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PubMed2003

Decreasing peak flow rate with a new bag-valve-mask device: effects on respiratory mechanics, and gas distribution in a bench model of an unprotected airway.

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. The purpose of this study was to assess the effects of a newly developed bag-valve-mask device (SMART BAG), O-Two Systems International, Ont., Canada) that limits peak inspiratory flow. A bench model simulating a patient with an unintubated airway was used consisting of a face mask, manikin head, training lung (lung compliance, 100 ml/cm H(2)O, airway resistance 4 cm H(2)O/l/s, lower oesophageal sphincter pressure 20 cm H(2)O and simulated stomach). Twenty nurses were randomised to each ventilate the manikin using a standard single person technique for 1 min (respiratory rate, 12/min) with either a standard adult self-inflating bag, or the SMART BAG. The volunteers were blinded to the experimental design of the model until completion of the experimental protocol. The SMART BAG vs. standard self-inflating bag resulted in significantly (P<0.05) lower mean+/-S.D. peak inspiratory flow rates (32+/-2 vs. 61+/-13 l/min), peak inspiratory pressure (12+/-2 vs. 17+/-2 cm H(2)O), lung tidal volumes (525+/-111 vs. 680+/-154 ml) and stomach tidal volumes (0+/-0 vs. 17+/-36 ml), longer inspiratory times (1.9+/-0.3 vs. 1.5+/-0.3 s), but significantly higher mask leakage (26+/-13 vs. 14+/-8%); mask tidal volumes (700+/-104 vs. 785+/-172 ml) were comparable. The mask leakage observed is not an uncommon factor in bag-valve-mask ventilation with leakage fractions of 25-40% having been previously reported. The differences observed between the standard BVM and the SMART BAG are due more to the anatomical design of the mask and the non-anatomical shape of the manikin face than the function of the device. Future studies should remove the mask to manikin interface and should introduce a standardized mask leakage fraction. The use of a two-person technique may have removed the problem of mask leakage. In conclusion, using the SMART BAG during simulated ventilation of an unintubated patient in respiratory arrest significantly decreased inspiratory flow rate, peak inspiratory pressure, stomach tidal volume, and resulted in a significantly longer inspiratory time when compared to a standard self-inflating bag.

Equipment Design↗
PubMed2003

Visual backward-masking deficits in schizophrenia: relationship to visual pathway function and symptomatology.

Patients with schizophrenia have information processing deficits which can be measured using visual backward-masking (VBM) tasks. There are two types of visual pathways: transient and sustained. The former is more sensitive to low spatial frequency (LSF) and the latter to high spatial frequency (HSF) stimuli. It has been hypothesized that the VBM deficit in schizophrenia is due to an overactive transient channel response to the mask. To examine this hypothesis, patients with schizophrenia and comparison volunteers were tested on a traditional backward-masking task as well as on tasks that altered the mask to bias stimulation toward transient (LSF) or sustained (HSF) channels. Medication effects and relationship to symptomatology were also examined. Patients with schizophrenia showed a significant deficit on the traditional backward-masking task and were also significantly impaired on the LSF- and HSF-masking tasks, though a differential deficit was not found on the latter two tasks. A U-shaped function, indicative of masking by interruption, was found on the LSF- and HSF-masking tasks. Masking performance was not altered when the same patients were tested on and off medication, and performance was related to positive and negative symptoms. In conclusion, the finding of a deficit in patients with schizophrenia on tasks producing a U-shaped function suggests that an aberrant transient response to the mask is producing increased interruption of the sustained response to the target.

Adult↗
PubMed1999

Spatial frequency masking in positive- and negative-symptom schizophrenia.

