A naturalistic approach to the cocktail party problem.

While studies of simple acoustic features have provided excellent bases for models of spatial hearing, we are seeking, here, to create a new paradigm for examination of shared attention and scene analysis in natural environments, where the listener is confronted with semantic information from multiple sources. In this new simulation of the cocktail party problem, a subject (S) is questioned, on-line, about information heard in multiple simultaneous stories spoken by different talkers. Questions based on brief passages in the stories are presented visually for manual response. To ensure that responses are based on semantic information rather than just keywords, the latter are replaced in the questions with synonyms. Pay is for performance, and S knows that while a majority of the questions come from a "primary talker," there is potential value in obtaining information from secondary sources. Results, to date, suggest that obtaining semantic information from separate stories is limited by two spatial factors, an exclusive filter that protects information from the attended talker and an inclusive filter that incorporates information from secondary talkers.

The effects of aging on auditory processing and cognition.

PURPOSE: To briefly summarize existing data on effects of aging on auditory processing and cognition. METHOD: A narrative review summarized previously reported data on age-related changes in auditory processing and in cognitive processes with a focus on spoken language comprehension and memory. In addition, recent data on effects of lifestyle engagement on cognitive processes are reviewed. RESULTS: There is substantial evidence for age-related declines in both auditory processes and cognitive abilities. Accumulating evidence supports the idea that the perceptual burden associated with hearing loss impacts the processing resources available for good comprehension and memory for spoken language, particularly in older adults with limited resources. However, many language abilities are well preserved in old age, and there is considerable variability among individuals in cognitive performance across the life span. The authors discuss how lifestyle factors and socioemotional engagement can help to offset declining abilities. CONCLUSIONS: It is clear that spoken language processing in adulthood and old age is affected by changes in perceptual, cognitive, and socioemotional processes as well as by interactions among these changes. Recommendations for further research include studying speech comprehension in complex conditions, including meaningful-connection spoken language, and tailoring clinical interventions based on patients' auditory processing and cognitive abilities along with their individual socioemotional demands.

Failure of the precedence effect with a noise-band vocoder.

The precedence effect (PE) describes the ability to localize a direct, leading sound correctly when its delayed copy (lag) is present, though not separately audible. The relative contribution of binaural cues in the temporal fine structure (TFS) of lead-lag signals was compared to that of interaural level differences (ILDs) and interaural time differences (ITDs) carried in the envelope. In a localization dominance paradigm participants indicated the spatial location of lead-lag stimuli processed with a binaural noise-band vocoder whose noise carriers introduced random TFS. The PE appeared for noise bursts of 10 ms duration, indicating dominance of envelope information. However, for three test words the PE often failed even at short lead-lag delays, producing two images, one toward the lead and one toward the lag. When interaural correlation in the carrier was increased, the images appeared more centered, but often remained split. Although previous studies suggest dominance of TFS cues, no image is lateralized in accord with the ITD in the TFS. An interpretation in the context of auditory scene analysis is proposed: By replacing the TFS with that of noise the auditory system loses the ability to fuse lead and lag into one object, and thus to show the PE.

A system to simulate and reproduce audio-visual environments for spatial hearing research.

The article reports the experience gained from two implementations of the "Simulated Open-Field Environment" (SOFE), a setup that allows sounds to be played at calibrated levels over a wide frequency range from multiple loudspeakers in an anechoic chamber. Playing sounds from loudspeakers in the free-field has the advantage that each participant listens with their own ears, and individual characteristics of the ears are captured in the sound they hear. This makes an easy and accurate comparison between various listeners with and without hearing devices possible. The SOFE uses custom calibration software to assure individual equalization of each loudspeaker. Room simulation software creates the spatio-temporal reflection pattern of sound sources in rooms which is played via the SOFE loudspeakers. The sound playback system is complemented by a video projection facility which can be used to collect or give feedback or to study auditory-visual interaction. The article discusses acoustical and technical requirements for accurate sound playback against the specific needs in hearing research. An introduction to software concepts is given which allow easy, high-level control of the setup and thus fast experimental development, turning the SOFE into a "Swiss army knife" tool for auditory, spatial hearing and audio-visual research.

Is there a hearing aid for the thinking person?

BACKGROUND: The history of auditory prosthesis has generally concentrated on bottom-up processing, that is, on audibility. However, a growing interest in top-down processing has focused on correlations between success with a hearing aid and such higher order processing as the patient's intelligence, problem solving and language skills, and the perceived effort of day-to-day listening. PURPOSE: Examination of two cases of cognitive effects in hearing that illustrate less-often-studied issues: (1) Individual subjects in a study use different listening strategies, a fact that, if not known to the experimenter, can lead to errors in interpretation; (2) A measure of shared attention can point to otherwise unknown functional effects of an algorithm used in hearing aids. RESEARCH DESIGN: In the two examples described above: (1) Patients with cochlear implants served in a study of the binaural precedence effect, that is, echo suppression. (2) Individuals identifying speech-in-noise benefit from noise reduction (NR) when the criterion was improved performance in simultaneous tests of verbal memory or visual reaction times. CONCLUSIONS: Studies of hearing impairment, either in the laboratory or in a fitting session, should include study of the complex stimuli that make up the natural environment, conditions where the thinking auditory brain adopts strategies for dealing with large amounts of input data. In addition to well-known factors that must be included in communication, such things as familiarity, syntax, and semantics, the work here shows that strategic listening can affect even how we deal with seemingly simpler requirements, localizing sounds in a reverberant auditory scene and listening for speech in noise when busy with other cognitive tasks.

A recency effect in sound localization?

