Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “MASKS”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,189 records · Page 66Linked to original sources
PubMed1983

Visual masking by flickering surrounds.

Observers detected drifting sine-wave gratings presented in a circular 3 dia test field which was surrounded by a 3.25 degrees wide annulus. Forced choice contrast thresholds were measured with surrounds consisting of a steady field of light or uniform sinusoidal flicker. The flickering surround raised detection thresholds only for gratings with spatial frequencies below 2-4 c/deg. Variations on the basic experiment revealed that: (1) low spatial frequency gratings drifting through the surround masked detection of uniform flicker presented to the center; (2) masking did not depend greatly on the drift rate of the test grating but could not be obtained with stationary targets; (3) flicker restricted to either the top or side borders of the test field was a sufficient condition to produce masking; (4) the size of the masking effect decreased with center-surround separation. These results suggest a destructive interaction between transient mechanisms subserving neighboring regions of the visual field.

Form Perception↗
PubMed1985

Transposition in backward masking. The case of the travelling gap.

The transfer of attributes from a test stimulus (TS) to a masking stimulus (MS) during backward masking was investigated. Results indicated that a gap inserted on a TS transferred to a MS and that the degree of transfer varied as an inverted U-shaped function of ISI. Two explanations of the findings were offered. One was based on preservation of distinctive features and the second was based on "filling in" theory and the decrease in masking which occurs with increased spatial separation. The suggestion was made that an explanation of the transposition effect should be consistent with theories of backward masking and apparent motion.

Female↗
PubMed1991

The shift effect can be elicited with both foveal and peripheral masks.

Foveal target detection thresholds are elevated by presenting a counterphasing, vertical squarewave grating in the peripheral retina. This psychophysical "shift effect" has been considered to be an analogue of the neurophysiological "periphery effect" first described by McIlwain (1964; Journal of Neurophysiology, 27, 1154-1173). Physiological response properties of cells from the retina and lateral geniculate nucleus of cat and primate visual systems predict that sensitivity thresholds should also be elevated for peripheral targets in the presence of a foveal counterphasing mask. In these experiments, contrast sensitivities for human observers were obtained using a two-interval forced-choice procedure for peripheral target sinusoids in the presence of a foveal counterphasing mask. A suppressive shift effect was elicited by the foveal counterphasing squarewave mask, but only for counterphasing peripheral sinusoids. Masking was only obtained at the lowest spatial frequencies for both the peripheral and foveal shift effects.

Contrast Sensitivity↗
PubMed1992

Effects of lateral masking and spatial precueing on gap-resolution in central and peripheral vision.

The data made available by this experiment add two points to the information obtained by previous studies on eccentric vision and lateral masking. First, they demonstrate a clear effect of target-mask similarity on visual gap-resolution in eccentric vision: increasing target-mask similarity systematically decreases resolution performance. Second, spatial precueing has no effect on gap-resolution performance. One implication of this experiment is that with the present stimulus configurations, visual resolution should decrease much more strongly with eccentricity than it does with classical isolated or bar-masked optotypes.

Humans↗
PubMed1993

Orientation, masking, and vernier acuity for line targets.

In an attempt to uncover the properties of the psychophysical spatial mechanisms which optimally respond to the vernier offset between two abutting lines, we investigated the effects of one-dimensional band-limited spatial noise masks superimposed with the target, on vernier thresholds. Unidirectional vernier thresholds were measured in the presence of masks varying in orientation, spatial frequency content and luminance modulation. Because of the dependence of vernier thresholds on target visibility, the effects of these masks on target detection thresholds were also measured. In accordance with the results of Findlay [(1973) Nature, 241, 135-137] but contrary to an hypothesis that the direction of the vernier offset is mediated by the differential output of spatial filters of a single orientation, our results reveal a bimodal orientation tuning function for vernier acuity. We propose that, for offset line targets, the differential responses of at least two filters with orientations which straddle the target lines are combined to extract relative position information. The spatial frequency tuning characteristics of the optimal mechanisms for mediating vernier information are similar to those optimal for detecting the target lines themselves, except that they are tuned to a slightly higher spatial frequency and have a slightly narrower bandwidth. The spatial mechanisms most sensitive to the vernier offset and to target detection exhibit similar responses to increases in mask modulation. This finding suggests that these tasks are limited by the same source of noise, and explains why under a variety of experimental manipulations, equally visible vernier targets result in similar vernier thresholds.

Humans↗
PubMed1994

Selectivity of cyclopean masking for the spatial frequency of binocular disparity modulation.

