Forward Masking Conditions Research Articles

Comparing the Influences of Masking, Crowding, Response Conflict, and Cortical Scaling on Simple Shape Identification with Foveal Targets

Two experiments were conducted to compare the effects of masking and crowding on simple shape perception. The target stimuli were presented in foveal vision, where masking effects are generally investigated and where crowding effects are typically small compared to peripheral vision. The second experiment investigated the potential involvement of the dorsal visual pathway by testing if a peripheral crowding stimulus could interfere with the perception of a target shape, if it were scaled to account for low visual acuity? The results of both experiments indicated strong congruency effects, especially for pattern and metacontrast masking (which, in some respects, is similar to crowding). Congruency effects were generally weak for distractors presented further from the target. In Experiment 2, cortically scaled distractors only showed a potential influence in the forward masking condition. Perhaps this is an indication of a priming effect from the distant crowding stimuli. Further research might reveal the extent to which crowding displays can test physiologically motivated hypotheses.

A notched-noise precursor affects both diotic and dichotic notched-noise masking

The present study investigates how diotic and dichotic masked thresholds, in a notched-noise masking paradigm, are affected by activation of the Medial OlivoCochlear (MOC) reflex. Thresholds were obtained for a 500-Hz pure tone diotic or a dichotic signal, S (S0 or Sπ respectively), in the presence of a simultaneous or forward diotic masker (bandpass noise with no notch or a 400-Hz notch). A diotic precursor sound (bandpass noise with a 400- or 800-Hz notch) was presented prior to the signal and masker to activate the MOC reflex. For simultaneous- and forward-masking conditions, the decrease in masked thresholds as a notch was introduced in the masker was larger for the diotic than for the dichotic condition. This resulted in a reduced binaural masking level difference (BMLD) for the masker with a notch. The precursor augmented these two effects. The results indicate that the effect of the precursor, eliciting the MOC reflex, is less pronounced when binaural cues are processed.

Masking Effects of Irrelevant Visual Information under Conditions of Basic and Superordinate Categorization of Complex Images

We analyzed the accuracy and reaction time (RT) of basic and superordinate image categorization under forward masking conditions in 41 healthy subjects. Images of man-made objects and animals were used as target stimuli, while images of man-made objects, animals, faces, and buildings were used as masks. The comparison of the psychometric characteristics of the basic and superordinate categorization showed the influence of mask and stimulus semantic similarity on the forward masking effectiveness, which depended on the type of experimental task performed by the subject (the level of categorization of the target stimulus). The masking effect at the basic-level categorization was more pronounced at a greater semantic similarity between the mask and the target stimulus. In contrast, a greater masking effect at the superordinate-level categorization was observed when the mask and the stimulus belonged to different categories. The images of faces and buildings had a less pronounced masking effect compared to the images of animals and man-made objects, regardless of the type of task. For basic-level categorization, the increase in RT under semantically related conditions was caused by distributional skewing. In contrast, for superordinate categorization, semantically unrelated conditions led to distributional shifting towards greater values. The results of this study suggest a hypothesis of temporal and spatial division of cognitive processes of the basic and superordinate categorization.

Nonuniform impacts of forward suppression on neural responses to preferred stimuli and nonpreferred stimuli in the rat auditory cortex.

In natural conditions, human and animals need to extract target sound information from noisy acoustic environments for communication and survival. However, how the contextual environmental sounds impact the tuning of central auditory neurons to target sound source azimuth over a wide range of sound levels is not fully understood. Here, we determined the azimuth-level response areas (ALRAs) of rat auditory cortex neurons by recording their responses to probe tones varying with levels and sound source azimuths under both quiet (probe alone) and forward masking conditions (preceding noise + probe). In quiet, cortical neurons responded stronger to their preferred stimuli than to their nonpreferred stimuli. In forward masking conditions, an effective preceding noise reduced the extents of the ALRAs and suppressed the neural responses across the ALRAs by decreasing the response strength and lengthening the first-spike latency. The forward suppressive effect on neural response strength was increased with increasing masker level and decreased with prolonging the time interval between masker and probe. For a portion of cortical neurons studied, the effects of forward suppression on the response strength to preferred stimuli was weaker than those to nonpreferred stimuli, and the recovery from forward suppression of the response strength to preferred stimuli was earlier than that to nonpreferred stimuli. We suggest that this nonuniform forward suppression of neural responses to preferred stimuli and to nonpreferred stimuli is important for cortical neurons to maintain their relative stable preferences for target sound source azimuth and level in noisy acoustic environments.

