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PubMed2004

High-level effects of masking on perceptual identification.

The extent to which visual form versus higher-level information is used to identify briefly flashed words is assessed in a perceptual identification task. In this task, a word is briefly flashed, post-masked, and a decision is made between two alternatives. The availability of visual (e.g., case or color) and higher-level information (e.g., abstract letter codes, phonology, and meaning) was manipulated by varying the information that discriminates the alternatives. Performance was better with higher-level than with visual information when pattern post-masks were used, but the reverse occurred without masking. The authors conclude that both higher-level and visual-form information can be used to identify words with the strategy depending on the information available at the time of the choice.

Cognition↗
PubMed1999

Facilitatory and inhibitory effects of masked prime stimuli on motor activation and behavioural performance.

Three experiments investigated the impact of information provided by masked stimuli on motor activation. Masked primes were presented prior to target stimuli and these primes were identical to the target on compatible trials, identical to the target mapped to the opposite response on incompatible trials and task-irrelevant on neutral trials. A previous study [Eimer, M., & Schlaghecken, F. (1998). Effects of masked stimuli on motor activation: Behavioural and electrophysiological evidence. Journal of Experimental Psychology: Human Perception and Performance, 24, 1737-1747] found performance costs for compatible trials and benefits for incompatible trials. Experiment 1 showed that these effects are not due to 'perceptual repetition blindness'. Experiments 2 and 3 obtained evidence for an initial response facilitation triggered by the primes that was followed by inhibition. With short intervals between prime presentation and response execution, performance benefits were found for compatible trials and these turned into costs at longer intervals. It is argued that an early response facilitation mediated by direct perceptuo-motor links is subsequently inhibited by a central mechanism operating to prevent behaviour from being controlled by irrelevant information.

Adult↗
PubMed2002

1 hz rTMS over the right prefrontal cortex reduces vigilant attention to unmasked but not to masked fearful faces.

BACKGROUND: Recent repetitive transcranial magnetic stimulation (rTMS) research in healthy subjects suggests that the emotions anger and anxiety are lateralized in the prefrontal cortex. Low-frequency rTMS over the right prefrontal cortex (PFC) shifts the anterior asymmetry in brain activation to the left hemisphere and reduces anxiety. The same rTMS technique results in enhanced anger-related emotional processing, observed as elevations in attention for angry faces. The current study used low-frequency rTMS over the right PFC and indexed selective attention to fearful faces, hypothesizing a reduction in attention for fearful faces, i.e., a reversal of the latter effect. METHODS: In a placebo-controlled design, 1 Hz rTMS at 130% of the individual motor threshold (MT) was applied continuously over the right PFC of eight healthy subjects for 20 minutes. Effects on motivated attention were investigated by means of an emotional Stroop task, indexing selective attention to masked and unmasked fearful faces. RESULTS: Vigilant attention for masked and unmasked fearful faces was observed after placebo stimulation. As hypothesized, rTMS reduced the vigilant emotional response to the fearful face, but only in the unmasked task. CONCLUSIONS: These data provide further support for the lateralization of the emotions anger and anxiety in the prefrontal cortex. In addition, the absence of an effect for masked fearful faces suggests that changes in emotional processing after a single session of rTMS predominantly involve the cortical affective pathways.

Adult↗
PubMed2003

Increased masking response to light after ablation of the visual cortex in mice.

Mice are known to suppress their wheel running when given a pulse of light in the night (masking response). The amount of suppression can be quantified; the response varies with the level of irradiance used during the light pulse. After ablation of the visual cortex, mice suppressed their activity more than sham-operated controls. In addition, the lesioned animals responded to lower levels of irradiance than controls. It is suggested that the visual cortex is not needed for the suppression of locomotor activity after a light pulse. Nevertheless it exerts an inhibitory influence on the masking response to light mediated by an irradiance detection system. When this inhibition is removed, even though pattern vision is lost, masking responses to ambient level of light are enhanced.

Animals↗
PubMed2003

Respiratory mechanics in conscious swine: effects of face mask, head position and bronchoconstriction evaluated by impulse oscillometry.