The role of transient and sustained channels in masking was investigated in groups with positive and negative symptoms in schizophrenia and in a control group. The target stimulus was a 3.0 c/deg sinusoidal grating, which was masked at 11 stimulus-onset asynchronies between -40 to 360 ms by a 1.0 c/deg mask or an 11.0 c/deg mask. The results showed that there was no difference between the control and positive-symptom groups in the perception of the 3 c/deg target stimulus, nor was there a difference when the target was masked by 1 or 11 c/deg masking stimuli. In comparison with the control and positive-symptom groups, the negative-symptom group showed a significantly higher threshold for the perception of the 3 c/deg target stimulus and more masking with a 1 c/deg mask, but not with an 11 c/deg mask. The results provide evidence for distinguishable differences in visual masking between groups with positive and negative symptoms in schizophrenia.

Adult↗
PubMed1979

Figural relationship effects and mechanisms of visual masking.

In each of three visual pattern masking experiments, four curved letters (C, O, Q, S) and four angular letters (E, I, L, T) served as targets preceded or followed by either a curved mask (Q,S, and C superimposed) or an angular mask (T and E superimposed). With a dark fixation and interstimulus interval field and target-mask engergies that produce clearly identifiable targets, the following figural relationship effects were found. At stimulus onset asynchronies (SOAs) from 0 to 20 msec (in both forward and backward masking), target recognition was more accurate when targets and masks overlapped exactly (same features) than when they did not (different features). At backward masking SOAs beyond 20 msec, this pattern was reversed, but there was no such reversal in forward masking. Such results indicate that the dominant mechanism of masking at SOAs from 0 to 20 msec is luminance summation over time but that luminance summation gives way to feature-specific interference at longer SOAs. Subsequent experiments demonstrate that (a) luminance summation effects are reduced by using bright fixation and interstimulus fields and (b) feature-specific interference is eliminated by using low-energy (and, therefore, less than perfectly identifiable) targets and masks.

Adult↗
PubMed2006

Fundamental properties of the N2pc as an index of spatial attention: effects of masking.

Masking is an important tool in many paradigms used to study the cognitive architecture. The N2pc is an electrophysiological event-related potential (ERP) that has been used as a tool to study the deployment of visual spatial attention. The aim of this paper was to study the effects of masking on the N2pc. Two stimuli were presented on the screen, one to left and one to right of fixation, and subjects reported the identity of one of them. The targets could be discriminated both by their category (letters vs. digit) and by their colour (pink vs. green). Backward masking was produced by presenting a second pair of bilateral stimuli after the offset of the first pair. The second pair of stimuli consisted of characters of the same colour and category as in the first pair. Forward masking was produced by using the very same stimuli as in the backward masking condition, but by instructing subjects to report the second stimulus. The forward mask trials had longer response times compared to no-mask trials, and backward mask trials had even longer response times, and also a higher error rate. Although the different masking procedures lead to clear behavioural effects, the N2pc was not affected, suggesting that the deployment of visual spatial attention, per se, was not affected by pattern masking. A sustained posterior contralateral negativity (SPCN) following the N2pc was also found (300 ms post-target, and beyond), and the amplitude of the SPCN was strongly modulated by the number of presented stimuli and the duration of the SPCN was positively correlated with RT in the behavioural task. We hypothesize that the SPCN reflects neural activity associated with the passage of information through visual short-term memory.

Adult↗
PubMed1999

The Noh mask test for analysis of recognition of facial expression.

A preliminary study on the Noh mask test for analysis of recognition of facial expression was performed. The present study was conducted on 15 normal subjects (mean age: 32 years, SD 9.7 years) as the first step to test for the differences between psychiatric patients and normal subjects. Stimuli were created by photographs of 15 Noh masks at different vertical angles. Subjects were given 12 tasks (12 emotion items), and each task consisted of 15 trials (15 Noh mask images). In each trial, the subject viewed a colour monitor, and was shown an emotion item, followed by a Noh mask image. The subject pressed either the yes or no key to indicate whether the Noh mask image expressed the emotion item. The subject's response and reaction time to each Noh mask image showed no deviation, although the subject's response and reaction time to each emotion item showed some deviation. As the vertical angle of the Noh mask changed, normal subjects recognized all emotion items except the 'uncanny' expression. Factor analysis of the 15 Noh mask images produced three factors, and the analysis of 12 emotion items produced five factors. Thus, the Noh mask test was simplified to nine images and nine items. Further developments of the Noh mask test may include the evaluation of the dysfunction of perception on delicate facial expression in psychiatric patients.

