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PubMed2004

The attentional dynamics of masked detection.

A dichoptic masking procedure was used to test whether the mask-dependent cuing effects found in luminance detection by P. L. Smith (2000a) were due to integration masking or interruption masking. Attentional cuing enhanced detection sensitivity (d') when stimuli were backwardly masked with either dichoptic or monoptic masks, whereas no cuing effect was found with unmasked stimuli, implying the mask dependencies were due to interruption of stimulus processing in visual cortex by the mask. The effect is predicted by a gated diffusion process model in which masks interrupt stimulus processing and attention controls the flow of information to a sequential-sampling decision mechanism. The model correctly predicts different patterns of performance for detection and discrimination and cuing effects in simple reaction time.

Attention↗
PubMed1991

Masking-level differences in the elderly: a comparison of antiphasic and time-delay dichotic conditions.

Four dichotic thresholds (S pi N0, S0 N pi, S0 N tau, and S pi N pi tau) were measured for young and old subjects using both burst and continuous broadband maskers. Masking-level differences (MLDs) were determined by subtracting dichotic thresholds from homophasic thresholds (S0 N0 or S pi N pi). The S0 N0 thresholds for the old subjects did not differ significantly from those for the young subjects in either the continuous or the burst masking noise conditions. The S pi N pi thresholds for the old subjects did not differ significantly from those for the young subjects in the continuous masking noise condition, but there was a significant age effect (3 dB) when burst masking noise was used. Both young and old subjects obtained larger MLDs in continuous masking noise than in burst masking noise. MLDs for old subjects were smaller than MLDs for young subjects by 4.3, 5.0, 2.7, and 1.6 dB in burst masking noise and by 4.9, 3.5, 2.5, and 1.4 dB in continuous masking noise, respectively in the S pi N0, S pi N pi tau, S0 N tau, and S0 N pi conditions. Four young subjects there was a hierarchy in the size of the MLD obtained in the four dichotic conditions, with the MLD being significantly larger in the S pi N0 and S pi N pi tau conditions; however, the size of the MLD was the same in all four conditions for the old subjects. Compared to young subjects, the performance of the old subjects was characterized by decreased ability to use homophasic cues in burst masking noise and decreased ability to use interaural difference cues. These findings were observed at four signal frequencies.

Acoustics↗
PubMed1998

Selective visual masking in speechreading.

Using digital video technology, selective aspects of a face can be masked by identifying the pixels that represent it and then, by adjusting the gray levels, effectively eliminate that facial aspect. In groups of young adults with normal vision and hearing, consonant-viseme recognition was measured for closed sets of vowel-consonant-vowel disyllables. In the first experiment viseme recognition was measured while the tongue and teeth were masked and while the entire mouth was masked. The results showed that masking of the tongue and teeth had little effect on viseme recognition, and when the entire mouth was masked, participants continued to identify consonant visemes with 70% or greater accuracy in the /a/ and /(ball)/ vowel contexts. In the second experiment, viseme recognition was measured when the upper part of the face and the mouth were masked and when the lower part of the face and the mouth were masked. The results showed that when the mouth and the upper part of the face were masked, performance was poor, but information was available to identify the consonant-viseme /f/. When the mouth and the lower part of the face were masked, viseme recognition was quite poor, but information was available to discriminate the consonant-viseme /p/ from other consonant visemes.

Adult↗
PubMed1998

The intubating laryngeal mask. Results of a multicentre trial with experience of 500 cases.

A multicentre trial of the use of the intubating laryngeal mask was carried out at seven centres in the United Kingdom using the same agreed protocol. Lung ventilation followed by blind tracheal intubation through the intubating laryngeal mask was attempted on 500 ASA grade 1 and 2 patients. It was possible to insert the intubating laryngeal mask in all 500 cases. Ventilation via the intubating laryngeal mask was described as satisfactory in 475 (95%) cases, difficult in 20 (4%) cases and unsatisfactory in 5 (1%) cases. Blind tracheal intubation through the intubating laryngeal mask was possible in 481 (96.2%) cases within three attempts. Intubation was successful at the first attempt in 399 (79.8%) cases, at the second attempt in 62 (12.4%) cases and at the third attempt in 20 (4%) cases. The tracheas of 19 (3.8%) patients were not successfully intubated within the three attempts. Ventilation via the intubating laryngeal mask was described as unsatisfactory during two of these cases but oxygenation remained satisfactory in spite of this. Seventeen of the 19 failures occurred during the individual operator's first 20 attempts. The intubating laryngeal mask provides a successful method for blind tracheal intubation in a large proportion of cases and appears to be superior to the standard laryngeal mask airway for this purpose. The intubating laryngeal mask may be of use when tracheal intubation has failed using conventional methods.

