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PubMed1985

The four factors leading to binaural masking-level differences.

A simple extension of the Webster-Jeffress model is presented together with its predictions for the effects of various stimulus parameters on the size of binaural masking-level differences (BMLDs). The four factors leading to BMLDs (just-noticeable differences (JNDs), temporal effects in simultaneous masking, binaural interaction, and temporal effects in non-simultaneous masking) are described, new measurements of the effect of signal duration on the detectability of interaural delay are presented, and the high degree of correlation between observers' sensitivity to changes in level and their sensitivity to changes in interaural delay is demonstrated. A number of examples illustrating where knowledge of JNDs for level and interaural delay and their joint dependence on certain stimulus parameters are sufficient to predict BMLDs are discussed.

Auditory Perception↗
PubMed1986

The influence of signal duration, signal frequency and masker duration on binaural masking level differences.

Binaural masked thresholds were measured to study the influence of masker and test signal duration on binaural unmasking for three different interaural phase relations (N0S0, N0S pi and N pi S0) and for test signal frequencies ranging from 200 to 800 Hz. Six observers participated in this study. An adaptive 3 Interval Forced Choice paradigm was employed. Reducing the signal duration from 250 to 20 ms results in an average binaural masking level difference (BMLD) increase of 2.5 dB for all frequencies and both dichotic conditions. Masker duration, however, has a more distinct influence on BMLD: a decrease from 500 to 25 ms reduces the BMLD in the N0S pi condition by 7 dB and in the N pi S0 condition up to 11 dB at low frequencies. These results reveal further evidence for different detection mechanisms in monaural and binaural masking experiments.

Adult↗
PubMed1987

Masking additivity in the hearing-impaired.

The purpose of the present study was to investigate how the effects of maskers combine in hearing-impaired listeners. The levels of two narrow bands of noise separated in frequency were selected so that each band individually produced the same amount of masking of a sinusoidal signal. Thresholds for the signal were then measured in the presence of both bands combined. For normal-hearing listeners, the effect of combining maskers was nonlinear, but, additive. A cube-root transformation of the masking produced by the individual and combined maskers preserved an additive relation among the effects of these maskers. This type of nonlinear additivity also characterized the results from the hearing-impaired listeners when the maskers were restricted to a region of normal sensitivity. In contrast, the effect of combining maskers was linear, additive without transformation, when the maskers were restricted to a region of significant loss. In many instances, the auditory filter model of masking may describe the detection performance of hearing-impaired listeners better than that of normal-hearing listeners.

Adult↗
PubMed1987

Auditory neurophonic responses to amplitude-modulated tones: transfer functions and forward masking.

Two auditory neurophonic responses - one recorded from the scalp (frequency following response or FFR) and one from the auditory nerve (auditory nerve neurophonic or ANN) - were obtained following stimulation of the cat cochlea with amplitude-modulated (AM) high-frequency tones. The carrier frequencies varied between 2 and 30 kHz. The modulation frequencies varied between 400 and 3000 Hz. The AM responses were compared with pure-tone neurophonic responses. The AM response waveforms were found to have a similar spectral composition, similar rates of adaptation, and similar rates of recovery from forward masking as the comparable pure-tone responses. As with the pure-tone neurophonics, an unmodulated masking stimulus can produce prolonged depression of the probe response. The amount and duration of this depression is dependent upon the level and frequency of the masker. The frequency dependence of the depression is demonstrated by forward masked tuning curves which indicate that the AM responses arise from fiber populations which have restricted characteristic frequency distributions centered on the carrier frequency. Response amplitude as a function of stimulus level (I/O) functions, response amplitude as a function of carrier frequency (carrier transfer functions or CTF) and response amplitude as a function of modulation frequency (modulation transfer functions or MTF) were also measured. It was found that the I/O functions were saturating monotonic functions of stimulus intensity, CTFs were flat for carrier frequencies from 6 to 30 kHz, and MTFs were flat for modulation frequencies from 100 to 1500 Hz. These results are compared with similar data for single units and compound action potentials.

Acoustic Stimulation↗
PubMed1989

Responses of single cells in the cat inferior colliculus to binaural masking level difference signals.

