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PubMed2002

Spatial-frequency-tuned mechanisms of the red-green channel estimated by oblique masking.

The sustained spatial-frequency-tuned (SF-tuned) mechanisms of nonoriented units were examined by means of orthogonal masking for the Red-Green (R-G) color channel, and those of oriented units by oblique masking for the achromatic channel but not for the color channels. An oblique-masking technique minimizes the artifacts that are due to spatial phase effects, local cues, spatial beats, spatial probability summation, and changing criteria. Therefore the spatial characteristics of the R-G color channel are now investigated by an oblique-masking technique and linked with my paper on orthogonal masking [J. Opt. Soc. Am. A 15, 1 (1998)]. The R-G channel was defined by the minimum-flicker and hue-cancellation techniques. A color monitor system was used to generate spatially localized (D6) vertical color test patterns [0.063-8 cycles per degree (cpd)] and sinusoidal oblique color masks (0.031-16 cpd, 1.2-60% contrasts). Color contrast sensitivity functions (CSFs), threshold elevation (TE) versus mask SF (TvSF) curves, and TE versus mask contrast (TvC) curves were measured by the method of constant stimuli with a two-interval forced-choice technique by using Powell's achromatizing lens under sustained (Gaussian, 2-s-duration) conditions. Results show the following: (1) The color CSF is a low-pass function of SF with average half-height SF of 0.7 cpd and cutoff SF of 14 cpd with the use of a color-detection criterion. (2) TvSF curves are broadly bandpass and fall into five groups, peaking at approximately 0.13, 0.5, 2, 4, and 8 cpd. The root-mean-square cone-color CSF is 3.8-5.4 times the stimulus-color CSF. (3) A "crowding effect" similar to that of the TvSF curves of the achromatic channel was also found, but the TvSF curves of the R-G channel are not sharply peaked, similar to the result for orthogonal masking. Data analysis led to the following conclusions: (1) A simple multiple-mechanism model yields one low-pass color mechanism (with average half-height SF of 0.54 cpd) and five bandpass SF-tuned color mechanisms; these six mechanisms are necessary to explain the CSF, TvSF, and TvC data simultaneously. (2) The bandpass mechanisms peaked at approximately 0.13, 0.5, 2, 4, and 8 cpd with average full bandwidths at half-heights of 3.6, 3.2, 2.1, 1.2, and 1.3 octaves, respectively. (3) Since oblique-masking color mechanisms (unlike achromatic oriented mechanisms) have broad orientation tuning under sustained conditions and there is a significant orthogonal masking, the oblique-masking color mechanisms may have contributions from both oriented and nonoriented units. (4) The high degree of similarity between the SF-tuned filters of mechanisms derived from oblique- and orthogonal-masking data suggests that most of the chromatic SF tuning is already accomplished by nonoriented units. (5) The quality of the fit to oblique- and orthogonal-masking data combined dropped enough to reject the hypothesis that the former taps the performance of only the same nonoriented mechanisms as those by the latter. Adding gain parameters that reduce the TEs for orthogonal masking gave a better fit, suggesting that orientation gains are one of the factors involved in the transformation of information from nonoriented to oriented mechanisms. However, the fit was still worse than that for oblique-(6) Since masking-alone or orthogonal-masking-alone data, suggesting that more factors may be involved. primate parvo lateral geniculate nucleus (pLGN) units behave in a fairly linear manner, the color contrast nonlinearity (which follows the linear filter) of a mechanism may be post-pLGN.

Color Perception↗
PubMed2004

Metacontrast masking is specific to luminance polarity.

UNLABELLED: A 1 degrees -spot was flashed up on a screen, followed by a snugly fitting annular mask. We measured the amount of masking as a function of stimulus luminance. The surround was always mid-gray, the masking ring was either black or white, and the luminance of the spot target ranged from 0% to 100% of white in 4% steps. Observers reported the apparent lightness of the masked spot by adjusting a matching spot. RESULTS: A black annular mask made all spots that were darker than the gray surround appear to be transparent, that is, of the same luminance as the surround (complete masking). The black ring had virtually no masking effect on spots that were lighter than the surround. Conversely, a white ring made all spots that were lighter than the gray surround look apparently the same luminance as the surround (complete masking), but had virtually no masking effect on spots that were darker than the surround. In summary, a black ring masked spatial decrements but not increments, whilst a white ring masked spatial increments but not decrements. Thus masking occurred only when the spot and the ring had the same luminance polarity. This same-polarity masking still occurred when the target spot was larger than the 'donut hole' of the masking ring, so that the target and ring partly overlapped. This ruled out simple edge-cancellation theories. Instead, masking disrupts the filling-in process that normally propagates inward from the edges of a spot [Vision Res. 31 (7-8) (1991) 1221]. We conclude that metacontrast masking occurs within, but not between, separate visual ON and OFF pathways.