Airway obstruction in pigs (sedated or non-sedated) fixed in a sling was studied using impulse oscillometry (IOS). (i) Vertical flexion of the pig's head was used to simulate an artificial obstruction of the upper airways. (ii) Bronchial obstruction was induced by inhaling differing quantities of an aerosol produced from 0.33% carbachol solution. The ventilatory pattern was examined by measuring respiratory rate (RR) and tidal volume (V(t)). To evaluate respiratory mechanics, impedance parameters resistance (R) and reactance (X) as well as coherence (Co) were examined, each at frequencies of 5, 10, 15, 20, 25 and 35 Hz. Using a simple 7-element-model introduced by J. Mead [Physiological Review 41 (1961) 281], distal respiratory resistance (R(dist)), proximal airway resistance (R(prox)), and additional shunt compliance (C(a)) of the animal's snout and the air inside the facemask were evaluated. By fitting this model to the primary measured impedance spectra, the influence of the face mask could be eliminated in the model calculation to allow assessment of the real respiratory impedance. This recalculation made clear that the facemask had an influence on the spectral course of R and X, depending on the clinical situation, and the upper frequency range was altered the most. Under conditions of (i) upper airway obstruction, especially the X values were distorted by facemask almost over the whole frequency range. Once the data were corrected for the mask, resistance was increased across all frequencies by a fixed amount while reactance was not affected. Under (ii) bronchial airway obstruction (bronchospasm) caused the resistance spectrum to be increased mainly in the lower frequency range. This became visible in both, originally measured impedance spectra and spectra after correction of the mask influence. The reactance course (originally measured and recalculated) decreased at all frequencies during bronchospasm. Coherence over the whole frequency range was lowered at both bronchial and upper airway obstruction.

Airway Obstruction↗
PubMed1997

Implicit masking constrained by spatial inhomogeneities.

Human contrast sensitivities to gratings were measured within windows of 3, 9.1 and 61.5 deg at spatial differences down to the nominal frequency of 0 c/deg (i.e., a uniform field), and the resulting curves were related to the Fourier spectra of the corresponding windows and of spatial inhomogeneities in the visual pathway. The data show that sensitivity approaches an asymptote about 1.5 log units below peak sensitivity as spatial frequency decreases, the so-called low frequency cut. Computations show that the fundamentals of the test files used here were detected and not their harmonics, and control experiments suggest that the edges of the gratings did not affect detection of the gratings. Most of the low frequency cut could be attributed to masking by the harmonics of the windows within which the gratings were introduced. The added contribution of the inhomogeneities in the retinal distribution of cones accounts for the remainder of the low frequency cut observed with the two smaller windows, and adding the effects of the inhomogeneities to the distribution of parvocellular ganglion cells accounts for the remainder of the low frequency attenuation with the largest field. Therefore, the attenuation of sensitivity to low frequencies that gives the contrast sensitivity curve its bandpass shape can be attributed entirely to implicit masking, i.e., to masking by the Fourier spectrum of the window within the test grating is presented, after further spreading by retinal inhomogeneities.

Adaptation, Ocular↗
PubMed1998

Chromatic masking in the (delta L/L, delta M/M) plane of cone-contrast space reveals only two detection mechanisms.

The post-receptoral mechanisms that mediate detection of stimuli in the (delta L/L, delta M/M) plane of color space were characterized using noise masking. Chromatic masking noises of different chromaticities and spatial configurations were used, and threshold contours for the detection of Gaussian and Gabor tests were measured. The results do not show masking that is narrowly-selective for the chromaticity of the noise. On the contrary, our findings suggest that detection of these tests is mediated only by an opponent chromatic mechanism (a red-green mechanism) and a non-opponent luminance mechanism. These results are not consistent with the hypothesis of multiple chromatic mechanisms mediating detection in this color plane [1].

Color Perception↗
PubMed2006

Visual masking approaches to visual awareness.

In visual masking, visible targets are rendered invisible by modifying the context in which they are presented, but not by modifying the targets themselves. Here I summarize a decade of experimentation using visual masking illusions in which my colleagues and I have begun to establish the minimal set of conditions necessary to maintain the awareness of the visibility of simple unattended stimuli. We have established that spatiotemporal edges must be present for targets to be visible. These spatiotemporal edges must be encoded by transient bursts of spikes in the early visual system. If these bursts are inhibited, visibility fails. Target-correlated activity must rise within the visual hierarchy at least to the level of V3, and be processed within the occipital lobe, to achieve visibility. The specific circuits that maintain visibility are not yet known, but we have deduced that lateral inhibition plays a critical role in sculpting our perception of visibility, both by causing interactions between stimuli positioned across space, and also by shaping the responses to stimuli across time. Further, the studies have served to narrow the number of possible theories to explain visibility and visual masking. Finally, we have discovered that lateral inhibition builds iteratively in strength throughout the visual hierarchy, for both monoptic and dichoptic stimuli. Since binocular information is not integrated until inputs from the two eyes reach the primary visual cortex, it follows that the early visual areas contain differential levels of monoptic and dichoptic lateral inhibitions. We exploited this fact to discover that excitatory integration of binocular inputs occurs at an earlier level than interocular suppression. These findings are potentially fundamental to our understanding of all forms of binocular vision and to determining the role of binocular rivalry in visual awareness.

