Peripheral Masking Research Articles

Discrimination of reproducible noise as a function of bandwidth and duration.

The discriminability of reproducible noise bursts was studied as a function of bandwidth and duration. Listeners discriminated between trials consisting of two identical noise waveforms or two independent noise waveforms. New noise waveforms were generated each trial. In general, discrimination improved with increasing bandwidth. However, discrimination improved with increasing duration only up to about 25 msec, beyond which it decreased. Additional experiments examined discriminability with (1) forward or backward maskers, which intervened or did not intervene temporally between the comparison stimuli, (2) two noise waveforms fixed over 50 or 300 trials, and (3) high- or low-frequency noise bands. Results suggested that the decrease in discriminability beyond 25 msec was due primarily to sensory interactions of a central origin but with some effect of peripheral masking, memory interference, and attentional limitations. Information at the offset was discriminated best, and low-frequency information was better discriminated than high-frequency information. The results also indicated that envelope cues were used in certain conditions.

Effects of high-contrast peripheral patterns on the detection threshold of sinusoidal targets.

Detection thresholds of sinusoidal gratings in the simultaneous presence of high-contrast peripheral masking stimuli partially overlapping the test gratings were determined as a function of the separation between the center of the test grating and the peripheral stimulus by a two-alternative forced-choice method. The results showed that the threshold-elevating effect of simultaneously present peripheral masking stimuli depends on how much of the test grating is left unexposed. An additional experiment, in which the detection thresholds in the absence of the peripheral stimulus were determined as a function of the number of cycles of the test grating, enabled us to show that the threshold-elevating effect is somewhat higher than the effect of simply cutting the test grating down in size. The threshold-elevating effects caused by high-contrast peripheral masking stimuli can be explained in terms of a lateral inhibition and a probability summation across space, taking into account the nonuniform sensitivity across the visual field.

Lateral masking vertically and horizontally

The greater effectiveness of peripheral over central masks was investigated in an experiment with 16 separate target-mask displays: a single mask letter above, to the left of, below, or to the right of a single target letter, and the pair of letters above, to the left of, below, and to the right of fixation. Close target-mask spacing was used, and the center points of the target-mask pairs were held constant. Peripheral masking was more effective than foveal masking in both the vertical and horizontal directions. Furthermore, masks on the same radius as the target (whether peripheral or central) were more effective than masks off that radius. The results were consistent with Wolford’s (1975) feature-perturbation model of visual masking.

Dichotic and Monotic Masking of CV Syllables by CV Second Formants with Different Steady-State Durations

Abstract Listeners were asked to identify 295-ms synthetic CVs (45-ms transitions + 250-ms steady states) in the presence of monotically or dichotically competing isolated second-formant ‘bleats’ from CVs. Bleat duration was varied, by cutting back the steady-state portions, from 295-ms total to a transition alone (45 ms). This temporal variation in the bleats was chosen to focus on the extent to which ‘nonphonetic’ structural characteristics of signals determine the presence and amount of interference. Dichotic identification varied as a continuous, monotonic function of bleat duration, with greatest interference observed with the largest steady-state value and least interference for no steady state (i.e., transition alone). In contrast, monotic identification was relatively poor and constant across duration values. These results, together with an analysis of errors, lead to the conclusion that monotic interference does not depend on signals’ steady-state durations; consistent with other peripheral masking studies, monotic results seem, instead, dependent upon which segments of two signals are simultaneous and whether these temporally overlapping parts have energy in similar frequency ranges. In contrast, dichotic interference does depend on steady-state duration. This suggests dichotic interference is a form of ‘central masking’ which occurs because of the disruption of processes concerned with specifying the overall time-by-frequency characteristics of signals, independent of their interpretation as phonetic events.

Some effects of spectral fusion and spectral‐temporal fusion on the perception of /ri‐li/ syllables

The effects of spectral fusion and spectral‐temporal fusion of dichotically separated components of single syllables were measured in normal‐hearing subjects by identification and discrimination tests. Frequency and amplitude parameters of a synthetic three‐formant /ri‐li/ continuum varying in initial F3 frequency and transition were constant over all conditions. In one condition, all three formants were presented binaurally; in the spectral fusion condition, F3 and F1F2 were presented dichotically; in the two spectral‐temporal fusion conditions, either the initial F3 or the initial F2F3 steady states and transitions were separated dichotically from the remainder of the syllable. Identification and discrimination results indicated shifts in phoneme boundaries and discrimination peaks towards the /li/ category when dichotic presentation released F3 from peripheral masking by lower formants. Slopes of identification functions, reflecting low intrasubject variability and sharpness in phonemic categorization, declined from binaural /ri‐li/ to spectrally fused /ri‐li/ to spectral‐temporally fused conditions. Separate discrimination testing was performed for each of the F3 spectral‐temporally fused “duplex” percepts—fused syllable and nonspeech “chirp.” Each duplex discrimination function differed from its binaural counterpart. [Work supported by NSF and NINCDS.]

Dichotic and monotic masking of CV's by CV second formants with different transition starting values.

Listeners were asked to identify ambiguous and unambiguous stop-vowel targets placed in monotic and dichotic competition with second formants (bleats) from voiced consonant-vowel (CV) syllables lying along a place-of-articulation continuum. Target performance varied with bleat-continuum position as well as bleat intensities. In cases where target errors occurred, either dichotically or monotically, they reflected predominantly the place cue of the bleat. This result, like that of previous studies, suggests the dominance of target or bleat reflects the relative "salience" of the two signals' cues. Differences were seen between monotic and dichotic conditions in the rate of change in performance with bleat intensity and continuum position. The rate of monotic performance change was a more precipitous (higher slope) function of these variables than was dichotic performance. This difference was interpreted as suggesting that monotic interference includes a peripheral masking component which is sensitive to the relative spectral energies of target and bleat. Dichotic effects, in contrast, seem to primarily reflect the operation of (central) processes which grant different perceptual weights to signals' cues depending on their intensity-dependent saliences. The observation that ambiguity, per se, of the targets (or the CV's from which the bleats were extracted) played little role in predicting results, was interpreted as reflecting a primarily prephonetic (i.e., auditory) locus for both monotic and dichotic interactions.

