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PubMed1985

On the effect of cross-hearing and clinical masking on the auditory brain-stem evoked response.

The effects of cross-hearing from the non-test ear were examined during the acquisition of the auditory brain-stem evoked response (ABR). Effective masking levels were derived from a normal hearing subject and the results used to obtain masked versus unmasked ABR thresholds in varying types of unilateral hearing loss. The results indicate that in the presence of a hearing loss adequate masking of the non-test ear is essential for valid ABR results.

Acoustic Stimulation↗
PubMed1978

A note on simultaneous and interleaved masking.

Speech and noise were switched periodically from ear to ear at a rate high enough to create a binaurally fused image. Two masking conditions were investigated. In one the speech and noise were switched in unison from ear to ear such that both speech and noise were presented simultaneoully to the same ear. In the other case, the speech and noise were interleaved such that there was no simultaneous overlap of the speech and noise at any one ear. The difference in masking levels between these two conditions was found to be on the order of 20 dB. The technique offers some interesting possibilities for investigating the relative effects of central and peripheral masking in both normal and hearing-impaired listeners.

Acoustic Stimulation↗
PubMed1978

Using competing speech to estimate articulatory automatization in children: the possible effect of masking level and subject grade.

In order to study the possible influence of masking level and subject grade on a procedure for determining a child's articulatory automatization (Manning et al., 1976) 47 first and second grade and 49 third and fourth grade children were administered the McDonald Deep Test of Articulation under one of five conditions of auditory masking (earphones only, or presentation of competing speech at 50, 60, 70, or 80 dB SPL). Results indicated no significant difference in subject performance across the factors of masking level and subject grade. The findings suggest that these factors do not appear to be critical in the clinical application of the suggested procedure for estimating children's automatization of newly acquired phonemes.

Age Factors↗
PubMed1981

Attribution of psychological characteristics from masked and unmasked conversations.

A specific contribution of this study was the development of a procedure for separating the semantic and physical parameters of conversation. This procedure permits testing of the hypothesis that coverbal dimensions of conversation, that is, patterns of sounds and silence, convey information to independent listeners about the psychological states of speakers engaged in conversation. The masking procedure destroyed intelligibility of the conversation, but not the sequences of sounds and silences. Listeners rated speakers on three dimensions--warmth, anxiety, and dominance--under two conditions--masked and unmasked. Significant correlations were found between the ratings under both masked and unmasked conditions and between the ratings and a number of physical parameters of speech.

Affect↗
PubMed1980

Dust in dental laboratories. Part III: Efficiency of ventilation systems and face masks.

The efficiency of local and electrostatic ventilation systems installed in dental laboratories has been measured. With local exhaust systems, dust amounts could be reduced in breathing air close to the emission source to levels lower than threshold limit values for various elements or compounds in dust produced through cutting, grinding, or polishing various dental materials such as chromium-cobalt, nickel, or gold alloys, porcelain, gypsum models, or denture base material. However, the local exhaust system did not enable a dust reduction from handling amalgam dies consistent with criteria of threshold limit values for mercury and silver. The efficiency of electrostatic filters installed in dental laboratories for general ventilation purposes was found to range from 37% to 73% based on weight reduction. Various ventilation systems with bag filters possessing a high efficiency based on weight reductions allowed small, respirable particles less than 5 micrometers to recirculate within the working environment. The efficiency of face masks for the reduction of inhaled dust revealed efficiencies for two commercial masks ranging from 70% to 95% based on weight reduction. However, such masks only partly retained the respirable dust.

Air Movements↗
PubMed1982

Low spatial-frequency channels in human vision: adaptation and masking.

Previous work showed that adapting to low spatial frequency gratings (below 1.5 cycles/degree) may cause maximal spatial adaptation at a significantly higher spatial frequency. It has been suggested that there are no adaptable spatial-frequency channels tuned to below 1.5 c/deg. Contrary to this view, we found that adaptation and masking with low spatial frequencies (0.12-1.0 c/deg) produced maximal threshold elevations when the test patterns were the same spatial frequency as the adapting or masking pattern. These results were obtained using test patterns that turned on and off gradually or sharply. The results suggest that there are form mechanisms optimally sensitive to very low spatial frequencies. Adaptation was selective to position (phase) and orientation at low spatial frequencies; masking was observed to be selective to orientation at a spatial frequency as low as 0.2 c/deg. A clear dichotomy between transient, motion channels and sustained, form channels at low spatial and temporal frequencies may represent an unrealistic simplification. There may exist directionally-selective motion mechanisms sensitive to very slow motion, and these may play a role in the discrimination of form. The discussion considers the bandwidths of the low spatial frequency mechanisms.

Adaptation, Ocular↗
PubMed1985

Eccentricity dependence of contrast matching and oblique masking.