Adolescent↗
PubMed2002

Masking of tinnitus and mental activity.

The aim of this study was to investigate the effects of tinnitus on mental activity. In a mixed design study, the performance of 20 subjects with tinnitus and 20 healthy control subjects was compared on the digit-symbol test, completed in three auditory conditions: silence, masking and intermittent masking. Results showed marked overall differences between patients and controls on all three conditions. Lower scores on the digit-symbol test were observed during the intermittent masking condition compared with the masking condition for the patients. There was no difference between silence (e.g. tinnitus) and the masking condition, or between silence and the intermittent masking condition. The control subjects scored lower on the task when exposed to the intermittent masking compared to both silence and masking. The patients had higher depression and anxiety scores than the controls. These findings suggest that there is a link between masking sounds and how tinnitus affects cognitive capacity.

Acoustic Stimulation↗
PubMed2001

Use of the intubating laryngeal mask in children: an evaluation using video-endoscopic monitoring.

BACKGROUND AND OBJECTIVE: The intubating laryngeal mask is designed to act as a ventilatory device and as an aid to blind tracheal intubation in adults. The aim of this study was to evaluate the efficacy of the intubating laryngeal mask for ventilation of the lungs and tracheal intubation in children using video-endoscopic control. METHODS: The handling and efficacy of the size 3 intubating laryngeal mask for tracheal intubation in 80 children weighing > or = 25 kg were assessed under video-endoscopic control. Ease of intubating laryngeal mask insertion, adequacy of lung ventilation through the intubating laryngeal mask and airway sealing pressures were recorded. Tracheal intubation was performed blindly by the intubator, while the supervisor observed the procedure on the video display. If blind intubation failed at the first attempt, the monitor view was used to guide the tracheal tube into the trachea. The success rate and time required for successfully placing the tracheal tube were recorded. RESULTS: Insertion of the intubating laryngeal mask was easy in all children. Lung ventilation through the intubating laryngeal mask was uniformly excellent. Blind tracheal intubation at the first attempt was successful in 53 children (66%) within 18.8 +/- 4.1 s. Twenty-four of the 27 failed blind intubation attempts were successfully intubated with video-endoscopic guidance within 28.6 +/- 9.4 s. Two children required replacing the intubating laryngeal mask, one child had to be intubated conventionally. CONCLUSIONS: The size 3 intubating laryngeal mask provides an airway that is easy to establish in children > or = 25 kg with excellent ventilation conditions and allows blind tracheal intubation at the first attempt with a high success rate. Endoscopic monitoring improves its safety and intubation success rate.

Adolescent↗
PubMed1998

[Effect of stimulus rise time and high-pass masking on early auditory evoked potentials].

BACKGROUND: Problems of frequency-specific objective assessment of hearing threshold by means of auditory brainstem response (ABR) have been discussed recently. While a number of workers have recommended methods of selective masking to improve the frequency specificity, others believe that frequency-specific potentials can also be obtained without masking. In this context, the effects of rise-decay time and high-pass masking on ABRs were investigated. METHOD: ABRs were recorded in normal-hearing subjects and patients with high and low frequency hearing loss by means of surface electrodes between the vertex and the ipsilateral mastoid. The frequency of the stimulus was 1 kHz, and the rise-decay time 1 ms (1-0-1) or 2 ms (2-0-2). High-pass filtered noise (cutoff frequency 1.5 kHz; filter slope 250 dB/octave) was employed for masking. Particular attention was paid to the problem of efficient masking. RESULTS: In normal-hearing subjects under the influence of high-pass masking compared to non-masked ABRs, longer mean latencies and diminished means of the amplitudes of wave V were found, with differences in the near-threshold domain being less pronounced. Similar results were observed in patients with high frequency hearing loss. In patients with low frequency hearing loss, the influence of high-pass masking was especially marked distinctly near to threshold. Furthermore, latency and amplitude differences of wave V of the 1-0-1 and the 2-0-2 stimuli were determined from the ABRs obtained with and without high-pass masking. The differences between the latency differences of both stimuli in the suprathreshold range (70 dB nHL) only were statistically significant. CONCLUSIONS: The results are suggestive of an inadequate frequency specificity of unmasked stimuli in the suprathreshold range. Evaluation of the latencies revealed for both rise-decay times a similar frequency specificity near the threshold and a higher frequency specificity of the longer stimulus in the suprathreshold range.

Acoustic Stimulation↗
PubMed1993

[The laryngeal mask--an overview 1983-1993].

