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PubMed2002

Masking interrupts figure-ground signals in V1.

In a backward masking paradigm, a target stimulus is rapidly (<100 msec) followed by a second stimulus. This typically results in a dramatic decrease in the visibility of the target stimulus. It has been shown that masking reduces responses in V1. It is not known, however, which process in V1 is affected by the mask. In the past, we have shown that in V1, modulations of neural activity that are specifically related to figure-ground segregation can be recorded. Here, we recorded from awake macaque monkeys, engaged in a task where they had to detect figures from background in a pattern backward masking paradigm. We show that the V1 figure-ground signals are selectively and fully suppressed at target-mask intervals that psychophysically result in the target being invisible. Initial response transients, signalling the features that make up the scene, are not affected. As figure-ground modulations depend on feedback from extrastriate areas, these results suggest that masking selectively interrupts the recurrent interactions between V1 and higher visual areas.

Animals↗

PubMed2004

Analysis and test of laws for backward (metacontrast) masking.

In backward visual masking, it is common to find that the mask has its biggest effect when it follows the target by several tens of milliseconds. Research in the 1960s and 1970s suggested that masking effects were best characterized by the stimulus onset asynchrony (SOA) between the target and mask. In particular, one claim has been that the SOA for which masking is optimal remains fixed, even as target and mask durations varied. Experimental evidence supported this claim, and it was accepted as an SOA law. However, recent modeling (Francis, 1997) and experimental studies (Macknik and Livingstone, 1998) argued for new ISI (interstimulus interval) and STA (stimulus termination asynchrony) laws, respectively. This paper reports a mathematical analysis and experimental tests of the laws. The mathematical analysis demonstrates unsuspected relationships between the laws. The experiments test the predictions of the SOA, ISI, and STA laws. The data favor the ISI law over the SOA and the STA laws.

Cognition↗

PubMed2000

Comparable efficacy of administration with face mask or mouthpiece of nebulized budesonide inhalation suspension for infants and young children with persistent asthma.

A randomized, double-blind, placebo-controlled, parallel-group study including 481 children at 37 centers in the United States demonstrated the efficacy and safety of budesonide inhalation suspension in doses of 0.25 mg once daily, 0.25 mg twice daily, 0.5 mg twice daily, and 1.0 mg daily in infants and young children with persistent asthma. The retrospective analysis presented here compares the efficacy of treatment with the suspension administered through a face mask or mouthpiece. All patients receiving budesonide inhalation suspension via face mask or mouthpiece showed clinical improvements in nighttime and daytime asthma symptoms as compared with administration of a placebo. The improvements were of similar magnitude as those observed in an analysis of all patients treated. Improvements in nighttime asthma symptoms were statistically significant with budesonide at 0.25 mg daily (p = 0.040), 0.25 mg twice daily (p = 0.008), and 0.5 mg twice daily (p = 0.046) delivered by face mask. In patients using mouthpieces, nighttime asthma symptoms improved significantly in the 0.25-mg twice-daily (p = 0.005) and 1.0-mg daily (p = 0.035) groups. Patients receiving budesonide at 0.5 mg twice daily via a face mask improved significantly in daytime asthma symptoms (p = 0.009). The use of breakthrough medication was reduced in patients receiving budesonide via face masks or mouthpieces relative to placebo, and treatment was well tolerated in all study groups. This retrospective analysis suggests that nebulized budesonide inhalation suspension can be administered effectively by either face mask or mouthpiece to young children with persistent asthma.

Administration, Inhalation↗

PubMed2003

An evaluation of the flexiguide introducer with the flexible laryngeal mask airway.

Insertion of the flexible Laryngeal Mask Airway has been achieved by a variety of techniques. We have evaluated the Flexiguide for aiding introduction of a flexible Laryngeal Mask Airway in 100 anaesthetised patients. We were successful in establishing a clear airway on the first attempt on 84 (84%) occasions and within two attempts in 97 (97%). The positioning of the laryngeal mask airway was assessed by five measures and was optimally placed in 85% of cases and good in 96%. A clear airway was achieved in 92% of cases. Insertion of the flexible Laryngeal Mask Airway with the Flexiguide was easy in 82 (82%) and slightly difficult in 15 (15%) of cases. Removal of the Flexiguide from the device was easy in 95 (95%) of cases. Airway manoeuvres were used to assist airway placement in 55% of cases with jaw thrust being most common. Minor complications occurred in three (3%) patients: two coughed and one experienced minor tissue trauma during mask insertion. There were no complications associated with use of the Flexiguide during the procedure or after anaesthesia. The Flexiguide is a useful tool to assist insertion of the flexible Laryngeal Mask Airway and is associated with few complications.