Previous studies have presented evidence for the existence of channels tuned to the spatial frequency (SF) of binocular disparity modulation. Bandwidths reported for masking curves were extremely narrow, possibly because of off-frequency viewing, whereby observers can best detect a signal with a channel tuned to an SF on the opposite side of the signal from the masker's SF, rather than with a channel tuned directly to the signal's SF. Herein are reported the results of four detection experiments. Experiment 1 measures unmasked threshold for detection of a cyclopean grating. Experiments 2-4 are masking experiments. Experiment 2 demonstrates that threshold for detection of a cyclopean grating is proportional to the intensity of masking noise, which is consistent with the operation of linear channels. Experiments 3 and 4 demonstrate that masking curves are narrower when obtained with narrowband-noise maskers than when obtained with notched-noise maskers, which render the off-frequency viewing ineffective. Implications for understanding the processing of cyclopean images are discussed.

Adult↗
PubMed1987

Backward masking of lateralized faces by noise, pattern, and spatial frequency.

Experiments 1 and 2 measured the critical interstimulus interval at which a face presented to the right or left visual field escaped a trailing noise, pattern, or spatial-frequency mask. The function relating target duration to critical ISI was multiplicative in the noise and spatial-frequency condition, but additive at longer durations in the pattern mask condition. An advantage of about 8 msec for the left visual field and 2 msec for the right field was found in the pattern and spatial-frequency masking condition, respectively. No consistent visual field differences were found in the noise mask condition. Taken together, these results suggest that hemispheric difference in face recognition are either absent or inconsistent at early, peripheral, energy-sensitive stages of processing, but emerge strongly at higher order central stages. The results also suggest that the left and right hemispheres are not differentially sensitive to the output of high- and low-spatial-frequency channels, respectively. If it is assumed that the central face processor is functionally localized to the right hemisphere, one can infer from these results that interhemispheric transmission time is not greater than 8 msec, and the output of sensory analysis and/or relational features are transferred across the interhemispheric commissures.

Adolescent↗
PubMed1981

Masking-period patterns and cochlear acoustical responses.

A suppression-period pattern' for acoustical responses has been measured in a similar way to the masking-period pattern. A triggered low-frequency masker decreases the acoustical response to a short test signal differently at different presentations within the period of the masker. The two patterns show such close relationships that a masking-period pattern can be developed out of a set of suppression-period patterns: masked threshold is reached with the same parameter conditions under which the acoustic responses diminish. The rules elaborated for masking-period patterns seem to hold for suppression-period patterns as well.

Acoustics↗
PubMed1982

Fluctuation strength and temporal masking patterns of amplitude-modulated broadband noise.

Fluctuation strength of sinusoidally amplitude modulated broadband noise was measured by a magnitude-estimation procedure. Fluctuation strength shows, as a function of modulation frequency, a bandpass characteristic with a maximum around 4 Hz. With increasing modulation depth and sound pressure level, fluctuation strength increases. For the same stimulus parameters as used in the experiments on fluctuation strength, temporal masking of amplitude modulated broadband noise was determined. The level difference delta L between the maximum and the minimum of the resulting temporal masking patterns shows a low-pass characteristic as a function of modulation frequency and increases with increasing modulation depth and sound pressure level. A model of fluctuation strength F based on the depth delta L of the temporal masking pattern and the modulation frequency fmod in relation to 4 Hz is proposed as follows: F approximately delta L/((fmod/4 Hz)+(4 Hz/fmod)). The model accounts for the dependence of fluctuation strength on some essential stimulus parameters. The usefulness of temporal masking patterns as an intermediate value for the description of hearing sensations is confirmed.

Adult↗
PubMed1988

Failure of a missing-fundamental complex to interact with masked and unmasked pure tones at its fundamental frequency.

Of interest here are the mechanisms underlying the extraction of temporal periodicities from complex acoustic stimuli. Two extreme versions of the underlying mechanisms are examined for possible psychophysical consequences, and experiments of two sorts are reported. In one, the detectability of a 200-Hz tone was measured in the presence, and the absence, of a tonal complex that gives rise to the experience of a missing fundamental having a pitch of 200 Hz in an attempt to see if the missing-fundamental waveform contributes to the masking of the tonal signal. We call this periodicity masking, but were unable to measure any, implying that if periodicity information was being used both to detect the signal and to perceive the missing fundamental, those two streams of afferent information are kept separate by the auditory nervous system, at least initially. In the second set of experiments, an "informational-masking" paradigm was used to introduce high uncertainty about the frequency of the tonal signal, and both detection and frequency discrimination were measured in the presence and absence of a missing-fundamental complex. This time the question was whether the periodicity information in the complex would produce a reduction in the frequency uncertainty about the signal and, thereby, improve performance. We call this possible effect periodicity cueing, but were unable to find evidence for its existence either. The failure to find either periodicity masking or periodicity cueing is discussed in regard to possible organizations of the auditory system, and in regard to the "periodicity-rate gap" seen in primary auditory fibers.

