Informational masking and auditory attention

Informational masking is broadly defined as a degradation of auditory detection or discrimination of a signal embedded ina context of other similar sounds; it is not related to energetic masking caused by physical interactions between signal and masker. In this paper, we report a systematic release from informational masking of a target tone in anine-tone rapid auditory sequence as the target is increasingly isolated in frequency or intensity from the remaieining sequence components. Improved target-tone frequency difference limens as isolation increases are interpreted as a reflection of increasingly focused auditory attention. The change from diffuse to highly focused attention is gradual over the frequency and intensity ranges examined, with each 1-dB increment in target intensity relative to the remaining components producing performance improvements equivalent to those produced by a 2% increase in frequency isolation. The results are modeled as bands of attention in the frequency and intensity domains. For attention directed by frequency isolation, there is a strong correspondence with auditory filters predicted by the power spectrum model of masking. These data also support the existence of an attention band of intensity, with a bandwidth of about 5–7 dB at the moderate levels used in this experiment.     

Aptitude-related differences in auditory recognition masking

An auditory backward recognition masking task (Massaro, 1970) was administered to undergraduates selected for extreme scores on the Scholastic Aptitude Test and the Cattell Culture Fair Intelligence Test. In two experiments, significant group differences were found in threshold interstimulus intervals (ISIs) required for 75% correct tone recognition. High-aptitude subjects required less time for correct identification of target tones as “high” or “low”. They were more able to overcome the constraints imposed on time-dependent information processing by a masking tone. These group differences were interpreted as indicating better information processing efficiency (h (higher signal-to-noise ratio) in the high-aptitude subjects.     

Informational masking and auditory attention.

Informational masking is broadly defined as a degradation of auditory detection or discrimination of a signal embedded in a context of other similar sounds; it is not related to energetic masking caused by physical interactions between signal and masker. In this paper, we report a systematic release from informational masking of a target tone in a nine-tone rapid auditory sequence as the target is increasingly isolated in frequency or intensity from the remaining sequence components. Improved target-tone frequency difference limens as isolation increases are interpreted as a reflection of increasingly focused auditory attention. The change from diffuse to highly focused attention is gradual over the frequency and intensity ranges examined, with each 1-dB increment in target intensity relative to the remaining components producing performance improvements equivalent to those produced by a 2% increase in frequency isolation. The results are modeled as bands of attention in the frequency and intensity domains. For attention directed by frequency isolation, there is a strong correspondence with auditory filters predicted by the power spectrum model of masking. These data also support the existence of an attention band of intensity, with a bandwidth of about 5-7 dB at the moderate levels used in this experiment.     

Infant auditory perception: Tonal masking

The results of an earlier study (Olsho, 1984) indicated that 5- to 8-month-old infants were relatively better at discriminating among high-frequency pitches than low. In the present study, sensory and nonsensory explanations for that effect were evaluated by examining infants' performance in a task requiring similar sensory processing but differing in the demands placed on processes such as memory. Infants' ability to resolve frequency was tested using a tonal masking paradigm, the psychophysical tuning curve. Twenty-four infants were tested at probe frequencies ranging from 500 to 4000 Hz; a group of young adults served as a comparison. Masked and unmasked thresholds were estimated using the visually reinforced head turn procedure in conjunction with an adaptive psychophysical method. Although infants' tuning curves fell below those of adults (indicating poorer performance), the widths and slopes of the infants' curves were not different from the adults'. Moreover, the difference between age groups remained constant across probe frequencies. These findings imply that by 5 months of age, the infant's ability to resolve sound frequency is similar to the adult's.     

Disinhibition of masking in auditory sensory memory

A series of experiments was performed on the difference between single- and double-masking agents in auditory memory. Single or double suffixes were presented following immediate memory lists, with parametric variation in the delay of the suffixes relative to the end of the list. The main interest was in the shape of the masking function produced by the timing of either the single suffix or the second of two suffixes. Disinhibition was shown to occur, although it was weak in absolute magnitude.     

Temporal course of perceived auditory duration

A series of experiments explored the temporal course of the perceived duration of an auditory stimulus. A backward recognition masking paradigm was utilized, in which the subject was to determine which of two target durations was presented on a given trial. The target tone was followed, after a variable silent intertone interval, by a masking tone which could assume one of three possible durations. Identification of the long target was found to improve consistently with increases in the intertone interval. In contrast, identification of the short target was as accurate at the short as at the long intertone intervals. Blocking the intertone interval across experimental sessions eliminated these differences between the two target tones. Performance on both the long and the short target tones improved monotonically with increases in the intertone interval. When masking tone duration was randomized within an experimental session, identification of the long (short) target was most accurate with the longer (shorter) masking tone. Blocking the duration of the masking tone across experimental sessions eliminated the effect of the duration of the mask, but did not alter any of the other results. A model, proposed to account for the results, assumes that the percept of target duration grows over time, and can be terminated by the onset of the masking tone. The masking tone also acts to lengthen the perceived duration of the target tone, and this lengthening is a direct function of the duration of the masking tone.     