Adolescent↗

PubMed2005

Comparison of the re-usable LMA Classic and two single-use laryngeal masks (LMA Unique and SoftSeal) in airway management by novice personnel.

In a single-blind randomized trial, three types of laryngeal masks: the reusable LMA Classic, the single-use LMA Unique and SoftSeal were inserted by novice medical officers in anaesthesia. Five successive attempts were undertaken with each mask type. The order of the mask type insertion was randomly selected. Mean (SD) insertion times for LMA Classic, LMA Unique and Soft Seal were 32.9 (12.3), 39.6 (23.4) and 49.4 (50.4) seconds respectively. Differences were only significant between LMA Classic and SoftSeal (P=0.012). There were no significant differences in first attempt success rates (LMA Classic 80%, LMA Unique 77% and SoftSeal 62%). The SoftSeal was most frequently associated with blood on the mask (32%) compared to the LMA Unique (9%) and LMA Classic (6%). Sore throat was experienced in 14% of patients in the LMA Unique group versus 41% and 42% in the LMA Classic and SoftSeal groups respectively. Mean +/- SD oropharyngeal leak pressure was significantly higher in the SoftSeal (21+/-6 cmH2O) compared to the LMA Classic (17+/-7 cmH2O) and LMA Unique (16+/-6 cmH2O). Novice medical doctors can be taught to insert disposable laryngeal masks. The SoftSeal took longer to insert, which resulted in a higher incidence of blood on the mask, but success rates did not differ The LMA Unique was associated with the lowest incidence of sore throat in the immediate postoperative period. A higher oropharyngeal leak pressure with the SoftSeal may indicate improved airway seal and protection against aspiration.

Adolescent↗

PubMed1994

Intensive care costing methodology: cost benefit analysis of mask continuous positive airway pressure for severe cardiogenic pulmonary oedema.

Costing data for intensive care admissions is important, not only for unit funding, but also for cost outcome analysis of new therapies. This paper presents an intensive care episode costing methodology using the example of a cost-benefit analysis of mask CPAP for severe cardiogenic pulmonary oedema (CPO). This analysis examines the intervention of admitting all patients with severe CPO to the intensive care unit for mask CPAP, compared with the previous practice of admitting only patients failing conventional non-CPAP treatment and requiring mechanical ventilation. The episode costs were determined from a prospective study which showed mask CPAP reduced the need for mechanical ventilation from 35% to 0%. The mean cost of a mask CPAP episode was $1,156, with a mean stay of 1.2 days, compared with ventilated patients, $5,055 and 4.2 days. The major contributors to cost in both groups were nursing and medical salaries, and hospital overheads. The cost of previous estimated yearly caseload of 35 ventilated patients ($176,925) was greater than the cost associated with an increased caseload of 100 mask CPAP patients ($115,600). We conclude that, despite an increase in admissions, mask CPAP for severe CPO is cost-effective.

Cost-Benefit Analysis↗

PubMed2003

Theatre staff's knowledge of surgical face masks.

Surgical face masks have been worn for over a century. Their initial implementation was to reduce wound infection by reducing droplet spread from the surgical team's mouth and nose. More recently face masks have been worn to protect the surgical team from contamination from patients and hazards within the operating theatre. To facilitate this, a range of face masks is available. The commonest are the standard face mask with a filtration ability of approximately 5 microns, and the LASER face mask with a filtration ability of 1.1 microns. The purpose of this study was to determine staff's knowledge of face masks.

Education, Professional↗

PubMed2003

Face mask spirometry and respiratory pressures in normal subjects.

Spirometry and maximal respiratory pressures are pulmonary function parameters commonly used to evaluate respiratory function. Prediction values are available for conventional lung function devices using a standard tube or flanged type of mouthpiece connection. This equipment is not suitable for patients with facial or buccal muscle weakness, because of air leakage around the mouthpiece. A face mask was used for the portable lung function devices used in the neuromuscular department. The aim of this study was to compare the face mask and the conventional mouthpiece for the measurement of spirometry and of respiratory pressures in 22 healthy subjects. Values obtained with the conventional mouthpiece differed significantly from values obtained with the face mask. With the mask, forced vital capacity and forced expiratory volume in one second were 200 mL lower, and maximal expiratory pressure was 3.2 kPa lower than with the mouthpiece. Subsequently, new prediction values for face mask spirometry and maximal respiratory pressures were obtained from 252 other healthy subjects, from which new prediction equations were derived. It was concluded that the face mask connection to the lung function device is a valid alternative, is easy to use and is most useful to monitor changes in patients. This study confirms the importance of appropriate prediction equations, depending on subject-instrument interfaces.

