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PubMed2000

A diffusion model account of masking in two-choice letter identification.

The diffusion model developed by R. Ratcliff (1978, 1981, 1985, 1988) for 2-choice decisions was applied to data from 2 letter identification experiments. In the experiments, stimulus letters were displayed and then masked, and the stimulus onset asynchrony between letter and mask was manipulated to vary accuracy from near chance to near ceiling. A standard reaction time procedure was used in one experiment and a deadline procedure in the other. Two hypotheses about the effect of masking on the information provided to the decision process were contrasted: (a) The output of perception to the decision process varies with time, so that the information used by the decision process rises and falls, reflecting the stimulus onset and mask onset. (b) The output of perception to the decision is constant over time, reflecting information integrated over the time between the stimulus and mask onsets. The data were well fit by the diffusion model only with the assumption of constant information over time.

Adult↗
PubMed2001

Learning to ignore the mask in texture segmentation tasks.

Although traditionally texture segmentation has been regarded as an automatic, preattentive process, participants confronted with texture segmentation in experimental settings (i.e., with brief presentation time and subsequent masking) are initially unable to perform the task. According to perceptual learning concepts, participants must learn to fine-tune their sensory channels before perception improves under restricted viewing conditions. The present article proposes an alternative perspective that emphasizes the role of the mask. Four experiments showed that the amount of observed learning depends on the structural and temporal homogeneity or heterogeneity of the mask. The authors suggest that learning consists of separating the task-relevant signal stemming from the texture from the task-irrelevant signal of the mask and of ignoring the mask.

Adult↗
PubMed1981

Backward masking by pattern stimulus offset.

The backward masking effects of the offset of a pattern stimulus on the apparent contrast of a target stimulus were determined to be a function of target onset-mask offset asynchrony. With spatially overlapping stimuli and binocular viewing, a monotonic function similar to that characterizing early dark adaptation was obtained; with a dichoptically presented disk onset as target and a surrounding ring offset as mask, a typical U-shaped metacontrast effect as a function of target onset-mask offset asynchrony was obtained. These mask-offset effects are related to the possible roles of (a) peripheral "off" mechanisms and (b) central metacontrast mechanisms in terminating visual response persistence in sustained channels.

Discrimination Learning↗
PubMed2000

Negative priming from masked words: retrospective prime clarification of center-surround inhibition?

Masked repetition and semantic priming effects were examined in 2 experiments. In Experiment 1, a masked-prime lexical decision task followed a phase of detection, semantic, or repetition judgments about masked words. In Experiment 2 participants made speeded pronunciations to target words after they tried to identify masked primes, and the proportion of semantically and identically related prime-target pairs was varied. Center-surround theory CT. H. Carr & D. Dagenbach, 1990; D. Dagenbach, T. H. Carr, & A. Wilhelmsen, 1989) predicts positive repetition priming but negative semantic priming when people attempt, but fail, to extract the meanings of masked words. A retrospective prime-clarification account, in contrast, predicts that semantic and repetition priming effects will vary (being positive or negative) as a function of expectations about the prime-target relation. The data support a retrospective prime-clarification account, which, unlike center-surround theory, correctly predicted negative repetition priming effects.

Adolescent↗
PubMed2004

Decoupling stimulus duration from brightness in metacontrast masking: data and models.

A brief target that is visible when displayed alone can be rendered invisible by a trailing stimulus (metacontrast masking). It has been difficult to determine the temporal dynamics of masking to date because increments in stimulus duration have been invariably confounded with apparent brightness (Bloch's law). In the research reported here, stimulus luminance was adjusted to maintain constant brightness across all durations. Increasing target duration yielded classical U-shaped masking functions, whereas increasing mask duration yielded monotonic decreasing functions. These results are compared with predictions from 6 theoretical models, with the lateral inhibition model providing the best overall fit. It is tentatively suggested that different underlying mechanisms may mediate the U-shaped and monotonic functions obtained with increasing durations of target and mask, respectively.

Cerebral Cortex↗
PubMed2005

On the role of object representations in substitution masking.

