Do age and linguistic background alter the audiovisual advantage when listening to speech in the presence of energetic and informational masking?

We examined how the type of masker presented in the background affected the extent to which visual information enhanced speech recognition, and whether the effect was dependent on or independent of age and linguistic competence. In the present study, young speakers of English as a first language (YEL1) and English as a second language (YEL2), as well as older speakers of English as a first language (OEL1), were asked to complete an audio (A) and an audiovisual (AV) speech recognition task in which they listened to anomalous target sentences presented against a background of one of three masker types (noise, babble, and competing speech). All three main effects were found to be statistically significant (group, masker type, A vs. AV presentation type). Interesting two-way interactions were found between masker type and group and between masker type and presentation type; however, no interactions were found between group (age and/or linguistic competence) and presentation type (A vs. AV). The results of this study, while they shed light on the effect of masker type on the AV advantage, suggest that age and linguistic competence have no significant effects on the extent to which a listener is able to use visual information to improve speech recognition in background noise.     

Effect of “backward” masker fringe on the detectability of pulsed diotic and dichotic tonal signals

The effects of backward masker “fringe” on performance in homophasic and antiphasic masking conditions were investigated. The results of the study indicate that (1) the presence of a backward masker fringe has only a small effect on performance in homophasic masking conditions; (2) under antiphasic masking conditions, the presence of a backward masker fringe improves performance; (3) similar to the results of studies investigating the effects of forward masker fringe, the magnitude of the improvement in performance increases as the duration of the fringe increases; and (4) the magnitude of the improvement caused by the presence of backward masker fringe is considerably smaller than the magnitude of the improvement caused by the forward masker fringe. It appears, then, that the presence of backward masker fringe may provide a baseline or reference phase similar to that which the forward fringe is presumed to provide. The presence of this reference phase after the offset of the signal apparently makes the phase shift associated with the signal-plus-noise waveform more discernible, thus leading to higher detectability. However, for reasons not yet clear, the presence of a baseline or reference phase after the offset of the signal (backward fringe conditions) does not make the signal-plus-noise phase shift as discernible as do either the presence of that same reference phase before the onset of the signal (forward fringe condition) or the presence of that same reference phase both before signal onset and after signal offset (continuous masker condition).     

Vibrotactile masking: A comparison of energy and pattern maskers

Subjects were required to identify vibrotactile patterns presented to their fingertips. The patterns, letters of the alphabet, were presented singly or in the presence of other vibrotactile masking stimuli. Two types of masking stimuli were used: an energy masker and a pattern masker. The effectiveness of these two types of maskers in interfering with letter recognition was tested, using them as forward and as backward maskers and presenting them at several different levels of intensity. The results showed more masking by the pattern masker, more backward than forward masking, and more masking as intensity increased. In addition, compared with the energy masker, the pattern masker showed both a greater difference between forward and backward masking and a greater increase in masking as masker intensity increased. The results are discussed in terms of a two-factor model of vibrotactfle masking.     

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.     

Masking-level differences in older adults: The effect of the level of the masking noise

In Experiment 1, masking-level differences (MLDs) for a 500-Hz tone at five masker levels were obtained from younger and older adults. For both age groups, there were no reliable increases in MLD once the spectrum level of the masker exceeded 27 dB SPL. MLDs were larger for younger than for older adults over the range of masker levels tested. In Experiment 2, the levels of both the signal and the masker in one ear were attenuated by either 15 or 30 dB relative to their level in the other ear, which was fixed at a spectrum level of 47 dB SPL. MLDs for both age groups declined with increasing IAA and age-related differences were observed in all conditions. The findings of these experiments indicate that (1) age-related differences in MLDs exist even when the level of the masker is sufficiently high that older adults achieve their plateau performance, and (2) older listeners are not disadvantaged more than younger listeners by interaural differences in the level of the input.     

Using the CLOX drawing task to educate the public of the effects of hearing loss

We describe a task used to educate the public on the importance of hearing and the experience of hearing loss. During an open day at Nottingham University, participants were presented with verbal instructions (with or without a background masker) and asked to draw the image of a clock face as accurately as possible. Poorest performance was observed when the instructions were presented with a background masker. We suggest that the task could be applied effectively by healthcare professionals who aim to educate younger individuals of the difficulties associated with hearing loss.     