Adult↗
PubMed1981

Does integration produce masking or protect from it?

To examine the role of integration in pattern masking, possible disruptive effects of integration were minimized by using a mask that overlaid completely all targets. Exposure durations were 10 ms, so under energy summation the target area was much darker than the rest. In another condition the mask was red and targets were blue, so under energy summation the target area could also be distinguished by hue. Masking magnitude increased with delay of mask onset, and it was established by four independent criteria that integration was negligible in the condition which produced most masking. It is deduced that integration is not necessary for masking; furthermore it is suggested that integration never produces masking, but rather may or may not protect from a disruptive effect of interruption. The argument is that were the visual system to have better visual resolution, it would suffer more given the same masking parameters. It is argued that type B masking functions arise from a combination of the facilitatory effect of integration and the detrimental effect of interruption.

Color Perception↗
PubMed1987

Contralateral visual masking may be an artifact.

There are serious methodological problems in studies which report contralateral visual masking. Contralateral masking occurs when detection of a hemifield target stimulus is impaired by a pattern-masking stimulus presented to the opposite hemifield. We demonstrate that, in studies which used positive stimuli (i.e., black letters on a white field), contralateral masking may be an artifact. Although we observed contralateral masking when positive stimuli were presented, there was no evidence of masking with negative stimuli (i.e., white letters on a black field). A special masking stimulus with a positive mask contralateral to the target and a black hemifield ipsilateral to the target also failed to produce masking. Contralateral masking in this experiment was due to the flash of light in the field ipsilateral to the target; it was this ipsilateral stimulation, rather than contralateral interference, which impeded target recognition.

Adult↗
PubMed2002

Randomized crossover comparison of the proseal with the classic laryngeal mask airway in unparalysed anaesthetized patients.

BACKGROUND: The ProSeal is a wire-reinforced laryngeal mask airway with an additional drain tube that leads to the distal tip of the laryngeal cuff. The design should improve the seal with the larynx. METHODS: The ProSeal and classic laryngeal mask airways were compared in 180 patients in a randomized crossover study. Patients were anaesthetized without neuromuscular blocking drugs. RESULTS: The ProSeal took more time and more attempts to insert successfully than the classic laryngeal mask airway. Insertion was successful on the first attempt in 81% of cases with the ProSeal and 90% with the classic laryngeal mask airway. The ProSeal required more air to achieve an intracuff pressure of 60 cm H2O (6 ml more for size 4 and 12 ml more for size 5). Laryngeal seal pressure was better with the ProSeal than the classic laryngeal mask airway. Median seal pressure was 29 cm H2O with the ProSeal and 18 cm H2O with the classic laryngeal mask airway. Laryngeal seal pressure was greater than 20 cm H2O in 87% of patients with the ProSeal and 41% with the classic laryngeal mask airway. Laryngeal seal pressure was greater than 40 cm H2O in 21% of patients with the ProSeal and in none of the patients with the classic laryngeal mask. Once placed, the ProSeal remained a stable and effective airway. Gastric tube insertion through the drain tube was attempted in 147 cases and was successful in 135 (92%). CONCLUSION: The ProSeal is more difficult to insert than the classic laryngeal mask airway but allows positive pressure ventilation more reliably than the classic laryngeal mask airway.

Adolescent↗
PubMed1998

Delivery of high concentrations of inspired oxygen via Tusk mask.