Modulation detection interference in cochlear implant listeners under forward masking conditions.

Little is known about cochlear implant (CI) users' ability to process amplitude modulation (AM) under conditions of forward masking (forward-modulation detection/discrimination interference, or F-MDI). In this study, F-MDI was investigated in adult CI listeners using direct electrical stimulation via research interface. The target was sinusoidally amplitude modulated at 50 Hz, and presented to a fixed electrode in the middle of the array. The forward masker was either amplitude modulated at the same rate (AM) or unmodulated and presented at the peak amplitude of its AM counterpart (steady-state peak, SSP). Results showed that the AM masker produced higher modulation thresholds in the target than the SSP masker. The difference (F-MDI) was estimated to be 4.6 dB on average, and did not change with masker-target delays up to 100 ms or with masker-target spatial electrode distances up to eight electrodes. Results with a coherent remote cue presented with the masker showed that confusion effects did not play a role in the observed F-MDI. Traditional recovery from forward masking using the same maskers and a 20-ms probe, measured in four of the subjects, confirmed the expected result: higher thresholds with the SSP masker than the AM masker. Collectively, the results indicate that significant F-MDI occurs in CI users.

Prenatal exposure to multiple pesticides is associated with auditory brainstem response at 9 months in a cohort study of Chinese infants

BackgroundPesticides are associated with poorer neurodevelopmental outcomes, but little is known about the effects on sensory functioning. MethodsAuditory brainstem response (ABR) and pesticide data were available for 27 healthy, full-term 9-month-old infants participating in a larger study of early iron deficiency and neurodevelopment. Cord blood was analyzed by gas chromatography–mass spectrometry for levels of 20 common pesticides. The ABR forward-masking condition consisted of a click stimulus (masker) delivered via ear canal transducers followed by an identical stimulus delayed by 8, 16, or 64 milliseconds (ms). ABR peak latencies were evaluated as a function of masker-stimulus time interval. Shorter wave latencies reflect faster neural conduction, more mature auditory pathways, and greater degree of myelination. Linear regression models were used to evaluate associations between total number of pesticides detected and ABR outcomes. We considered an additive or synergistic effect of poor iron status by stratifying our analysis by newborn ferritin (based on median split). ResultsInfants in the sample were highly exposed to pesticides; a mean of 4.1 pesticides were detected (range 0–9). ABR Wave V latency and central conduction time (CCT) were associated with the number of pesticides detected in cord blood for the 64ms and non-masker conditions. A similar pattern seen for CCT from the 8ms and 16ms conditions, although statistical significance was not reached. Increased pesticide exposure was associated with longer latency. The relation between number of pesticides detected in cord blood and CCT depended on the infant's cord blood ferritin level. Specifically, the relation was present in the lower cord blood ferritin group but not the higher cord blood ferritin group. ConclusionsABR processing was slower in infants with greater prenatal pesticide exposure, indicating impaired neuromaturation. Infants with lower cord blood ferritin appeared to be more sensitive to the effects of prenatal pesticide exposure on ABR latency delay, suggesting an additive or multiplicative effect.