Neurones with low best frequency (less than 2 kHz) and sensitive to interaural phase differences were recorded in the dorsal part of the central nucleus of the cat inferior colliculus. Best frequency tone (S) and noise (N) bursts were delivered binaurally via closed field sound systems either in phase (S0, N0) at both ears or inverted at one ear (SII, NII). The responses to tone + noise bursts in the stimulus configurations S0N0, SIINII and SIIN0 and noise bursts (N0 and NII) were compared. The latter two tone + noise configurations (S0NII and SIIN0) give a binaural masking level difference (BMLD) of up to 15 dB in psychophysical experiments, i.e. an increase in noise level is necessary to mask perception of the tone. Most cells responded better to in phase stimuli (here called 0 cells). A minority of cells responded better to out of phase stimuli (here called II cells). Each cell's response was correlated with the level of acoustic stimulus (tone or masker) in the preferred configuration and not with the BMLD situation: for the 0 cells, the responses were therefore maximal for S0N0 and minimal for SIINII. For II cells, the gradation was reversed: the response to SIINII was maximal and that to S0N0 minimal. For both populations, the responses to S0NII and SIIN0 were intermediate between the S0N0 and SIINII responses. Cells that responded best to S0NII or SIIN0, i.e. cells selectively coding BMLD, were not found. This was also true for the synchronized spike rates of those cells showing phase locked responses to the stimulus frequency. Some cells appeared to be strongly suppressed by the addition of an non-preferred masker (i.e. in the configuration that resulted in less response to a noise-alone burst; e.g. NII for the 0 cells). Other cells were more suppressed by the addition of a preferred masker (N0 for the 0 cells). The difference in the number of spikes evoked by the tone + noise and the noise burst was analyzed according to signal detection theory and neuronal masked threshold determined. Some 0 cells showed lower thresholds in the configuration S0NII whereas others had higher thresholds in this configuration. This correlated with the binaural suppression effects noted above: when the noise in the preferred configuration (N0) gave more suppression, the threshold was lower for S0NII; when NII gave more suppression the threshold was higher for S0NII. Over the whole population, these effects cancelled out and the neuronal threshold was not significantly affected by the BMLD configuration.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed1990

Absence of tonic activity of the crossed olivocochlear bundle in determining compound action potential thresholds, amplitudes and masking phenomena in anaesthetised guinea pigs with normal hearing sensitivities.

In Nembutal- or Urethane-anaesthetised guinea pigs N1 audiograms and N1 input-output functions were measured as were compound action potential (CAP) tuning curves under forward masking and simultaneous masking conditions. Then the crossed olivocochlear bundle was lesioned at the floor of the fourth ventricle and the cochlear responses were re-measured. There were never any changes in the N1 audiograms, input-output functions, or the CAP tuning curves. Thus, the crossed efferent pathways do not appear to play any tonic role in determining cochlear threshold sensitivities, selectivities or masking phenomena in anaesthetised guinea pigs with normal hearing sensitivities.

Action Potentials↗
PubMed1992

Binaural masking level differences in infants with and without otitis media with effusion.

The binaural masking level difference (MLD) was measured in two groups of infants (aged 7-10 months) who either had or did not have a documented history of otitis media with effusion (OME). Subjects were trained to detect a 500 Hz signal (either in or out-of-phase between the ears) against an in-phase, narrow band noise masker centred at 500 Hz. Non-OME infants had elevated masked thresholds and reduced MLDs compared with normal-hearing older (7-12 years) children and adults (20-27 years). OME infants also had elevated masked thresholds and reduced MLDs but, in contrast to studies using older subjects, their results were similar to those of the non-OME infants. These results suggest that, during at least the first year of life, infants are disadvantaged compared with adults or children when listening in noisy environments. They also suggest that OME does not further compromise infants' ability to detect sounds in those environments.

Acoustic Stimulation↗
PubMed1995

Possible origins of the non-monotonic intensity discrimination function in forward masking.

