Suppression effects in backward and forward masking

The joint effect of forward and backward visual masking appears to be more extended in time than that predicted from an algebraic summation of individual forward and backward masking effects. It is suggested that this apparent extension of the temporal range of masking arises from the summation of forward and backward masking effects which in themselves are insufficient to influence observed performance. Such latent masking effects are possible if it is not assumed that when stimulus identification reaches the 100% level the mask has no effect at all on the stimulus.

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.

To determine the diagnostic yield of the nerve-muscle-skin (NMS) biopsy in paediatric neurology practice. A consecutive series of 98 paediatric NMS biopsies done 1989-1994 retrospectively reviewed in the context of pre-biopsy clinical and laboratory parameters. Bivariate associations based on chi-square test. Unconfounded associations between pre-biopsy variables and positive diagnostic yield (PDY) assessed by multiple logistic regression. Fifty seven out of 98 patients central (global delay, seizures, abnormal CNS imaging) process; 41/98 patients peripheral (motor delay, weakness) process, electromyography-nerve conduction studies (EMG-NCS) 87/98 cases; abnormal 43/87. Positive diagnostic yield (PDY) in 42/98 (43%) biopsies. Statistically significant bivariate associations between PDY and pre-biopsy; age, presenting symptom, developmental delay, weakness, reflexes, CPK, lactate, EMG-NCS and process. Unconfounded associations demonstrated with PDY and age, reflexes and process. The presence of a peripheral process or an abnormal EMG-NCS strongly predictive of PDY: 34/41 (83%) peripheral process cases had PDY, 32/40 (80%) abnormal EMG-NCS cases had PDY, and 29/31 (93.5%) peripheral process and abnormal EMG-NCS cases had PDY. Abnormal EMG-NCS with central process improved PDY to 3/9 (33%) from 4/37 (11%) for normal EMG-NCS. NMS biopsy is a valuable diagnostic tool, particularly in the context of a suspected peripheral process or a central processes with an abnormal EMG-NCS.

Exploring facial emotion perception in schizophrenia using transcranial magnetic stimulation and spatial filtering

Monaural-intelligibility functions for monosyllabic words were obtained for seven subjects with normal hearing under the following major experimental conditions: (1) speech interrupted by silence at the rates of 1, 10, and 100 interruptions per second (ips); (2) speech alternating with noise (80 dB SPL) at rates of 1, 10, and 100 ips; (3) speech in interrupted noise (80 dB SPL) at rates of 1, 10, and 100 ips. The comparison between the intelligibility functions for Conditions 1 and 2 yielded a measure of the effects of forward and backward masking during the noise-free interval. The comparison between the intelligibility functions for Conditions 2 and 3 yielded a measure of the extent to which the speech signal during the noise burst contributed to intelligibility. The results indicated that the effect of forward and backward masking on intelligibility was substantial at 10 ips and even more pronounced at 100 ips. However, at 1 ips little masking effect was observed except at very adverse signal-to-noise (S/N) ratios. The findings also demonstrated that the speech heard within the noise burst contributed to intelligibility at favorable S/N ratios when the noise was interrupted one time per second. At 100 ips, the speech signal within the noise burst made only a small contribution to the total intelligibility score, and at 10 ips the function was formed almost entirely by the speech heard during the noise-free intervals.

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.

1 The Relevance of Psychophysics for Speech Perception.- The role of psychophysics in understanding speech perception.- Central and peripheral processes in the perception of speech and nonspeech sounds.- Psychophysics versus specialized processes in speech perception: an alternative perspective.- Speech perception and the role of long-term memory.- Levels of representation of phonemes and bandwidth of spectral-temporal integration.- General discussion of session 1.- 2 Separation of Acoustic Events.- The meaning of duplex perception: sounds as transparant objects.- Perceptual separation of speech from concurrent sounds.- Sound separation and auditory perceptual organization.- On the significance of spectral synchrony for signal detection.- Auditory enhancement in speech perception.- General discussion of session 2.- 3 Dynamic Aspects.- Trading relations, acoustic cue integration, and context effects in speech perception.- Perceptual integration of rise time and silence in affricate/fricative and pluck/bow continua.- Reversal of the rise-time cue in the affricate/fricative contrast: an experiment on the silence of sound.- Possible acoustic bases for the perception of voicing contrasts.- Is there a natural sensitivity at 20ms in relative tone-onset-time continua? A reanalysis of Hirsh's (1959) data.- Auditory constraints on speech perception.- Studies of possible psychoacoustic factors underlying speech perception.- Perception of tone, band, and formant sweeps.- Psychophysical representation of stop consonant and temporal masking in speech.- Effects of stimulus dynamics on frequency discrimination.- Extending the search for a psychophysical basis for dynamic phonetic patterns.- General discussion of session 3.- 4 Timbre (Peripheral Constraints and Central Processes in the Perception of Complex Signals)..- Psychophysics of audio signal processing and the role of pitch in speech..- Does the human auditory system include large scale spectral integration?.- Some aspects of the sound of speech sounds.- Involvement of the critical band in identification, perceived distance, and discrimination of vowels.- Profile analysis and speech perception.- General discussion of session 4.- 5 Physiological Correlates of Speech Perception.- Peripheral auditory processing of speech information: implications from a physiological study of intensity discrimination.- Organization of the cochlear nucleus for information processing.- Changes in the phonemic quality and neural representation of a vowel by alteration of the relative phase of harmonics near F1.- Phase vowels.- Nonlinear responses, in the auditory nerve to vowel-related complex stimuli.- Discussion of physiological correlates of speech perception.- General discussion of session 5.- 6 Primary Speech Percepts.- English and French speech processing: some psycholinguistic investigations.- Units of organization and analysis in the perception of speech.- Implications from infant speech studies on the unit of perception.- General discussion of session 6.- 7 Psychophysics and Speech Perception in the Hearing-Impaired.- Relationship between psychophysical abilities and speech perception for subjects with unilateral and bilateral cochlear hearing impairments.- Speech-reception threshold in a fluctuating background sound and its possible relation to temporal auditory resolution.- Differences in listening strategies between normal and hearing-impaired listeners.- Critical bands in the perception of speech signals by normal and sensorineural hearing loss listeners.- Phase and the hearing-impaired.