OBJECTIVES: Nonrebreather face masks (NRM) are frequently used in patients with respiratory distress and profound hypoxemia. A simpler modification to the partial rebreather face mask, using only two pieces of respiratory tubing or "tusks," has also been shown to increase FiO2 compared with the NRM in five normal subjects. Clinically, we have observed this modification to further increase PaO2 in critically ill patients already using the NRM in the intensive care unit. This study was designed to compare the Tusk mask with the NRM in both a larger group of normal subjects and in patients with underlying lung disease. DESIGN: Prospective, randomized, crossover study. SETTING: A university teaching hospital and tertiary care referral center. SUBJECTS: Sixteen normal subjects (11 male and 5 female; age 30.4+/-6.8 [SD] yrs) and seven patients with interstitial lung disease (ILD) (3 male and 4 female; age 68.1+/-11.9 yrs). INTERVENTIONS: Subjects and patients served as their own controls and were randomized to wear either the NRM or Tusk mask for a 30-min period. After a 60-min washout period, the other mask was applied. MEASUREMENTS AND MAIN RESULTS: Arterial blood gas measurements were performed immediately before and at the end of each 30-min test period. Respiratory synchronization during the study period was achieved, using a metronome. In the normal subjects, PaO2 using the NRM and Tusk masks increased 290.0+/-57.1 torr (38.6+/-7.6 kPa) and 330.0+/-68.9 torr (44.0 +/-9.2 kPa), respectively (p=.032). PaO2 increased 293.4+/-38.0 torr (39.1+/-5.1 kPa) with the NRM and 378.4+/-61.7 torr (50.4+/-8.2 kPa) with the tusk mask (p=.001) in the patients with ILD. There was no statistically significant change seen in mean PaCO2 with either mask in either group. The mean PaO2 returned to within 6% of baseline in both groups after the washout period. CONCLUSIONS: Both normal subjects and patients with compromised pulmonary function achieved a higher PaO2 using a Tusk mask than when using the conventional NRM, at the same oxygen flow rate. Patients with hypoxemia may obtain lifesaving benefit from the additional concentration of oxygen delivered via the Tusk mask.

Adult↗
PubMed2000

Physiologic evaluation of noninvasive mechanical ventilation delivered with three types of masks in patients with chronic hypercapnic respiratory failure.

OBJECTIVE: The efficacy of noninvasive mechanical ventilation (NIMV) in improving breathing pattern and arterial blood gases (ABG) in hypercapnic patients has been well documented; however, little attention has been given to the choice of the interface and the ventilatory mode. We evaluated the effects of three types of masks and two modes of ventilation on patients' ABG, breathing pattern, and tolerance to ventilation. DESIGN: Prospective randomized study. SETTING: Two respiratory weaning centers. PATIENTS: A total of 26 stable hypercapnic patients (pH, 7.38 +/- 0.04; PaCO2, 59.2. +/- 10.9 torr) had not received NIMV and were affected by restrictive thoracic disease or obstructive pulmonary disease. INTERVENTIONS: Three 30-min runs of NIMV, delivered using volume-assisted (n = 13) or pressure-assisted modes of partial mechanical support (n = 13), were performed in random order with a full-face mask, a nasal mask, and nasal plugs. MEASUREMENTS: ABG, breathing pattern, and patients' tolerance to ventilation. MAIN RESULTS: Compared with spontaneous breathing, the application of NIMV significantly improved ABG and minute ventilation, irrespective of the ventilatory mode, the underlying pathology or the type of mask. Overall, a nasal mask was better tolerated than the other two interfaces (p < .005 vs. nasal plugs and full-face mask). PaCO2 was significantly lower (p < .01) with a full-face mask or nasal plugs than with a nasal mask (49.5 +/- 9.4 torr, 49.7 +/- 8 torr, and 52.4 +/- 11 torr, respectively). Minute ventilation was significantly higher with a full-face mask than with a nasal mask because of an increase in tidal volume. No differences were observed in tolerance to ventilation, ABG, or breathing pattern, using assist control or pressure-assisted modes. CONCLUSIONS: In this physiologic study, we have shown that in patients with hypercapnic respiratory failure, irrespective of the underlying pathology, the type of interface affects the NIMV outcome more than the ventilatory mode.