掩蔽刺激对目标识别加工的作用：来自fNIRS的证据

信息掩蔽刺激(如随机字母群)对字母视觉搜索的干扰大于能量掩蔽刺激(如将字母群像素随机化后的散点), 但相应的中枢机理还不清楚。本研究采用记录脑代谢激活模式的功能性近红外光学脑成像技术(fNIRS), 考察年轻成年被试分别在字母掩蔽、字母碎片掩蔽、像素掩蔽条件下判断上、下、左、右四个目标字母是否相同时的大脑皮层氧合血红蛋白浓度的变化。结果显示, 依字母、字母碎片、随机散点掩蔽条件顺序, 被试的搜索任务成绩显著递增, 而顶-枕皮层的激活范围与程度显著递减, 表明信息掩蔽较匹配的能量掩蔽对视觉搜索有更大的干扰作用, 并在初级和联合视觉皮层引发更大的激活。在字母碎片掩蔽条件下, 视觉初级皮层部分区域的激活水平与搜索行为绩效的相关显著, 而在字母掩蔽条件下, 视觉联合皮层部分区域的激活水平与搜索行为绩效的相关显著。这进一步说明信息掩蔽中的字母掩蔽和字母碎片掩蔽的掩蔽作用在大脑皮层上所造成的加工负载存在差异。     

Vibrotactile masking: Effects of oneand two-site stimulation

Masked vibrotactile thresholds at the index fingertip were measured as a function of masker intensities, which were applied to the thenar eminence of the same hand. Test and masker frequencies were selected so that the Pacinian and non-Pacinian receptor systems were selectively activated. Remote-site masking was effective only when both masker and test stimulus were within the frequency range of the Pacinian system. Cross-channel masking did not occur.     

Central masking: Some steady-state and transient effects

The contralateral threshold shift was investigated as a function of various parameters of the masking and masked stimuli. Because of a measured high acoustic attenuation between the ears, the threshold shift is interpreted as central masking. Both steady-state and pulsed maskers were used and their effect on the contralateral threshold was determined as a function of the masker intensity, the frequency difference between the masking and masked tones, the time delay from the masker onset, and the duration of an intermittent masker.     

Relative contributions of envelope maxima and minima to comodulation masking release

Comodulation masking release (CMR) is a phenomenon that demonstrates the sensitivity of the auditory system to across-frequency differences in the temporal modulation pattern of a complex waveform. In this paper, we review briefly some of the data on the physical parameters that affect CMR and describe models that have been proposed to account for CMR -- namely, models based upon envelope equalization/cancellation, across-frequency envelope correlation, and “dip listening”. The present literature is ambiguous with regard to the relative importance of energy in the peak and dip regions of the waveform envelope. We therefore performed a series of experiments to investigate this issue. In the first experiment, we examined CMR for signals that resulted either in a uniform increment or in uniform decrement in the masking noise centred on the signal frequency. This was accomplished by using a 20-Hz-wide noise band centred on 700 Hz as both the masker and as the signal, adjusting the phase angle between the signal and masker to either 0° (increment) or 180° (decrement). Conditions were examined where either zero, one, two, four, or six comodulated flanking bands were present. Results indicated positive CMRs for all conditions in which a comodulated flanking band was present. CMR increased as the number of flanking bands increased for intensity increments, but not for intensity decrements. The remaining experiments examined conditions where signals were present only in masker peaks, or only in masker dips. The results of these experiments indicated relatively large CMRs when the signal occurred in dip regions, but no CMR when the signal occurred in peak regions. Whereas some of the results of the above experiments would be difficult to account for in terms of the dip listening hypothesis of CMR, the present findings did indicate that the stimulus cues that give rise to CMR appear to be derived primarily from the dip regions of the masking noise.     

Vibrotactile difference thresholds for intensity and the effect of a masking stimulus

Vibrotactile difference thresholds for intensity were measured at several intensity levels of a test stimulus in the absence of a masking vibration and in the presence of three different amplitudes of a masking vibration. The test stimulus was a 160-Hz vibration delivered to the right index finger. The masking stimulus was a 160-Hz vibration delivered to the right little finger. For the same amplitudes of the test stimulus, △I varied as a direct function of the amplitude of the masking vibration. The smallest △Is resulted from measurements made in the absence of the masking stimulus. The Weber fraction, △I/I, was constant only for the more intense test stimuli in the absence of any masking stimuli. Independent of the presence or level of the masker, the Weber fraction for all stimuli approached approximately the same value, .25, when the test stimuli were raised to 20-dB sensation level. A model is proposed to account for the increase in the Weber fraction as a function of masker intensity and to predict masked thresholds.     