The laryngeal mask which was developed by Brain in 1981 and described for the first time in 1983 has been employed worldwide a million times since 1989. Traditionally, all anaesthesiologists are oriented towards the techniques of conventional mask anaesthesia or endotracheal intubation. This new alternative, however, amazes by its easy handling and its concept: insertion of the mask directly onto the larynx without irritating it and sealing the pharynx at the same time thus allowing sufficient ventilation. On the one hand, the laryngeal mask does not even fail in desperate cases of "can't intubate-can't ventilate", on the other hand, the new "old" problem reappears to the anaesthesiologist used to endotracheal intubation: mask anaesthesia and aspiration--a discussion which needs to be continued in case of the laryngeal mask. This is also true for the use of the laryngeal mask in emergency medicine and resuscitation. However, cases of difficult intubation may be greatly facilitated. All users appreciate the reliability of the laryngeal mask in daily routine even though some fear that more difficult and safer techniques of anaesthesia might be forgotten. The indications of the laryngeal mask expand rapidly at the moment and the fast trend in its spread might continue if this method is not discredited by violations of its contraindications: full stomach, extreme obesity and low compliance of the lungs.

Anesthesia, Obstetrical↗
PubMed1988

Reaction time measures of backward masking.

We employed both simple and choice reaction time (RT) paradigms in which the subjects were required to respond to 3.0 cycles per degree (c/d) square-wave gratings presented to one eye, while checkerboard masks were presented at various stimulus-onset asynchronies to the other eye. No masking was evident using the simple RT paradigm, but with the choice RT task, checkerboard masks presented to the contralateral eye of three subjects resulted in substantial decreases in response speed when the test preceded the mask by stimulus-onset asynchronies of 25 to 75 ms. Masks that contained lower fundamental spatial frequencies (1.0 c/d) than the target were more effective than masks containing fundamental spatial frequencies (6.0 c/d) higher than the target, while masks that contained fundamental components identical to those in the target (3.0 c/d) produced maximum masking. The results offer support for the sustained-transient theory of visual processing and validate RT as a technique for examining spatio-temporal factors in masking.

Adult↗
PubMed1999

Re-evaluation of appropriate size of the laryngeal mask airway.

We have assessed 32 males and 31 females in a randomized, crossover study to see if there was any difference in the correct positioning of the laryngeal mask, optimal ventilation (defined as no gas leak around the mask at an airway pressure of 18 cm H2O) and cuff visibility between sizes 4 and 5 masks in males and sizes 3 and 4 in females. The position of the mask in relation to the glottis was assessed using a fibreoptic bronchoscope. There was no significant difference in correct positioning between the two sizes in either sex. Gas leak was significantly less frequent for a larger than a smaller mask (P < 0.01 for both sexes), whereas the cuff was more often seen in the mouth with larger masks (P < 0.02 for males and P < 0.01 for females). Therefore, larger masks (size 4 in females and size 5 in males) provided a better seal than smaller sizes without worsening the relative position of the mask to the glottis; however, the larger mask came up within the mouth more often, which could interfere with tonsillectomy and could increase the risk of sore throat or lingual nerve damage.

Adult↗
PubMed2005

Intubating laryngeal mask for airway management in lateral decubitus state: comparative study of right and left lateral positions.

BACKGROUND: The intubating laryngeal mask has been used for the emergency management of the airway in patients placed in the lateral decubitus position. We have conducted this prospective study to compare the feasibility of placement of an intubating laryngeal mask and blind tracheal intubation guided by the intubating laryngeal mask in patients placed in the right and the left lateral positions. METHODS: A total of 82 adults of both sexes with normal airways, scheduled for cholecystectomy, were allocated randomly to be placed in either the right (n=41) or left (n=41) lateral position for the insertion of an intubating laryngeal mask and blind tracheal intubation guided by the intubating laryngeal mask under balanced general anaesthesia. A sequence of standard manoeuvres was performed after each failed attempt at intubating laryngeal mask placement and intubation. RESULTS: The intubating laryngeal mask was placed in all patients at the first attempt. Ventilation of the lungs through the intubating laryngeal mask was possible in 40 patients (97.5%) from each group after the first attempt at insertion (P=1). Following adjustments, adequate ventilation could be achieved in all patients. The first attempt success rates of blind tracheal intubation were 85.3% (35/41) and 87.8% (36/41) in the right and left lateral groups, respectively (P=1). The remaining patients from both groups (except for one patient in the left lateral group who had a failed intubation) were intubated at the second attempt. CONCLUSION: Insertion of the intubating laryngeal mask and blind tracheal intubation through it in the lateral position is feasible in patients with normal airways. These procedures have a high and comparable success rate when patients are placed in the right and left lateral positions.