Animals↗
PubMed1999

The visual backward masking deficit in schizoaffective disorder.

1. Subjects with schizoaffective disorder have an impairment in early visual information processing known as backward masking. 2. Backward masking studies in schizoaffective disorder have not established if the deficit: is state- or trait-related; is associated with negative symptoms or neuroleptic treatment; or is partially attributable to lithium treatment. 3. Integration and interruption are mechanisms of backward masking in schizoaffective disorder, but experiments maximizing interruption only, have not been performed. 4. Studies isolating the transient visual channels have not been performed in patients with schizoaffective disorder.

Humans↗
PubMed1995

[Assisted ventilation via nasal mask in patients hospitalized in a pneumology ward for decompensation of their chronic air-flow obstruction].

Our aim was to evaluate the efficacy of assisted ventilation through a nasal mask (AVN) in treating chronic obstructive pulmonary disease (COPD) patients who were admitted to a pneumology ward due to decompensation, with PaCO2 > 60 mmHg and pH < 7.35. We studied 13 COPD patients who were first observed for 1-2 days until adaptation and then given 2 daily sessions of AVN lasting 4 hours with double positive pressure (DP90) devices through Sullivan mask with a cannula for hyperoxia. Gasometric readings were recorded, along with subjective assessment of condition and problems with the mask. Gasometric readings were taken as follows: the first upon admission to the ward (AW), the second with AVN 2 days after adaptation and the third 3 hours after the second (POST). Statistical analysis was with a Student t-test for paired series. Mean age was 64 +/- 3 years and FEV1 was 0.69 +/- 0.14 l. Interruptions were due to the need for mouth opening even at minimum pressures, and the inability to adapt to the consequent tachypnea. No other problems were reported by the remaining patients and all perceived improvement subjectively. The pH of 7.29 +/- 0.03 at AW increased to 7.41 +/- 0.03 with AVN (p < 0.001) and held steady at 7.39 +/- 0.01 at POST (p < 0.001 POST-AW and p = NS POST-AVN). PaO2/FiO2 was 223 +/- 49 mmHg at AW and 267 +/- 41 mmHg at the POST reading (p = 0.06). PaO2 with AVN was 67 +/- 8 mmHg.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1998

Tracheal intubation via the laryngeal mask airway: a viable alternative to direct laryngoscopy for nursing staff during cardiopulmonary resuscitation.

Eight nurses with no previous experience of advanced airway management were randomly assigned to be taught tracheal intubation either by direct laryngoscopy or via a laryngeal mask. Once competent in the technique using a manikin, they attempted a maximum of ten intubations on anaesthetised patients. They were then taught the alternative technique and the assessment repeated. Median times for practice were the same for both techniques. Intubation in under 30 s was successful via the laryngeal mask in 60% of patients (42/70) compared to 39% (27/70) when using a laryngoscope (P = 0.11). It appears that non-medical personnel can be successfully taught to intubate the trachea using the laryngeal mask as a conduit, for those circumstances where a cuffed tracheal tube is considered essential during resuscitation.

Adult↗
PubMed2000

The relative role of beats and combination tones in determining the shapes of masking patterns at 2 kHz: I. Normal-hearing listeners.

Masking patterns for a 2-kHz sinusoidal masker at 45, 65 or 85 dB SPL were measured for three normal-hearing subjects, using a 3-AFC method with feedback (condition 1). The patterns showed distinct irregularities, particularly at the highest masker level. In condition 2, a lowpass noise was added to mask combination tones. The noise increased thresholds mainly for the 85 dB masker, for signal frequencies of 2.3-3.0 kHz. In condition 3, a pair of high-frequency tones ('modulation detection interference (MDI) tones') was used to introduce beats at the same rate as produced by the interaction of the masker and signal. Thresholds were higher than for condition 1, particularly for signal frequencies adjacent to the masker frequency. In condition 4, the lowpass noise was presented simultaneously with the MDI tones. Thresholds were well predicted as a combination of the effects of the lowpass noise and the MDI tones. In condition 5, a pair of low-frequency MDI tones was added to the masker. The thresholds had the same overall pattern as in condition 4. We conclude that the shapes of masking patterns measured using a 2-kHz masker are influenced by the detection of beats for masker-signal frequency separations up to at least 300 Hz and by the detection of combination tones for separations between 300 and 1000 Hz.