In a free-field pointing task, listeners localized trains of 4-32 spatially distributed Gabor clicks (narrowband impulses) centered at 4-kHz carrier frequency and repeating at an interval of 5 ms. Multiple regression coefficients estimated the perceptual "weight" applied to each click in a train during location judgments. Temporal weighting functions obtained in this way exhibited two key features: onset dominance, as evidenced by high weight on the initial click, and "upweighting" of late-arriving sound, as evidenced by weights that gradually increased over the duration of each click-train. Across all tested click-train durations, and despite randomly varying the durations from trial to trial, the greatest post-onset weights were consistently found for clicks at or near the offset. The results imply a special importance of late-arriving sound rather than feedforward recovery from onset dominance, and are broadly consistent with recency effects resulting from temporal integration.

Pitch discrimination interference: the role of ear of entry and of octave similarity.

Gockel et al. [(2004). J. Acoust. Soc. Am. 116, 1092-1104] reported that discrimination of the fundamental frequency (F0) of two sequentially presented complex tones (the target) was impaired when an additional complex tone (the interferer) was presented simultaneously with and to the same ear as the target, even though the target and interferer were filtered into separate frequency regions. This pitch discrimination interference (PDI) was greatest when the target and interferer had similar F0s. The current study examined the role of relative ear of entry of the target and interferer and whether the dependence of the PDI effect on the relative F0 of target and interferer is based on pitch height (F0 as such) or pitch chroma (the musical note). Sensitivity (d(')) was measured for discrimination of the F0 of a target with a nominal F0 of 88 Hz, bandpass filtered from 1375 to 1875 Hz. The interferer was bandpass filtered from 125 to 625 Hz. The contralateral interferer produced marked PDI, but smaller than for ipsilateral presentation. PDI was not larger when the interferer's F0 was twice the nominal target F0 than when it was a factor of 1.9 or 2.1 higher.

Predicting the path of a changing sound: velocity tracking and auditory continuity.

Three studies demonstrate listeners' ability to use the rate of a sound's frequency change (velocity) to predict how the spectral path of the sound is likely to evolve, even in the event of an occlusion. Experiments 1 and 2 use a modified probe-signal method to measure attentional filters and demonstrate increased detection to sounds falling along implied paths of constant-linear velocity. Experiment 3 shows listeners perceive a suprathreshold tone as falling along a trajectory of constant velocity when the frequency is near to the region of greatest detection as measured in Experiments 1 and 2. Further, results show greater accuracy and decreased bias in the use of velocity information with increased exposure to a constant-velocity sound. As the duration of occlusion lengthens, results also show a downward shift (relative to a trajectory of constant velocity) in the frequency at which listeners' detection and experience of a continuous trajectory are greatest. A preliminary model of velocity processing is proposed to account for this downward shift. Results show listeners' use of velocity in extrapolating sounds with dynamically changing spectral and temporal properties and provide evidence for its role in perceptual auditory continuity within a noisy acoustic environment.

Amplitude modulation sensitivity as a mechanism increment detection.

Detectability of a tonal signal added to a tonal masker increases with increasing duration ("temporal integration"), up to some maximum duration. Initially assumed to be some form of energy integration over time, this phenomenon is now often described as the result of a statistical "multiple looks" process. For continuous maskers, listeners may also use a mechanism sensitive to changes in stimulus intensity, possibly a result of inherent sensitivity to amplitude modulation (AM). In order to examine this hypothesis, change detection was investigated in the presence of AM maskers presented at either the same carrier frequency as the target signal or at a distant frequency. The results are compatible with the hypothesis that listeners detect intensity increments by using change-detection mechanisms (modeled here as the outputs of a bank of modulation filters) sensitive to envelope modulation at both low (4-16 Hz) and high (around 100 Hz) rates. AM masking occurred even when the masker was at a carrier frequency more than two octaves above that of the signal to be detected. This finding is also compatible with the hypothesis that similar mechanisms underlie sensitivity to AM (where across-frequency masking is commonly shown) and detection of intensity increments.

The detection of increments and decrements is not facilitated by abrupt onsets or offsets.

Two experiments measured thresholds for the detection of increments and decrements in the intensity of a quasi-continuous broadband-noise (experiment 1) or increments in a 477-Hz pure-tone pedestal (experiment 2). A variety of onset and offset ramps for the intensity change were tested, from instantaneous onsets or offsets to ramps lasting several tens of milliseconds. For increments and decrements with equal duration, the characteristics of the ramps had little effect on performance. Abrupt rise times, which are associated with strong transient responses in auditory neurons, did not facilitate detection in comparison to much slower rise times. The temporal window model of temporal resolution provided a good account of the data when the decision statistic was the maximum magnitude of the change in the output of the window produced by the increment or decrement, but provided a poor account of the data when the decision statistic was the maximum rate of change in the output of the window over time. Overall the results suggest that, in the absence of cues in the audio-frequency domain, rapid changes in envelope contribute little to near-threshold increment or decrement detection.

Temporal weighting in sound localization.

The dynamics of sound localization were studied using a free-field direct localization task (pointing to sound sources) and an observer-weighting analysis that assessed the relative influence of each click in a click-train stimulus. In agreement with previous studies of the precedence effect and binaural adaptation, weighting functions showed increased influence of the onset click when the interclick interval (ICI) was short (<5 ms). For longer ICIs, all clicks in a train contributed roughly the same amount to listeners' localization responses. Finally, when a short gap was introduced in the middle of a train, the influence of the click immediately following the gap increased, in agreement with the "restarting" results obtained by Hafter and Buell [J. Acoust. Soc. Am. 88, 806-812 (1990)].