The effect of compression on tuning estimates in a simple nonlinear auditory filter model

Behavioral experiments using auditory masking have been used to characterize frequency selectivity, one of the basic properties of the auditory system. However, due to the nonlinear response of the basilar membrane, the interpretation of these experiments may not be straightforward. Specifically, there is evidence that human frequency-selectivity estimates depend on whether an iso-input or an iso-response measurement paradigm is used [Eustaquio-Martin et al. (2011)]. This study presents simulated tuning estimates using a simple compressive auditory filter model, the bandpass nonlinearity (BPNL), which consists of a compressor between two bandpass filters. The BPNL forms the basis of the dual-resonance nonlinear (DRNL) filter that has been used in a number of modeling studies. The location of the nonlinear element and its effect on the estimated tuning in the two measurement paradigms was investigated. The results show that compression leads to (i) a narrower tuning estimate in the iso-response paradigm when a compressor precedes a filter, and (ii) a wider tuning estimate in the iso-input paradigm when a compressor follows a filter. The results imply that if the DRNL presents a valid model of the basilar membrane, then compression alone may explain a large part of the behaviorally observed differences in tuning between simultaneous and forward-masking conditions.

Characterizing auditory processing and perception in individual listeners with sensorineural hearing loss

This study considered consequences of sensorineural hearing loss in ten listeners. The characterization of individual hearing loss was based on psychoacoustic data addressing audiometric pure-tone sensitivity, cochlear compression, frequency selectivity, temporal resolution, and intensity discrimination. In the experiments it was found that listeners with comparable audiograms can show very different results in the supra-threshold measures. In an attempt to account for the observed individual data, a model of auditory signal processing and perception [Jepsen et al., J. Acoust. Soc. Am. 124, 422-438 (2008)] was used as a framework. The parameters of the cochlear processing stage of the model were adjusted to account for behaviorally estimated individual basilar-membrane input-output functions and the audiogram, from which the amounts of inner hair-cell and outer hair-cell losses were estimated as a function of frequency. All other model parameters were left unchanged. The predictions showed a reasonably good agreement with the measured individual data in the frequency selectivity and forward masking conditions while the variation of intensity discrimination thresholds across listeners was underestimated by the model. The model and the associated parameters for individual hearing-impaired listeners might be useful for investigating effects of individual hearing impairment in more complex conditions, such as speech intelligibility in noise.

Abnormal auditory forward masking pattern in the brainstem response of individuals with Asperger syndrome

Abnormal auditory information processing has been reported in individuals with autism spectrum disorders (ASD). In the present study auditory processing was investigated by recording auditory brainstem responses (ABRs) elicited by forward masking in adults diagnosed with Asperger syndrome (AS). Sixteen AS subjects were included in the forward masking experiment and compared to three control groups consisting of healthy individuals (n = 16), schizophrenic patients (n = 16) and attention deficit hyperactivity disorder patients (n = 16), respectively, of matching age and gender. The results showed that the AS subjects exhibited abnormally low activity in the early part of their ABRs that distinctly separated them from the three control groups. Specifically, wave III amplitudes were significantly lower in the AS group than for all the control groups in the forward masking condition (P < 0.005), which was not the case in the baseline condition. Thus, electrophysiological measurements of ABRs to complex sound stimuli (eg, forward masking) may lead to a better understanding of the underlying neurophysiology of AS. Future studies may further point to specific ABR characteristics in AS individuals that separate them from individuals diagnosed with other neurodevelopmental diseases.

Directional effects between rapid auditory processing and phonological awareness in children

Deficient rapid auditory processing (RAP) has been associated with early language impairment and dyslexia. Using an auditory masking paradigm, children with language disabilities perform selectively worse than controls at detecting a tone in a backward masking (BM) condition (tone followed by white noise) compared to a forward masking (FM) condition (tone preceded by white noise). Tallal's (1980) auditory processing hypothesis posits that abnormal RAP leads to reduced (or impaired) phonological awareness (PA), resulting in reading and language difficulties. Alternative theories suggest that impaired PA may have more of a top-down effect on auditory processing. The current study examines RAP in children tested at two time points, average age 5.6 and average age 8.3, in order to test causal relations between RAP and PA in a path analysis. Additional hierarchical regressions examine how well RAP predicts reading ability when accounting for PA and vocabulary. The path analysis indicates a top-down effect, such that PA has a larger impact on BM over time than the reverse. Regressions indicate no direct impact of RAP on reading ability. The path analysis provides evidence against the auditory processing hypothesis and instead suggests that between the ages of 5 and 8 it is variability in early phonological representations that predicts subsequent lower-level rapid auditory processing.