Acoustic Stimulation↗
PubMed2002

Contralateral inhibition in a release from forward masking.

The current study investigated contralateral inhibition involved in a release from forward masking. The masker and probe were 1-kHz pure tones shaped by a 20-Hz modulation. Durations of the masker and probe were 500 ms and 50 ms (single cycle) respectively. A 10-ms delay between the masker and probe was added to rule out any confusion. A contralateral component (cue), with various spectral and temporal properties, could be added during the masker. The first experiment showed that masking release occurred more often or increased with an increasing number of spectral cue components. The second experiment showed that increasing cue duration, leaving the cue and masker offsets synchronous, increased detection thresholds. In the third experiment the temporal position of a short cue relative to the masker was varied. The lowest thresholds were obtained for 0- and 150-ms delays between the cue and masker offsets. Despite large individual differences, the obtained release from forward masking provided support for a contralateral inhibition process. Contralateral inhibition seemed to be dependent on the number of spectral cue components and on the delay between the cue onset and the masker offset.

Acoustic Stimulation↗
PubMed1998

Masking of tones and speech by Schroeder-phase harmonic complexes in normally hearing and hearing-impaired listeners.

Tone detection and sentence recognition were measured for normally hearing and hearing-impaired listeners using maskers consisting of harmonic series with components summed in positive or negative Schroeder phase. Each task was carried out with the signal set at 60, 70, or 80 dB SPL. For listeners with normal hearing, positive Schroeder-phase complexes masked tones and sentences less than negative Schroeder-phase maskers. In the two experimental tasks, to achieve the same amount of masking, positive Schroeder-phase complexes had to be set as much as 12-15 dB higher than negative Schroeder-phase complexes. Large phase effects were observed on both tasks at all three test levels. The two maskers were more nearly equal in effectiveness in the presence of cochlear damage. The findings support an interpretation that involves differences in the shape of the basilar-membrane waveform generated by each masker and active cochlear processing which enhances the internal signal-to-masker ratio for signals presented in the positive Schroeder masker. This spectral enhancement appears to require nonlinear active gain that is characteristic of normal auditory processing at moderate presentation levels. The results of the sentence recognition task suggest that group differences observed in tone detection transfer fairly directly to speech perception under masking.

Acoustic Stimulation↗
PubMed1999

Auditory brainstem response forward-masking recovery functions in older humans with normal hearing.

We investigated the auditory brainstem response (ABR) recovery from forward masking using toneburst maskers and probes. Two subject groups matched for hearing thresholds were evaluated: normal-hearing young adults (21-40 years) and older subjects (63-77 years) with normal audiometric thresholds. Stimuli consisted of 1, 4 and 8 kHz tonebursts, with 2-4 cycle rise/fall time and no plateau. Forward maskers were tonebursts of the same frequency, with a 5 ms rise/fall time and a 20 ms plateau time. Probes were presented at 40 dB above threshold, and the forward masker was adjusted to a level that just eliminated the ABR to the 40 dB sensation level toneburst when the probe onset occurred at masker offset. Forward-masker intervals varied from 2 to 64 ms. ABR wave V latencies were similar for the young and old age groups regardless of toneburst frequency. Under forward-masking conditions, wave V latency was prolonged for the shorter intervals, and recovered to baseline latency by 64 ms. The forward-masker recovery functions were nearly identical for the two age groups for the 1 kHz toneburst. In contrast, there were clear differences in the recovery functions for the two age groups for the 4 and 8 kHz tonebursts. Specifically, the mean latency shift was greater for the aged group for forward-masker intervals of 16 ms or less. The two age groups showed identical latency shifts for longer forward-masker intervals. These data demonstrate prolonged recovery from forward masking in older human subjects. As these subjects had audiometric thresholds within normal limits, one plausible interpretation of this finding is that the prolonged recovery time is a manifestation of an aging effect on the central auditory nervous system rather than the periphery.

Acoustic Stimulation↗
PubMed1998

[Noninvasive postoperative ventilation using a buccal mask].