Effect of masker level on infants' detection of tones in noise

In adult listeners, the signal-to-noise ratio at masked threshold remains constant with increases in masker level over a wide range of stimulus conditions. This relationship was examined in 7-month-old infants by obtaining masked thresholds for .5- and 4-kHz tones presented in four levels of continuous masking noise. Adults were also tested for comparison. Masker spectrum levels ranged from 5 to 35 dB/Hz for .5-kHz tones, and from -5 to 25 dB/Hz for 4-kHz stimuli. Thresholds were determined for stimuli of both 10 and 100 msec in duration. The results indicated that infants' performance was more adult-like for 4-kHz stimuli. Although mean thresholds for both 10- and 100-msec, 4-kHz tones were approximately 7 dB higher in infants than in adults, E/N0 at threshold remained essentially constant over the 30-dB range of maskers employed. By contrast, infants' thresholds for .5-kHz tones were exceptionally high at lower levels of the masker. Threshold E/N0 decreased significantly as masker level increased from 5 to 35 dB/Hz, and this decrease was significantly greater for 10- than for 100-msec stimuli. Temporal summation of .5-kHz tones, measured as the difference between thresholds obtained at the two signal durations, was greater for infants than for adults at low levels of the masker. However, because infants' thresholds improved more rapidly with level for 10- than for 100-msec tones, age differences in temporal summation were no longer significant when masker spectrum level was 35 dB/Hz. These results suggest that the relationship between signal-to-noise ratio at masked threshold and level of the masker is dependent on both signal frequency and duration during infancy.     

Vibrotactile masking: Some spatial and temporal aspects

Threshold elevations (TE) were determined for three Os at a test site on the left thigh with a masker placed singly at each of 10 widespread loei on the trunk. Although lateral changes in masker placement did not produce a significant alteration in TE (p> .10), there was a systematic decrease in TE with longitudinal separation between masker and test sites on the body. Appropriate manipulations of the time interval between masker and test signals were found effective in offsetting these decreases. It appeared that longitudinal separations were differentially affecting temporal delays by producing unequal neural distances from the test and masker sites to the CNS. There were, however, some spatial changes that could not be accounted for by temporal offsets. Thresholds at a finger test site were significantly less elevated (p< .01) by contralateral placement of maskers than by ipsilateral placement, and the particular test site chosen for threshold determinations, either index finger or thigh, determined the amount of TE.     

Auditory forward and backward masking interaction

Recent research on forward masking and backward masking has led us to the hypothesis that combined forward and backward masking may involve at least two different types of interaction patterns. The previously documented interaction results in masking are greater than predicted by the simple summation of masking effects obtained with each masker alone (Lynn & Small, 1977; Patterson, 1971; Wilson & Carhart, 1971). Another possible type of interaction is based upon the finding that backward masking, but not forward masking, can be reduced by cues providing timing information (Puleo & Pastore, 1980). A forward masker appears to involve minimum temporal uncertainty (Pastore & Freda, 1980) and, therefore, should be able to act as such a source of timing information to reduce the contribution of a later occurring backward masker. Both types of interaction patterns were found, with the specific forward and backward masker parameters determining which pattern is observed.     

Mechanism of age-related differences in frequency discrimination with backward masking: speed of processing or stimulus persistence?

In Experiment 1, frequency-discrimination thresholds were estimated in a 2-interval, forced-choice, backward masking procedure with a masker acoustically dissimilar to the targets. Young subjects were more efficient in escaping the effects of masking than were their elderly counterparts. In Experiment 2, young and elderly subjects performed the same task, with a masker acoustically similar to the targets and with a target-dissimilar masker. Under target-similar masking and at short target-masker intervals, the elderly demonstrated significant improvement, reaching the level of performance of the young, whereas under the target-dissimilar masker, the age-related differences were restored. Both age-related slowing of information processing and increase in stimulus persistence can account for the results of Experiment 1, but only increased stimulus persistence explains the results of Experiment 2.     