Are Masking Abnormalities in Schizophrenia Limited to Backward Masking?

Schizophrenia, it has been proposed, is associated with deficits in the magnocellular part of the visual system. In support of this suggestion, it has been claimed that schizophrenic subjects have abnormal backward masking. However, if this abnormality is to be linked specifically to magnocellular defects, then it must be specific to backward masking, and not, also effect, for example, forward masking. We examined this issue by reviewing the studies of masking in schizophrenic subjects. We find: (i) Most studies (56 out of 67) of backward masking have researched only backward masking. This makes it impossible to determine if the abnormalities found in these studies are exclusively confined to backward masking. (ii) Of those studies (11) that have included both forward and backward masking conditions, the majority found some degree of abnormality under both forward and backward masking conditions. It is concluded that the evidence for linking the abnormalities found in those with schizophrenia specifically to backward masking, rather than masking in general, or more general visual impairments, is at present relatively weak. Given the rationale for using backward masking as a test of magnocellular sensitivity, research in this area does not point to a deficit specific to the magnocellular system.

Facilitation of intensity discrimination of short stimuli in noise occurs not far from a stimuli detection threshold

Adaptation is a main property of sensory receptors. In a basis of adaptation are properties of peripheral receptors and central neuron. There is a question: what is the auditory adaptation mechanism to short high frequency stimuli? How the auditory system can trace stimulus amplitude changes? The probable answer is: stimuli are mixed with noise of different origin. Noise adapts hearing and improves discrimination of stimulus. Simulation researches of peripheral encoding were shown the amplitude structure of short stimulus acting in isolation or in noise could be preserved when intensity are not far from thresholds of fibers. For each stimulus level there is the certain noise level, when amplitude structure can be detected without losses. In this work the validity of these statements was checked up in auditory experiments. The thresholds of intensity discrimination (ID) for short stimulus presented in silence and in conditions of simultaneous and forward masking have been estimated. In a range of average stimulus intensity and for each stimulus level there is the certain noise level when ID is better in noise but not in silence. The ID facilitation is registered near to the stimulus detection thresholds and after adaptation of hearing by noise. Results of auditory researches correspond to the simulation results.

Response growth using a low-frequency suppressor

Numerous psychophysical studies on two-tone suppression have been carried out. More recently, researchers have attempted to relate the magnitude of suppression to the level of suppressee. [Wojtczak, M., Viemeister, N.F., 2005. Psychophysical response growth under suppression. In: Pressnitzer, D., de Cheveigne, A., McAdams, S., Collet, L. (Eds.), Auditory Signal Processing: Physiology, Psychoaccoustics, and Models. Springer, New York, pp. 67–74] demonstrated that the magnitude of suppression for a higher-frequency, fixed-level suppressor decreases with increasing level of the suppressee. This suggests a linearization of the basilar membrane response in presence of a high-frequency suppressor. The present study expands these results to a low-frequency suppressor of varying intensity levels. Detection of a 10-ms, 4.0-kHz probe was measured under different forward-masking conditions: one with a 200-ms, 4.0-kHz masker (suppressee) presented with no suppressor and another with the same masker paired with a 2.2-kHz, 200-ms suppressor. The 4.0-kHz masker level was varied adaptively and a range of probe levels was used to measure the growth of suppression. Results indicate that (1) the magnitude of suppression increases with increasing suppressor level and (2) generally, the probe level was not related to the magnitude of suppression.

