in performance with age in all three masking paradigms. There was no evidence for later or more gradual improvement in performance on the backward-masking paradigm. However, backward-masking thresholds were more variable than those in the other conditions and were subject to greater individual differences, even in the adult data set. Manipulation of masker bandwidth yielded no evidence for more adult-like performance in the child data with the wider bandwidth masker. Additional data collected on two naive adult observers show a marked improvement in backward-masking performance over time, suggesting that detection with these stimuli might be particularly subject to practice effects.

Adult↗

PubMed1998

Timing of removal of the laryngeal mask airway.

Previous studies reported that complications associated with removal of the laryngeal mask were more frequent in awake patients than in anaesthetised patients; however, these studies did not comply with the method described in the manufacturer's instruction manual. The reported incidences of regurgitation during the use of the laryngeal mask also differ considerably between studies. We studied these factors in 66 patients in whom the method described in the manual was used. After induction of anaesthesia, the laryngeal mask and a pH probe were inserted and the cuff of the mask was inflated with a minimum volume of air. Anaesthesia was maintained with nitrous oxide and isoflurane in oxygen. At the end of the operation, we randomly allocated patients to one of two groups and the laryngeal mask was removed either while they were still deeply anaesthetised or after they had regained consciousness. No apparent regurgitation occurred in any patient during operation, but one patient in the anaesthetised group regurgitated immediately after removal of the mask. The incidence of complications during or after removal of the laryngeal mask was significantly greater in the anaesthetised group than that in the awake group (p << 0.001; difference [95% CI]: 48.5 [30.5-66.5]%). Therefore, the laryngeal mask can be safely left in place until the patient has regained consciousness after emergence from anaesthesia.

Adolescent↗

PubMed1998

The laryngeal mask airway as an aid to training in fibreoptic nasotracheal endoscopy.

We have investigated the extent to which the laryngeal mask airway, when used as an aid to fibreoptic nasotracheal video-endoscopy training, could reduce endoscopy apnoeic time in anaesthetised, paralysed oral surgery patients. Twenty anaesthetic trainees were randomly allocated to the laryngeal mask airway or control group. Laryngeal mask airway group endoscopies were performed in three stages following insertion of the laryngeal mask airway; stage 1: nasendoscopy, with the lungs ventilated automatically through the laryngeal mask airway; stage 2: removal of the laryngeal mask airway; stage 3: pharyngoscopy, larygoscopy and tracheoscopy. Control group endoscopies were performed conventionally, in one stage. Each trainee performed five nasotracheal intubations. Though total endoscopy time in the laryngeal mask airway group (stage 1 + stage 2 + stage 3 times) was significantly longer (average 136 s vs. 108 s), apnoeic time (stage 2 + stage 3 times) was significantly shorter (average 59 s vs. 108 s) than endoscopy time in the control group. This application of the laryngeal mask airway may have a useful role to play in ensuring patient safety during early fibreoptic training.

Adult↗

PubMed1998

Nasal fibreoptic tracheal intubation in anaesthetised patients breathing via a modified laryngeal mask airway.

A modified laryngeal mask airway was used to facilitate nasotracheal intubation with a fibreoptic laryngoscope. A size 4 laryngeal mask airway was modified by creating a defect at the base of the stem and removing the bars to allow passage of the fibreoptic laryngoscope from the nasopharynx to the larynx. The laryngeal mask airway cuff was split and the cut edges were sealed with silicone. This design allowed the cuff to function normally and allowed removal of the split laryngeal mask airway after the tracheal tube had been 'railroaded' into place. Thirty-four patients were studied. The split laryngeal mask airway was easily inserted with satisfactory airway maintenance in 32 patients. Nasal airway endoscopy and laryngoscopy were successfully achieved with the split laryngeal mask airway in place in 31 of 32 patients. Railroading the tracheal tube over the fibreoptic laryngoscope with the split laryngeal mask airway in place was successful in all 31 of these patients. This prototype split laryngeal mask airway allows good airway maintenance while fibreoptic nasotracheal intubation is performed.

Adolescent↗

PubMed2000

The effect of facial hair and sex on the dispersal of bacteria below a masked subject.