Three experiments were conducted to investigate the role of object representations in object substitution masking (OSM). OSM occurs when a very sparse mask is presented simultaneously with a target stimulus and the target offsets first, leaving the mask to linger in the display for some time. Results confirm earlier claims that there is an isolatable object-level component to OSM and indicate that a target can be protected from OSM if, prior to offsetting, it can be represented as a distinct object from the mask. When the mask was presented as sliding past the target (Experiment 1), as jiggling independently of the target (Experiment 2), or in a different color from the target (Experiment 3), OSM was reduced or eliminated. This suggests that OSM reflects basic updating processes that allow the perception of continuity of object identity over change.

Humans↗
PubMed2001

Cortical brain regions engaged by masked emotional faces in adolescents and adults: an fMRI study.

Face-emotion processing has shown signs of developmental change during adolescence. Functional magnetic resonance imaging (fMRI) was used on 10 adolescents and 10 adults to contrast brain regions engaged by a masked emotional-face task (viewing a fixation cross and a series of masked happy and masked fearful faces), while blood oxygen level dependent signal was monitored by a 1.5-T MRI scanner. Brain regions differentially engaged in the 2 age groups were mapped by using statistical parametric mapping. Summed across groups, the contrast of masked face versus fixation-cross viewing generated activations in occipital-temporal regions previously activated in passive face-viewing tasks. Adolescents showed higher maxima for activations in posterior association cortex for 3 of the 4 statistical contrasts. Adolescents and adults differed in the degree to which posterior hemisphere brain areas were engaged by viewing masked facial displays of emotion.

Adolescent↗
PubMed2001

Cerebral mechanisms of word masking and unconscious repetition priming.

We used functional magnetic resonance imaging (fMRI) and event-related potentials (ERPs) to visualize the cerebral processing of unseen masked words. Within the areas associated with conscious reading, masked words activated left extrastriate, fusiform and precentral areas. Furthermore, masked words reduced the amount of activation evoked by a subsequent conscious presentation of the same word. In the left fusiform gyrus, this repetition suppression phenomenon was independent of whether the prime and target shared the same case, indicating that case-independent information about letter strings was extracted unconsciously. In comparison to an unmasked situation, however, the activation evoked by masked words was drastically reduced and was undetectable in prefrontal and parietal areas, correlating with participants' inability to report the masked words.

Adult↗
PubMed1999

Clinical masking in speech audiometry: a simplified approach.

The optimal masking level during speech audiometry is one that falls above the minimum and below the maximum masking levels. The goal is to select a masking level that falls at the middle of the masking plateau. This article presents a simplified approach to selecting an appropriate level of contralateral masking during suprathreshold speech audiometry. The underlying theoretical concepts and prerequisite conditions are reviewed. The advantages of insert earphones when using the simplified approach are discussed.

Adult↗
PubMed1976

The use of auditory masking to estimate automatization of correct articulatory production.

In order to estimate automatization of correct articulatory production in 71 elementary school children about to be dismissed from training, auditory masking was used during administration of the Deep Test of Articulation. White noise was presented binaurally at 86 dB SPL. The children's articulation was tested under three conditions: Condition I without masking, Condition II with masking, and Condition III without masking three to four months after Condition II testing. Children's performances on Conditions I and II were compared with their performances during Condition III. Results demonstrated that performance on the Deep Test during auditory masking as a criterion for dismissal would have resulted in children being correctly dismissed from therapy more of the time (94%) than the traditional (nonmasked) administration of the test (77%). In addition, use of experimental administration of the test would have resulted in 6% of the children being incorrectly dismissed from therapy while traditional administration would have resulted in 23% of the children being incorrectly dismissed. Clinical importance and implications for further investigation are discussed.

Auditory Perception↗
PubMed1976

The influence of selected masking noises on Lombard and sidetone amplification effects.

The present experiments were designed to test the notion that the Lombard and sidetone amplification effects are related to the masking ability of a presented background noise. In Experiment 1, eight normal-hearing college students spoke in quiet and while listening to five frequency bands of noise which were equated for intensity but differed in ability to interfere with speech intelligibility. Vocal intensity increased as the frequency band, and thus the masking ability of the noise increased. In Experiment 2, eight additional students spoke in quiet and while listening to four of the frequency bands of noise used in Experiment 1. The noises were equated for loudness rather than intensity. Again, vocal intensity increased as the masking ability of the noise increased. In Experiment 3, 20 additional students spoke while listening to 0 and 20 dB of sidetone amplification mixed with three of the noise bands from Experiment 1. The noises were equated for intensity and mixed with sidetone. The sidetone amplification effect increased as the masking ability of the noise increased. The results of these experiments indicate that interference with speech intelligibility is directly related to elicitation of the Lombard and sidetone amplification effects. The loudness or intensity of a noise has little control over vocal intensity independent of the contribution to masking of speech.