Adolescent↗

PubMed1985

Temporal properties of visual channels measured by masking.

Threshold elevations for spatially localized test stimuli were measured as a function of the temporal frequency of a sinusoidal mask grating. Ten of these temporal-masking curves were determined, each using a test stimulus of different temporal frequency. It was found that these data could be accounted for by four temporal-tuning curves: one low-pass curve with a corner frequency of 8.0 Hz and three bandpass curves with bandwidths of 2.0-2.5 octaves and peaks all within the region 4.0-8.0 Hz. In another set of experiments, a series of 1 spatial-masking curves was determined, each using a test stimulus of different spatial frequency. Measurement of the entire series was repeated using 1.0- and 8.0-Hz mask temporal modulations. Spatial-masking data collected under the two temporal conditions could both be accounted for by a single set of seven spatial-tuning curves, without changing the shape of any of these curves. The data are therefore compatible with spatiotemporal separability. Finally, a large set of contrast-response curves (threshold elevation as a function of mask contrast) was collected. These curves were found to follow a power law whose exponent varied with the spatiotemporal conditions of the experiment.

Form Perception↗

PubMed2000

Heated humidification or face mask to prevent upper airway dryness during continuous positive airway pressure therapy.

STUDY OBJECTIVES: The objectives of this study were (1) to evaluate the way in which nasal continuous positive airway pressure (CPAP) therapy influences the relative humidity (rH) of inspired air; and (2) to assess the impact on rH of the addition of an integrated heated humidifier or a full face mask to the CPAP circuitry. DESIGN: The studies were performed in 25 patients with obstructive sleep apnea syndrome receiving long-term nasal CPAP therapy and complaining of nasal discomfort. During CPAP administration, temperature and rH were measured in the mask either during a night's sleep for 8 patients or during a daytime study in which the effects of mouth leaks were simulated in 17 patients fitted with either a nasal mask (with or without humidification) or a face mask alone. SETTING: University hospital sleep disorders center. MEASUREMENTS AND RESULTS: Compared with the values obtained with CPAP alone, integrated heated humidification significantly increased rH during the sleep recording, both when the mouth was closed (60 +/- 14% to 81 +/- 14%, p < 0.01) and during mouth leaks (43 +/- 12% to 64 +/- 8%, p < 0.01). During the daytime study, a significant decrease in rH was observed with CPAP alone. Compared with the values measured during spontaneous breathing without CPAP (80 +/- 2%), the mean rH was 63 +/- 9% (p < 0.01) with the mouth closed and 39 +/- 9% (p < 0. 01) with the mouth open. The addition of heated humidification to CPAP prevented rH changes when the mouth was closed (82 +/- 12%), but did not fully prevent the rH decrease during simulation of mouth leaks (63 +/- 9%) compared with the control period (80 +/- 2%, p < 0. 01). Finally, attachment of a face mask to the CPAP circuitry prevented rH changes both with the mouth closed (82 +/- 9%) and with the mouth open (84 +/- 8%). CONCLUSIONS: These data indicate that inhaled air dryness during CPAP therapy can be significantly attenuated by heated humidification, even during mouth leaks, and can be totally prevented by using a face mask.

Circadian Rhythm↗

PubMed2004

Noninvasive ventilation by helmet or face mask in immunocompromised patients: a case-control study.

