Peripheral Masking Research Articles

Tactile facilitation during actual and mere expectation of object reception

During reaching and grasping movements tactile processing is typically suppressed. However, during a reception or catching task, the object can still be acquired but without suppressive processes related to movement execution. Rather, tactile information may be facilitated as the object approaches in anticipation of object contact and the utilization of tactile feedback. Therefore, the current study investigated tactile processing during a reception task. Participants sat with their upper limb still as an object travelled to and contacted their fingers. At different points along the object’s trajectory and prior to contact, participants were asked to detect tactile stimuli delivered to their index finger. To understand if the expectation of object contact contributed to any modulation in tactile processing, the object stopped prematurely on 20% of trials. Compared to a pre-object movement baseline, relative perceptual thresholds were decreased throughout the object’s trajectory, and even when the object stopped prematurely. Further, there was no evidence for modulation when the stimulus was presented shortly before object contact. The former results suggest that tactile processing is facilitated as an object approaches an individual’s hand. As well, we purport that the expectation of tactile feedback drives this modulation. Finally, the latter results suggest that peripheral masking may have reduced/abolished any facilitation.

Frequency-to-Place Mismatch: Characterizing Variability and the Influence on Speech Perception Outcomes in Cochlear Implant Recipients.

The spatial position of a cochlear implant (CI) electrode array affects the spectral cues provided to the recipient. Differences in cochlear size and array length lead to substantial variability in angular insertion depth (AID) across and within array types. For CI-alone users, the variability in AID results in varying degrees of frequency-to-place mismatch between the default electric frequency filters and cochlear place of stimulation. For electric-acoustic stimulation (EAS) users, default electric frequency filters also vary as a function of residual acoustic hearing in the implanted ear. The present study aimed to (1) investigate variability in AID associated with lateral wall arrays, (2) determine the subsequent frequency-to-place mismatch for CI-alone and EAS users mapped with default frequency filters, and (3) examine the relationship between early speech perception for CI-alone users and two aspects of electrode position: frequency-to-place mismatch and angular separation between neighboring contacts, a metric associated with spectral selectivity at the periphery. One hundred one adult CI recipients (111 ears) with MED-EL Flex24 (24 mm), Flex28 (28 mm), and FlexSOFT/Standard (31.5 mm) arrays underwent postoperative computed tomography to determine AID. A subsequent comparison was made between AID, predicted spiral ganglion place frequencies, and the default frequency filters for CI-alone (n = 84) and EAS users (n = 27). For CI-alone users with complete insertions who listened with maps fit with the default frequency filters (n = 48), frequency-to-place mismatch was quantified at 1500 Hz and angular separation between neighboring contacts was determined for electrodes in the 1 to 2 kHz region. Multiple linear regression was used to examine how frequency-to-place mismatch and angular separation of contacts influence consonant-nucleus-consonant (CNC) scores through 6 months postactivation. For CI recipients with complete insertions (n = 106, 95.5%), the AID (mean ± standard deviation) of the most apical contact was 428° ± 34.3° for Flex24 (n = 11), 558° ± 65.4° for Flex28 (n = 48), and 636° ± 42.9° for FlexSOFT/Standard (n = 47) arrays. For CI-alone users, default frequency filters aligned closely with the spiral ganglion map for deeply inserted lateral wall arrays. For EAS users, default frequency filters produced a range of mismatches; absolute deviations of ≤ 6 semitones occurred in only 37% of cases. Participants with shallow insertions and minimal or no residual hearing experienced the greatest mismatch. For CI-alone users, both smaller frequency-to-place mismatch and greater angular separation between contacts were associated with better CNC scores during the initial 6 months of device use. There is significant variability in frequency-to-place mismatch among CI-alone and EAS users with default frequency filters, even between individuals implanted with the same array. When using default frequency filters, mismatch can be minimized with longer lateral wall arrays and insertion depths that meet the edge frequency associated with residual hearing for CI-alone and EAS users, respectively. Smaller degrees of frequency-to-place mismatch and decreased peripheral masking due to more widely spaced contacts may independently support better speech perception with longer lateral wall arrays in CI-alone users.