Sources of auditory masking in infants: Distraction effects

Previous work has demonstrated that infants’ thresholds for a pure tone are elevated by a masker more than would be predicted from their critical bandwidths. The present studies explored the nature of this additional masking. In Experiment 1, detection thresholds of 6-month-old infants and of adults for a 1-kHz tone were estimated under three conditions: in quiet, in the presence of a 4- to 10-kHz bandpa] noise at 40 dB SPL, and in the presence of the same noise at 50 dB SPL. The noise was gated on at the beginning of each trial. Adult thresholds were the same in all three conditions, indicating that little or no sensory masking took place in the presence of the noise. Infant thresholds were about 10 dB higher in the presence of the noise. We term this effectdistraction masking. In Experiment 2, the effect of gating the noise on at trial onset was examined. Thresholds for the same tone were estimated in quiet and in the presence of the bandpass noise at 40 dB SPL, but the noise was presented continuously during the session. Under these conditions, distraction masking was still observed for infants. These findings suggest that a masker can have nonsensory effects on infants’ performance in a psychoacoustic task.     

Sources of auditory masking in infants: distraction effects.

Previous work has demonstrated that infants' thresholds for a pure tone are elevated by a masker more than would be predicted from their critical bandwidths. The present studies explored the nature of this additional masking. In Experiment 1, detection thresholds of 6-month-old infants and of adults for a 1-kHz tone were estimated under three conditions: in quiet, in the presence of a 4- to 10-kHz bandpass noise at 40 dB SPL, and in the presence of the same noise at 50 dB SPL. The noise was gated on at the beginning of each trial. Adult thresholds were the same in all three conditions, indicating that little or no sensory masking took place in the presence of the noise. Infant thresholds were about 10 dB higher in the presence of the noise. We term this effect distraction masking. In Experiment 2, the effect of gating the noise on at trial onset was examined. Thresholds for the same tone were estimated in quiet and in the presence of the band-pass noise at 40 dB SPL, but the noise was presented continuously during the session. Under these conditions, distraction masking was still observed for infants. These findings suggest that a masker can have nonsensory effects on infants' performance in a psychoacoustic task.     

The effect of masker duration on forward and backward masking

Temporal masking of clicks by noise was investigated using forward and backward masking paradigms. Both the noise duration and the temporal separation, ΔT, between the click and noise were varied. For very brief ΔTs (100 microsec) and for very long ΔTs (100 msec), the duration of the masker did not greatly affect the click threshold. However, for intermediate ΔTs (3 msec), the threshold increased by as much as 44 dB as the noise duration increased from 0.1 to 100 msec. Temporal weighting functions, which describe the relative effectiveness of the noise as a function of ΔT, were computed from these data.     

An aftereffect in judgment of auditory duration

Two experiments were designed to investigate the occurrence of atemporal aftereffect following auditory spatial stimulation. The task required Ss to compare by means of a motorresponse the duration of a test tone presented at a variable interval after stimulation with a standard tone. In both experiments the posttest duration was underestimated relative to the pretest duration, i.e., there was a temporal aftereffect(TAE). A control experiment which involved Ss making estimates of the duration of the test tones, without the presentation of interpolated standard tones, did not show this effect. The temporal aftereffect followed a function analogous to the “distance paradox” forspatial aftereffects.     

Nonsimultaneous auditory masking in the budgerigar (Melopsittacus undulatus)

The frequency resolving power of budgerigars and that of humans were compared on several nonsimultaneous masking procedures in which one pure tone is used to mask another. Similar patterns of frequency selectivity were found for all three masking procedures (forward, backward, and combined forward-backward) for both species. Budgerigars showed considerably greater frequency resolving power on all three procedures than humans. Budgerigars also showed differences in frequency resolving power across masking conditions, but human listeners did not. These results indicate that the budgerigar auditory system may be even more highly tuned than was previously thought and suggest fundamental differences between the mechanisms of frequency selectivity of bird and those of humans.     

Some characteristics of auditory spatial attention revealed using rhythmic masking release

The tuning of auditory spatial attention with respect to interaural level and time difference cues (ILDs and ITDs) was explored using a rhythmic masking release (RMR) procedure. Listeners heard tone sequences defining one of two simple target rhythms, interleaved with arhythmic masking tones, presented over headphones. There were two conditions, which differed only in the ILD of the tones defining the target rhythm: For one condition, ILD was 0 dB and the perceived lateral position was central, and for the other, ILD was 4 dB and the perceived lateral position was to the right; target tone ITD was always zero. For the masking tones, ILD was fixed at 0 dB and ITDs were varied, giving rise to a range of lateral positions determined by ITD. The listeners' task was to attend to and identify the target rhythm. The data showed that target rhythm identification accuracy was low, indicating that maskers were effective, when target and masker shared spatial position, but not when they shared only ITD. A clear implication is that at least within the constraints of the RMR paradigm, overall spatial position, and not ITD, is the substrate for auditory spatial attention.