Chronic Disease↗
PubMed2006

A comparison of the Soft Seal disposable and the Classic re-usable laryngeal mask airway.

Many new supraglottic airway devices have been recently introduced, their development motivated by the need for a single-use equivalent to the original re-usable laryngeal mask airway. We performed a randomised cross-over study in spontaneously breathing patients comparing the re-usable Laryngeal Mask Airway-Classic (LMA) and the disposable Soft Seal Laryngeal Mask in sizes 3, 4 and 5. Sixty patients had an LMA and a disposable laryngeal mask placed in random order. The primary outcome was first attempt insertion success rate. Ease of insertion was similar in both groups and there was no difference in first attempt success rates (96% with LMA and 92% with disposable laryngeal mask). The disposable laryngeal mask required significantly less air to inflate the cuff to produce a seal (10 [10-25] ml with disposable laryngeal mask and 15 [10-30] ml with laryngeal mask) and the cuff pressure produced was significantly lower (35 [20-80] cmH(2)O with disposable laryngeal mask and 75 [20-120] cmH(2)O with LMA). Data are median and range. We conclude that the disposable laryngeal mask is an acceptable alternative to the re-usable LMA.

Adult↗
PubMed2006

Six dimensional analysis with daily stereoscopic x-ray imaging of intrafraction patient motion in head and neck treatments using five points fixation masks.

The safety margins used to define the Planning Target Volume (PTV) should reflect the accuracy of the target localization during treatment that comprises both the reproducibility of the patient positioning and the positional uncertainty of the target, so both the inter- and intrafraction motion of the target. Our first aim in this study was to determine the intrafraction motion of patients immobilized with a five-point thermoplastic mask for head and neck treatments. The five-point masks have the advantage that the patient's shoulders as well as the cranial part of the patient's head is covered with the thermoplastic material that improves the overall immobilization of the head and neck region of the patient. Thirteen patients were consecutively assigned to use a five-point thermoplastic mask. The patients were positioned by tracking of infrared markers (IR) fixed to the immobilization device and stereoscopic x-ray images were used for daily on-line setup verification. Repositioning was carried out prior to treatment as needed; rotations were not corrected. Movements during treatment were monitored by real-time IR tracking. Intrafraction motion and rotation was supplementary assessed by a six-degree-of-freedom (6-D) fusion of x-ray images, taken before and after all 385 treatments, with DRR images generated from the planning CT data. The latter evaluates the movement of the patient within the thermoplastic mask independent from the mask movement, where IR tracking evaluates the movement of the mask caused by patient movement in the mask. These two movements are not necessarily equal to each other. The maximum intrafraction movement detected by IR tracking showed a shift [mean (SD; range)] of -0.1(0.7; 6.0), 0.1(0.6; 3.6), -0.2(0.8;5.5) mm in the vertical, longitudinal, and lateral direction, respectively, and rotations of 0.0(0.2; 1.6), 0.0(0.2; 1.7) and 0.2(0.2; 2.4) degrees about the vertical, longitudinal, and lateral axis, respectively. The standard deviations and ranges found with the 6-D fusion demonstrate intrafraction patient displacements of -0.5(1.2; 7.4), 0.3(0.7; 5.3), 0.0(0.7; 5.7) mm in the vertical, longitudinal, and lateral direction, respectively, and rotations of -0.1(0.6; 4.1), 0.1(0.7; 8.3) and -0.2(0.8; 8.2) degrees about the vertical, longitudinal, and lateral axis, respectively. The 6-D fusions are considerably larger (p < 0.05) than detected by IR tracking. This indicates that the external marker tracking underestimates the magnitude of the actual intrafraction motion and rotation of the patient. The intrafraction motion detected for the patients immobilized with a conventional thermoplastic mask was relatively large. The feasibility to reduce this intrafraction movement by the application of alternative five-point thermoplastic mask types was evaluated as a second aim of this study. The preliminary results showed a clear reduction in the range, being an indication for the random movements, of both the intrafraction shift and rotation for both alternative mask types. The 6-D fusion is found a useful tool for a fast evaluation of the actual patient's intrafraction shift and rotation and shows the latter is not negligible and needs to be taken into account additional to the initial setup accuracy when determining the PTV margin.