Central Auditory Processing of Temporal and Spectral-Variance Cues in Cochlear Implant Listeners.

Cochlear implant (CI) listeners have difficulty understanding speech in complex listening environments. This deficit is thought to be largely due to peripheral encoding problems arising from current spread, which results in wide peripheral filters. In normal hearing (NH) listeners, central processing contributes to segregation of speech from competing sounds. We tested the hypothesis that basic central processing abilities are retained in post-lingually deaf CI listeners, but processing is hampered by degraded input from the periphery. In eight CI listeners, we measured auditory nerve compound action potentials to characterize peripheral filters. Then, we measured psychophysical detection thresholds in the presence of multi-electrode maskers placed either inside (peripheral masking) or outside (central masking) the peripheral filter. This was intended to distinguish peripheral from central contributions to signal detection. Introduction of temporal asynchrony between the signal and masker improved signal detection in both peripheral and central masking conditions for all CI listeners. Randomly varying components of the masker created spectral-variance cues, which seemed to benefit only two out of eight CI listeners. Contrastingly, the spectral-variance cues improved signal detection in all five NH listeners who listened to our CI simulation. Together these results indicate that widened peripheral filters significantly hamper central processing of spectral-variance cues but not of temporal cues in post-lingually deaf CI listeners. As indicated by two CI listeners in our study, however, post-lingually deaf CI listeners may retain some central processing abilities similar to NH listeners.

The Effects of Energetic and Informational Masking on the Words-in-Noise Test (WIN)

In certain masking paradigms, the masker can have two components, energetic and informational. Energetic masking is the traditional peripheral masking, whereas informational masking involves confusions (uncertainty) between the signal and masker that originate more centrally in the auditory system. Sperry et al (1997) used Northwestern University Auditory Test No. 6 (NU-6) words in multitalker babble to study the differential effects of energetic and informational masking using babble played temporally forward (FB) and backward (BB). The FB and BB are the same except BB is void of the contextual and semantic content cues that are available in FB. It is these informational cues that are thought to fuel informational masking. Sperry et al found 15% better recognition performance (∼3 dB) on BB than on FB, which can be interpreted as the presence of informational masking in the FB condition and not in the BB condition (Dirks and Bower, 1969). The Words-in-Noise Test (WIN) (Wilson, 2003; Wilson and McArdle, 2007) uses NU-6 words as the signal and multitalker babble as the masker, which is a combination of stimuli that potentially could produce informational masking. The WIN presents 5 or 10 words at each of seven signal-to-noise ratios (S/N, SNR) from 24 to 0 dB in 4 dB decrements with the 50% correct point being the metric of interest. The same recordings of the NU-6 words and multitalker babble used by Sperry et al are used in the WIN. To determine whether informational masking was involved with the WIN. Descriptive, quasi-experimental designs were conducted in three experiments using FB and BB in various paradigms in which FB and BB varied from 4.3 sec concatenated segments to essentially continuous. Eighty young adults with normal hearing and 64 older adults with sensorineural hearing losses participated in a series of three experiments. Experiment 1 compared performance on the normal WIN (FB) with performance on the WIN in which the babble segment with each word was reversed temporally (BB). Experiment 2 examined the effects of continuous FB and BB segments on WIN performance. Experiment 3 replicated the Sperry et al (1997) experiment at 4 and 0 dB S/N using NU-6 words in the FB and BB conditions. Experiment 1-with the WIN paradigm, recognition performances on FB and BB were the same for listeners with normal hearing and listeners with hearing loss, except at the 0 dB S/N with the listeners with normal hearing at which performance was significantly better on BB than FB. Experiment 2-recognition performances on FB and BB were the same at all SNRs for listeners with normal hearing using a slightly modified WIN paradigm. Experiment 3-there was no difference in performances on the FB and BB conditions with either of the two SNRs. Informational masking was not involved in the WIN paradigm. The Sperry et al results were not replicated, which is thought to be related to the way in which the Sperry et al BB condition was produced.