Contrast Sensitivity↗
PubMed1998

Comparison of nose and face mask CPAP therapy for sleep apnoea.

BACKGROUND: Many patients with sleep apnoea/hypopnoea syndrome (SAHS) find nasal continuous positive airway pressure (CPAP) treatment unsatisfactory due to side effects related to mouth air leakage. A study was performed to compare side effects with face mask and nose mask CPAP therapy in patients with SAHS, with and without uvulopalatopharyngoplasty (U3P). METHODS: Twenty newly diagnosed patients with SAHS took part in a randomised double limb trial of face or nose mask CPAP therapy (four weeks per limb) in which CPAP compliance in terms of machine run time was measured and patients answered a symptom questionnaire on side effects resulting from the mask. Ten patients with SAHS with U3P (SAHS/U3P) who were already regular users of nasal CPAP were also given a four week trial of face mask CPAP to compare compliance and symptoms. Ten patients with SAHS were matched with the 10 SAHS/U3P patients for body mass index, age, apnoea/hypopnoea index, and CPAP pressure. Long term compliance was estimated one year after the mask comparison studies. RESULTS: For patients with SAHS nightly compliance was higher with a nose mask (mean (SE) 5.3 (0.4) hours/night CPAP) than with a face mask (4.3 (0.5) hours/night CPAP), p = 0.01 (mean difference 1.0 hour/night, 95% CI 1.8 to 0.3). Nose masks were rated more comfortable by 19 of 20 patients (p < 0.001) despite more mouth leak related symptoms. For SAHS/U3P patients compliance was marginally higher with nose masks (5.1 (0.7) hours/night CPAP) than with face masks (4.0 (0.8) hours/night CPAP), p = 0.07 (mean difference 1.1 hour/night, 95% CI 2.1 to 0.1). Nose masks were rated more comfortable by seven of 10 patients. There were no significant differences in side effect scores with face and nose masks. At one year nine of 10 SAHS patients and nine of 10 SAHS/U3P patients were still using CPAP. Compliance was 5.4 (0.6) hours/night for the SAHS patients and 3.5 (0.4) hours/night for the SAHS/U3P patients, p = 0.02 (mean difference 1.9 hour/night, 95% CI 3.6 to 0.3). CONCLUSIONS: Compliance is greater with nose mask CPAP than with face mask CPAP because the overall comfort is better and compensates for increased symptoms associated with mouth leakage. Improved face mask design is needed.

Double-Blind Method↗
PubMed1986

Neural mechanisms of tone-on-tone masking: patterns of discharge rate and discharge synchrony related to rates of spontaneous discharge in the chinchilla auditory nerve.

Responses of chinchilla auditory nerve fibers to brief probe tones in the presence of a fixed tonal masker were obtained. The stimulus conditions were analogous to those that have been used in many psychophysical experiments. The relation between previously described response properties of auditory nerve fibers and features of psychophysical tone-on-tone masking was examined. In psychophysical studies, a fixed narrowband masker produces a characteristic pattern of masked thresholds, which becomes broad and asymmetrical at high masker levels. In the present experiment 1, a 5,000-Hz masker was presented at 30, 50, and 70 dB SPL. Masked thresholds based on the average rate of response to probe tones were estimated for single auditory nerve fibers. The lowest of these masked thresholds formed a pattern similar to the psychophysical masking pattern, becoming broader and more asymmetrical as the masker was increased to 70 dB SPL. The masked thresholds of fibers with low and medium rates of spontaneous discharge (SR) were as low as or lower than the masked thresholds of fibers with high SRs. In certain frequency regions, masked thresholds based on responses to cochlear distortion products were lower than the masked thresholds of any fiber responding to the probe tone; this result is also similar to previous psychophysical observations. In experiment 2, responses of chinchilla auditory nerve fibers to probe tones in the presence of a masker at 1,000 Hz and 50 dB SPL were studied. Probe tone thresholds in the presence of this masker have been measured psychophysically in chinchillas. Thus the relation between behavioral and neural masked thresholds in the same species could be examined. Masked thresholds were estimated from average discharge rate responses and also from discharge synchrony. Good quantitative agreement was observed between the probe tone levels at which changes in average discharge rate were observed and the chinchilla's behavioral masked thresholds. For fibers matched for characteristic frequency, the masked thresholds based on average discharge rate of high-SR fibers tended to be elevated compared with the thresholds of medium-SR fibers. Changes in discharge rate synchronized to the probe tone occurred at levels lower than the chinchilla's behavioral masked thresholds. If discharge synchrony can be used for detection, the code would appear to be based on the relative synchrony to the probe tone and to the masking tone. Low synchrony masked thresholds were obtained from fibers with all SRs.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2005

