Auditory temporal summation in infants and adults: Effects of stimulus bandwidth and masking noise

A visually reinforced operant procedure was employed to determine the behavioral thresholds of 6- to 7-month-old infants and adults for stimuli of various bandwidths and durations. Experiment 1 compared absolute thresholds for broadband and 1/3-octavefiltered clicks and 300-msec noise bursts. For adult subjects, the difference in threshold for clicks and noise bursts was -quite comparable in the two bandwidth conditions, but infants’ click-noise threshold differences were significantly larger for broadband than for 1/3-octave stimuli. In Experiment 2, 2-point threshold-duration functions were compared for 4-kHz tones and octave-band noise bursts presented in backgrounds of quiet and continuous noise. Infants’ threshold-duration function for octave-band noise bursts was significantly steeper than the comparable adult function in quiet, but not in masking noise. These results suggest that young infants may have particular difficulty detecting low intensity broadband sounds when durations are very short.     

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.     

Asymmetry of masking between noise and tone

A pure tone was used to mask narrow and wide bands of noise centered on the frequency of the tone. In a given experimental session, the sound-pressure level (SPL) of the tone was held constant and loudness balances were obtained between a masked and unmasked noise band of equal width. These results are compared to earlier measures of the partial masking of tone by noise. The comparison shows that noise masks a tone more effectively than the tone masks the noise. Although the effect of the tone on a critical band of noise is greater than its effect on either an octave-band noise or wide-band noise, it is considerably smaller than the effect of the noise on the tone. Decreasing the noise bandwidth still further to a subcritical width reduces the asymmetry of masking somewhat, but a difference at high intensities of about 20 dB between the masking effects of an equally intense noise and tone remains. Whether the masker is a tone or noise, masking ceases when the effective energy of the masked and masking stimuli is the same.     

Noise effects on human performance: a meta-analytic synthesis

Noise is a pervasive and influential source of stress. Whether through the acute effects of impulse noise or the chronic influence of prolonged exposure, the challenge of noise confronts many who must accomplish vital performance duties in its presence. Although noise has diffuse effects, which are shared in common with many other chronic forms of stress, it also exerts its own specific influences on various forms of cognitive and motor response. We present a quantitative evaluation of these influences so that their harmful effects can be mitigated, their beneficial effects exploited, and any residual effects incorporated and synthesized into selection, training, and design strategies to facilitate human performance capacities. Predictions of single and joint moderator effects were made on the basis of major theories of noise and performance, specifically those explanations based on arousal, masking, or cognitive-resource mechanisms. These predictions were tested through moderator analyses of effects as a function of task type, performance measure, noise type and schedule, and the intensity and duration of exposure. Observed outcome effects (797 effect sizes derived from 242 studies) varied as a function of each of these moderators. Collective findings identified continuous versus intermittent noise, noise type, and type of task as the major distinguishing characteristics that moderated response. Mixed evidence was obtained for the traditional arousal and masking explanations for noise effects. The overall pattern of findings was most consistent with the maximal adaptability theory, a mental-resource-based explanation of stress and performance variation.     

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.     

Detection by the guinea pig of acoustic stimulation and of electrical stimulation of the brain

A threshold procedure using operant behavioral techniques with positive reinforcement was developed after initial efforts with avoidance behavioral procedures proved unsatisfactory. In the first of three experiments the operant threshold procedure was tested by determining masked auditory thresholds for trains of clicks. In a second experiment, similar techniques were used to measure thresholds for electrical stimulation of the brain. The last experiment, again an auditory problem, involved a determination of the absolute thresholds for trains of short noise bursts as a function of the time between bursts. Middle ear malfunction proved to be a more severe problem than had been anticipated on the basis of reports in the literature. The threshold procedure, however, seems to be adequate for determination of absolute or masked thresholds with auditory or electrical stimuli.     