Cues↗
PubMed1995

Recovery of forward-masked responses in ventral cochlear nucleus neurons.

Single unit responses were obtained from 8 classes of cells in the ventral cochlear nucleus: Primarylike, Primarylike with characteristic frequencies below 1 kHz, Primarylike-Notch, Sustained Chopper, Transient-Chopper, Low-intensity Chopper; Onset with later activity and On-Chopper. Stimuli were paired tonebursts, a masker preceding a probe, separated by time delta t ms. The decrement in discharge rate to the probe was measured as a function of delta t and constituted the forward-masking recovery function. The recovery functions of primarylike units were similar to those reported for auditory nerve fibers, but recovered more slowly than all other classes of units in the ventral cochlear nucleus. Some units, such as onset units, were completely masked at short masker-probe intervals, while others, such as the low-intensity choppers, were less affected by the masker. More masking occurred in the first 2 ms of the response (onset rate) than in the overall response (average rate). Using shorter maskers and measuring the onset rate produced greater differences in masking functions between unit classes. Units with high spontaneous activity were more resistant to the effects of the masker than units with low and medium spontaneous activity. This was especially evident at high masker levels and short masker-probe intervals. Units other than primarylike often showed non-monotonic relationships between the firing rate evoked by the masker and the firing rate decrement in response to the probe, suggesting that both adaptation and inhibition are operating to produce the observed effects.

Acoustic Stimulation↗
PubMed1994

Using an excitation-pattern model to predict auditory masking.

This paper evaluates the extent to which auditory masking can be reliably predicted from excitation patterns. For this purpose a quantitative model proposed by Glasberg and Moore [Hear. Res. 47, 103-138 (1990)] was used to calculate excitation patterns evoked by stationary sounds. Model simulations were performed for a number of masking experiments, reported in the literature, by calculating excitation patterns for the masker-alone as well as for the masker-plus-target conditions. As a threshold criterion, a difference between the two patterns of 1 dB at any frequency was imposed. For narrow-band-noise masking patterns, the method yields a fairly precise prediction of experimental data. For other conditions, however, systematic deviations between model predictions and data are observed. For instance, the model does not reproduce the typical tip-tail shape of psychophysical tuning curves. Furthermore, the nonlinearities in level dependence are not correctly described, and the model fails to reproduce a realistic two-tone masking curve.

Acoustic Stimulation↗
PubMed1995

The effects of contralateral noise on masked compound action potential in humans.

The effects of contralateral noise on the masked compound action potential (CAP) were examined in human subjects. Small but significant enhancements of masked CAP amplitude (anti-masking effects) were observed in some patients with facial palsy, as well as in some subjects with healthy ears when noise was added to the contralateral ear. There were no significant differences in fractional changes of CAP by the addition of contralateral noise between subjects with healthy ears and patients with facial palsy in which acoustic reflexes of middle ear muscles (MEMs) had disappeared or were impaired. It is suggested that the anti-masking effects seen in the present study were possibly caused via the olivocochlear (OC) efferent system.

Acoustic Stimulation↗
PubMedDate not supplied

The laryngeal mask airway.

The laryngeal mask airway (LMA) is a new concept in airway management. A miniature inflatable mask is positioned in the hypopharynx, forming a low-pressure seal around the laryngeal inlet. The mask is attached via a tube to the breathing circuit. It is inserted after induction of anesthesia without the need for muscle relaxants or laryngoscopy. The LMA can be used to facilitate both spontaneous and controlled ventilation in adults and children. The LMA has been used for a wide variety of surgical procedures but is probably best suited to short procedures, especially if a light general anesthetic is used in combination with a regional technique. It may be particularly useful in outpatient anesthesia, as it avoids the need for intubation or muscle relaxants. It can be used as an alternative to mask anesthesia or when an endotracheal tube would have been inserted to allow surgical access. It has been used successfully in cases of difficult or failed intubation, although its role here needs further appraisal. It does not protect against aspiration of stomach contents and should not be used when aspiration is a risk. Controversy exists regarding its use to facilitate positive-pressure ventilation (PPV) due to concern that gases under pressure may be forced into the stomach and predispose the patient to regurgitation. It may be more difficult to use in children. It is now widely used in the United Kingdom; however, it is not yet available for sale in the U.S. It has already had a major effect on practice in Britain and has the potential to do the same in the United States.