Sentence recognition in noise promoting or suppressing masking release by normal-hearing and cochlear-implant listeners

Normal-hearing (NH) listeners maintain robust speech understanding in modulated noise by "glimpsing" portions of speech from a partially masked waveform--a phenomenon known as masking release (MR). Cochlear implant (CI) users, however, generally lack such resiliency. In previous studies, temporal masking of speech by noise occurred randomly, obscuring to what degree MR is attributable to the temporal overlap of speech and masker. In the present study, masker conditions were constructed to either promote (+MR) or suppress (-MR) masking release by controlling the degree of temporal overlap. Sentence recognition was measured in 14 CI subjects and 22 young-adult NH subjects. Normal-hearing subjects showed large amounts of masking release in the +MR condition and a marked difference between +MR and -MR conditions. In contrast, CI subjects demonstrated less effect of MR overall, and some displayed modulation interference as reflected by poorer performance in modulated maskers. These results suggest that the poor performance of typical CI users in noise might be accounted for by factors that extend beyond peripheral masking, such as reduced segmental boundaries between syllables or words. Encouragingly, the best CI users tested here could take advantage of masker fluctuations to better segregate the speech from the background.

Global Not Local Masker Features Govern the Auditory Continuity Illusion

When an acoustic signal is temporarily interrupted by another sound, it is sometimes heard as continuing through, even when the signal is actually turned off during the interruption-an effect known as the "auditory continuity illusion." A widespread view is that the illusion can only occur when peripheral neural responses contain no evidence that the signal was interrupted. Here we challenge this view using a combination of psychophysical measures from human listeners and computational simulations with a model of the auditory periphery. The results reveal that the illusion seems to depend more on the overall specific loudness than on the peripheral masking properties of the interrupting sound. This finding indicates that the continuity illusion is determined by the global features, rather than the fine-grained temporal structure, of the interrupting sound, and argues against the view that the illusion arises in the auditory periphery.

Binaural Electric-Acoustic Interactions Recorded from the Inferior Colliculus of Guinea Pigs: The Effect of Masking Observed in the Central Nucleus of the Inferior Colliculus

ObjectivesTo investigate the electric-acoustic interactions within the inferior colliculus of guinea pigs and to observe how central masking appears in invasive neural recordings of the inferior colliculus (IC).MethodsA platinum-iridium wire was inserted to scala tympani through cochleostomy with a depth no greater than 1 mm for intracochlear stimulation of electric pulse train. A 5 mm 100 µm, single-shank, thin-film, penetrating recording probe was inserted perpendicularly to the surface of the IC in the coronal plane at an angle of 30-40° off the parasagittal plane with a depth of 2.0-2.5 mm. The peripheral and central masking effects were compared using electric pulse trains to the left ear and acoustic noise to the left ear (ipsilateral) and to the right ear (contralateral). Binaural acoustic stimuli were presented with different time delays and compared with combined electric and acoustic stimuli. The averaged evoked potentials and total spike numbers were measured using thin-film electrodes inserted into the central nucleus of the IC.ResultsIpsilateral noise had more obvious effects on the electric response than did contralateral noise. Contralateral noise decreased slightly the response amplitude to the electric pulse train stimuli. Immediately after the onset of acoustic noise, the response pattern changed transiently with shorter response intervals. The effects of contralateral noise were evident at the beginning of the continuous noise. The total spike number decreased when the binaural stimuli reached the IC most simultaneously.ConclusionThese results suggest that central masking is quite different from peripheral masking and occurs within the binaural auditory system, and this study showed that the effect of masking could be observed in the IC recording. These effects are more evident and consistent with the psychophysical data from spike number analyses than with the previously reported gross potential data.