A unified view of the temporal-window and the adaptation-loop model in conditions of forward- and simultaneous masking

Two different mechanisms have been discussed in the literature as a possible explanation for forward masking: persistence (or temporal integration) and adaptation. In this study, two well established models of temporal processing in the auditory system are compared in a unified modeling framework. The temporal-window model representing a temporal-integration mechanism and the adaptation-loop model as the representative for the adaptation mechanism. The unified modeling framework shared a compressive, non-linear auditory filter stage and a template-based (optimal detector) decision stage. Predictions from both models were obtained in conditions of forward masking at 1 and 4 kHz for masker-to-signal gaps of 0 to 160 ms, and in conditions of simultaneous masking, where the signal was temporally overlapping with the masker. The signal was a 10- or 12-ms raised-cosine ramped pure tone and the masker a 200-ms broadband noise. It was found that when both models are adjusted to behave similarly, the two mechanisms can be considered as being essentially equivalent. In fact, the combination of integration and the signal-to-noise-ratio based detection criterion in the temporal-window model can be interpreted as adaptation. Suggestions for a unified model of auditory processing are presented. [Work supported by the Danish Research Council.]

Estimates of human cochlear tuning at low levels using forward and simultaneous masking.

Auditory filter shapes were derived from psychophysical measurements in eight normal-hearing listeners using a variant of the notched-noise method for brief signals in forward and simultaneous masking. Signal frequencies of 1, 2, 4, 6, and 8 kHz were tested. The signal level was fixed at 10 dB above absolute threshold in the forward-masking conditions and fixed at either 10 or 35 dB above absolute threshold in the simultaneous-masking conditions. The results show that filter equivalent rectangular bandwidths (ERBs) are substantially narrower in forward masking than has been found in previous studies using simultaneous masking. Furthermore, in contrast to earlier studies, the sharpness of tuning doubles over the range of frequencies tested, giving Q(ERB) values of about 10 and 20 at signal frequencies of 1 and 8 kHz, respectively. It is argued that the new estimates of auditory filter bandwidth provide a more accurate estimate of human cochlear tuning at low levels than earlier estimates using simultaneous masking at higher levels, and that they are therefore more suitable for comparison to cochlear tuning data from other species. The data may also prove helpful in defining the parameters for nonlinear models of human cochlear processing.

The mid-level hump at 2 kHz.

Shortening the duration of a Gaussian-shaped 2-kHz tone-pip causes the intensity-difference limen (DL) to depart from the "near-miss to Weber's law" and swell into a mid-level hump [Nizami et al., J. Acoust. Soc. Am. 110, 2505-2515 (2001)]. For some subjects the size of this hump approaches or exceeds the size reported for longer tones under forward masking, suggesting that forward masking might make little difference to the DL for very brief probes. To test this hypothesis, DLs were determined over 30 to 90 dB SPL for a brief Gaussian-shaped 2-kHz tone-pip. DLs were obtained first without forward masking, then with the pip placed 10 or 100 ms after a 200-ms 2-kHz tone of 50 dB SPL, or 100 ms after a 200-ms 2-kHz tone of 70 dB SPL. DLs inflated significantly under all forward-masking conditions. DLs also enlarged under an 80 dB SPL forward masker at pip delays of 4, 10, 40, and 100 ms. The peaks of the humps obtained under forward masking clustered around a sensation level (SL) that was significantly lower than the average SL for the peaks of the humps obtained without forward masking. Overall, the results do not support the neuronal-recovery-rate model of Zeng et al. [Hear. Res. 55, 223-230 (1991)], but are not incompatible with the Carlyon and Beveridge hypothesis [J. Acoust. Soc. Am. 93, 2886-2895 (1993)] that nonsimultaneous maskers corrupt the memory trace evoked by the probe.