Surgical face masks prevent the dispersal of bacteria from the upper airway to surfaces immediately in front of and below the face during talking. However, mask wiggling has been reported to increase dermabrasion and bacterial contamination of surfaces immediately below the face. Facial hair and recent shaving may alter the quantity of particles shed by dermabrasion when the mask is wiggled. We investigated the effect of mask wiggling in 10 bearded and 10 clean-shaven male subjects, and 10 female subjects. Wiggling the mask significantly increased the degree of bacterial shedding onto agar plates 15 cm below the lips in bearded males (p = 0.03) and females (p = 0.03), but not in clean-shaven males. At rest without mask wiggling the bearded subjects shed significantly more bacteria than clean-shaven males (p = 0.01) or females (p = 0.001). To reduce the risks of contamination of the sterile field when face masks are worn females and bearded males should avoid wiggling the face mask. Bearded males may also consider removing their beards.

Colony Count, Microbial↗

PubMed1989

[Surgical masks--effective protection against cytostatic aerosols?].

A surgical mask, a coarse-dust mask and five types of fine-dust masks were tested by enhanced light microscopy and cross-sectional thickness measurements for their effectiveness against inhalation of cytostatic aerosols. The construction of surgical masks most nearly resembles that of coarse-dust masks with respect to quality and number of layers. They are thus not suitable as protection against inhalation of cytostatic aerosols. Such masks must be at least particle-filtering half-masks of type DIN 58645 FHM - P2 (fine-dust masks of protective stage P2).

Aerosols↗

PubMed1978

Spatial-frequency masking with briefly pulsed patterns.

Spatial-frequency masking was studied with briefly pulsed (25 ms) vertical gratings. The mask was a noise grating, and the test pattern was a sinusoidal grating. A low-frequency band of noise masked a low- but not high-spatial-frequency test grating when the patterns were presented simultaneously. A high-frequency band of noise did not mask a low-frequency test grating when the patterns were presented simultaneously or when the mask was presented after the test pattern (backward masking). Masking was, however, observed when the mask or test pattern was of sufficiently high contrast so that the stimuli had nonlinear distortion and thus produced DC shifts of the field luminance.

Humans↗

PubMed2000

Comparing contrast-modulated and luminance-modulated masking: effects of spatial frequency and phase.

The masking of a sinusoidal test grating by contrast-modulated (CM) gratings could, in principle, be attributable to the presence of a distortion product, injected into the stimulus during some nonlinear transformation at an early level of visual processing (e.g. Nachmias, 1989 Vision Research 29 137-142). If so, CM gratings and luminance-modulated (LM) gratings of similar effective contrast and spatial frequency should mask the detection of sinusoids in a similar fashion. We compared the effects of masking by 1 cycle deg-1 CM gratings [both simple beats (8 + 9 cycles deg-1) and amplitude-modulated gratings (8 + 9 + 10 cycles deg-1)], with those of masking by 1 cycle deg-1 LM gratings of low contrast. We found that: (i) CM and low-contrast LM grating masks yielded similar spatial-frequency tuning functions around the modulation frequency of 1 cycle deg-1; (ii) low-contrast LM gratings masked the detection of test sinusoids in a highly phase-dependent fashion, while masking by CM gratings did not vary systematically with relative spatial phase. The results suggest that masking produced by CM gratings cannot simply be explained by the presence of a distortion product at the beat or modulation frequency.

Contrast Sensitivity↗

PubMed2006

Do masks terminate the icon?

Iconic memory is operationally defined by part-report experiments (Sperling, 1960). If a mask is presented after the target, the mask is thought to be superposed on the target in the iconic representation, or to displace it from the representation. But could a cue presented after a pattern mask still allow selection within the target array? A target array of letters was followed by a checkerboard mask. We compared two target-mask interstimulus intervals (ISIs; 0 and 100 ms), and six cue delays. At ISI = 0 ms, performance was at chance, for part report and whole report. At ISI = 100 ms, with the shortest cue delay, observers demonstrated a part-report advantage of 25-30%. As cue delay increased the part-report advantage decreased. These results are inconsistent with an iconic memory that is automatically displaced or overwritten by new information. We consider two alternatives: a second-stage store, which represents letters in terms of their high-level features and which the mask cannot penetrate, or a four-dimensional store that preserves separately the representations of the target and its aftercoming mask. We discuss the implications of our results for studies that use backward masking to "terminate the icon".

Cues↗

PubMed2003

Comparison of the LMA-classic with the new disposable soft seal laryngeal mask in spontaneously breathing adult patients.