Adult↗
PubMed1990

Backward masking as a function of spatial frequency. A comparison of MMPI-identified schizotypics and control subjects.

The present investigation relied upon a neurophysiological explanation of visual masking and compared the backward masking susceptibility of hypothetical schizotypal individuals with that of control subjects. Masking functions were assessed within two masking conditions: high spatial frequency (HSF) and low spatial frequency (LSF). Schizotypal subjects (those with a 2-7-8 or an 8-9 MMPI profile type) were compared with "psychiatric" control subjects (those with a spike 9 or a 4-9 profile type) and normal control subjects. Group differences were expected only in the transient-facilitating, LSF masking condition in this study's assessment of the hypothesis that a transient channel abnormality underlies the schizophrenia spectrum backward masking deficit. As predicted, schizotypal subjects displayed greater masking susceptibility in the LSF transient-facilitating condition as compared with the HSF, sustained-facilitating condition that produced no group differences. These results suggest that multichannel neurophysiological models of masking may help to direct research designed to gain an increased understanding of the specific nature of the spectrum masking deficit.

Adolescent↗
PubMed2005

Nitrous oxide diffusion into the cuffs of disposable laryngeal mask airways.

The aim of this study was to investigate cuff pressure changes found in disposable size 3 laryngeal mask airways (LMAs) from different manufacturers during nitrous oxide exposure and to compare the results with the re-usable Classic LMA. In an in vitro experiment, laryngeal mask airway cuff pressures starting from a baseline pressure of 40 cm H(2)O were recorded using a pressure transducer for 60 min with the laryngeal mask airway cuff exposed to 66% N(2)O in oxygen. Cuff pressure increases within 5 min of nitrous oxide exposure were > 250% in the Classic LMA and were not significantly different from those found in the Marshall laryngeal mask airway. However, they were significantly greater than those in the Soft Seal, the Unique, the AMBU, and Intersurgical laryngeal mask airways, all of which demonstrated stable cuff pressure levels within the first 5 min. The cuff pressure increase following 60 min of nitrous oxide exposure was 13.0 +/- 1.1 and 14.6 +/- 0.7 cm H(2)O in the Intersurgical and Unique laryngeal mask airways, respectively, which was significantly lower than the cuff pressure increase in the Soft Seal and in the Ambu laryngeal mask airways (28.3 +/- 2.9 and 30.9 +/- 1.2 cm H(2)O, respectively). Unlike the re-usable Classic LMA and the disposable Marshall laryngeal mask airway, which have silicone cuffs, the disposable Ambu, Intersurgical, Portex Soft Seal and Unique laryngeal mask airways have cuffs constructed from PVC, which seems to be less susceptible to hyperinflation caused by nitrous oxide diffusion.

Anesthetics, Inhalation↗
PubMed2006

High concentration potassium permanganate eliminates protein and particle contamination of the reusable Classic laryngeal mask airway.

In this three-stage study, we test the hypothesis that supplementary cleaning with potassium permanganate > or =4 mg.l(-1) eliminates protein and particle contamination from the reusable Classic laryngeal mask airway. The first stage involved supplementary cleaning of 70 1 x 1 cm segments from deliberately contaminated laryngeal mask airways using potassium permanganate at 0, 2, 4, 8, 16, 32 and 64 mg.l(-1) and testing for protein staining. This showed that the lowest concentration required to eliminate protein contamination was 8 mg.l(-1). The second stage involved supplementary cleaning of 50 used laryngeal mask airways with either potassium permanganate 8 mg.l(-1) or saline and testing for protein staining. This showed that protein contamination was lower in the potassium permanganate group (p < 0.00001): all laryngeal mask airways in the control group and none in the potassium permanganate group were contaminated. The third stage involved scanning electron microscopic examination of 1 x 1 cm segments from three laryngeal mask airways used in the control group, three from the potassium permanganate group, plus three brand new laryngeal mask airways. The mean density of > or =1 mum surface particles was lower in the potassium permanganate 8 mg.l(-1) than the control group (21 vs. 121 .cm(-2), p < 0.0001) and was similar to brand new laryngeal mask airways (24 .cm(-2)). We conclude that supplementary cleaning with potassium permanganate 8 mg.l(-1) eliminates protein deposits from reusable laryngeal mask airways and reduces particle contamination to similar levels to brand new laryngeal mask airways.

Creutzfeldt-Jakob Syndrome↗
PubMed2003

Temporal masking of multidimensional tactual stimuli.