Ipsilateral masking between acoustic and electric stimulations

Residual acoustic hearing can be preserved in the same ear following cochlear implantation with minimally traumatic surgical techniques and short-electrode arrays. The combined electric-acoustic stimulation significantly improves cochlear implant performance, particularly speech recognition in noise. The present study measures simultaneous masking by electric pulses on acoustic pure tones, or vice versa, to investigate electric-acoustic interactions and their underlying psychophysical mechanisms. Six subjects, with acoustic hearing preserved at low frequencies in their implanted ear, participated in the study. One subject had a fully inserted 24 mm Nucleus Freedom array and five subjects had Iowa/Nucleus hybrid implants that were only 10 mm in length. Electric masking data of the long-electrode subject showed that stimulation from the most apical electrodes produced threshold elevations over 10 dB for 500, 625, and 750 Hz probe tones, but no elevation for 125 and 250 Hz tones. On the contrary, electric stimulation did not produce any electric masking in the short-electrode subjects. In the acoustic masking experiment, 125-750 Hz pure tones were used to acoustically mask electric stimulation. The acoustic masking results showed that, independent of pure tone frequency, both long- and short-electrode subjects showed threshold elevations at apical and basal electrodes. The present results can be interpreted in terms of underlying physiological mechanisms related to either place-dependent peripheral masking or place-independent central masking.

Abstract LB-139: Laser scanning cytometry for the imaging and quantitation of membrane lipid rafts in cancer cells

Abstract The role of lipid trafficking in the physiological and patho-physiological processes is a subject of intense investigation. The enrichment of a large array of signal transduction components in caveolae and lipid rafts provide testimony to their role as signal portals. Similarly, the formation of intracellular lipid droplets, which were originally thought to be lipid storage organelles, now are known to play an important role in signaling and lipid trafficking. While these cellular components can be assessed using TPLC, mass spectrometry or western blotting, they can also be identified based on the staining of specific lip ids and proteins and analyzed by flow cytometry or using a microscope. We have employed fluorescent based techniques with the laser scanning cytometry (LSC), which allows quantification and localization of fluorescence signals as well as generating digital based images, to investigate lipid rafts and lipid droplets in 3 different cell culture models: 1) B cell lymphomas(Raji and DG75 cell lines) in which we previously reported mislocalization of the apoptosis adaptor protein APAF-1 in the lipid rafts. Nystatin, methyl-beta cyclodextrin and cytocholasin B were used to validate the labeling technique, 2) macrolipophagy, induced during autophagy, in the lung cancer cell line A549 and the cervical cancer cell line HeLa (ECACC) to evaluate the changes in lipid droplets accompanying the induction of autophagic vesicles, and 3) the formation of lipid droplets and raft structures in A549 cells following exposure to a panel of anti-cancer agents. To monitor these events, a sequential multi-colored labeling strategy was employed that allowed for the labeling of the plasma membrane using an antibody to pan-cadherin or by staining with Alexa Fluor 647 conjugated wheat germ agglutinin, prior to fixation, in combination with the labeling of lipid rafts using biotin cholera toxin B coupled with avidin conjugate Q dot 655 and antibodies to caveolin and the pro-apoptotic protein APAF-1. This labeling protocol was used in both cell cultures and in tissues. To detect the formation of lipid droplets, nile red and oil red were used to characterize the lipid content and where possible the number and localization of droplets. A threshold based segmentation strategy was employed that allows for the detection of changes to the total amount of lipid rafts, droplets, or vesicles, together with the digital maxpixel which permits monitoring of clustering or diffusion of events, and the correlation with the cell cycle. Using the profile and segmentation tools, the distance from the plasma membrane or nucleus was calculated and the localization of the events in the cytoplasm, nucleus and plasma membrane were determined using peripheral contouring and masking filters. Furthermore the digital generated images were processed using a set of image filters to generate a “3D” image of the cell or tissue giving a better resolution of events. Results provide a novel imaging strategy for the detection of lipid raft-like structures in cells and tissues, and given their importance in diverse biological systems and pathways could have potential clinical implications Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-139.

Combining information across frequency regions in fundamental frequency discrimination.