Auditory Perception↗
PubMed1980

Two-tone forward masking patterns and tinnitus.

Forward masking is the masking of a signal by a preceding masker. For normal observers, if two tones are employed as the forward masker, the addition of the second tone (which increases the masker energy) may make the signal easier to hear. This decrease in the masking effect (or unmasking) has been interpreted as evidence for lateral suppression in hearing. For five subjects with tinnitus, all of whom have a sensorineural loss caused by noise trauma or noise exposure, there is no unmasking for (at least) one signal frequency in the region of the tinnitus. However, unmasking does occur for (at least) one signal frequency in the region without tinnitus. The frequency region of the tinnitus is inferred from pitch matches and from determination of the frequency region of the noise needed to mask it. For comparison, data from three normal subjects also are included. For the subjects with tinnitus, two-tone forward masking patterns are decidedly different in the normal and the tinnitus regions.

Audiometry↗
PubMed1982

Visual backward masking of selected visemes.

Five adult subjects with normal hearing and vision viewed tachistoscopically projected photographs of a talker uttering six phonemes. Experiment 1 determined discrimination of the visemes as a function of exposure duration (12-44 msec) and demonstrated that recognition of certain lip postures was a direct function of duration whereas for other postures duration appeared to interact with other variables. In Experiment 2, fixed duration stimuli (17 msec) were followed immediately by a variable duration masking stimulus (12-45 msec), and in Experiment 3 the test stimuli varied (22-52 msec) and the masking stimulus was fixed (45 msec). Results showed that under both conditions test stimuli were masked when the masker was at least as long as the test stimuli. In Experiment 4, the test stimuli and masking stimulus were held constant (15 msec and 45 msec, respectively) while a variable (7-37 msec) ISI was interposed. Delaying the masker did not improve recognition scores. Conclusions were (a) lip postures are subject to backward recognition masking and the effect varies in degree; (b) the processing of lip postures begins with a short-term storage of the posture; and (c) the initial stage of perceptual processing requires more than 37 msec. To the extent that this task parallels the speechreading process, the results would not support training procedures based at the level of single visemes.

Adolescent↗
PubMed1988

Babble and random-noise masking of speech in high and low context cue conditions.

"Perceptual" masking of speech by multitalker speech (babble) has been widely reported but poorly quantified. Furthermore, the validity of the construct of perceptual masking is questionable. This report describes an experiment using a newly standardized test of speech perception in noise (SPIN) with both babble and spectrally matched random-noise maskers. Classical psychophysical ogive curves were used to model speech recognition as a function of signal-to-noise ratio (S/N). The two maskers yielded speech recognition functions of the same steepness but different locations on the S/N axis. The high-context items of SPIN yielded speech recognition curves with steeper slope and different locations on the S/N axis than the low-context items. These data are used to argue that perceptual masking was not documented (under certain assumptions) and that the superior masking of babble may be explained in purely acoustical terms. Speculations are offered about the possible acoustical differences that could be responsible for the differences in masking effect.

Acoustics↗
PubMed1989

Auditory time constants for off-frequency forward masking in normal-hearing and hearing-impaired listeners.

Previous research has shown that frequency-specific estimates of auditory time constants for recovery from short-term adaptation can be made using a fixed-probe forward-masking procedure (Nelson & Freyman, 1987) if the masker and the probe stimuli are at the same frequency. This study examines the validity of time-constant estimates for off-frequency forward-masking conditions in which the masker frequency is below (900 Hz) or above (1100 Hz) the probe frequency (1000 Hz). Fixed-probe-level temporal masking functions were obtained from four normal-hearing and four hearing-impaired listeners. Auditory time constants were estimated with iterative least-squares procedures to derive parameter values for an exponential model of recovery from forward masking. After appropriate corrections were made for attenuation to the maskers provided by the auditory filter centered at the probe frequency, recovery from forward masking produced by either off-frequency or on-frequency maskers could be described by a single time constant. That time constant was around 50 ms in normal-hearing listeners and was larger in those hearing-impaired listeners who demonstrated moderate hearing loss at the probe frequency.