Signal detectability in the presence of monotic or dichotic noise bands of equal or unequal levels

The application of the power-spectrum model of masking to the detectability of a signal masked by dichotic noise was investigated in three experiments. In each experiment, the signal was a 2-kHz sinusoid of 400-msec duration, masked by either one or two 800-Hz wide bands of noise presented singly or in pairs. In Experiment 1, we compared the detectability of a diotic signal masked by dichotic noise with the detectability of a monaural signal masked by each of the noises separately. The spectrum level of the noise was 35 dB SPL. For dichotic presentations, the signal was sent to both ears while pairs of noise bands, one below and one above the signal frequency, were presented together, one band to each ear. Threshold levels with the dichotic stimuli were lower than or equal to the thresholds with either ear's stimulus on its own. Similar dichotic stimuli were used in Experiment 2, except that the signal frequency was nearer to one or the other of the bands of masking noise, and the noise had a spectrum level of 50 dB SPL. In Experiment 3, thresholds were obtained with two sets of symmetrically and asymmetrically placed notched-noise maskers. For one of these sets, the spectrum level of both noise bands was 35 dB SPL; for the other set, interaural intensity differences were introduced in the form of an inequality in the levels of the noise bands on either side of the signal. In one ear, the spectrum level of the lower frequency noise band was 35 dB SPL and the spectrum level of the higher frequency noise band was 25 dB SPL, whereas in the other ear, the allocation of noise level to noise band was reversed. The dichotic thresholds obtained with the unequal noise maskers could be predicted from the shapes of the auditory filters derived with equal noise maskers. The data from all three experiments suggest that threshold signal levels in the presence of interaural differences in masker intensity depend principally on the ear with the higher signal-to-masker ratio at the output of its auditory filter, a finding consistent with the power-spectrum model of masking.     

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.     

Dominance of persistence over adaptation in forward masking

Persistence of excitation and neural adaptation are competing theories proposed to explain the mechanisms underlying psychophysical forward masking. Previous research has been directed towards finding models that accurately describe the phenomenon but cannot account for the underlying explanation. The current study was designed to determine which theory best accounts for results obtained from behavioral gap duration adjustment tasks. Thirteen adults adjusted the gap within asymmetrical noise markers to be subjectively equal to the gap within equal-intensity-noise markers. The duration of the perceived gap between the asymmetrical markers is expected to vary depending on which theory dominates perception. The persistence of excitation mechanism would lead to longer duration gaps when the second noise marker is lower in intensity than the preceding. Neural adaptation would result in matched gaps that are shorter in duration when the second noise marker was lower in level. The outcome of our data analysis is consistent with the persistence of excitation as a dominant mechanism in forward masking.     

A comparison of thresholds for 1/3-octave filtered clicks and noise bursts in infants and adults

Behavioral thresholds of 6-month-old infants and adults were determined for 1/3-octave filtered clicks and 300-msec noise bursts with center frequencies ranging from .5 to 8 kHz. For noise bursts, differences between infant and adult thresholds were largest at low frequencies and smallest at 8 kHz. For clicks, infants’ thresholds were most like adults’ at 4 kHz, and age differences increased at both lower and higher frequencies. Differences between click and noise thresholds were significantly larger for infants than for adults at .5, 1, and 8 kHz, but not at 2 and 4 kHz. These results suggest that improvements in threshold for long-duration stimuli during infancy may not be accompanied by comparable changes in threshold at short durations. The delayed development of sensitivity to low- and high-frequency clicks appears consistent with maturational trends recently described for the auditory brainstem response.     

Behavioral and electrophysiological evidence of species-specific face processing

Several recent reports suggest that the behavioral and cortical specificity of face processing may be influenced by experience. To test this hypothesis, behavioral and electrophysiological data were recorded from adults in response to human and monkey faces differing in familiarity and orientation. An analysis of event-related potential and behavioral data revealed differentiation across species, familiarity, and orientation. Behavioral measures were correlated with amplitude and latency measures for each factor of interest. These analyses revealed that accuracy was positively related to the amplitude of the vertex positive potential in the human face task but not in the monkey face task. These findings suggest that previous experience with different categories of faces modulates the link between behavioral and electrophysiological measures of face processing.     