Recently a model of spatial vision was derived by fitting foveal masking data. This model is composed of a small number of medium bandwidth mechanisms, each composed of a spatial filter followed by a compressive nonlinearity. The present study incorporates eccentricity variation into this model by scaling the peak frequency (but not the shape) of the spatial filters with eccentricity. Predictions of this scaled model were compared with both oblique masking data and contrast matching data gathered at peripheral locations and were found to produce good fits. Therefore, the mode of analysis that was used for foveal masking data is also applicable peripherally once the scaling factor is applied.

Fixation, Ocular↗
PubMed1988

Time course of the subjective contrast enhancement for a second stimulus in successively paired above-threshold transient forms: perceptual retouch instead of forward masking.

Subjects estimated apparent contrast of an invariant test stimulus (the letter H), exposed either after an inducing stimulus (from the set of 12 alternatives) with SOAs varying from 20 to 290 msec, or alone (a control condition). With inducing stimuli, at certain SOAs the subjective contrast of the TS was enhanced relative to single-stimulus control. This enhancement appeared as a curvilinear function of SOA with the most pronounced enhancement at SOA = 110 msec. The effect was present also if the Ss had to recognize the inducing, backward-masked stimulus (the recognition function being U-shaped). The enhancement effect increased with increase in the intensity-level of the inducer. The separate functions for the conditions of inducing letters of high and low figural similarity with TS were coinciding, thus pointing to the nonspecific nature of the obtained effect within the given spatial constraints (1 deg of the visual angle). A small forward masking effect present with SOAs less than or equal to 40 msec was rapidly replaced by the enhancement with increase in SOA. The results are discussed in terms of the visual masking theories and the hypothetical perceptual retouch mechanism.

Adult↗
PubMed1991

Different effects from spatial frequency masking in texture segregation and texton detection tasks.

The paper reports psychophysical experiments set up to study the visual cues used in texture discrimination. In particular, the special role of "textons", i.e. distinct visual features such as blobs of different size, lines at different orientation, line intersections ("crossings") and line ends ("terminators") which have been proposed to provide the basis of perceptual segregation of texture areas, has been investigated. Texture pairs were briefly presented and simultaneously masked with two-dimensional visual noise at various spatial frequency bands. In different tasks on similar patterns, observers had to estimate the orientation of globally dissecting texture areas ("texture segregation") and to identify and distinguish the texture elements themselves ("texton detection"). Differential masking effects between these tasks indicate that texture segregation is often based on visual cues different from the supposed texton features. The segregation of crossing or terminator differences is also achieved from associated differences in the spatial frequency composition, that of differences in blob size from associated differences in mean luminance. Only differences in line orientation revealed similar masking curves in texture segregation and texton detection tasks.

Adult↗
PubMed1991

Nonadditivity of masking by narrow-band noises.

Characterization of the visual system as a linear system has many consequences. One property implied by such a characterization is that signal-to-noise ratio at threshold is constant, so that the contrast energy of a sinusoidal grating at threshold depends on the effective noise passed by the filter used to detect the target. When the contrast energy in an external noise is sufficiently high, the contribution of internal noise may be conveniently ignored. In such circumstances, the effectiveness of a given noise is measured by its ability to mask the target. One consequence of the linearity assumption is that if the energy of the effective noise is increased by a factor k, then threshold energy of the signal is increased by the same amount. The contrast energy at threshold in the presence of a masker created by adding two maskers should be the sum of the threshold energies in the individual maskers. We have tested this hypothesis for spectrally nonoverlapping maskers. We find that the contrast energy required to detect the target in the presence of the combined maskers is much greater than the sum of the threshold energies for the two maskers. This "excess masking" violates the linearity assumption. On the other hand, when maskers do have spectral overlap, no excess masking is found.

Contrast Sensitivity↗
PubMed1993

An orientation-tuned component in the contrast masking of stereopsis.

A masking paradigm was used to evaluate the orientation selectivity of the mechanisms mediating human stereopsis. Two experienced and eleven naive observers viewed stereograms, spatially filtered to contain contrast energy with Gaussian passbands in spatial frequency and orientation. Using forced-choice procedures we measured contrast thresholds for stereopsis in the presence of oriented masking patterns. Our results show that the masking of stereopsis consists of two components: one is orientation dependent, the other is non-oriented and has greatest magnitude at lower spatial frequencies. Contrary to an earlier study, these results imply that stereopsis mechanisms may have similar orientation tuning to mechanisms mediating contrast detection.

Depth Perception↗
PubMed1996

Masking of spatial frequency in visual memory depends on distal, not retinal, frequency.