OBJECTIVE: To compare the efficacy of noninvasive positive pressure ventilation (NPPV) by helmet and face mask in immunocompromised patients with hypoxemic acute respiratory failure (ARF). DESIGN: Case-control study. SETTING: The general ICU of a university hospital. PATIENTS: Nineteen immunocompromised patients (hematologic malignancies [n = 8], solid-organ recipients [n = 8], AIDS [n = 3]) with hypoxemic ARF, fever, and lung infiltrates were treated with NPPV delivered by a helmet. Nineteen immunocompromised patients matched for diagnosis, age, simplified acute physiology score II, and Pao(2)/fraction of inspired oxygen (Fio(2)) receiving NPPV through a facial mask served as case-control subjects. RESULTS: The use of NPPV delivered via helmet was as effective as NPPV delivered via face mask in avoiding endotracheal intubations (intubation rate, 37% vs 47%, respectively; p = 0.37) and improving gas exchange; 14 patients (74%) in the helmet group showed a sustained improvement in Pao(2)/Fio(2) ratio (ability to increase Pao(2)/Fio(2) ratio > 200, or an increase > 100 from the baseline) in comparison with 7 patients (34%) in the mask group (p = 0.02), whose Pao(2)/Fio(2) at treatment discontinuation was higher (p = 0.02) and had fewer complications related to NPPV (ie, skin necrosis, p = 0.01). Moreover, the patients receiving ventilation via helmet required significantly less NPPV discontinuations in the first 24 h of application (p < 0.001) than patients receiving ventilation via face mask. CONCLUSIONS: The helmet may represent a valid alternative to a face mask in immunocompromised patients with lung infiltrates and hypoxemic ARF, increasing the patient's tolerance (ie, the number of hours of continuous NPPV use without interruptions) and decreasing the rate of complications directly related to the administration of NPPV.

Case-Control Studies↗

PubMed2006

Masking by inaudible sounds and the linearity of temporal summation.

Many natural sounds, including speech and animal vocalizations, involve rapid sequences that vary in spectrum and amplitude. Each sound within a sequence has the potential to affect the audibility of subsequent sounds in a process known as forward masking. Little is known about the neural mechanisms underlying forward masking, particularly in more realistic situations in which multiple sounds follow each other in rapid succession. A parsimonious hypothesis is that the effects of consecutive sounds combine linearly, so that the total masking effect is a simple sum of the contributions from the individual maskers. The experiment reported here tests a counterintuitive prediction of this linear-summation hypothesis, namely that a sound that itself is inaudible should, under certain circumstances, affect the audibility of subsequent sounds. The results show that, when two forward maskers are combined, the second of the two maskers can continue to produce substantial masking, even when it is completely masked by the first masker. Thus, inaudible sounds can affect the perception of subsequent sounds. A model incorporating instantaneous compression (reflecting the nonlinear response of the basilar membrane in the cochlea), followed by linear summation of the effects of the maskers, provides a good account of the data. Despite the presence of multiple sources of nonlinearity in the auditory system, masking effects by sequential sounds combine in a manner that is well captured by a time-invariant linear system.

Auditory Perception↗

PubMed1995

Effect of a face mask on respiratory water loss during sleep in cold conditions.

The purpose of this study was to test the hypothesis that a heat-and-moisture-retaining mask would result in a significant decrease in respiratory water loss among healthy subjects sleeping in a cold environment. The study was done in a backyard near a tertiary-care center during winter nights with ambient temperatures of less than 0 degrees C. Subjects were 10 healthy volunteers, 8 males and 2 females, aged 23-40 years, with a mean of 30.9 years. In a crossover design study, subjects slept alone in mountaineering tents on two nights (8 h each night) using sleeping bags and ground insulation. On one night, they wore heat-and-moisture-retaining masks designed for cold weather exercise. On the other night, they wore no mask. Subjects were weighed before and after each session to obtain an estimate of respiratory water loss. Comparisons were made of weight loss with and without the mask. We found the use of the masks resulted in decreased weight loss in all but one subject. The mean reduction in weight loss was 0.13 kg (SD +/- 0.18 kg). Using a one-tailed t-test, this difference was found to be significant (p < .05). We conclude that the use of a simple and inexpensive face mask can result in a meaningful decrease in overnight respiratory water loss while sleeping in a cold environment.

Adult↗

PubMed1978

Opponent hues in visual masking.

Temporal interactions among opponent and non-opponent hues were investigated in a visual masking paradigm in which both backward and forward temporal sequences were employed. Subjective confidence ratings rather than identification thresholds alone served as response indicators for masking sequences. Results indicate that in the backward sequence (test stimulus followed by masking stimulus) a greater masking effect occurred when the stimuli were of non-opponent hue pairs (red-yellow, red-blue, green-yellow, green-blue) than when compared with opponent hue pairs (red-green, yellow-blue). For the forward sequence (test stimulus preceded by masking stimulus) the masking effect was reduced when compared with the backward sequence. These findings appear to reflect the presumed temporal and spatial antagonistic qualities of opponent hue processes as postulated in the Hering model of color vision.

Color↗

PubMed1985

Frequency-specific contributions to the auditory brain stem response derived by means of pure-tone masking.