In this preliminary study we assessed the feasibility and efficiency of non-invasive ventilation (NIV) with a buccal mask (NIV-BM), not fitted with a mouthpiece, in surgical patients in acute respiratory failure whose lungs could not be ventilated with a face mask. In the eight patients enrolled in the study, NIV-BM increased tidal volume, decreased respiratory rate and improved PaO2. In two patients the trachea had to be intubated and one of them died of septic shock. NIV-BM can act as a valuable alternative in surgical patients in acute respiratory failure in whom a face mask cannot be used because of leaks or bad tolerance.

Adult↗
PubMed2001

Comparison of no airway device, the Guedel-type airway and the Cuffed Oropharyngeal Airway with mask ventilation during manual in-line stabilization.

STUDY OBJECTIVE: To compare two different types of oropharyngeal airway: the Guedel-type oral airway and the Cuffed Oropharyngeal Airway (COPA), with respect to the effectiveness of positive-pressure ventilation (PPV) through a face mask in patients with in-line stabilization of the head and neck. DESIGN: Prospective, randomized, crossover study. SETTING: University hospital. PATIENTS: 30 ASA physical status I and II patients undergoing elective surgery. INTERVENTIONS: General anesthesia was induced with propofol and muscle relaxation was produced with vecuronium. In a random sequence, no airway device, the Guedel-type airway, and the COPA were used in each patient while applying a face mask and lifting the jaw forward. MEASUREMENTS AND MAIN RESULTS: Tidal volumes were measured during PPV in each option. The position of the distal tip of each airway was assessed using a fiberscope, and the resulting views were graded and compared. When the Guedel-type airway was used, tidal volumes (V(T)s; means +/- SD) were significantly greater (12.3 +/- 4.5 mL/kg) than those with no airway device (8.5 +/- 4.5 mL/kg) (p < 0.001). When the COPA was used, V(T)s (14.6 +/- 4.4 mL/kg) were significantly greater than those with the Guedel-type airway (p < 0.05). The grade of the fiberscopic view through the distal tip was significantly better with the COPA than with the Guedel-type airway (p < 0.05). CONCLUSIONS: Although clinical differences often appear trivial, the COPA is more effective on mask ventilation than the Guedel-type airway when used in patients with manual in-line stabilization.

Adult↗
PubMed2003

Standard Laryngeal Mask Airway and LMA-ProSeal during laparoscopic surgery.

STUDY OBJECTIVE: To compare the frequency of airway seal and sore throat with the LMA-ProSeal (PLMA) and the standard Laryngeal Mask Airway (LMA) during laparoscopic surgery. DESIGN: Prospective, controlled, randomized, nonblinded clinical study. SETTING: University-affiliated hospital. PATIENTS: 60 adult, ASA physical status I, II, and III patients undergoing laparoscopic surgery with general anesthesia, without contraindication to the use of the laryngeal mask. INTERVENTIONS: Patients were randomized to receive mechanical ventilation [tidal volume (V(T)) 7 mL/kg(-1); positive end-expiratory pressure (PEEP) 10 cmH(2)O] through the PLMA or the standard LMA, both equipped with a gastric tube. MEASUREMENTS: Heart rate, arterial pressure, inspiratory and expiratory V(T), airway pressure, end-tidal CO(2) partial pressure, and pulse oximetry were recorded. The leak fraction was calculated as the difference between the inspiratory and expiratory V(T) divided by the inspiratory V(T). Postoperative sore throat frequency was scored in the recovery room ("early") and 1 week after surgery ("late"). MAIN RESULTS: All patients were successfully ventilated through the assigned laryngeal mask. The leak fraction was 7 +/- 3% with the LMA and 7 +/- 4% with the PLMA (p = 0.731). In one patient, the PLMA drainage tube was not patent despite a leak fraction of 5%, and there was no clinically detectable air leak. During the recovery room stay, the frequency of sore throat was scored as mild in 13% and 10% of patients with the standard LMA and the PLMA, respectively, and was absent in the remaining patients (p = 0.99, between groups). There were no differences in the frequency of sore throat between the "early" and "late" evaluations (p = 0.99). CONCLUSIONS: The PLMA and the LMA show similar airtight efficiency during laparoscopy. The patency of the PLMA drainage tube should always be confirmed. The sore throat evaluation performed in recovery room appears as reliable as later evaluations.

Anesthesia, General↗