A non-monotonic intensity discrimination function in forward masking has been recently reported [Zeng et al. (1991) Hear. Res. 55, 223-230; Zeng and Turner (1992) J. Acoust Soc. Am. 92, 782-787] in which just-noticeable-differences (jnds) in intensity are largest for midlevel tones and smaller for soft and loud tones following an intense narrow-band noise. One hypothesis was that this midlevel hump reflects the contribution of low-spontaneous rate (SR) neurons to intensity coding, based on the differential recovery from forward masking of low-SR and high-SR neurons [Relkin and Doucet (1991) Hear. Res. 55, 215-222]. The present study conducted three experiments stimulating different stages of the auditory system in an attempt to determine the peripheral and central origins of the midlevel hump. First, in two cochlear implant (CI) listeners, the forward masker produced a midlevel hump on the intensity discrimination function, suggesting that the synapses between the hair cell and the eighth nerve are probably not responsible for the hump, as they are bypassed and the eighth nerve is stimulated directly. Second, in auditory brainstem implant (ABI) listeners, the forward masker produced no midlevel hump, but the masked jnds were larger than those without a masker. The absence of the midlevel hump in the ABI listeners suggests that the occurrence of the hump requires physiological mechanisms in the auditory nerve transmission, or the intrinsic processing circuits of the cochlear nuclei, or both. Third, in normal-hearing listeners, an ipsilateral, 90 dB SPL, pure-tone forward masker produced a midlevel hump, which is similar to that using a narrow-band noise masker; whereas a contralateral forward masker produced essentially no midlevel hump, suggesting that binaural interactions at superior olivary complex and more central sites are probably not responsible.

Acoustic Stimulation↗
PubMed1996

[Inspiratory aid with facial masks during acute respiratory failure without hypercapnia].

This prospective study assessed, in 10 conscious patients without a history of chronic respiratory disease, the feasibility of mechanical pressure support ventilation with PEEP by face mask for the treatment of acute respiratory failure without hypercapnia. Pressure support level was determined to obtain a VT of 5 to 10 mL.kg-1 and a decrease of respiratory rate of more than 20%. FIO2 and PEEP levels were determined to obtain a SpO2 > 92% and a PaO2 > 70 mmHg. The efficiency of the technique was assessed through the time course of respiratory rate, PaO2, PaCO2 and SaO2. The technique was efficient in all patients and tracheal intubation was not required. During face mask ventilation, a significant decrease in respiratory rate and an increase in PaO2 and SaO2 were observed. Pressure support ventilation with PEEP by face mask is an efficient technique for the treatment of acute non hypercapnic respiratory failure in conscious and cooperative patients.

Acute Disease↗
PubMed1995

Laryngeal mask airway: a more successful method of insertion.

STUDY OBJECTIVE: To compare the ease of insertion of the laryngeal mask airway (LMA) by two methods. DESIGN: Prospective, randomized study. SETTING: Operating room of a university-affiliated teaching hospital. PATIENTS: 350 ASA I, II, and III patients undergoing general anesthesia, in whom use of the LMA was not contraindicated. INTERVENTIONS: With all routine monitors in place and after the induction of anesthesia with propofol, we compared the ease of insertion of the LMA in the two groups of 175 patients each. The timing of insertion was made on clinical grounds. In one group, the LMA was inserted with the cuff fully deflated, in the other group, the cuff was partially inflated (i.e., filled with half the recommended air in the cuff). When correct placement of the mask was not successful by one method, the other method was tried and the insertion graded in the same manner. MEASUREMENTS AND MAIN RESULTS: The ease of insertion of the LMA was graded by the user on a scale of 1-4. Insertion of the LMA with the cuff partially inflated was significantly more successful (97.7%) than when the cuff was fully deflated (92%) (p < 0.05). When correct placement of the mask was not possible with the cuff fully deflated, partial inflation resulted in correct placement. CONCLUSIONS: Inserting the LMA with the cuff partially inflated is likely to be more successful than with the cuff fully deflated. When it is not possible to insert the LMA with the cuff fully deflated, partial inflation before insertion may result in correct placement.

Anesthesia↗
PubMed2006

[Introduction of the intubating Laryngeal Mask Airway in a prehospital emergency medical unit].