Spectral, intensive, and temporal factors influencing overshoot

Threshold was measured for a 10-msec, 4.0-kHz signal presented near the onset or in the temporal centre of a 400-msec noise masker. Overshoot, the difference (in dB) between these two thresholds, was seen only for masker bandwidths wider than a critical band. The threshold near masker onset, and hence overshoot, could be reduced by the presence of an additional noise that was presented continuously or gated on and off prior to masker onset. The spectral, intensive, and temporal properties of this effect were studied. When the additional noise was continuous and either bandpass filtered with a variable bandwidth or notch filtered with a variable notchwidth, the results indicated that energy both near and remote from the signal frequency contributed to the reduction in overshoot. The effect of this additional noise was highly dependent upon its relative level. When the additional noise was 400 msec in duration and the delay between its offset and the onset of the masker was varied, overshoot “recovered” to its maximum value within about 50 msec. Finally, as the duration of the additional noise was varied from 3 to 400 msec while the time between its offset and masker onset was fixed, the reduction in overshoot was virtually complete for durations of about 25-50 msec. The results are consistent with the notion that overshoot at least partly reflects peripheral adaptation, and that this adaptation is not restricted to the signal frequency channel but, rather, extends in both directions over several channels.     

Does the information content of an irrelevant source differentially affect spoken word recognition in younger and older adults?

To determine whether older adults find it difficult to inhibit the processing of irrelevant speech, the authors asked younger and older adults to listen to and repeat meaningless sentences (e.g., "A rose could paint a fish") when the perceived location of the masker (speech or noise) but not the target was manipulated. Separating the perceived location (but not the physical location) of the masker from the target speech produced a much larger improvement in performance when the masker was informational (2 people talking) than when the masker was noise. However, the size of this effect was the same for younger and older adults, suggesting that cognitive-level interference from an irrelevant source was no worse for older adults than it was for younger adults.     

Weber’s law,the “near miss,” and binaural detection

Weber functions (ΔI/I in dB) for gated 250-Hz tones were studied for monaural and several binaural stimulus configurations (homophasic, and antiphasic with varying phase angle for addition of signal to masker). The various cues for discrimination of signal plus masker from masker alone are functions of intensity increments at one or both ears, an intensity increment at one ear coupled with a decrement at the other, or the introduction of a phase difference between the ears. The decline of the Weber fraction with increasing masker level (the “near miss” to Weber’s law) was confirmed for monaural discrimination over the entire 40-dB range, and a similar rate of decline was found for various binaural stimuli over the lower half of that range. The data also confirm the individual differences found in other studies for sensitivity favoring either interaural amplitude or interaural phase shifts.     

Effect of masker level on infants’ detection of tones in noise

In adult listeners, the signal-to-noise ratio at masked threshold remains constant with increases in masker level over a wide range of stimulus conditions. This relationship was examined in 7-month-old infants by obtaining masked thresholds for .5- and 4-kHz tones presented in four levels of continuous masking noise. Adults were also tested for comparison. Masker spectrum levels ranged from 5 to 35 dB/Hz for .5-kHz tones, and from ?5 to 25 dB/Hz for 4-kHz stimuli. Thresholds were determined for stimuli of both 10 and 100 msec in duration. The results indicated that infants’ performance was more adultlike for 4-kHz stimuli. Although mean thresholds for both 10- and 100-msec, 4-kHz tones were approximately 7 dB higher in infants than in adults, E/N₀ at threshold remained essentially constant over the 30-dB range of maskers employed. By contrast, infants’ thresholds for .5-kHz tones were exceptionally high at lower levels of the masker. Threshold E/N0 decreased significantly as masker level increased from 5 to 35 dB/Hz, and this decrease was significantly greater for 10- than for 100-msec stimuli. Temporal summation of .5-kHz tones, measured as the difference between thresholds obtained at the two signal durations, was greater for infants than for adults at low levels of the masker. However, because infants’ thresholds improved more rapidly with level for 10- than for 100-msec tones, age differences in temporal summation were no longer significant when masker spectrum level was 35 dB/Hz. These results suggest that the relationship between signal-to-noise ratio at masked threshold and level of the masker is dependent on both signal frequency and duration during infancy.     

Interference in localizing tactile stimuli

A series of experiments investigated the ability of subjects to localize a tactile stimulus in the presence of an additional, extraneous tactile stimulus. The subject's task was to localize a tactile stimulus (target) presented at one of several locations on his or her left index fingerpad. The target stimulus, generated on a 6 x 24 array of stimulators, was presented either by itself or in the presence of an extraneous stimulus (masker) that either preceded or followed the target. The localizability of the target was affected by the temporal separation between the target and masker in much the same way as previous studies have shown identification of tactile patterns to be affected. Unlike previous identification results, presenting the masking stimulus to the same location as the target interfered with localizability, although not as much as did presenting the masker to a different location. The results are discussed in terms of their implications for identification and discrimination of tactile patterns.