Regional brain activity associated with visual backward masking.

In visual backward masking, the visibility of a briefly presented visual target is disrupted by a mask that is presented shortly thereafter. The goal of the current study was to identify regions in the human cortex that may provide the neural basis of visual masking. We searched for areas whose activity correlated with perception as we systematically varied the strength of masking. A total of 13 subjects performed a backward masking task during functional magnetic resonance imaging. Target and mask were presented at three delay intervals (34, 68, and 102 msec) and behavioral measures confirmed that the targets were more visible at longer masking intervals. Two sets of regions of interest were identified: Distinct regions in the visual cortex (V1/V2, LO, hMT+) were segregated using scans to localize visual processing drawn from the existing literature. Additional cortical regions were selected in a data-driven approach based on their activity during the backward masking task. For each set, we determined the regions whose magnitude of activation increased at longer masking intervals. Nine of the subjects provided valid behavioral performance data on the visual masking task and imaging data from these subjects were used for subsequent analysis. The scans of visual processing areas identified four regions, including: early visual areas (V1 and V2), the motion-sensitive regions in the lateral occipital (LO) lobe (hMT+), and two components (dorsal and ventral) of the object-sensitive region, LO. Of these, the ventral and dorsal LO regions were sensitive to the strength of the mask. For the data-driven approach, six regions were identified on the basis of a difference map in which all masking intervals were contrasted with rest. These included the inferior parietal, anterior cingulate, precentral, insula, thalamic, and occipital areas. The predicted effects of more activity with weaker masking were seen in the thalamus, inferior parietal, and anterior cingulate. This study isolated three types of visual processing areas. The first included regions that subserve key stages of vision (including object and motion processing). The second type responded to the presentation of brief ly presented visual stimuli, regardless of masking interval. The third type (selected from the first two) included regions sensitive to the interval between the target and mask. These latter regions (including ventral LO, inferior parietal, anterior cingulate, and thalamus) may form the neural substrate of backward masking.

Adult↗
PubMed2004

Randomized evaluation of the single-use SoftSeal and the re-useable LMA Classic laryngeal mask.

A number of laryngeal masks are available, including both re-usable and single-use masks. Single-use laryngeal masks may decrease the risk of transmitting prion infections. We performed a single-blind randomized trial in 200 spontaneously breathing female patients under general anaesthesia with nitrous oxide, to compare a new single-use laryngeal mask, the SoftSeal (Portex Ltd, U.K.), with a re-usable laryngeal mask, the LMA Classic (Laryngeal Mask Company Ltd., Cyprus). The primary outcome was successful insertion at the first attempt. Size 4 single-use (n = 99) or re-usable (n = 100) laryngeal masks, inserted by experienced anaesthetists, were equivalent for successful placement at the first attempt (90% versus 91% respectively). The single-use mask was less easy to insert (47% difficult versus 9%, P < 0.001). Clinical and anatomical tests of position and function were similar. The cuff pressure of the re-usable mask increased significantly compared with the single-use mask (median +10 cm versus -2 cm H2O, P < 0.001). Forty per cent of patients allocated the single-use mask and 20% of those allocated the re-usable mask experienced sore throat at 24 hours postoperatively (P < 0.05). An estimation of cost per patient use was greater for the re-usable mask. We conclude that the SoftSeal single-use laryngeal mask and the LMA Classic re-usable laryngeal mask airway are of similar clinical utility in terms of successful insertion and airway maintenance. The re-usable laryngeal mask was easier to insert and associated with less postoperative sore throat, but costs were higher.