Backward masking interrupts spatial attention,slows downstream processing,and limits conscious perception

The attentional blink (AB) is a difficulty in correctly processing a target when it follows one or more other targets after a short delay. When no backward mask is presented after the last critical target, there is no or little behavioral AB deficit. The mask plays an important role in limiting conscious access to target information. In this electrophysiological study, we tested the impact of masking on the deployment and engagement of attention by measuring the N2pc and P3 components in an RSVP paradigm. We found that the presence of a mask in an AB paradigm reduced the amplitude of the N2pc, P3a, and P3b components. In addition to reducing encoding in memory, masking also reduced the effectiveness of the deployment and engagement of attention on the last target. We discuss the role of these findings in the context of current masking, consciousness, and AB models.     

Masked repetition priming using magnetoencephalography

Masked priming is used in psycholinguistic studies to assess questions about lexical access and representation. We present two masked priming experiments using MEG. If the MEG signal elicited by words reflects specific aspects of lexical retrieval, then one expects to identify specific neural correlates of retrieval that are sensitive to priming. To date, the electrophysiological evidence has been equivocal. We report findings from two experiments. Both employed identity priming, where the prime and target are the same lexical item but differ in case (NEWS-news). The first experiment used only forward masking, while the prime in the second experiment was both preceded and followed by a mask (backward masking). In both studies, we find a significant behavioral effect of priming. Using MEG, we identified a component peaking approximately 225 ms post-onset of the target, whose latency was sensitive to repetition. These findings support the notion that properties of the MEG response index specific lexical processes and demonstrate that masked priming can be effectively combined with MEG to investigate the nature of lexical processing.     

CS-dependent response probability in an auditory masked-detection task: considerations based on models of Pavlovian conditioning.

Experimental studies were performed using a Pavlovian-conditioned eyeblink response to measure detection of a variable-sound-level tone (T) in a fixed-sound-level masking noise (N) in rabbits. Results showed an increase in the asymptotic probability of conditioned responses (CRs) to the reinforced TN trials and a decrease in the asymptotic rate of eyeblink responses to the non-reinforced N presentations as a function of the sound level of the T. These observations are consistent with expected behaviour in an auditory masked detection task, but they are not consistent with predictions from a traditional application of the Rescorla-Wagner or Pearce models of associative learning. To implement these models, one typically considers only the actual stimuli and reinforcement on each trial. We found that by considering perceptual interactions and concepts from signal detection theory, these models could predict the CS dependence on the sound level of the T. In these alternative implementations, the animals response probabilities were used as a guide in making assumptions about the "effective stimuli".     

Reexamination of spectral mechanisms in the rat (Rattus norvegicus)

The spectral mechanisms of the rat were studied in electrophysiological and behavioral experiments. The photopic electroretinogram (ERG) was recorded (a) to rapidly flickering lights, (b) during the cone phase of dark adaptation, and (c) with a flicker photometric procedure. Each procedure indicated the presence of a single cone mechanism having a lambda max of about 510 nm. Increment-threshold spectral sensitivity functions measured in a behavioral test situation yielded the same conclusion. A behavioral experiment failed to produce any evidence for the presence of color vision in this rodent. The consistent conclusion from both behavioral and electrophysiological experiments is that the rat retina contains only a single photopic spectral mechanism.     

Attentional mechanisms in visual signal detection: the effects of simultaneous and delayed noise and pattern masks

The attentional cuing effects in detection and some discrimination tasks depend on the use of backward masks and on the presence of external noise in the display. These effects have been attributed to an interruption masking mechanism, which terminates stimulus processing prematurely, and an external noise exclusion mechanism, which minimizes the perceptual effects of noise. To test whether the dependencies on masking and external noise are expressions of a single mechanism, observers detected grating patch stimuli, masked with noise masks or pattern masks, presented either simultaneously or after a delay of 60-90 msec. Contrary to an external noise exclusion account, but consistent with an interruption masking account, cuing effects were largest when the masks were delayed. However, weaker cuing effects were obtained with simultaneous masks, contrary to an interruption masking account. These results suggest that attentional effects in simple visual judgments are affected by mechanisms of both kinds.     

