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At least 631 records · Page 35Linked to original sources
PubMed2006

Attentional modulation of unconscious "automatic" processes: evidence from event-related potentials in a masked priming paradigm.

Automatic processes are usually thought to occur independently of any cognitive resources. This traditional view has been recently challenged by showing that temporal attention to a target stimulus is a prerequisite for "automatic" response priming. The event-related potential (ERP) study reported here extends this research by pursuing a somewhat different approach. In two experiments, it was investigated whether masked semantic priming effects can be modulated by temporal attention to the prime using a cueing procedure. We hypothesized that masked priming is amplified when attention is directed to the stimulus stream in the time window of masked prime presentation, even in the absence of any prime awareness. ERPs were recorded while subjects performed a primed lexical decision task. Target words were preceded by semantically related or unrelated masked prime words, which were not consciously identified. A cue stimulus prompted subjects to direct their attention to the stimulus stream either shortly before the masked prime (short cue interval) or a long time interval before. Priming affected the amplitude of the N400 ERP component, an electrophysiological index of semantic processing. Unrelated prime-target pairs elicited a larger N400 than related pairs (N400 priming effect). Most importantly, this masked N400 priming effect was strongest when the cue interval and the stimulus onset asynchronies were short. The present results show that temporal attention to the prime is a prerequisite for obtaining masked N400 priming effects. They also demonstrate that unconscious automatic processes are susceptible to attentional modulation.

Adolescent↗
PubMed2005

The dynamics of visual pattern masking in natural scene processing: a magnetoencephalography study.

We investigated the dynamics of natural scene processing and mechanisms of pattern masking in a scene-recognition task. Psychophysical recognition performance and the magnetoencephalogram (MEG) were recorded simultaneously. Photographs of natural scenes were briefly displayed and in the masked condition immediately followed by a pattern mask. Viewing the scenes without masking elicited a transient occipital activation that started approximately 70 ms after the pattern onset, peaked at 110 ms, and ended after 170 ms. When a mask followed the target an additional transient could be reliably identified in the MEG traces. We assessed psychophysical performance levels at different latencies of this transient. Recognition rates were reduced only when the additional activation produced by the pattern mask overlapped with the initial 170 ms of occipital activation from the target. Our results are commensurate with an early cortical locus of pattern masking and indicate that 90 ms of undistorted cortical processing is necessary to reliably recognize a scene. Our data also indicate that as little as 20 ms of undistorted processing is sufficient for above-chance discrimination of a scene from a distracter.

Brain Mapping↗
PubMed1996

Backward-masking deficit in adolescents with schizophrenic disorders or attention deficit hyperactivity disorder.

OBJECTIVE: Backward masking is a cognitive task that involves the earliest phases of visual information processing. Disrupted task performance caused by a visual mask has been found repeatedly in schizophrenic patients; however, the specificity to schizophrenia of deficits in backward masking has received only limited study. METHOD: In this study 20 patients with early-onset schizophrenic disorders were compared to 20 adolescents with attention deficit hyperactivity disorder (ADHD) and 30 normal adolescents on a two-digit identification task in three backward-masking conditions: no mask, a short stimulus interval (33.0 msec), and a long stimulus interval (49.5 msec). RESULTS: The performance of the two groups of patients was similar, and both groups showed a statistically significant masking deficit after the long stimulus interval and a nearly significant deficit after the short stimulus interval in comparison with the normal subjects. CONCLUSIONS: Increased vulnerability to the masking stimulus was confirmed in schizophrenic subjects, but it is not specific to schizophrenia and is not accounted for by psychotic symptoms alone, since the subjects with ADHD performed similarly.

Adolescent↗
PubMed2001

Do anaesthetists need to wear surgical masks in the operating theatre? A literature review with evidence-based recommendations.