Anesthesiology↗
PubMed2006

[Clinical study of the laryngeal mask in paediatric. Comparison of the LMA-ProSeal and LMA-classic].

OBJECTIVES: To compare the Classic laryngeal mask airway (MLC) and the ProSeal LMA (MLP), size 2 and 2.5 in terms of ease of insertion, leak pressure and side effects during insertion and extraction in the recovery room. STUDY TYPE: Randomised prospective. MATERIAL AND METHOD: All children between 10 and 30 kg scheduled for general anaesthesia with laryngeal mask (ML) were included. There was no imposed protocol for the anaesthesia. The ML size was determined according to the child's weight. The MLC was inserted using the standard technique. The MLP was inserted following the recommendations, with or without the handle according to the operator's choice. The data analysed were: insertion type, ease of insertion of the mask, of the nasogastric tube (SG), number of attempts of mask insertion, complications, gastric leaks. RESULTS: One hundred (and) twenty children were included. There was no statistical difference in terms of difficulty of insertion, number of failed attempts, leak pressure or side effects. The use of the handle did not make insertion easier. Insertion of a nasogastric tube was possible in 92% cases. CONCLUSION: MLP is as easy to use in children as the MLC. MLP has the advantage of allowing rapid access to the stomach. It seems that the MLP is safer since its correct position is confirmed by easy gastric tube insertion.

Air Pressure↗
PubMed2006

Alternative ventilation strategies: laryngeal masks.

The appropriate role for laryngeal masks during delivery room resuscitation has not been established. The authors systematically reviewed the literature to answer three clinical questions: (1) In newborns requiring positive-pressure ventilation for resuscitation, would a laryngeal mask achieve safe and effective ventilation faster than facemask ventilation? (2) In newborns unable to be ventilated effectively with a facemask during resuscitation, would a laryngeal mask achieve effective ventilation faster than endotracheal intubation? (3) In newborns requiring resuscitation, would a laryngeal mask achieve effective ventilation when facemask ventilation and endotracheal intubation have been unsuccessful?

Humans↗
PubMed2006

Masked phonological priming effects in English: are they real? Do they matter?

For over 15 years, masked phonological priming effects have been offered as evidence that phonology plays a leading role in visual word recognition. The existence of these effects-along with their theoretical implications-has, however, been disputed. The authors present three sources of evidence relevant to an assessment of the existence and implications of these effects. First, they present an exhaustive meta-analytic literature review, in which they evaluate the strength of the evidence for masked phonological priming effects on English visual word processing. Second, they present two original experiments that demonstrate a small but significant masked priming effect on English visual lexical decision, which persists in conditions that may discourage phonological recoding. Finally, they assess the theory of visual word recognition offered by the DRC model (Coltheart, Rastle, Perry, Langdon, & Ziegler, 2001) in the context of their empirical data. Through numerous simulations with this model, they argue that masked phonological priming effects might best be captured by a weak phonological (i.e., dual-access) theory in which lexical decisions are made on the basis of phonological information.

Humans↗
PubMed2006

Temporal masking curves for hearing-impaired listeners.

The decay of forward masking was investigated for three subjects with moderate sensorineural hearing loss. For such subjects, compression on the basilar membrane (BM) is thought to be largely absent, enabling one to determine the decay of masking without the influence of compression. Temporal masking curves (TMCs), plots of the masker level at threshold against delay between masker offset and signal onset, were measured for delays of 0, 15, 30, 45, 60, and 75 ms, for signal frequencies, fs, of 500, 1000, 2000, 4000, and 6000 Hz. Masker frequencies were 0.5, 0.8, 1.0, 1.15, and 1.3 times fs. Most of the TMCs were well fitted with single-segment straight lines, which, except for high masker levels, were roughly parallel for each fs, supporting the belief that BM compression was largely absent in these subjects. However, the slopes of the TMCs were greater for fs = 500 and 1000 Hz than for higher frequencies, which may indicate that the decay of forward masking is not the same for all signal frequencies. The results suggest that it may not be valid to infer BM compression at low signal frequencies by using a reference TMC for a high fs.

Acoustic Stimulation↗