Adolescent↗
PubMed1998

Does masking author identity improve peer review quality? A randomized controlled trial. PEER Investigators.

CONTEXT: All authors may not be equal in the eyes of reviewers. Specifically, well-known authors may receive less objective (poorer quality) reviews. One study at a single journal found a small improvement in review quality when reviewers were masked to author identity. OBJECTIVES: To determine whether masking reviewers to author identity is generally associated with higher quality of review at biomedical journals, and to determine the success of routine masking techniques. DESIGN AND SETTING: A randomized controlled trial performed on external reviews of manuscripts submitted to Annals of Emergency Medicine, Annals of Internal Medicine, JAMA, Obstetrics & Gynecology, and Ophthalmology. INTERVENTIONS: Two peers reviewed each manuscript. In one study arm, both peer reviewers received the manuscript according to usual masking practice. In the other arm, one reviewer was randomized to receive a manuscript with author identity masked, and the other reviewer received an unmasked manuscript. MAIN OUTCOME MEASURE: Review quality on a 5-point Likert scale as judged by manuscript author and editor. A difference of 0.5 or greater was considered important. RESULTS: A total of 118 manuscripts were randomized, 26 to usual practice and 92 to intervention. In the intervention arm, editor quality assessment was complete for 77 (84%) of 92 manuscripts. Author quality assessment was complete on 40 (54%) of 74 manuscripts. Authors and editors perceived no significant difference in quality between masked (mean difference, 0.1; 95% confidence interval [CI], -0.2 to 0.4) and unmasked (mean difference, -0.1; 95% CI, -0.5 to 0.4) reviews. We also found no difference in the degree to which the review influenced the editorial decision (mean difference, -0.1; 95% CI,-0.3 to 0.3). Masking was often unsuccessful (overall, 68% successfully masked; 95% CI, 58%-77%), although 1 journal had significantly better masking success than others (90% successfully masked; 95% CI, 73%-98%). Manuscripts by generally known authors were less likely to be successfully masked (odds ratio, 0.3; 95% CI, 0.1-0.8). When analysis was restricted to manuscripts that were successfully masked, review quality as assessed by editors and authors still did not differ. CONCLUSIONS: Masking reviewers to author identity as commonly practiced does not improve quality of reviews. Since manuscripts of well-known authors are more difficult to mask, and those manuscripts may be more likely to benefit from masking, the inability to mask reviewers to the identity of well-known authors may have contributed to the lack of effect.

Authorship↗
PubMed2005

Mask fear in children presenting for anesthesia: aversion, phobia, or both?

BACKGROUND: Anesthesia induction in children is commonly accomplished by introducing volatile agents by mask. Occasionally a child describes an excessive fear of the anesthesia facemask. Little is known of the cause of the fear or of the quality or magnitude of the feelings the child is experiencing. The purpose of this study was to allow children who have established mask fear as demonstrated by volunteering the presence of fear and requesting no mask be placed on the face during the induction of anesthesia and their parents to describe and compare the distress from the mask to the alternative intravenous anesthesia induction. METHODS: Eight children describing mask fear on the preanesthetic examination were studied. An Anesthesia Mask Fear questionnaire developed by the investigators was answered by the children and their parents. RESULTS: Six children and their parents completed the study. The age at presentation of mask fear ranged from 1.4 to 14 years. There were one to 16 anesthetic exposures prior to reporting mask fear. One child described an aversion to the odor of the mask. Another boy developed mask fear after a single anesthetic exposure. He was subsequently diagnosed with a generalized anxiety disorder. Four female children developed mask fear after repeated anesthetic exposures. These children rated mask fear with the greatest discomfort possible while venous cannulation was scored at half or less that of the mask discomfort. CONCLUSIONS: Care must be taken when developing a plan for anesthesia induction in children requiring multiple procedures. Children may develop an aversion to the odor or feel of the mask, or have a true phobia (irrational fear) of the mask. Those children with a phobia might also have other underlying anxieties.

Adolescent↗
PubMed2005

The role of suppression in the upward spread of masking.