BACKGROUND: The laryngeal mask airway LMA-Classic has been used widely in clinical practice. A new disposable supraglottic airway device, the Soft Seal LM, has been introduced recently. In a randomized study, the authors compared the LMA-Classic and the disposable Soft Seal LM in terms of their clinical performance, cuff pressures during nitrous oxide anesthesia, position of the laryngeal mask in situ by fiberoptic evaluation, and morbidity in a wide range of routine general surgery procedures. METHODS: A total of 200 adult patients were randomly assigned to a size 4 laryngeal mask in two equal-sized groups for airway management during surgery: (1) LMA-Classic (Intavent Orthofix Ltd., Maidenhead, Berkshire, United Kingdom); or (2) Soft Seal LM (Portex Ltd., Hythe, Kent, United Kingdom). Anesthesia was administered with fentanyl, propofol, nitrous oxide, oxygen, and sevoflurane. The variables studied were ease of insertion, fiberoptic view, time in situ, incidence of blood on the laryngeal mask at the time of removal, and the incidence of postoperative sore throat at 2 and 24 h. The laryngeal mask cuff pressures were measured continuously. Intracuff pressure limitation was not attempted. RESULTS: The LMA-Classic and the Soft Seal LM showed similar clinical performances, as shown by their insertion time (successful insertion at first attempt was achieved within 20 s in 97% with LMA-Classic trade mark vs. 95% with Soft Seal LM), fiberoptic evaluation of the anatomic position of the laryngeal mask, and satisfactory anesthesia conditions. Laryngeal mask cuff pressures increased from 45 to 100.3 mmHg in the LMA-Classic and from 45 to 46.8 mmHg in the Soft Seal LM (P < 0.001). Macroscopic blood was seen on only four occasions in the LMA-Classic group. The incidence of sore throat was significantly increased at 2 h postoperatively when using the LMA-Classic, although there was no difference at 24 h after surgery. CONCLUSIONS: In spontaneously breathing adult patients requiring a size 4 laryngeal mask airway, the new disposable Soft Seal LM device is an acceptable alternative to the reusable LMA-Classic trade mark, resulting in a good laryngeal seal and offering similar clinical performance. Cuff pressures increase substantially when the LMA-Classic is used but not when using the Soft Seal LM. There was less trauma to patients using the Soft Seal LM, as assessed by the incidence of sore throat in the early postoperative period.

Adolescent↗

PubMed2004

Laryngeal mask airway insertion by anesthetists and nonanesthetists wearing unconventional protective gear: a prospective, randomized, crossover study in humans.

BACKGROUND: Mass casualty situations impose special difficulties in airway management, even for experienced caregivers. The laryngeal mask airway is part of the difficult airway algorithm. The authors evaluated the success rate and the time to secure airways by mask by anesthetists, surgeons, and novices when wearing either surgical attire or full antichemical protective gear that included butyl rubber gloves and a filtering antigas mask. METHODS: Twenty anesthetists and 22 surgeons with 2-5 yr of residency inserted a laryngeal mask airway in 84 anesthetized patients, and 6 novices repetitively inserted masks in 57 patients under both conditions in a prospective, randomized, crossover manner. The duration of insertion was measured from the time the device was first grasped until a normal capnography recording was obtained. RESULTS: Anesthetists needed 39 +/- 14 s to insert the masks when wearing surgical attire and 40 +/- 12 s with protective gear. In contrast, surgery residents needed 64 +/- 40 and 102 +/- 40 s (P = 0.0001), respectively. Anesthetists inserted masks in a single attempt, whereas the surgeons needed up to four attempts with no hypoxia or failure associated. The initial attire-wearing novices' insertions took as long as the surgeons'; three of them then reached the mean performance time of the anesthetists after four (protective gear) and two (surgical attire) trials, with only one occurrence of hypoxia and a failure rate similar to that of the surgeons. CONCLUSIONS: Anesthesia residents insert laryngeal mask airways at a similar speed when wearing surgical attire or limiting antichemical protective gear and two to three times faster than surgical residents or novices wearing either outfit. Novices initially perform at the level of surgical residents, but their learning curve was quick under both conditions.

Adult↗

PubMed1990

Auditory brain stem response in newborn infants--masking effect on ipsi- and contralateral recording.