Many operating theatre staff believe that the surgical face mask protects the healthcare worker from potentially hazardous biological infections. A questionnaire-based survey, undertaken by Leyland' in 1993 to assess attitudes to the use of masks, showed that 20% of surgeons discarded surgical masks for endoscopic work. Less than 50% did not wear the mask as recommended by the Medical Research Council. Equal numbers of surgeons wore the mask in the belief they were protecting themselves and the patient, with 20% of these admitting that tradition was the only reason for wearing them. Policies relating to the wearing of surgical masks by operating theatre staff are varied. This indicates some confusion about the role of the surgical mask in modern surgical and anaesthetic practice. This review was undertaken to collate current evidence and make recommendations based on this evidence.

Anesthesiology↗
PubMed2001

How should airways resistance be measured in young children: mask or mouthpiece?

The reproducibility and acceptability of airways resistance measurements using the interrupter technique (MicroRint) obtained using a mouthpiece were compared with those using a face mask. Fifty children aged 4-7 yrs performed four sets of six Rint measurements; two using a mouthpiece and two using a face mask with integral mouthpiece. Complete data were obtained from 45 (90%) children using the mouthpiece and 43 (86%) children using the mask. The two methods were equally repeatable with comparable intraclass correlation coefficients (ICC) and coefficients of variation. Mean Rint values obtained using the mouthpiece were significantly lower than those using the face mask ((mean+/-SD) mouthpiece=0.81+/-0.18 kPa x L(-1) x s, mask=0.88+/-0.24 kPa x L(-1) x s p=0.0002). Although the mean paired differences between the two methods were small (0.07 kPa x L(-1) x s), the ICC and limits of agreement confirmed that the two methods could not be used interchangeably. Sixty-seven per cent of children preferred the face mask but this was more time-consuming (p = 0.03). Children did not produce more repeatable results using their preferred method, nor did they improve with practice. Repeatable airway resistance measurements using the interrupter technique can be obtained from young children using either a mouthpiece or a face mask, but there are significant clinical and statistical differences between the results obtained.

Child↗
PubMed2004

Dynamic dead space in face masks used with noninvasive ventilators: a lung model study.

The aim of this study was to determine what the influence of different designs of face masks and different noninvasive ventilator modes would be upon total dynamic dead space. Using a spontaneous breathing model, total dynamic dead space was measured when using 19 commercially available face masks and a range of ventilators in various ventilation modes. Total dynamic dead space during spontaneous ventilation was increased above physiological dead space from 32% to 42% of tidal volume by using face masks. The use of noninvasive ventilation modes such as bilevel and continuous positive airway pressure, with continuous pressure throughout the expiratory phase, reduced total dynamic dead space to approach physiological dead space with most face masks. Pressure assist and pressure support ventilation decreased total dynamic dead space to a lesser degree, from 42% to 39% of tidal volume. Face masks with expiratory ports over the nasal bridge resulted in beneficial flow characteristics within the face mask and nasal cavity, so as to decrease total dynamic dead space to less than physiological dead space from 42% to 28.5% of tidal volume. Exhaust ports over the nasal bridge in face masks effect important decreases in dynamic dead space provided positive pressure throughout the expiratory phase is used.

Equipment Design↗
PubMed1999

A simple new technique to measure the effective dead space of the face mask with a water volumeter in infants.

Measuring the effective dead space (EDS) of a face mask has been difficult in infants and the appropriate volume being deducted from lung volume measurements has varied between laboratories. This study measured EDS in 16 infants (age range, 5-36 months) who have cystic fibrosis, undergoing lung volume measurement by N2 washout. A thin plastic bladder, whose neck resided in the mask port, was shaped to fill a size 1 clear face mask. A water volumeter was made by inserting the body of a 20 mL plastic syringe into the neck of the bladder forming a tight seal with a snug fit against the inner surface of the mask port. The mask was placed on a horizontal surface and water was added until a level appeared in the syringe body (V1). At end-inspiration, the mask was briefly placed on the mouth and nose of the sleeping infant, causing the water level to rise in the syringe body (V2). The actual total dead space (V) of the mask when connected to the mouth port of the slide valve was 23 mL. EDS = V- (V2 - V1). Mean (95% confidence interval (95%CI)) EDS was 12.4 (95% CI 11.2, 13.6) mL. The smallest EDS was 8 mL since the connected ports (dead space, 8 mL) were unlikely to be penetrated by the infant's nose or lips. EDS decreased with increasing body weight and height, but seemed to be influenced by individual facial features too. In conclusion, a reliable noninvasive volumetric technique for the routine measurement of the effective dead space in infants has been developed.