The upward spread of masking refers to the higher growth rate of masking for maskers lower in frequency than the signal, compared to maskers at the signal frequency (Wegel RL, Lane CE. The auditory masking of one pure tone by another and its possible relation to the dynamics of the inner ear. Physics Rev. 23:266-285, 1924; Egan JP, Hake HW. On the masking pattern of a simple auditory stimulus. J. Acoust. Soc. Am. 22:622-630, 1950; Delgutte B. Physiological mechanisms of psychophysical masking: Observations from auditory-nerve fibres. J. Acoust. Soc. Am. 87:791-809, 1990a, Delgutte B. Two-tone rate suppression in auditory-nerve fibres: Dependence on suppressor frequency and level. Hear Res. 49:225-246, 1990b). The upward spread of simultaneous masking may arise from a combination of excitatory and suppressive effects. In this study, growth of masking functions were obtained for a 4-kHz signal masked by an on-frequency (4 kHz) or off-frequency (2.4 kHz), simultaneous or forward masker, in the presence of a notched noise with a center frequency of 4 kHz presented to restrict off-frequency listening. Compression was estimated from the slopes of the off-frequency growth of masking functions. Suppression was estimated by comparing the off-frequency simultaneous- and forward-masked growth of masking functions. Results showed that, for midlevel signals (35-60 dB SPL), the compression exponent estimated from simultaneous and forward masking averaged 0.31 and 0.26, respectively. The maximum amount of suppression (defined as the decrease in the basilar-membrane response to the signal) was variable, ranging from about 6 to 17 dB across subjects. Despite the substantial reduction in the response to the signal, the results suggest that suppression has a minimal effect on the slope of the masking function at mid levels. Rather, upward spread of masking seems to be mainly determined by the compressive basilar-membrane response to the signal in relation to the linear response to the lower-frequency masker.

Acoustic Stimulation↗
PubMed1995

Comodulation masking release in a songbird.

Comodulation masking release (CMR) describes the reduced masking of a pure tone when the masking is a noise that is coherently amplitude modulated (comodulated) over the total range of the spectrum compared to masking by an unmodulated noise of the same bandwidth and overall energy. The masking release results from cues available within a critical band and from cues generated by comparisons across critical bands ('true' CMR). Here we report data on masking release and 'true' CMR in a songbird, the European starling (Strunus vulgaris), that was demonstrated in a psychoacoustic experiment using a GO/NOGO paradigm. Masked thresholds for 2-kHz tones centered in digitally generated continuous masking noise of different bandwidths were determined, and the amount of masking release was calculated as the threshold difference between the unmodulated and the comodulated condition. In the first experiment the modulator was a 50-Hz lowpass noise. A masking release of 11.8 dB was found for the noise masker with the largest bandwidth (1600 Hz). With the masker bandwidth decreasing to 50 Hz, the birds' release from masking was reduced to 1.6 dB. The starling's 'true' CMR was 4 dB or 8 dB, depending on the definition that was applied. In a second experiment the masker bandwidth was constant (1600 Hz) and the cut-off frequency of the modulator was varied. A release from masking of 17.8 dB was found for a modulator cut-off frequency of 12.5 Hz. It decreased to 6.1 dB with an increase in the modulator cut-off frequency to 400 Hz. The duration of the test signal (100-750 ms) had little effect on the release from masking. Given the similarities in the release from masking and in CMR of starlings and humans, the starling may provide an excellent model for studying the mechanisms that underlie the generation of CMR.

Acoustic Stimulation↗
PubMed2001

A binocular site for contrast-modulated masking.

Contrast-modulated (CM) gratings, composed of two luminance-modulated sinusoids of similar spatial frequency, mask the detection of test sinusoids at the difference frequency. However, the mechanism underlying masking by CM gratings remains poorly understood. In this paper, we aimed to determine whether the masking of 1 cycle deg(-1) LM test gratings by a 1 cycle deg(-1) beat (formed from a pair of carriers at 8 and 9 cycles deg(-1)) occurs in monocular channels or after the site of binocular combination, or both. Threshold elevations for the detection of a 1 cycle deg(-1) test grating were obtained for a number of stimulus conditions, including: (1) dichoptic CM (both 8 and 9 cycles deg(-1) mask components presented to one eye, with the 1 cycle deg(-1) test grating to the other); (2) dichoptic variant (8 and 9 cycles deg(-1) mask gratings presented to separate eyes, with the 1 cycle deg(-1) test grating presented to one eye); (3) binocular CM (all mask and test gratings presented to both eyes). As a control, masking magnitude was also measured for LM mask gratings of similar frequency (1 cycle deg(-1)) and effective contrast (3%) to that of the beat. For both LM and CM masks, the dichoptic condition yielded threshold elevations that were similar or greater than the binocular condition. When 8 and 9 cycles deg(-1) mask components were presented to separate eyes (the dichoptic variant condition), no beat pattern was visible and no elevations in detection threshold occurred. The results demonstrate that, like LM masking, detection of a target in the presence of a CM mask does not involve purely monocular mechanisms. Further, that the site of CM masking must occur beyond the stage at which monocular matching for stereopsis takes place. This is consistent with other studies which suggest that dichoptic masking is contingent on stereo matching, and thus occurs relatively late in the hierarchy of binocular visual processing.