Head↗
PubMed2003

Recovery from prior stimulation: masking of speech by interrupted noise for younger and older adults with normal hearing.

In a previous study [Dubno et al, J. Acoust. Soc. Am. 111, 2897-2907 (2002)], older subjects benefitted less than younger subjects from momentary improvements in signal-to-noise ratio when listening to speech in interrupted maskers. It has been hypothesized that the benefit derived from interrupted maskers may be related to recovery from forward masking, i.e., the recovery of a response to a suprathreshold signal from prior stimulation by a masker. The effect of interrupted maskers on speech recognition may be well suited to test hypotheses regarding recovery from prior stimulation, given that both involve the perception of signals following a masker. Here, younger and older adults with normal but not identical audiograms listened to nonsense syllables at moderate and high levels in a speech-shaped noise that was modulated by a 2-, 10-, 25-, or 50-Hz square wave. An additional low-level noise was always present that was shaped to produce equivalent masked thresholds for all subjects. To assess recovery from forward masking, forward-masked thresholds were measured at 0.5 and 4.0 kHz as a function of the delay between the speech-shaped masker and the signal. Speech recognition in interrupted noise was poorer for older than younger subjects. Small but consistent age-related differences were observed in the decrease in score with interrupted noise relative to the score without interrupted noise. Forward-masked thresholds of older subjects were higher than those of younger subjects, but there were no age-related differences in the amount of forward masking or in simultaneous masking. Negative correlations were observed between speech-recognition scores in interrupted noise and forward-masked thresholds. That is, the benefit derived from momentary improvements in speech audibility in an interrupted noise decreased as forward-masked thresholds increased. Stronger correlations with forward masking were observed for the higher frequency signal, for higher noise interruption rates, and when the signal-to-noise ratio was poor. Comparisons of speech-recognition scores at moderate and high levels for younger and older subjects were not consistent with the hypothesis of an age-related difference in the contribution of low-spontaneous-rate fibers to speech recognition in interrupted noise.

Adult↗
PubMed2005

Informational masking release in children and adults.

This study assessed informational masking and utilization of cues to reduce that masking in children aged 4-9 years and in adults. The signal was a train of eight consecutive tone bursts, each at 1 kHz and 60 ms in duration. Maskers were comprised of a pair of synchronous tone-burst trains, with randomly chosen frequencies spanning 200-5000 Hz, with a protected region 851-1175 Hz. In the reference condition, maskers were eight bursts in duration, with a fixed frequency within intervals. Experiment 1 tested two monotic masking release conditions: within-interval randomization of masker burst frequency and the introduction of leading masker bursts. Experiment 2 examined masking release in which the signal was presented to one ear and masking components were presented to both ears (masker components in the contralateral ear were 10 dB higher than those in the ipsilateral ear). Both adults and children demonstrated a significant informational masking effect, with children showing a larger effect on average. Both groups also showed significant release from masking in the two monotic conditions, although children received somewhat less benefit from the masking release cues. The binaural condition supported a moderate release from informational masking in adults, but resulted in increased informational masking in children.

Acoustic Stimulation↗
PubMed1981

Auditory filter shapes derived in simultaneous and forward masking.