Cystic Fibrosis↗
PubMed1997

Postreceptoral chromatic detection mechanisms revealed by noise masking in three-dimensional cone contrast space.

We used a noise masking technique to test the hypothesis that detection is subserved by only two chromatic postreceptoral mechanisms (red-green and blue-yellow) and one achromatic (luminance) mechanism. The task was to detect a 1-c/deg Gaussian enveloped grating presented in a mask of static, spatially low-passed binary or Gaussian distributed noise. In the main experiment, the direction of the test stimulus (termed the signal) was constant in cone contrast space, and the direction of the noise was sampled in equally spaced directions within a plane (the noise plane) in the space. The signal was chosen to coincide with one of the three cardinal directions of three postulated mechanisms. The noise plane was selected to span two of the cardinal directions, including that chosen as the signal direction. As the noise direction was sampled around the noise plane, the signal detection threshold was found to vary in accordance with a linear cosine model, which predicted noise directions yielding maximum and minimum masking of the signal. In the direction of minimum masking (termed a null direction), the noise was found to have no masking effect on the signal. Moreover, the null was not orthogonal to the signal direction but lay instead in one of the cardinal directions. Our findings suggest that detection is mediated by only three mechanisms. In a further experiment we found little or no cross masking between each pair of cardinal directions up to the limit of our noise mask contrasts. This further supports the presence of no more than three independent postreceptoral mechanisms.

Artifacts↗
PubMed1990

Visual masking at different polar angles in the two-dimensional Fourier plane.

Human contrast thresholds were measured at 86 points in the two-dimensional Fourier plane with and without masks. The test stimuli were sinusoidal gratings in a 2.55-deg circular field. The superimposed masks were sinusoidal gratings having a polar spatial frequency of 8 cycles/deg, a contrast of 0.31, and one of five polar angles: 90, 105, 120, 135, and 180 deg. The test grating contrast for 75.5% correct detection in a three-alternative, forced-choice paradigm was determined by a maximum-likelihood adaptive psychophysical procedure. Three other observers were tested on subsets of these conditions. The threshold elevation surfaces produced by the masks lead to the following conclusions: spatial-frequency bandwidth is independent of mask orientation and has a value of approximately 2 octaves, orientation bandwidth is wider for oblique masks than for horizontal and vertical masks, the principle of spectral polar separability is violated, and two-dimensional Gabor functions in the frequency domain account for the masking effects. Individual differences were found among the observers.

Adult↗
PubMed1980

Loudness summation across frequency under masking and in sensorineural hearing loss.

The loudness summation across frequency was measured in unmasked and masked normally hearing subects, using noise bands centered at 1 kHz. Homolateral masking reduced the loudness summation of supracritical noise bands to a degree roughly proportional to the degree of threshold shift produced by the masking. Between thresholds and moderate sensation levels, the loudness summation increased at an invariable rate in the unmasked and the masked condition, reflected in an invariable supracritical growth of loudness with increasing stimulus bandwidth at identical sensation levels. At high intensities, the loudness summation decreased to roughly similar values in both conditions. Similar results were obtained by pooling the data from patients with sensorineural hearing losses and comparable threshold elevation. The critical bands appeared to be identical in unmasked and masked normally hearing subjects and in patients with sensorineural hearing losses. Contralateral, 35 dB effective masking produced a slight but consistent central masking effect; compared to the unmasked condition, the loudness summation of supracritical noise bands was reduced between threshold and medium stimulus levels, while it was increased at high levels.

Adolescent↗
PubMed1983

The masking of tinnitus with pure tones.

The tinnitus of 32 subjects was studied. The tinnitus in each subject was matched to tones and bands of noise. Tones were then used to determine masking curves. Four types of masking curves were found. These types are similar to those previously reported. The findings also supported previous studies where tinnitus masking curves were found to differ significantly from conventional masking curves. Audiometric curves were grouped according to severity of hearing loss in order to determine whether subjects with similar threshold curves had similar masking curves. Similarities were noted in only one group: those with the least hearing loss. The relation between masking curves and the success of masking therapy is discussed.