Contrast Sensitivity↗
PubMed2003

Stability of the LMA-ProSeal and standard laryngeal mask airway in different head and neck positions: a randomized crossover study.

BACKGROUND AND OBJECTIVE: The LMA-ProSeal laryngeal mask airway is a new laryngeal mask airway with a modified cuff and drainage tube. We compared oropharyngeal leak pressure, intracuff pressure and anatomical position (assessed fibreoptically) for the Size 5 LMA-ProSeal laryngeal mask airway and the classic laryngeal mask airway in different head-neck positions and using different intracuff inflation volumes. METHODS: Thirty paralysed anaesthetized adult male patients were studied. The LMA-ProSeal laryngeal mask airway and the classic laryngeal mask airway were inserted into each patient in random order. The oropharyngeal leak pressure, intracuff pressure, and anatomical position of the airway tube and drainage tube (LMA-ProSeal laryngeal mask airway only) were documented in four head and neck positions (neutral first, then flexion, extension and rotation in random order), and at 0-40 mL cuff volumes in the neutral position in 10 mL increments. RESULTS: Compared with the neutral position, the oropharyngeal leak pressure for both the LMA-ProSeal laryngeal mask airway and the classic laryngeal mask airway was higher in flexion and rotation (all P < or = 0.02), but lower in extension (all P < or = 0.01). Changes in head-neck position did not alter the anatomical position of the airway tube or the drainage tube. The oropharyngeal leak pressure was always higher for the LMA-ProSeal laryngeal mask airway (all P < or = 0.005) and anatomical position better for the classic laryngeal mask airway (all P < or = 0.04). CONCLUSIONS: The anatomical position of the LMA-ProSeal and the classic laryngeal mask airway is stable in different head-neck positions, but head-neck flexion and rotation are associated with an increase, and head-neck extension a decrease, in oropharyngeal leak pressure and intracuff pressure. The Size 5 LMA-ProSeal laryngeal mask airway is capable of forming a more effective seal than the Size 5 classic laryngeal mask airway in males.

Adolescent↗
PubMed1997

Cortical dynamics of lateral inhibition: metacontrast masking.

The dynamic properties of a neural network model of visual perception, called the boundary contour system, explain characteristics of metacontrast visual masking. Computer simulations of the model, with a single set of parameters, demonstrate that it accounts for 9 key properties of metacontrast masking: Metacontrast masking is strongest at positive stimulus onset asynchronies (SOAs); decreasing target luminance changes the shape of the masking curve; increasing target duration weakens masking; masking effects weaken with spatial separation; increasing mask duration leads to stronger masking at shorter SOAs; masking strength depends on the amount and distribution of contour in the mask; a second mask can disinhibit the masking of the target; such disinhibition depends on the SOA of the 2 masks; and such disinhibition depends on the spatial separation of the 2 masks. No other theory provides a unified explanation of these data sets. Additionally, the model suggests a new analysis of data related to the SOA law and makes several testable predictions.

Attention↗
PubMed2003

Benefits of the laryngeal mask for airway management during electroconvulsive therapy.