Auditory Fatigue↗
PubMed1998

Pre-oxygenation using face mask or mouthpiece with and without nose clip: patient preferences and efficacy.

We assessed the effectiveness of mouthpieces for oxygenation before induction of anaesthesia. In part 1 of the study we asked 52 day case patients whether they would prefer mask, mouthpiece, or mouthpiece with nose clip, and which they would be willing to use. In part 2 we pre-oxygenated 18 volunteers using each of the three methods in a crossover study. We measured time to 90% end tidal oxygen concentration (FE'O2), or maximum FE'O2 after 3 min if less than 90%. Of the patients surveyed, 20 (39%) preferred mask, 23 (44%) mouthpiece, one mouthpiece with nose clip and nine (17%) expressed no preference. Only 88% would be willing to use the face mask, but all would accept either the face mask or the mouthpiece with nose clip. In part 2 of the study, the mouthpiece alone proved significantly worse than the mask or mouthpiece with nose clip. The latter two did not differ significantly. Offering the alternative of mouthpiece with nose clip would increase patient acceptance of effective pre-oxygenation.

Adolescent↗
PubMed1998

An evaluation of the factors influencing selection of the optimal size of laryngeal mask airway in normal adults.

The purpose of this randomised single blinded study was to determine the optimal size of laryngeal mask airway in the normal adult population, to test the validity of the current selection criteria and to determine if any externally measured anatomical variable correlated with optimal size. In each of 30 apnoeic anaesthetised adults weighting less than 100 kg, size 3, 4 and 5 laryngeal mask airways were inserted in random order by a skilled user and the cuff inflated to a standard pressure (60 cm H2O). Optimal size was based on four criteria in order of priority: number of attempts at placement, oropharyngeal leak pressure, fiberoptic score and percentage of vocal cords seen. The size 5 laryngeal mask airway was optimal in 19/30 and the size 4 in 11/30. In no patient was the size 3 the optimal fit. Oropharyngeal leak pressure was significantly higher for each progressively large size and the fiberoptic view was significantly better for the size 4 and size 5. There was no significant predictive value in any externally measured anatomical variable, but height was the most useful. The best current selection strategy was to choose a size 5 for males and size 4 for females. Potentially useful new strategies may be to use the size 5 in all adults, or a size 5 > or = 165 cm in height and size 4 for < 165 cm. We conclude that predicting the optimal size of laryngeal mask airway for individual adult patients is complex. The best size selection strategies involve use of the size 4 and 5 laryngeal mask airways in adults.

Adolescent↗
PubMed1998

The intubating laryngeal mask. Clinical appraisal of ventilation and blind tracheal intubation in 110 patients.

This study assesses the efficacy of the intubating laryngeal mask as a ventilation device and blind intubation guide. Following induction of anaesthesia with propofol, the device was successfully inserted at the first attempt in 110/110 (100%) patients. Placement took less than 10 s in all patients. Size selection was based on nose-chin distance. Adequate ventilation was achieved in 104/110 (95%) patients. Blind tracheal intubation using an 8-mm internal diameter straight silicone cuffed tracheal tube was attempted 3 min after the administration of vecuronium. Passage of a lighted stylet through the intubating laryngeal mask was used to determine the position of the intubating laryngeal mask cuff before blind intubation. If resistance was felt during intubation, a sequence of adjusting manoeuvres was used, based on the depth at which resistance occurred. Tracheal intubation was possible in 104/104 (100%) patients. In 42 (40%) patients, no resistance was encountered and the trachea was intubated at the first attempt. Sixty-two (60%) patients required one adjusting manoeuvre. The mean (range) time taken to successful intubation, i.e. the time from disconnection of the intubating laryngeal mask from the breathing system to successful tracheal intubation, was 79 (12-315) s. Six patients with potential or known intubation problems were included in the study. The tracheas of all six patients were successfully intubated. We conclude that the intubating laryngeal mask is an effective ventilation device and intubation guide with potential for use in patients who may present difficulty in tracheal intubation.

Adult↗