Sensitivity to fundamental frequency (F0) differences was measured for two complex tones, A and B, which had the same F0 but were filtered into two different frequency regions. Tones were presented either alone or together. A signal-detection analysis was used to predict effects of combining F0 information across frequency regions. For 400-ms tones containing only unresolved harmonics, the first experiment showed that performance (in terms of d(')) for the combined presentation was better than for the isolated tones but was not optimal (assuming independent channels and noises) and was independent of the relative timing of pulses in the envelopes of tones A and B (varied by changing the starting phase of components of tone B relative to those of tone A). The nonoptimal performance was shown not to be due to peripheral masking (experiment II), or to listeners paying attention mainly to one frequency region (experiment III), nor was it specific to conditions where all harmonics were unresolved (experiment IV). In contrast, optimal performance in F0 discrimination for combined presentation was observed for 50-ms tones (experiment V). The results may reflect the limited ability of the human auditory system to integrate information simultaneously in the time and the frequency domains.

Effects of reverberation on fusion of lead and lag noise burst stimuli

The purpose of this investigation was to determine the effects of reverberation on the precedence effect by obtaining thresholds for perception of leading and lagging noise burst stimuli as separate auditory events. In Experiment 1, lag burst thresholds for 4-ms noise bursts were measured in a simulated reverberant and anechoic environment for nine subjects with normal hearing at presentation levels of 10, 20, and 30 dB SL. Results indicated that lag burst thresholds obtained in the reverberant environment were higher than those obtained in the anechoic environment, with no effect of sensation level. In Experiment 2, three new stimulus conditions, two monaural and one binaural control, were employed. For one monaural condition, the stimuli were equal in level and for the other, the leading stimulus was more intense than the lagging stimulus. For the binaural control condition, the stimuli were presented from a perceived spatial location of 0° azimuth. In the monaural and binaural control conditions, lag burst thresholds were lower than those obtained in the reverberant environment of Experiment 1. There was no difference between lag burst thresholds obtained in either environment for the monaural and binaural control conditions compared to the anechoic condition of Experiment 1. Results of Experiment 2 indicate that the higher lag burst thresholds observed in Experiment 1 are not fully explained by a peripheral masking effect.

F0 discrimination interference: Effects of resolved tone complexes and noise on fundamental frequency discrimination of unresolved complex tones

F0 discrimination of a 400-ms complex tone with only unresolved components (‘‘target’’) was investigated in the absence and presence of a synchronously gated resolved complex tone (‘‘interferer’’). The target and the interferer were bandpass filtered from 1375–15<th>000 Hz and 125–625 Hz, respectively. In a 2I-2AFC task, listeners indicated the interval containing the target with the higher pitch. The nominal F0 of the target was 88 Hz; that of the interferer was constant across the two intervals and was either 88 Hz or increased by various amounts. Although the target and interferer were in well-separated frequency regions, performance (percent correct) dropped by about 16% when the interferer’s F0 was 88 Hz. The impairment was halved when the interferer’s F0 was 10% higher than that of the target, and almost eliminated when it was 30% higher. Increasing the level of a 1375-Hz low-pass-filtered noise, gated synchronously with the target and the interferer (F0 equaled 88 Hz), improved performance, further demonstrating that the deterioration produced by the resolved complex was not due to peripheral masking. The results are consistent with a form of across-frequency interference at the level of pitch perception. [Work supported by EPSRC Grant GR/R65794/01.]

Early peripheral and foveal processing in fixations during scene perception

To compare early foveal and peripheral information extraction, visual scenes were masked either foveally or peripherally during the initial part of fixations, using an eye-movement contingent display-change technique. The sequential attention model of eye-movement control predicts a substantial effect of early foveal masking, and early peripheral masking should not affect the ongoing processing. Foveal masking indeed postponed foveal processing as reflected by a considerable increase of average fixation durations with longer masking (Experiments 1 and 3). However, there was also an effect of peripheral masking, mainly on the saccade target selections with an increased number of fixations (Experiment 3) in conjunction with smaller saccade amplitudes (Experiments 2 and 3). Overall, scene perception was more influenced by early foveal masking than by early peripheral masking, and this is partly in agreement with the sequential attention model of eye-movement control.