Accumulation of carbon dioxide (CO2) can disturb systemic hemodynamics and increase the seizure threshold in patients receiving electroconvulsive therapy (ECT). The purpose of this study was to investigate the effects of the laryngeal mask on blood gas, hemodynamics, and seizure duration during ECT under propofol anesthesia. Ventilation was assisted using either a face mask (n=23) or laryngeal mask (n=23) and 100% oxygen. There was no significant difference in PaO2 between the two groups. PaCO2 was greater in the face mask group than the laryngeal mask group at 3 minutes (54 +/- 11 mm Hg, 41 +/- 8 mm Hg, respectively) and 5 minutes (52 +/- 11 mm Hg, 43 +/- 15 mm Hg, respectively) after electrical stimulation (p<0.01). Mean blood pressure was higher than the corresponding preanesthesia value at 1 to 5 minutes after electrical stimulation in the face mask group and at 1 to 3 minutes after electrical stimulation in the laryngeal mask group. Mean seizure duration in the face mask group was significantly shorter than that in the laryngeal mask group (33 +/- 11 seconds, 42 +/- 10 seconds, respectively p<0.01). The change in PaCO2 was minor in the laryngeal mask group compared with the face mask group and seizure duration was longer in the laryngeal mask group. Laryngeal mask may be suitable for airway management during ECT anesthesia, especially when fitting a face mask is difficult.

Adult↗
PubMed2003

Controlled trial of oronasal versus nasal mask ventilation in the treatment of acute respiratory failure.

OBJECTIVE: Noninvasive positive pressure techniques such as continuous and bilevel positive airway pressure avoid intubation and its attendant complications in selected patients with acute respiratory failure. However, mask intolerance remains a common cause for failure of noninvasive ventilatory techniques. The aim of our study was to assess patient tolerance of oronasal vs. nasal mask ventilation in acute respiratory failure. DESIGN: Randomized, controlled trial. SETTING: Emergency department or intensive care units at a university hospital. PATIENTS: Seventy patients with acute respiratory failure as evidenced by clinical or blood gas criteria. INTERVENTIONS: Patients randomly received either a disposable nasal or an oronasal mask (Respironics, Pittsburgh, PA) when they met study criteria. MEASUREMENTS AND MAIN RESULTS: Thirty-five patients were randomized into each arm of the study; most of the patients had acute cardiogenic pulmonary edema (48.6% of the nasal mask group and 42.8% of the facial mask group) or chronic obstructive airway disease (34.3% of the nasal mask group and 31.4% of the facial mask group). Baseline clinical characteristics of the two groups of patients were similar. Heart and respiratory rates and blood gases improved similarly for patients in both mask groups. Rates of intubation were also similar (eight in each group). However, mask intolerance was significantly higher in the nasal than the oronasal mask group (12 vs. 4, respectively, p=.023). Four patients in the nasal (11.4%) and two in the oronasal mask group (5.7%) died later during the hospitalization. The overall success rate tended to be greater in the oronasal (65.7%) than the nasal group (48.6%), but the difference was not statistically significant. CONCLUSION: Although both masks performed similarly with regard to improving vital signs and gas exchange and avoiding intubation, the nasal mask was less well tolerated than the oronasal mask in patients with acute respiratory failure.

Acute Disease↗
PubMed2004

Low spatial frequencies are suppressively masked across spatial scale, orientation, field position, and eye of origin.

Masking is said to occur when a mask stimulus interferes with the visibility of a target (test) stimulus. One widely held view of this process supposes interactions between mask and test mechanisms (cross-channel masking), and explicit models (e.g., J. M. Foley, 1994) have proposed that the interactions are inhibitory. Unlike a within-channel model, where masking involves the combination of mask and test stimulus within a single mechanism, this cross-channel inhibitory model predicts that the mask should attenuate the perceived contrast of a test stimulus. Another possibility is that masking is due to an increase in noise, in which case, perception of contrast should be unaffected once the signal exceeds detection threshold. We use circular patches and annuli of sine-wave grating in contrast detection and contrast matching experiments to test these hypotheses and investigate interactions across spatial frequency, orientation, field position, and eye of origin. In both types of experiments we found substantial effects of masking that can occur over a factor of 3 in spatial frequency, 45 degrees in orientation, across different field positions and between different eyes. We found the effects to be greatest at the lowest test spatial frequency we used (0.46 c/deg), and when the mask and test differed in all four dimensions simultaneously. This is surprising in light of previous work where it was concluded that suppression from the surround was strictly monocular (C. Chubb, G. Sperling, & J. A. Solomon, 1989). The results confirm that above detection threshold, cross-channel masking involves contrast suppression and not (purely) mask-induced noise. We conclude that cross-channel masking can be a powerful phenomenon, particularly at low test spatial frequencies and when mask and test are presented to different eyes.

Contrast Sensitivity↗
PubMed1994

Efficacy of a new full face mask for noninvasive positive pressure ventilation.