OBJECTIVES: Assessment of the intubating Laryngeal Mask Airway(trade mark) in a prehospital emergency mobile unit (PEMU). STUDY DESIGN: Observational study. METHODS: All the emergency physicians and nurses of the PEMU were trained with the intubating laryngeal mask (ILMA) handling on manikin and a learning curve was carried out. One year after the initial formation, a reassessment of the operators was performed. Following the initial formation, all the vehicles of the PEMU were equipped with ILMA and during 15 months all cases of ILMA use were recorded. The success rate and the difficulties met were analysed. RESULTS: Initial formation on manikin showed that at least 8 handling of the device were mandatory to achieve a 100% success rate. A significant reduction of tracheal tube insertion delay was observed up to the eight manipulations. One year after the initial formation, a significant loss of performance was observed. Over the clinical study period 20 ILMA were used with adequate ventilation through the mask in all cases and a possible intubation in 80% of the patients. CONCLUSION: The ILMA is a potential useful device in the prehospital setting. Initial formation and maintenance of the skill acquired with this technique are essential.

Ambulances↗
PubMed2006

Amygdala activation during masked presentation of emotional faces predicts conscious detection of threat-related faces.

It has been argued that critical functions of the human amygdala are to modulate the moment-to-moment vigilance level and to enhance the processing and the consolidation of memories of emotionally arousing material. In this functional magnetic resonance study, pictures of human faces bearing fearful, angry, and happy expressions were presented to nine healthy volunteers using a backward masking procedure based on neutral facial expression. Activation of the left and right amygdala in response to the masked fearful faces (compared to neutral faces) was significantly correlated with the number of fearful faces detected. In addition, right but not left amygdala activation in response to the masked angry faces was significantly related to the number of angry faces detected. The present findings underscore the role of the amygdala in the detection and consolidation of memory for marginally perceptible threatening facial expression.

Adult↗
PubMed2006

Simultaneous masking in a dichotic emotion detection task.

The present study investigated the possible role of ceiling effects in producing laterality effects of small magnitude in dichotic emotion detection. Twenty two right-handed undergraduate students participated in the present experiment. They were required to detect the presence of a target emotion in the expressions tones of happiness, sadness, anger, and neutrality presented dichotically. Stimuli were adjusted to 70 dB and occurred simultaneously with a white noise mask that had an intensity of 65, 70, 80, or 85 dB. Results showed a left ear advantage (LEA) for the 65 dB mask and a right ear advantage for the 85 dB mask, but only after two testing sessions. The possible existence of a generalized right ear bias that might affect the observed LEA for non-verbal tasks is discussed. Alternative explanations and limitations of the present experiment are also presented.

Adolescent↗
PubMed2005

The effects of prime visibility on ERP measures of masked priming.

In two experiments, the effect of the duration (40, 80 and 120 ms) of pattern masked prime words on subsequent target word processing was measured using event-related potentials. In Experiment 1, target words were either repetitions of the prior masked prime (car-CAR) or were another unrelated word (job-CAR). In Experiment 2, primes and targets were either semantically related (cap-HAT) or were unrelated (car-HAT). Unrelated target words produced larger N400s than did repeated (Exp 1) or semantically related (Exp 2) words across the different prime durations and these N400 priming effects tended to be smaller overall for semantic than repetition priming. Moreover, there was only a modest decline in the size of N400 repetition priming at the shortest prime durations, and there was no relationship between this N400 effect and a measure of prime categorization performance. However, the size of semantic priming at the shortest durations was relatively smaller than at longer durations and was correlated with prime categorization performance. The findings are discussed in the context of the functional significance of the N400 as well as a model that argues for different mechanisms during masked repetition and semantic priming.

Adult↗
PubMed2005

The effect of perceived spatial separation on informational masking of Chinese speech.

The effect of perceived spatial separation, induced by the precedence effect, on release from noise or speech masking was investigated. Listeners were asked to orally repeat Chinese nonsense sentences, which were spoken by a female talker and presented by both the left (-45 degrees) and right (+45 degrees) loudspeakers, when maskers, which were either speech-spectrum noise sounds or Chinese nonsense sentences spoken by two other female talkers, were presented by the same two loudspeakers. Delays between identical sounds presented over the two loudspeakers were used to control the perceived locations of the target (right only) and masker (right, center, or left). The results show that perceived 45 degrees and 90 degrees separations of target speech from masking speech led to equivalently marked improvement in speech recognition, even though the degree of improvement was smaller than that reported in [J. Acoust. Soc. Am. 106 (1999) 3578 (using English nonsense speech)]. When the masker was noise, however, perceived separation only marginally improved speech recognition. These results indicate that release from informational masking, due to perceived target/masker spatial separation induced by the precedence effect, also occurs for tonal Chinese speech. Compared to the 45 degrees perceived within-hemifield separation, the 90 degrees perceived cross-hemifield separation does not produce further unmasking.