Audiometry↗
PubMed1990

Effects of contralateral masking on high-frequency bone-conduction thresholds.

The present study reports effects of contralateral masking on high-frequency threshold force levels in 28 normal-hearing subjects. High-frequency air- and bone-conduction thresholds were measured with a high-frequency auditory evaluation system using matched Koss HV/1A earphones and the Pracitronic KH 70/5 bone vibrator. Measurements were made for both unmasked and masked bone-conduction thresholds at the ipsilateral mastoid of the better ear. The contralateral masked condition was performed using 30-dB-SL 400-Hz narrow-band masking noise centered at frequency of test tone. The results demonstrated that masked high-frequency bone-conduction thresholds were 1.5 to 3.4 dB poorer than the unmasked thresholds and that these differences were statistically significant at 0.01 level of confidence except at 12 kHz. ANSI and ISO standards for bone-conduction threshold force levels for frequencies below 8.0 kHz have been established with contralateral masking stimuli. This study supports the need to use effective contralateral masking to eliminate cross hearing in investigations of high-frequency bone-conduction threshold measurements.

Adult↗
PubMed1992

High-frequency audiometry. Masking in electric bone-conduction audiometry.

Recently, the 'electric bone-conduction' (EBC) audiometer (Audimax 500) has been used to measure high-frequency (HF) hearing. With this audiometer stimulation is binaural. No commercial masking method was available. In this study, white noise from a Madsen OB822 audiometer and presented via Sony MDR-V4 dynamic earphones, was used for masking. The masking and cross-hearing effect was measured in 8 unilaterally deaf subjects and the masking procedure was tested with 104 young normal-hearing subjects. The results showed that the EBC signals can be masked with air-conduction signals, and thus, the EBC measurements reflect monaural thresholds. The minimum masking level was 50-60 dB SPL in the HF range. There were no cross-hearing problems in the HF range with the earphones used. At the frequencies 0.5-14 kHz, the better ear's masked EBC thresholds were on the average 2.6 dB (range 0-4.5 dB) poorer, compared with the binaural EBC thresholds, indicating a binaural summation effect.

Acoustic Stimulation↗
PubMed1983

The effects of contralateral masking upon brainstem electric responses.

Brainstem electric responses (BSER) were recorded simultaneously to give records which were ipsilateral and contralateral to the test ear. Eight normally hearing subjects were presented with a fixed stimulus level in one ear and various levels of masking in the other ear. Responses to binaural stimulation were also recorded. It appears from the analysis of results that, for normal subjects, contralateral masking has no statistically significant effect upon the BSER. For the responses obtained from the stimulated side the analyses of variance showed a significant subject effect but no significant masking level effect from 0 to 80 dB Sensation Level of masking. For the responses obtained from the masked side the same conclusions seem to apply. As contralateral masking has no adverse effect upon the BSER in normal subjects and has had considerable use on clinical patients, with no significant problem, the normal audiometric use of masking is recommended for BSER recording.

Adult↗
PubMed1990

Spatial features of vibrotactile masking effects on airpuff-elicited sensations in the human hand.

It was recently shown that the cutaneous sensitivity to airpuffs is decreased by a low-frequency vibrotactile masker in the hairy skin, and by a low-frequency but especially by a high-frequency masker in the glabrous skin. In the current study, the spatial features of this masking effect were determined in four healthy human subjects, using a reaction time paradigm. The masking effect decreased monotonically with increasing interstimulus distance, and identically in longitudinal and transverse (i.e., lateral) directions in the palm or dorsal surface of the hand. The masking effect was stronger in the glabrous than in the hairy skin, especially in the fingers. In the glabrous skin, the spread of masking effect produced by a high-frequency masker was more extensive than that produced by a low-frequency masker. The mechanical spread of high-frequency vibration was less extensive than that of low-frequency vibration in the skin. In the glabrous skin, a masker applied to the tip of the finger produced a stronger masking effect on sensations in the base of the finger than when the masker was located at the base and the test stimulus was located at the tip. It is concluded that mechanical spread of vibration in the skin is of minor importance in explaining the masking effects. Different peripheral neural mechanisms underlie the airpuff-elicited sensations in the hairy and glabrous skin. The afferent inhibitory mechanisms are stronger for signals coming from the glabrous skin of the fingers than for signals coming from the hairy skin. Furthermore, the peripheral innervation density and size of the cortical representational areas may be of importance in determining the magnitude of the masking effect.