Spatial frequency discrimination thresholds measured in a two-interval forced choice paradigm are virtually constant across inter-stimulus intervals ranging from 400 to 30,000 msec, demonstrating that an accurate representation of spatial frequency is maintained in short-term memory. This representation can be degraded by briefly flashing a grating during the retention interval. Moreover, this memory masking effect varies with the spatial frequency of the mask, suggesting that the mechanisms used to store spatial frequency in memory are similar to low-level visual filters. In this paper we replicate those previous findings and extend them by showing (1) that accurate memory for spatial frequency lasts as long as 1 min; (2) that memory masking is based on distal (c/cm), not retinal (c/deg), spatial frequency.

Differential Threshold↗
PubMed1996

Masking of the achromatic system: implications for saccadic suppression.

Brief (10 msec) increments, presented on a white adapting background, are known to elicit a spectral sensitivity function with a broad mid-spectral peak (King-Smith & Carden, 1976). We have found that a luminance decrement, presented as either a forward or backward mask, dramatically alters the form of the resultant sensitivity function: the broad mid-spectral peak is replaced by a color-opponent function with narrow peaks at 520 and 620 nm. Over the region of the spectrum where this change in shape occurs, there is a substantial reduction in sensitivity. We also find that the mask is more effective when it precedes the stimulus than when it follows it, and that the masking can be characterized as a type A effect. The implications of these data for mechanisms of saccadic suppression are discussed.

Adult↗
PubMed1991

Flexible laryngoscopy in neonates and infants: insertion through a median opening in the face mask.

The most common reasons for laryngoscopy in newborns and infants are inspiratory stridor and/or dyspnea. With the help of flexible endoscopes, especially with instruments of diminished diameter, laryngoscopy can be carried out even in premature newborns. We report on a technique of flexible laryngoscopy without the need for restraint and with improved safety. A modified face mask is used for endoscopy. An additional hole is made into the mask with a 4.5 mm drill. It is located in the midline just above the nostrils, about 2.5 cm above the ventilation opening. The flexible endoscope is passed into the nose and pharynx with ease. It does not interfere with the anesthetist's ventilation by the mask. In inhalation anesthesia with halothane, 100% oxygen is supplied. The larynx remains in its physiological position. The head is not retroflexed, and the tongue is not supported by an endoscope as in direct laryngoscopy. No muscle relaxation is used, and muscular activity of the larynx can be observed during spontaneous and assisted ventilation.

Anesthesia, Inhalation↗
PubMed1980

Forward and backward auditory masking in the parakeet (Melopsittacus undulatus).

Backward, foward and simultaneous masking of brief tone pulses was examined in four parakeets. The pattern of non-simultaneous masking in parakeets is quite similar to that observed in humans with rates of threshold recovery faster for backward compared to forward masking conditions. These results may have relevance for the design of vocal signals and the coding of species-specific information in parakeets.

Animals↗
PubMed1982

Intensity coding in the auditory periphery of the cat: responses of cochlear nerve and cochlear nucleus neurons to signals in the presence of bandstop masking noise.

The dynamic range over which fine intensity discrimination is possible has been reported to be largely unaffected by limitation of the spread of neuronal activity to neighbouring frequency regions by bandstop noise masking. We have therefore examined the responses of cochlear nerve and nucleus neurons to tone and noise signals in the presence of a bandstop masking noise designed to be comparable to that employed in the psychophysical experiments. Under these conditions, the vast majority of cochlear nerve fibres were saturated by sound levels at which some 50% of our sample of cochlear nucleus neurons still responded to signal level differences. The extended dynamic ranges of these cochlear nucleus neurons was shown to be a result of activation, by the masking noise, of the lateral inhibitory side-bands 'biassing' the neuron's discharge. A small proportion of cochlear fibres, having low spontaneous discharge rates and showing strong two-tone suppression effects, demonstrated analogous but not so pronounced effects. It is unclear in what form information on the level of stimuli under these conditions is transmitted by the majority of apparently saturated cochlear nerve fibres, but several possible mechanisms are discussed.

Animals↗
PubMed1984

Measurement of the combination tone 2f1-f2 using two-tone forward masking and compound action potential responses.

The presence of the 2f1-f2 combination distortion tone generated when two tones are presented to the cochlea, can be detected using a two-tone complex to forward mask a probe tone. The combination tone is the effective masking agent and the amplitude of the compound action potential response to the probe tone reflects the degree of masking. Excitation patterns, frequency relationships and intensity functions that are obtained with this procedure are consistent with previously published data.

Action Potentials↗
PubMed1984

Binaural masking-level difference as a function of masker and test-signal duration.

The binaural masking-level difference (BMLD) is measured as a function of duration of the masker (uniform masking noise) and of the test tone (400 and 800 Hz). Four observers used a Békésy tracking method which proved to be a time-saving procedure for BMLD measurements. Although the masked threshold depends on the test-tone duration, the BMLD does not. The latter, however, increases from about 5 to 10 dB as the masker duration increases from 10 to 200 ms.

Auditory Threshold↗