Phase effects in simultaneous and forward masking

We estimated masked thresholds for a 20-ms (two 10-ms ramps), 1-kHz sinusoid as a function of its temporal relation to a 400-ms, 1-kHz sinusoid in the transition from simultaneous to forward masking conditions (signal center minus masker offset times of −200, −20, −10, −3.75, −2.40, −1.25, 0.00, 1.25, 2.40, 3.75, 10, and 20 ms). In simultaneous masking conditions, thresholds for signals presented in phase with the masker were lower than for signals added in quadrature, but there was no such phase effect in forward masking conditions. When there was partial overlap of signal and masker, the phase effect was apparent until +3.75-ms center-offset time, where the phase effect disappeared and thresholds decreased. Thresholds for just the portions of the 20-ms signal that occurred during the masker (simultaneous partial signals) and for the portions of the 20-ms signals after the masker (forward partial signals), generally were consistent with results for whole (20-ms) signals: when thresholds for the whole signal appeared to be determined by simultaneous masking, thresholds for the simultaneous partial signals matched those of the whole signal and also showed a phase effect, whereas thresholds for the forward partial signals were higher and showed no phase effect.

Binaural processing model based on contralateral inhibition. III. Dependence on temporal parameters.

This paper and two accompanying papers [Breebaart et al., J. Acoust. Soc. Am. 110, 1074-1088 (2001); 110, 1089-1104 (2001)] describe a computational model for the signal processing of the binaural auditory system. The model consists of several stages of monaural and binaural preprocessing combined with an optimal detector. Simulations of binaural masking experiments were performed as a function of temporal stimulus parameters and compared to psychophysical data adapted from literature. For this purpose, the model was used as an artificial observer in a three-interval, forced-choice procedure. All model parameters were kept constant for all simulations. Model predictions were obtained as a function of the interaural correlation of a masking noise and as a function of both masker and signal duration. Furthermore, maskers with a time-varying interaural correlation were used. Predictions were also obtained for stimuli with time-varying interaural time or intensity differences. Finally, binaural forward-masking conditions were simulated. The results show that the combination of a temporal integrator followed by an optimal detector in the time domain can account for all conditions that were tested, except for those using periodically varying interaural time differences (ITDs) and those measuring interaural correlation just-noticeable differences (jnd's) as a function of bandwidth.

Properties of derived cochlear action potentials in forward tonal masking in guinea pigs.

Chronic experiments on guinea pigs were used to study the characteristics of cochlear nerve action potentials and the derived potential in conditions of forward masking. The auditory nerve action potential was recorded from the round window of the cochlea. The derived potential was obtained by subtracting the action potential recorded with masking from the response obtained in silence. These studies showed that the derived potential showed higher sensitivity to masking than the traditional measure of masking, i.e., the decrement in the amplitude of the auditory nerve action potential. The derived potential reflects not only changes in the action potential during masking, but also changes in its shape. Differences between the derived potential and the action potential decrement provide evidence that the amplitude and time changes in the derived potential provide more complete information on the nature of activity in the auditory fibers.

Perception of speech and non-speech sounds by listeners with real and simulated sensorineural hearing loss

The effects of sensorineural and simulated hearing loss on the perception of speech and non-speech sounds are evaluated and compared. Two simulations of hearing loss are considered: one introduces additive masking noise to elevate the detection thresholds of listeners with normal hearing, the other applies multiband dynamic expansion to attenuate sound components towards these detection thresholds. Measures of speech perception are derived from intelligibility tests for consonant-vowel syllables presented in a background of speech-spectrum noise. The perception of non-speech sounds was evaluated through measurements of the detection of tones in quiet and in the presence of broadband and narrowband masking noise, psychoacoustic tuning curves measured under forward masking conditions, and intensity discrimination for tone pulses. For mild and moderate hearing losses, both types of simulation alter the perception of speech in noise in a manner similar to sensorineural impairment. These simulations also produce effects similar to sensorineural impairment on the detection of tones in quiet and on simultaneous and forward masking. The expansion simulation tends to improve the ability to discriminate tone intensities, an effect generally not seen in listeners with sensorineural impairments.