Mechanisms of attention in touch

A series of experiments demonstrated the role of higher level cognitive processes, such as attention, in tactile perception.The first series of experiments demonstrated that automatic orienting to a tactile stimulus resulted in inhibition of subsequent stimuli at that body site- inhibition of return (IOR). A possible explanation suggests that inhibition of saccades to a body site can cause the inhibition of subsequent stimuli presented to that same site. In contrast, when the subjects strategically oriented attention to the stimulus, the processing of subsequent stimuli at that body site was facilitated. In both of these experiments the skin received exactly the same test stimuli, (100 Hz sine wave presented for 50 ms), but very different effects were observed depending upon attentional strategy. Experimental manipulations showed that this cannot be due to a peripheral masking of the receptors after cue presentation to the target. Rather the results may be explained centrally by cognitive, particularly attentional mechanisms. Cross-modal interactions suggest that tactile processes are facilitated when vision is oriented to the body site receiving stimulation. Possible explanations come from recent findings of spatiotopic maps of different sensory modalities in the superior colliculus of the midbrain and in the parietal lobe. These are integrated with motor systems that control saccades and head orientation towards sensory inputs. Excitatory links among these maps could be the source of the observed facilitation effects.

Asymmetry of masking revisited: Generalization of masker and probe bandwidth

A band of noise masked by a tone is audible at a much lower intensity increment between masker alone and masker plus just-detectable probe than is a tone masked by a band of noise. To better understand the mechanisms responsible for this asymmetry of masking, we measured thresholds of probe signals ranging in bandwidth from 0 to 256 Hz in the presence of masking signals also ranging in bandwidth from 0 to 256 Hz. Masker and probe center frequencies were 1 kHz in all cases. Two versions of the experiment are reported: (1) masker intensity constant at 70 dB SPL and (2) masker intensity roved over the range 65–75 dB SPL. The results confirm and extend previous results. For a fixed masker bandwidth, threshold intensity increments are essentially constant, and accounted for by a model based on long-term average energy, so long as probe bandwidth does not exceed masker bandwidth. If probe bandwidth exceeds masker bandwidth, threshold intensity increments decrease sharply for all masker bandwidths tested. Roved-intensity results are consistent with the hypothesis that detection is based on long-term average energy for probe bandwidth equal to or less than masker bandwidth, but that for probe bandwidth greater than masker bandwidth other cues are utilized. In addition, we investigated the possible contribution of off-frequency listening by developing and presenting results from a frequency-selective model of peripheral masking. Model results argue against detection based on spectral cues associated with off-frequency listening for signal bandwidths less than a critical band. The conclusion is that detection must utilize the temporal structure of the signal for probe bandwidth greater than masker bandwidth.

Discrimination of envelope frequency in one spectral region in the presence of modulation in another

This paper examines how discrimination of envelope frequency in one spectral region is affected by the presence of either correlated or uncorrelated modulation in another spectral region. Envelope-frequency discrimination thresholds, delta fe's, for a 60-dB SPL two-tone complex centered at 2 kHz were measured in the presence or absence of an auxiliary two-tone complex at another frequency. When present, the auxiliary complex had either the same envelope as the standard signal or an envelope that was uncorrelated with both the standard and variable signal. The results show that listeners can take advantage of correlation between simultaneous envelopes in different frequency regions to improve discrimination of a small change in envelope frequency, whereas the presence of uncorrelated envelopes causes interference with discrimination. Except when the auxiliary complex and the signal are close together in frequency, the discrimination advantage afforded by the correlated auxiliaries appears to reflect across-channel envelope processing. The discrimination interference caused by the uncorrelated auxiliaries, on the other hand, may reflect primarily within-channel interaction such as peripheral masking, although a small amount of across-channel masking also is apparent.

Understanding the central processing limit in consistent-mapping visual search tasks.