Temporal masking of auditory evoked brainstem responses in human newborns and adults.

The paper presents a concept of lifelong plasticity of peripheral vision. Central vision processing is accepted as critical and irreplaceable for normal perception in humans. While peripheral processing chiefly carries information about motion stimuli features and redirects foveal attention to new objects, it can also take over functions typical for central vision. Here I review the data showing the plasticity of peripheral vision found in functional, developmental, and comparative studies. Even though it is well established that afferent projections from central and peripheral retinal regions are not established simultaneously during early postnatal life, central vision is commonly used as a general model of development of the visual system. Based on clinical studies and visually deprived animal models, I describe how central and peripheral visual field representations separately rely on early visual experience. Peripheral visual processing (motion) is more affected by binocular visual deprivation than central visual processing (spatial resolution). In addition, our own experimental findings show the possible recruitment of coarse peripheral vision for fine spatial analysis. Accordingly, I hypothesize that the balance between central and peripheral visual processing, established in the course of development, is susceptible to plastic adaptations during the entire life span, with peripheral vision capable of taking over central processing.

Backward masking (BM) is an auditory phenomenon in which the threshold of an auditory signal is elevated due to the presence of another signal (masker) that follows it. Models related to central auditory temporal processes, such as the 'temporal window' model, have been suggested to explain this phenomenon. If this assumption is correct then BM thresholds are expected to improve as a function of age. Electrophysiological data suggest that the central auditory system undergoes maturation in the first two decades of life. Empirical data on the development of BM with age are limited. Therefore, the goals of the present study were to study the effect of age on the performance of backward masking in normal developing children and to determine the age at which children reach adult-like performance. Subjects were 30 normal developing children divided into three groups according to age: 7, 9 and 11 years old. Stimuli consisted of a 1000 Hz pure tone and a bandpass masker (600-1400 Hz). Three BM threshold estimates were obtained for each subject using a three-alternative forced-choice adaptive procedure. The data show a trend for improvement in backward-masking thresholds with increasing age. Specifically, 7 and 9 year-old children performed significantly poorer than those reported for adults, whereas 11 year-old children reached adult-like performance. These data contribute to the small body of literature on backward masking in normal developing children. They are in keeping with what is known regarding the age of physiological maturation of the auditory system and have important clinical implications in the assessment of children with suspected temporal processing deficits.

Forward masking occurs when noise is presented before the target signal, making the latter difficult to be perceived. It is related to temporal auditory processing and consequently to speech recognition in noisy environments, which may decline with age. Interest in forward masking has grown in the last years. Studies investigate psychoacoustic and electrophysiological recordings in different age- groups. The purpose of the study was to investigate the effect of forward masking on frequency following response (FFR) as a function of age. Cross-sectional analytical observational study. We assessed 69 normal-hearing participants of both genders assigned to three groups: 40 young individuals (aged 18-25 years, mean age = 22 years 8 months), 21 middle-age individuals (aged 25-55 years, mean age = 37 years 2 months), and 8 seniors (aged <55 years, mean age = 65 years 3 months). FFRs were recorded using the /da/ syllable with and without noise. The /da/ syllable and speech-shaped noise were monaurally presented to the participants' right ears through ER-3a insert earphones. Electrodes were placed in M1 and M2 (-), Fz (+), and Fpz (ground). Acquisition occurred under two conditions: (1) the/da/ syllable presented without the noise and (2) the /da/ syllable presented 4 msec after the noise. Data show that (1) considering the mean values of all participants, there was a significant latency delay of all waves (PV, A, PW, PX, PY, PZ, and O) when the /da/ syllable was presented 4 msec after the masking noise as compared with the condition without noise, that is, forward masking occurred in all components of the FFR responses, and (2) for the youngest group and the middle-age group, forward masking was seen for all waves, except PX in the latter one; for the senior group, an irregular pattern was observed (presence of forward masking in PA, PY, PZ, and O). This pattern may be due to an aging effect on FFR responses even without noise presence, which makes it more difficult to identify forward masking effect in this population. Although it is well documented in the literature that forward masking increases with age, this is less evident on FFR recordings in the senior population. An aging effect was identified in FFR responses. Forward masking was identified in FFR responses of all groups but less evident in senior population.