Ipsilateral and contralateral auditory brain stem responses (ABR) were recorded in 10 full-term neonates. We investigated the effect of the masking level on the peak latency and amplitude on ipsi- and contralateral recordings. Clicks were presented at 85 dB HL to the ipsilateral ear and the masking white noise was presented at 75, 65, 55, 45 and 0 dB HL on the contralateral one, respectively. Masking had no significant effect on the ipsi- and contralateral recording in regard to latency and amplitude except for wave CVI (contralateral wave VI). In addition, ABR was recorded in an infant with total unilateral hearing loss. Crossover responses on both sides were observed with-out contralateral masking, but these responses were completely eliminated when 45 dB HL contralateral masking masked the 85 dB HL clicks to the dead ear. Therefore, it is suggested that such crossover responses will contribute to the ipsi- and contralaterally recorded ABR waveform when an ABR recording is carried out without contralateral masking. Our results indicate that contralateral masking is necessary and should be used in cases of unilateral hearing loss.

Audiometry, Evoked Response↗

PubMed1996

Wearing of masks for obstetric regional anaesthesia. A postal survey.

A postal survey of 801 members of the Obstetric Anaesthetists Association was carried out in the United Kingdom and Ireland to investigate the use of surgical facemasks whilst performing spinal and epidural blocks. Two hundred and twenty three out of 539 respondents (41.3%) routinely wore masks for both spinals and epidurals; 22 (4.1%) wore masks only for epidurals; 21 (3.9%) wore masks only for spinals and 273 (50.6%) did not wear masks for either spinals or epidurals. Fifty out of 240 (21%) of those who routinely wore masks did not believe that wearing a mask reduced the risk of infection. Only 83 out of 259 (32%) mask wearers changed their masks between cases.

Anesthesia, Epidural↗

PubMed2006

Protein cross-contamination during batch cleaning and autoclaving of the ProSeal laryngeal mask airway.

We tested the hypothesis that protein cross-contamination occurs during batch cleaning and autoclaving of a reusable extraglottic airway device, the ProSeal laryngeal mask airway. At the end of each day for 10 days, nine laryngeal mask airways that had been used for non-intra-oral surgery were cleaned and autoclaved alongside a new unused laryngeal mask airway. In addition, a new unused laryngeal mask airway underwent the same cleaning and autoclaving procedures in isolation. Protein staining was more frequently detected on the unused laryngeal mask airways that were processed by batch rather than in isolation (p < 0.01). Protein staining was detected on all unused laryngeal mask airways that were processed by batch, but none on those processed in isolation. Protein staining was more severe with the used compared with the unused laryngeal mask airways (p < 0.001). We conclude that protein cross-contamination of the laryngeal mask airway occurs during batch cleaning and autoclaving and recommend that reusable airway devices are cleaned in isolation.

Cross Infection↗

PubMed1998

Effects of peripheral flicker masking on M- and P-pathway response.

PURPOSE: The effects of metahue and metacontrast masking on the responses of the M- and P-pathways of the human visual system were investigated using temporal analysis of the multifocal flash visually evoked potential (VEP) (VERIS system). METHODS: The experiments were carried out at three achromatic luminance contrasts, 24, 70 and 96%, with three peripheral masks: a steady 65% grey mask, a grey flicker mask and an isoluminant red/green flicker mask. The stimuli were viewed monocularly and the mask and VERIS stimuli superposed with a mirror-aperture system. RESULTS/CONCLUSIONS: The masks had no significant effect on the behaviour of the M-pathway as stimulus contrast increased. The amplitude of the P-pathway was found to be approximately level at all contrasts of the stimulus and with all three masks rather than showing the expected steady increase in activity with increasing stimulus contrast.

Adult↗

PubMed2003

Children's detection of pure-tone signals: informational masking with contralateral maskers.

When normal-hearing adults and children are required to detect a 1000-Hz tone in a random-frequency multitone masker, masking is often observed in excess of that predicted by traditional auditory filter models. The excess masking is called informational masking. Though individual differences in the effect are large, the amount of informational masking is typically much greater in young children than in adults [Oh et al., J. Acoust. Soc. Am. 109, 2888-2895 (2001)]. One factor that reduces informational masking in adults is spatial separation of the target tone and masker. The present study was undertaken to determine whether or not a similar effect of spatial separation is observed in children. An extreme case of spatial separation was used in which the target tone was presented to one ear and the random multitone masker to the other ear. This condition resulted in nearly complete elimination of masking in adults. In young children, however, presenting the masker to the nontarget ear typically produced only a slight decrease in overall masking and no change in informational masking. The results for children are interpreted in terms of a model that gives equal weight to the auditory filter outputs from each ear.

Adolescent↗