The pure-tone masking technique has been employed to determine the contributions of neural activity from different cochlear regions to the click-evoked auditory brain stem response (compound ABR). ABR to broad-band clicks were recorded without and with simultaneous presentation of pure tones of frequencies ranging from 8 to 0.5 kHz. Derived ABRs for individual frequency bands were obtained by subtracting the masked responses from the unmasked ones. To determine the contributions to the compound ABR, masked and derived ABRs were compared with unmasked responses. The frequency specificity of the contributions was more distinct at lower rather than at higher stimulus intensities. Independent of stimulus intensity, the 8- to 2-kHz regions turned out to be the main sources of waves I-V in the compound ABR, whereas waves VI and VII seem to be predominantly generated by contributions from regions specific for 1 and 0.5 kHz. The main advantage of the pure-tone masking technique as compared with the tone pip stimulation is that contributions from the low-frequency regions become more clearly detectable. The validity of this technique has been proved by comparing the compound ABR with the sum of the derived ABRs. The comparison of ABRs derived by pure-tone masking with those derived by conventional high-pass noise masking did prove the validity of the technique as well.

Acoustic Stimulation↗

PubMed1991

Growth of masking in sensorineural hearing loss.

The purpose of the present study was to measure the growth of masking in both normal-hearing and sensorineural hearing-impaired subjects. The masker was a narrow band of noise centered at 1,000 Hz, and masked thresholds for signal frequencies both above and below the masker frequency were obtained for a range of masker levels. For signal frequencies above the masker frequency, the slopes of the growth of masking functions were greater than 1 dB/dB for the normal-hearing group, while for the hearing-impaired subjects the slopes were less than those of the normal subjects, and in many cases slopes were less than 1. The slope of masking was inversely related to the threshold at the signal frequency. These data support the concept that a loss of nonlinearity at the signal place is responsible for the slower growth of masking in hearing-impaired subjects for signal frequencies greater than the masker. In addition, the slower-than-normal growth of masking of the hearing-impaired subjects suggests that some hearing aid signal-processing strategies which provide greater amounts of high-frequency emphasis at high input levels may not be appropriate.

Acoustics↗

PubMed1992

Low-frequency specificity of the auditory brainstem response threshold elicited by clicks masked with 1590-Hz high-pass noise in subjects with sloping cochlear hearing losses.

In this study, the frequency specificity of the ABR threshold to stimulation with a click masked with 1590-Hz high-pass noise was determined in subjects with sloping cochlear hearing losses both high- and low-frequency in character. The results show that the ABR threshold elicited by this stimulus is low-frequency specific. The standard error in estimating the 1,000-Hz pure-tone threshold from the high-pass-noise-masked click-evoked ABR threshold is 10.2 dB which equals that for estimating the 3,000-Hz pure-tone threshold from the routinely used unmasked click ABR threshold. The ABR threshold elicited by a click masked with 1590-Hz high-pass noise can therefore be regarded as an accurate tool to predict the pure-tone hearing loss at 1,000 Hz. However, this method is less suitable for routine clinical testing because of the masking noise needed: the occasional high loudness level adversely affects the response quality and reduces the dynamic range of pure-tone hearing losses to be assessed. A third disadvantage is that determining the masking level electrophysiologically for each ear is time consuming. The search for a method with no or less masking noise should therefore continue.

Acoustic Stimulation↗

PubMed1981

Brain-stem responses when masking with wide-band and high-pass filtered noise.

Investigations, using click stimuli masked by wide-band and high-pass filtered noise with cut-off frequencies of 2 600, 1 250 and 850 Hz were carried out. The latency shift of a response evoked by a click of 60 dB HL and wide-band masking at 80 dB HL is 0.2 - 0.3 ms for wave I and about 0.6 ms for wave V. The results obtained with high-pass masking at various cut-off frequencies differ distinctly from those found by other authors. For instance, when using high-pass masking noise of a lower limiting frequency of 850 Hz and levels of 85 and 90 dB no clear brain-stem responses were discernible. Therefore, the appearance of the brain-stem responses with masking noise at various frequency limits and at various levels was examined. With high-ass noise masking at decreasing cut-off frequencies from 1 800 Hz down to 600 Hz and increasing noise levels, wave V disappears with a slight latency shift, but subsequently to wave V an additional wave occurs which remains stable even in the case of high noise intensities. Further studies are necessary to clarify the properties of this additional wave.

Acoustic Stimulation↗