Forward masking of faces by spatially quantized random and structured masks: On the roles of wholistic configuration, local features, and spatial-frequency spectra in perceptual identification

The forward masking of faces by spatially quantized masking images was studied. Masks were used in order to exert different types of degrading effects on the early representations in facial information processing. Three types of source images for masks were used: Same-face images (with regard to targets), different-face images, and random Gaussian noise that was spectrally similar to facial images. They were all spatially quantized over the same range of quantization values. Same-face masks had virtually no masking effect at any of the quantization values. Different-face masks had strong masking effects only with fine-scale quantization, but led to the same efficiency of recognition as in the same-face mask condition with the coarsest quantization. Moreover, compared with the noise-mask condition, coarsely quantized different-face masks led to a relatively facilitated level of recognition efficiency. The masking effect of the noise mask did not vary significantly with the coarseness of quantization. The results supported neither a local feature processing account, nor a generalized spatial-frequency processing account, but were consistent with the microgenetic configuration-processing theory of face recognition. Also, the suitability of a spatial quantization technique for image configuration processing research has been demonstrated.     

Effects of acoustic degradation on syntactic processing: implications for the nature of the resource system used in language processing

This study investigated the effect of noise masking on on-line syntactic processing. Ninety college students were tested on measures of working memory and on-line sentence comprehension. Subjects were divided equally into three listening conditions: no noise masking, -3 dB signal-to-noise ratio (S:N), -4.5 dB S:N. The auditory moving windows (AMW) paradigm was used to measure on-line sentence processing. In the AMW paradigm, subjects pressed a button for the successive presentation of each phrase in two types of sentences (syntactically simple and complex), and listening times were recorded for each phrase. Previous studies have shown that the verb in the more complex sentence type is the most capacity demanding portion of the sentence. Listening times were longer overall with increased noise masking, and listening times were longer overall at the verb of the harder sentence type. However, the increase at the verb was not larger with increased noise masking. All three groups showed similar effects of syntactic structure in the on-line data. The on-line syntactic effects were not due to problems in word recognition. Correlational analyses did not indicate a relationship between the increase in processing time at the capacity demanding region of the harder sentence types and any of the measures of working memory capacity in any of the three listening conditions. Results indicate that on-line sentence processing is not affected by noise masking if lexical access (e.g., word recognition) remains intact.     

The Edinburgh Masker: A clinical analog study

This article will describe the effects of instructions and practice on the vocal intensities of normal speakers and stutterers while reading in the presence of masking moise generated by the Edinburgh Masker. Both the normal speakers and the stutterers reacted in similar ways: They increased vocal intensity with the introduction of the noise, reduced vocal intensity in the presence of the noise, given instructions and practice, but failed to reduce vocal intensity to pre-noise reference levels. While these results are hardly reflective of long-term change in clinical behavior, a recommendation is made for a reexamination of the role of the increased vocal intensity as at least one factor, of perhaps many, responsible for whatever the long-term clinical effectiveness of the Masker.     

Response latencies of rats during behavioral thermoregulation

The cutaneous thermal stimulation that elicits behavioral thermoregulatory behavior was investigated in these experiments. In Experiment I, rats were placed in a cool environment and allowed to barpress for 3-sec bursts of radiant heat reinforcement. In various phases of the study, rats could earn different intensities of anterior, posterior, or whole-body radiation. Identical response rates were exhibited at each intensity for all exposure conditions; this information, when considered with existing literature on behavioral and neurophysiological studies, suggests that the rat’s thermoregulatory behavior depends on information carried by nonmyelinated fibers that supply thermoreceptors in the skin. Experiment II investigated the hypothesis that cooling of the skin is the stimulus that elicits each thermoregulatory response. Time series measures of skin temperature fluctuations and reaction times (RTs) were obtained. Tails of the RT distributions were shown to conform to exponential probability density functions, and mean RT varied linearly over the domain of reinforcement intensities used. A computer simulation model that describes temperature gradients across layers of skin was employed to estimate temperature fluctuations at the level of the cool receptors. Comparison of simulated skin temperatures with obtained RTs suggests that momentary thermoregulatory behavior is controlled mainly by cooling skin temperature.