Adult↗
PubMed2006

Looking at object-substitution masking in depth and motion: toward a two-object theory of object substitution.

When attention is divided, a briefly presented target surrounded by four small dots is difficult to identify when the dots persist beyond target offset, but not when these dots terminate with the target. This object-substitution masking effect likely reflects processes at both the image level and the object level. At the image level, visual contours of the mask make feature extraction difficult. Recent data (Lleras & Moore, 2003) suggest that, at the object level, an object file is created for the target-plus-mask, and this single-object token later morphs into a single-object token containing the mask alone. In the present experiments, we used stimuli presented in 3-D space and apparent motion; the results indicate that object-substitution masking also arises when the mask and the target are represented in two separate object tokens and the mask token interferes with the target token.

Attention↗
PubMed2003

One factor underlies individual differences in auditory informational masking within and across age groups.

Masked threshold for a pure-tone signal can be substantially elevated whenever the listener is uncertain about the spectral or temporal properties of the masker, an effect referred to as auditory informational masking. Individual differences in the effect are large, with young children being most susceptible. When masker uncertainty is introduced by randomizing the frequencies of a multitone masker on each presentation, the function relating a child's pure-tone signal threshold to the number of masker components is found to be substantially elevated above that of most adults. The age effect and the individual differences among adults are not well understood, though a difference in the shapes of the masking functions suggests that different detection strategies may be involved. The present study reports results from a principal components analysis of informational masking functions obtained from 38 normal-hearing children ranging in age from 4 to 16 years and 46 normal-hearing adults ranging in age from 19 to 38 years. The premise underlying the analysis is that if different detection strategies are involved, they should add independent sources of variance to the masking functions. Hence, more than one principal component (PC) should be required to account for a substantial proportion of the variance in these functions. The results, instead, supported the operation of a single underlying strategy with all but 17% of the variance accounted for by the first PC within and across age groups. An analysis of variance on the first two PCs showed that only the first changed with age, and a cluster analysis of the masking functions showed complete separation of clusters along this PC for all but 1 listener. The results are taken to suggest that large individual differences informational masking at all ages reflect differences in the extent to which masker uncertainty adds variance to the decision variable of an otherwise optimal decision strategy.

Adolescent↗
PubMed1989

Unconscious processing of dichoptically masked words.

In three experiments, the subjects' task was to decide whether each of a series of words connoted something good (e.g., fame, comedy, rescue) or bad (stress, detest, malaria). One-half second before the presentation of each such target word, an evaluatively polarized priming word was presented briefly to the nondominant eye and was masked dichoptically by either the rapidly following (Experiment 1) or simultaneous (Experiments 2 and 3) presentation of a random letter-fragment pattern to the dominant eye. (The effectiveness of the masking procedure was demonstrated by the subjects' inability to discriminate the left vs. right position of a test series of words.) In all experiments, significant masked priming effects were obtained; evaluative decisions to congruent masked prime-target combinations (such as a positive masked prime followed by a positive target) were significantly faster than those to incongruent (e.g., negative prime/positive target) or noncongruent (e.g., neutral prime/positive target) combinations. Also, in two of the three experiments, when subjects were at chance accuracy in discriminating word position, their position judgments were nevertheless significantly influenced by the irrelevant semantic content (LEFT vs. RIGHT) of the masked position-varying words. The series of experiments demonstrated that two very different tasks--speeded judgment of evaluative meaning and nonspeeded judgment of word position--yielded statistically significant and replicable influences of the semantic content of apparently undetectable words. Coupled with previous research by others using the lexical decision task, these findings converge in establishing the reliability of the empirical phenomenon of semantic processing of words that are rendered undetectable by dichoptic pattern masking.

Adult↗