Visual masking: Mechanisms and theories.

Two complementary interpretations of visual masking exist, each based on an analogy with a nonneural system. Peripheral integrative masking is said to occur when masking is energy dependent, by analogy with photographic emulsions. Central interruptive masking is said to occur when masking is time de

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 simultaneously 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.

Identification of dichotic fusions

Seven synthetic syllables from a ’’place continuum’’ (/bae/–/dae/–gae/) were presented in all dichotic combinations for identification. These syllables fused completely, so that dichotic pairs were perceived as single stimuli. The response pattern could not easily be explained by an ’’auditory averaging’’ hypothesis. Rather, stimuli that were good instances of a category seemed to ’’dominate’’ stimuli that were closer to a category boundary. To account for this finding, a three-stage pattern recognition (’’prototype’’) model is proposed, according to which the information from the two ears is linearly combined after ’’multicategorical’’ processing, which follows auditory processing and precedes the final phonetic decision. Electronically mixed stimuli led to a response pattern that was similar to that for dichotic syllables (apart from some systematic deviations ascribed to peripheral masking), so that the same processes of central interaction seem to be involved. Average dichotic right-ear advantages of small magnitude were obtained for the dichotic fusions. They could not be reliably discriminated from binaural stimuli, and selective attention to one ear had little effect. With respect to the measurement of dichotic ear asymmetries, dichotic fusions offer certain methodological advantages over other dichotic stimuli. The problem of determining the ’’true’’ ear advantage is discussed. Subject Classification: [43]70.30; [43]65.75.

Spectral and aerodynamic properties of normal vs defective /s/

Temporary anterior open-bite malocclusion was experimentally induced in 15 normal speakers by introducing posterior bite blocks. Speech samples produced at 0, 1, 3, and 6 mm incisal spacing, both with and without peripheral masking, were analyzed for spectral and aerodynamic features. Selected /s/ sounds were judged for acceptability by naive and phonetically trained listeners. Preliminary analysis indicates (1) judged dysfluency increased both with increasing anterior spacing and in the presence of masking noise; (2) the presence of masking noise had little effect on oral constriction; (3) the relationship between anterior spacing and degree of constriction was complex, speakers with wider than average constriction widening further with increasing spacing, those with normally tight constriction narrowing still further; (4) dysfluent /s/ spectra tended to have lower amplitude and frequency than normal productions by the same speaker. These data indicate differences among speakers in adaptive response to anterior spacing. [Supported by NIH Grant No. AF446, NIDR Grant No. DE03533, and SRS Grant No. 44P20078.]

Letter: Dichotic release from masking for speech.

A dichotic method of listening to synthetic CV speech syllables was investigated, where the first formant (F1) is presented to one ear and the second and third formants (F2, F3) to the other ear. As a test parameter, the intensity of F2, F3 was varied. Compared to the binaural condition, dichotic presentation permits F2, F3 to remain effective as speech cues at significantly lower intensity levels. The results are given the following interpretation: peripheral masking, which occurs for ordinary binaural listening, is avoided when speech is heard dichotically. A similar release from masking was found in a second, related experiment where only the initial F2, F3 transitions were presented to one ear and the remainder of the syllable to the other.

Effects of Attenuation of One of Two Channels on Perception of Opposing Pairs of Nonsense Syllables When Monotically and Dichotically Presented

A two-channel listening experiment was carried out in which subjects had to identify each member of pairs of nonsense syllables which coincided in time of onset and offset. The purpose of the experiment was to compare the effect of varying the intensity of the stimuli in one channel when stimuli pairs were presented dichotically (one to each ear) with the effect that occurred when both stimuli were directed monotically to a single ear. We could thus compare the effect of attenuation of one of the two competing speech signals when the competition involved peripheral masking (the monotic condition) with the effect obtained when the locus of masking was exclusively central (the dichotic condition). In the monotic case, the decrement in identification performance was nearly asymptotic with 10 dB of attenuation, whereas in the dichotic case the decrement in performance with attenuation was much less steep, not having reached asymptote at 25 dB of attenuation. These results agree with findings in visual masking studies with respect to the relatively greater importance of intensity difference among stimuli in peripheral masking than in central masking. [This research was supported in part by NSF Grant No. GJ-9.]

The Effect of Temporal Overlap on the Perception of Dichotically and Monotically Presented CV Syllables

When stop consonant-vowel syllables, 390 msec in duration, are presented dichotically, with an onset asynchrony of 50–70 msec, subjects identify the temporally lagging stop more accurately than the leading. When the same pairs are presented monotically, the leading stop has the advantage. This difference has been interpreted in terms of central versus peripheral masking [M. Studdert-Kennedy, D. Shankweiler, and S. Schulman, J. Acoust. Soc. Amer. 48, 599–602 (1970)]. Dichotically, the signals travel separate peripheral pathways, and central masking effects are revealed. Monotically, the lagging signal is masked peripherally by the overlapping leading signal. This experiment was designed to determine the effect that the elimination of the temporal overlap would have on the dichotic and monotic masking functions. Syllables 75 msec long were presented at six asynchronies between 0 and 100 msec. The dichotic masking function was unaffected, whereas the monotic lead advantages were substantially reduced at the nonoverlapping asynchronies. Implications of these results will be discussed. [Work supported by NIH.]