Acoustic Stimulation↗
PubMed2005

Relationship between masking levels and phonatory stability in normal-speaking women.

Disruption of auditory feedback such as masking has been shown to influence vocal production. A reliable finding is an increase in intensity level; an increase in fundamental frequency (F0) is a less robust finding. Research is lacking concerning the effects of auditory masking on measures of phonatory stability such as jitter and harmonics-to-noise ratio (HNR). This study investigated changes in intensity, F0, jitter, and HNR in 22 normally speaking college aged women. Subjects produced the vowel /a/ under three conditions: no masking level (0-dB ML), 50-dB ML, and 80-dB ML. Significant differences between conditions emerged for intensity; means for the other measures were not significantly different. Intraindividual differences between conditions for each variable are discussed in the framework of auditory versus kinesthetic feedback.

Adult↗
PubMed2004

Successful management of a neonate with Pierre-Robin syndrome and severe upper airway obstruction by long term placement of a laryngeal mask airway.

The severity of airway obstruction varies in infants with Pierre-Robin syndrome (PRS). Some have severe upper airway obstruction that results in respiratory failure and even death. We report a case of neonate with isolated PRS who had a severe airway obstruction and respiratory failure after birth. She had complications of bilateral pneumothorax, subcutaneous emphysema, and hypoxaemia due to difficult tracheal intubation. Respiratory failure recurred immediately after extubation; she was resuscitated by inserting a laryngeal mask airway. The laryngeal mask airway was left inserted for 6 days. It was successful in this patient and eliminated the need for invasive surgical procedures. In conclusion, the relatively long term use of a laryngeal mask airway, which has not been reported before, could be an alternative therapy for patients with PRS with airway obstruction.

Airway Obstruction↗
PubMed2004

Effects of decreasing peak flow rate on stomach inflation during bag-valve-mask ventilation.

Reducing inspiratory flow rate and peak airway pressure may be important in order to minimise the risk of stomach inflation when ventilating an unprotected airway with positive pressure ventilation. This study was designed to yield enough power to determine whether employing an inspiratory gas flow limiting bag-valve device (SMART BAG, O-Two Medical Technologies Inc., Ontario, Canada) would also decrease the likelihood of stomach inflation in an established bench model of a simulated unintubated respiratory arrest patient. The bench model consists of a training lung (lung compliance, 50 ml/cm H2O; airway resistance, 4 cm H2O/l/s) and a valve simulating lower oesophageal sphincter opening at a pressure of 19 cm H(2)O. One hundred and ninety-one emergency medicine physicians were requested to ventilate the manikin utilising a standard single-person technique for 1 min (respiratory rate, 12/min; Vt, 500 ml) with both a standard adult bag-valve-mask and the SMART BAG. The volunteers were blinded to the experimental design of the model until completion of the experimental protocol. The SMART BAG versus standard bag-valve-mask resulted in significantly (P < 0.001) lower (mean +/- S.D.) mean airway pressure (14 +/- 2 cm H2O versus 16 +/- 3 cm H2O), respiratory rates (13 +/- 3 breaths per min versus 14 +/- 4 breaths per min), incidence of stomach inflation (4.2% versus 38.7%) and median stomach inflation volumes (351 [range, 18-1211 ml] versus 1426 [20-5882 ml]); lung tidal volumes (538 +/- 97 ml versus 533 +/- 97 ml) were comparable. Inspiratory to expiratory ratios were significantly (P < 0.001) increased (1.7 +/- 0.5 versus 1.5 +/- 0.6). In conclusion, the SMART BAG reduced inspiratory flow, mean airway pressure and both the incidence and actual volume of stomach inflation compared with a standard bag-valve-mask device while maintaining delivered lung tidal volumes and increasing the inspiratory to expiratory ratio.

Equipment Design↗