This experiment demonstrated a relationship between prepulse inhibition (PPI) of the startle eyeblink and visual backward masking in college students. It was hypothesized that recovery from backward masking effects is due in part to sensory gating, as assessed by auditory and visual PPI. Visual presentations of letters served as targets or visual prepulses in an intermixed session of backward masking and PPI. Backward masking and PPI (both auditory and visual) were assessed at stimulus onset asynchronies of 30, 45, 60, 120, and 150 ms. A repeated-measures regression revealed that there was a relationship between backward masking and PPI for both visual and auditory PPI, with higher levels of PPI being associated with greater recovery from backward masking. The data are consistent with the hypothesis that recovery from backward masking effects is affected by sensory gating acting in part to gate out the interruptive effects of the mask.

Background: Forward masking occurs when noise is presented before the target signal, making thelatter difficult to be perceived. It is related to temporal auditory processing and consequently to speechrecognition in noisy environments, which may decline with age. Interest in forward masking has grown inthe last years. Studies investigate psychoacoustic and electrophysiological recordings in different age groups.&lt;br /&gt;Purpose: The purpose of the study was to investigate the effect of forward masking on frequency followingresponse (FFR) as a function of age.&lt;br /&gt;Research Design: Cross-sectional analytical observational study.&lt;br /&gt;Study Sample: We assessed 69 normal-hearing participants of both genders assigned to three groups: 40young individuals (aged 18–25 years,mean age = 22 years, 8 months), 21 middle-age individuals (aged 25–55years, mean age = 37 years, 2 months), and 8 seniors (aged &lt; 55 years, mean age = 65 years, 3 months).&lt;br /&gt;Intervention: FFRs were recorded using the /da/ syllable with and without noise.&lt;br /&gt;Data Collection and Analysis: The /da/ syllable and speech-shaped noise were monaurally presentedto the participants’ right ears through ER-3a insert earphones. Electrodes were placed in M1 and M2 (-),Fz (+), and Fpz (ground). Acquisition occurred under two conditions: (1) the /da/ syllable presented withoutthe noise and (2) the /da/ syllable presented 4 msec after the noise.&lt;br /&gt;Results: Data show that (1) considering the mean values of all participants, there was a significant latencydelay of all waves (PV, A, PW, PX, PY, PZ, and O) when the /da/ syllable was presented 4 msecafter the masking noise as compared with the condition without noise, that is, forward masking occurredin all components of the FFR responses, and (2) for the youngest group and the middle-age group, forwardmasking was seen for all waves, except PX in the latter one; for the senior group, an irregular patternwas observed (presence of forward masking in PA, PY, PZ, and O). This pattern may be due to an agingeffect on FFR responses even without noise presence, which makes it more difficult to identify forwardmasking effect in this population. Although it is well documented in the literature that forward maskingincreases with age, this is less evident on FFR recordings in the senior population.&lt;br /&gt;Conclusions: An aging effect was identified in FFR responses. Forward masking was identified in FFRresponses of all groups but less evident in senior population.&lt;br /&gt;

The frequency selectivity of the peripheral ear (e.g., at the VIIIth nerve level) is so acute that onset and offset transients in responses to short signals produce a nonnegligible extension of the signal duration. Thus, peripheral excitation patterns produced by signals which were separated in time can overlap and thereby mask each other. We refer to this type of masking as transient masking. Published data on nonsimultaneous masking and the results of two new experiments are compared with the masking that may be expected from filter transients. It is concluded that backward masking is mainly due to interactions at the level of the filter outputs, and that in forward masking, in addition to a short-term component, a long-term component is distinguishable. The latter has an exponential decay with a time constant of approximately 75 msec, and is probably related to physiological adaptation effects.

A low-pass noise (1500-Hz cutoff) with a sinusoidal variation in its amplitude spectrum (ripple noise) was used to mask a 1000-Hz signal (10 msec) in both a forward and a simultaneous masking procedure. The masked thresholds of the signal were measured as a function of the number of peaks (ripples) in the amplitude spectrum of the noise. The procedure was similar to that used by Houtgast who reported it at the 83rd meeting of the Acoustical Society. Houtgast used a pulsation threshold technique with ripple noise to study frequency selectivity. Pulsation threshold is similar to simultaneous forward and backward masking. The data of the present study indicate that results similar, but not identical, to Houtgast's can be obtained with forward masking alone. The frequency selectivity obtained with the forward masking procedure is sharper than has been previously obtained and might indicate the presence of lateral inhibition.