Effects of load (i.e., the number of stimuli in the display) have been observed in multiple-frame studies using a consistent mapping of stimuli to responses (e.g., Fisher, 1982, 1984). In a series of four experiments, it is shown that these effects are not the consequence of differences across the high- and low-load conditions in either decision noise or peripheral masking. Additionally, it is shown that of two modes of limited capacity (a limited-channel and divided-capacity model) considered as possible explanations of load effects in tasks where subjects are required to locate a target, only one--the limited-channel model--is consistent with the results from all three location tasks. Finally, it is argued that the limited-channel model predicts not only the behavior observed in the four consistent-mapping experiments reported in this article but also the behavior observed in several related consistent-mapping tasks (Kleiss & Lane, 1986; Shiffrin & Gardner, 1972).

The profile-analysis bandwidth

Detection of a change in spectral shape, or profile analysis, appears to be mediated by comparisons across widely separated frequency ‘‘channels’’ rather than by local comparisons among adjacent frequency regions [e.g., Green et al., J. Acoust. Soc. Am. 73, 639–643 (1983)]. Two experiments were conducted in order to determine the ‘‘resolution bandwidth’’ of these channels. The first involved detection of an increment to a single component of a multicomponent background as a function of the number of components in the background. Performance improved as the number of components was increased from 3 to 21. Further increases yielded poorer performance and the estimate of the ‘‘resolution bandwidth’’ from these data suggests that this poorer performance was due simply to masking. The second experiment involved discrimination of a multicomponent complex having a flat amplitude spectrum from one having a sinusoidally ‘‘rippled’’ amplitude spectrum. The latter experiment yielded somewhat larger estimates of the ‘‘resolution bandwidth’’ than did the former. Finally, profile analysis was investigated under a dichotic condition that precluded peripheral masking of the signal. Our results, like those of Green and Kidd [J. Acoust Soc. Am. 73, 1260–1265 (1983)], suggest that, although spectral analysis can be achieved using information across ears, performance is inferior to that obtained with diotic stimuli.

Auditory induction of discrete tones in signal detection tasks.

Auditory induction is the apparent continuation of a fainter sound when alternated rapidly with a more intense interrupting sound. In the present study, induction of discrete (nonalterhating) tones by “contextual” tones was examined in three experiments using signal detection methods. Listeners were asked to detect pure tone signals of constant, rising, or falling frequency embedded in noise bursts. The noise bursts were preceded and followed by contextual tones that were designed to produce a constant or changing frequency context. The results of the first two experiments showed that detection of “in-context” signals (e.g., a rising-frequency signal in a rising-frequency context) was associated with an increased false-alarm rate and lowered sensitivity, as compared with “out-of-context” signals (e.g., a falling-frequency signal in a rising-frequency context). To examine the possible influence of peripheral masking, a third experiment was conducted in which signals and contextual tones were presented to different ears. The same pattern of selective contextual impairment of detection performance was obtained. The results indicated that auditory induction can occur with discrete presentation of tones: the contextual tones are perceived as continuing through the noise bursts, and this illusion degrades detection performance. However, the effect occurs only when a signal to be detected is consistent with its context. The results suggest that auditory induction and peripheral masking are independent processes that can cumulatively degrade detection performance with nonspeech sounds.

Effects of auditory maskers on whistling and voicing

The effects of high‐intensity auditory maskers on whistling and voicing pitch matching tasks were studied. Subjects whistled or produced the vowel /ah/ to match the frequency of a target tone. Nine experimental masking conditions were presented randomly: no masker, white noise, a pure tone at the target frequency, three tones above and three tones below the target frequency. Masker tones were presented at either 80 or 100 dB SPL. Mean fundamental frequency of voicing was essentially unaffected by auditory manipulations, i.e., productions obtained during masking conditions were no different than productions in quiet. For whistling, mean fundamental frequency of production appeared to be differentially affected by masker frequency. Masker frequencies lower than the target generally resulted in higher frequency of production. Similar effects were observed for both levels of masking stimuli which argues against an interpretation of the observed effects in terms of a peripheral masking of the production. Rather, we would suggest that the results are consistent with a hypothesis that the behaviors involved in the whistling and voicing tasks are differentially affected by auditory information. [Work supported by NIH Grant 07555.]