In this paper we describe a method for comparing frequency selectivity in simultaneous and forward masking. The method is designed to eliminate off-frequency listening, which may have had a confounding influence in earlier studies. Thresholds for 1-kHz sinusoidal signals were measured as a function of the width of a spectral notch, centered at 1 kHz, a noise masker. In experiment I thresholds were measured in forward masking for signal durations of 5, 15, and 45 ms, with a noise spectrum level of 40 dB SPL/Hz. Thresholds decreased with increasing notch width for all signal durations. However, the change was more gradual at longer signal durations. This is consistent with a model in which the process of decay of masking follows the auditory filter. For each signal duration, threshold was also measured as a function of the level of a noise without a spectral notch. Each signal threshold for the notch-noise condition was then expressed as the level of a flat-spectrum noise which would give the same masking. When transformed in this way, the data for the three signal durations coincide, and can be interpreted in terms of the same auditory filter. In experiment II the 5-ms signals, whose level was fixed, followed the masker with delays of 5, 15, or 25 ms. The noise spectrum level was varied to find threshold. The change in threshold with notch width was independent of signal delay, confirming that the process of decay of masking follows the auditory filter. Experiment III showed that short-term spectral changes produced by differences in the shapes of the envelopes of signal and masker did not influence the results. In experiment IV thresholds for a 5-ms signal were measured in simultaneous and forward masking, both for a fixed noise level and for a fixed signal level. The derived auditory filters are similar for the two types of measure for each type of masking. However, the auditory filters derived in forward masking have bandwidths 17% smaller and slopes 48% greater than those in simultaneous masking. The differences between simultaneous and forward masking are interpreted in terms of suppression.

Acoustic Stimulation↗
PubMed1983

Additivity of forward masking.

Masked thresholds for a 1000-Hz sinusoidal signal were measured as a function of masker level in both forward and simultaneous masking for two types of maskers: a 1000-Hz sinusoid and a narrowband noise, 60-Hz wide, centered at 1000 Hz. In forward masking, the noise masker produced much steeper growth-of-masking functions than the sinusoid. Presenting a contralateral broadband noise "cue" with the forward masker dramatically reduced the slope of masking for the noise masker but did not influence results for the sinusoidal masker. The noise remained the more effective masker. The amount of masking produced by combinations of equally effective narrowband-noise and sinusoidal maskers was compared to that produced by each masker individually with and without the contralateral cue. No additional masking beyond that predicted by energy summation was measured for forward masking. Additional masking beyond energy-sum predictions was measured for analogous conditions in simultaneous masking. Comparisons of results obtained with and without the contralateral cue suggest that signal thresholds in the presence of narrowband-noise forward maskers can reflect nonperipheral auditory processes.

Acoustic Stimulation↗
PubMed1994

Vibrotactile temporal masking: effects of multiple maskers.

Previous investigations of temporal masking effects in vibrotactile detection tasks have generally produced results suggesting considerable similarities in stimulus processing between the tactile system and the auditory system. Auditory presentation of combinations of maskers (e.g., two forward maskers) has yielded masking effects in excess of the level of masking predicted by a simple intensity sum of each masker's individual effect. This "additional masking" has led to predictions of compressive nonlinearities in auditory stimulus processing. In the present study, two experiments were conducted to investigate further temporal masking phenomena for the tactile system. In the first experiment vibrotactile temporal masking functions for single forward and backward maskers were generated to examine trade-offs among values of masker duration, masking intensity, and interstimulus interval to maintain constant detectability of a target. Results suggested that stimuli in very close temporal proximity to the target might follow somewhat different trading equations from those farther removed. Overall, results were consistent with previous findings of temporal integration in the tactile system, and support the notion of an energy integrating mechanism. In the second experiment, pairs of maskers were presented to determine whether additional masking effects occurred in vibrotactile detection. In contrast to findings for auditory presentation, in which all masker configurations generated additional masking, the tactile results showed substantial amounts of additional masking only for pairs of backward maskers. Several possible explanations for this results are evaluated, and results are discussed in terms of similarities and dissimilarities in auditory and tactile temporal processing.

Adult↗