Experiments were performed to examine the temporal masking properties of multidimensional tactual stimulation patterns delivered to the left index finger. The stimuli consisted of fixed-frequency sinusoidal motions in the kinesthetic (2 or 4 Hz), midfrequency (30 Hz), and cutaneous (300 Hz) frequency ranges. Seven stimuli composed of one, two, or three spectral components were constructed at each of two signal durations (125 or 250 ms). Subjects identified target signals under three different masking paradigms: forward masking, backward masking, and sandwiched masking (in which the target is presented between two maskers). Target identification was studied as a function of interstimulus interval (ISI) in the range 0 to 640 ms. For both signal durations, percent-correct scores increased with ISI for each of the three masking paradigms. Scores with forward and backward masking were similar and significantly higher than scores obtained with sandwiched masking. Analyses of error trials revealed that subjects showed a tendency to respond, more often than chance, with the masker, the composite of the masker and target, or the combination of the target and a component of the masker. The current results are compared to those obtained in previous studies of tactual recognition masking with brief cutaneous spatial patterns. The results are also discussed in terms of estimates of information transfer (IT) and IT rate, are compared to previous studies with multidimensional tactual signals, and are related to research on the development of tactual aids for the deaf.

Deafness↗
PubMed1978

Backward masking: detection versus recognition.

The backward detection masking of 10-ms tonal targets by a 150-ms tonal mask was contrasted with the backward recognition masking of the same tones by the same mask. The target-mask interval required for 75% correct performance was about eight times as great in the recognition condition as in the detection condition. Furthermore, a generalized improvement in performance occurred over the initial course of training in both the detection and recognition conditions. In a second experiment it was found that a remote mask produced greater backward recognition masking but less backward detection masking. That these differences were observed with the same subjects, at the same level of training, and with identical stimuli, indicates that procedural differences alone cannot account for the differences between backward detection and recognition masking.

Discrimination, Psychological↗
PubMed1984

On the growth of masking asymmetry with stimulus intensity.

Masking asymmetry was investigated over a wide range of stimulus intensities for two signal frequencies, fo = 1.0 and 4.0 kHz, using both fixed-masker and fixed-signal paradigms. The masker was a notched noise with the upper and lower edges of the notch, fu and fl, respectively, placed asymmetrically about fo. For various notch widths, the asymmetry of masking was measured as the difference between the masked threshold obtained when fl was nearer fo and that obtained when fu was nearer fo. For maskers with wide notches, (fu - fl)/fo greater than 0.15, masking asymmetry changed with stimulus level; at the highest level, masked threshold was greatest when fl was nearer fo, and, at the lowest level the asymmetry reversed slightly for fo = 1.0 kHz so that masked threshold was actually greater when fu was nearer fo. Nonparallel growth of masking functions reveal changes in masking asymmetry with signal level as well as with masker level. It is concluded that the nonlinear growth of masking with level is due primarily to changes in the auditory filter, rather than changes in the detector following the filter.

Auditory Threshold↗
PubMed1986

Comparisons of frequency selectivity in simultaneous and forward masking for subjects with unilateral cochlear impairments.

Two experiments are described in which frequency selectivity was estimated, in simultaneous and forward masking, for each ear of subjects with moderate (25-60 dB HL) unilateral cochlear hearing losses. In both experiments, the signal level was fixed for a given ear and type of masking (simultaneous or forward), and the masker level was varied to determine threshold, using an adaptive, two-alternative forced-choice procedure. In experiment I, the masker was a noise with a spectral notch centered at the signal frequency (either 1.0 or 1.5 kHz); threshold was determined as a function of notch width. Signal levels were chosen so that the noise level required at threshold for a notch width of zero was similar for the normal and impaired ear of each subject in both simultaneous and forward masking. The function relating threshold to notch width had a steeper slope for the normal ear than for the impaired ear of each subject. For the normal ears, these functions were steeper in forward masking than in simultaneous masking. This difference was interpreted as resulting from suppression. For the impaired ears, significant differences in the same direction were observed for three of the five subjects, but the differences were smaller. In experiment II, psychophysical tuning curves (PTCs) were determined in the presence of a fixed notched noise centered at the signal frequency (1.0 kHz). For the normal ears, the PTCs were sharper in forward masking than in simultaneous masking. For the impaired ears, the PTCs were similar in simultaneous and forward masking, but those in forward masking tended to be sharper at masker frequencies far removed from the signal frequency. Overall, the results suggest that suppression is reduced, but not completely absent in cases of moderate cochlear hearing loss.

Aged↗