Previous studies have shown that noninvasive positive pressure ventilation (NPPV) improves gas exchange in acute and chronic respiratory failure. However, some patients are unable to tolerate NPPV due to air leaks around the mask, facial discomfort, and claustrophobia. A new mask that covers the entire face (Total, Respironics, Monroeville, Pa), attempts to overcome these obstacles. We studied the efficacy of NPPV via the Total face mask (TFM) in nine patients with chronic respiratory failure. In three patients, respiratory failure was due to chronic obstructive lung disease, and in six patients, it was secondary to restrictive disorders. None of the patients were previously able to tolerate NPPV via nasal (N) or nasal-oral (NO) masks. At baseline, all patients had impaired gas exchange with low PaO2/FIO2 (241 +/- 14), elevated PaCO2 (79 +/- 5 mm Hg), and poor functional status (1.89 +/- 1.45, on a scale of 1 to 7). After NPPV in the hospital for 7.1 +/- 1.5 h per night for 22 +/- 26 days, the PaCO2 fell to 59 +/- 3 mm Hg, and the PaO2/FIO2 rose to 304 +/- 27. Following nocturnal NPPV via the TFM for 6.7 +/- 1.5 h a night 6 +/- 5 weeks after hospital discharge, sustained improvements in PaCO2 (58 +/- 3 mm Hg, p < 0.05), PaO2/FIO2 (304 +/- 18), and functional status (5.38 +/- 1.06, p < 0.05) were observed. In four patients, measurements of respiratory rate, tidal volume, minute ventilation, dyspnea, discomfort with the face mask, and mask and mouth leaks were made during 30-min sessions of NPPV applied at constant levels via all three masks (N, NO, TFM). Discomfort with the face mask (0.38 +/- 0.18 vs 1.44 +/- 0.34 vs 2.38 +/- 0.32, p < 0.05) and mask leaks (0.44 +/- 0.18 vs 1.89 +/- 0.39 vs 1.89 +/- 0.35, p < 0.05) were least during NPPV via TFM compared with the N or NO masks, respectively. Moreover, expired tidal volume was highest (804 +/- 10 vs 498 +/- 9 vs 537 +/- 13 ml, p < 0.05) and PaCO2 lowest (51 +/- 2 vs 57 +/- 2 vs 58 +/- 3, p < 0.05) during NPPV via the TFM compared with N or NO masks. We conclude that NPPV delivered via a Total mask ensures a comfortable, stable patient-mask interface and improves gas exchange in selected patients intolerant of more conventional N or NO masks.

Adult↗
PubMed2001

Auditory backward masking and the effect of training in normal hearing adults.

Recent renewed interest in auditory backward masking has stemmed from studies of children with language impairments who were found to have significant, elevated thresholds for this paradigm, compared to normal cohorts. There are, however, many unresolved theoretical and procedural issues. The present study was conducted to investigate some of these issues. Specific purposes were: 1) To establish the differences between backward masking and simultaneous masking in normal hearing subjects; 2) To investigate the effect of listening conditions, i.e., monaural versus binaural; 3) To measure the effect of training on the performance of a backward masking paradigm; and 4) To measure generalization of the trained condition to untrained conditions. Two experiments were conducted: In experiment I, we compared the performance of 10 normal-hearing adult subjects for backward masking and simultaneous masking paradigms in both monaural and binaural modes of presentation. Stimuli consisted of a 1000 Hz pure-tone and bandpass masker (600-1400 Hz). Tone thresholds for backward masking were significantly lower than those of the simultaneous masking. The binaural mode of presentation yielded lower thresholds than those of the monaural mode only for the backward masking condition. A significantly large inter- and intra-subject variability was observed in the backward masking paradigm. Experiment II was conducted to measure the effects of training and generalization. Two groups of subjects were included: a trained group and a control group of six and eight normal hearing adults, respectively. The trained group received 10 sessions of backward masking training with feedback. The control group was tested only twice, with a 2-week interval between testing. Only the trained group showed a significant improvement in backward masking thresholds, which amounted to an average of 10.7 dB. No significant improvement was observed in the non-trained group. A nonsignificant trend of generalization occurred for the trained task to the untrained ear. No generalization was evident in the untrained condition (simultaneous masking). The data have important clinical and theoretical implications regarding the ability to train for auditory tasks in general, and for backward masking in particular.

Acoustic Stimulation↗