Adaptation to Reverberation for Speech Perception: A Systematic Review.

In everyday acoustic environments, reverberation alters the speech signal received at the ears. Normal-hearing listeners are robust to these distortions, quickly recalibrating to achieve accurate speech perception. Over the past two decades, multiple studies have investigated the various adaptation mechanisms that listeners use to mitigate the negative impacts of reverberation and improve speech intelligibility.

Time scales of adaptation to context in horizontal sound localization.

Psychophysical experiments explored how the repeated presentation of a context, consisting of an adaptor and a target, induces plasticity in the localization of an identical target presented alone on interleaved trials. The plasticity, and its time course, was examined both in a classroom and in an anechoic chamber. Adaptors and targets were 2 ms noise clicks and listeners were tasked with localizing the targets while ignoring the adaptors (when present).

Toward a Unified Theory of the Reference Frame of the Ventriloquism Aftereffect.

The ventriloquism aftereffect (VAE), observed as a shift in the perceived locations of sounds after audio-visual stimulation, requires reference frame (RF) alignment since hearing and vision encode space in different RFs (head-centered vs. eye-centered). Previous experimental studies reported inconsistent results, observing either a mixture of head-centered and eye-centered frames, or a predominantly head-centered frame.

Auditory-visual interactions in egocentric distance perception: Ventriloquism effect and aftereffect.

This study describes data on auditory-visual integration and visually-guided adaptation of auditory distance perception using the ventriloquism effect (VE) and ventriloquism aftereffect (VAE). In an experiment, participants judged egocentric distance of interleaved auditory or auditory-visual stimuli with the auditory component located from 0.7 to 2.

Calibration of Consonant Perception to Room Reverberation.

Purpose We examined how consonant perception is affected by a preceding speech carrier simulated in the same or a different room, for different classes of consonants. Carrier room, carrier length, and carrier length/target room uncertainty were manipulated. A phonetic feature analysis tested which phonetic categories are influenced by the manipulations in the acoustic context of the carrier.

Reweighting of Binaural Localization Cues Induced by Lateralization Training.

Normal-hearing listeners adapt to alterations in sound localization cues. This adaptation can result from the establishment of a new spatial map of the altered cues or from a stronger relative weighting of unaltered compared to altered cues. Such reweighting has been shown for monaural vs.

Sound Externalization: A Review of Recent Research.

Sound externalization, or the perception that a sound source is outside of the head, is an intriguing phenomenon that has long interested psychoacousticians. While previous reviews are available, the past few decades have produced a substantial amount of new data.In this review, we aim to synthesize those data and to summarize advances in our understanding of the phenomenon.

Cortical auditory distance representation based on direct-to-reverberant energy ratio.

Auditory distance perception and its neuronal mechanisms are poorly understood, mainly because 1) it is difficult to separate distance processing from intensity processing, 2) multiple intensity-independent distance cues are often available, and 3) the cues are combined in a context-dependent way. A recent fMRI study identified human auditory cortical area representing intensity-independent distance for sources presented along the interaural axis (Kopco et al. PNAS, 109, 11019-11024).

Hemisphere-specific properties of the ventriloquism aftereffect.

Visual calibration of auditory space requires re-alignment of representations differing in (1) format (auditory hemispheric channels vs visual maps) and (2) reference frames (head-centered vs eye-centered). Here, a ventriloquism paradigm from Kopčo, Lin, Shinn-Cunningham, and Groh [J. Neurosci.

Nonnative implicit phonetic training in multiple reverberant environments.

Speech intelligibility is adversely affected by reverberation, particularly when listening to a foreign language. However, little is known about how phonetic learning is affected by room acoustics. This study investigated how room reverberation impacts the acquisition of novel phonetic categories during implicit training in virtual environments.

A "Buildup" of Speech Intelligibility in Listeners With Normal Hearing and Hearing Loss.

The perception of simple auditory mixtures is known to evolve over time. For instance, a common example of this is the "buildup" of stream segregation that is observed for sequences of tones alternating in pitch. Yet very little is known about how the perception of more complicated auditory scenes, such as multitalker mixtures, changes over time.

Temporal characteristics of contextual effects in sound localization.

Two experiments examined plasticity induced by context in a simple target localization task. The context was represented by interleaved localization trials with the target preceded by a distractor. In a previous study, the context induced large response shifts when the target and distractor stimuli were identical 2-ms-noise clicks [Kopčo, Best, and Shinn-Cunningham (2007).

Streaming and sound localization with a preceding distractor.

Localization of a 2-ms click target was previously shown to be influenced by a preceding identical distractor for inter-click-intervals up to 400 ms [Kopčo, Best, and Shinn-Cunningham (2007). J. Acoust.

Intracortical depth analyses of frequency-sensitive regions of human auditory cortex using 7TfMRI.

Despite recent advances in auditory neuroscience, the exact functional organization of human auditory cortex (AC) has been difficult to investigate. Here, using reversals of tonotopic gradients as the test case, we examined whether human ACs can be more precisely mapped by avoiding signals caused by large draining vessels near the pial surface, which bias blood-oxygen level dependent (BOLD) signals away from the actual sites of neuronal activity. Using ultra-high field (7T) fMRI and cortical depth analysis techniques previously applied in visual cortices, we sampled 1mm isotropic voxels from different depths of AC during narrow-band sound stimulation with biologically relevant temporal patterns.

Modeling of speech localization in a multi-talker mixture using periodicity and energy-based auditory features.

A recent study showed that human listeners are able to localize a short speech target simultaneously masked by four speech tokens in reverberation [Kopčo, Best, and Carlile (2010). J. Acoust.

Contextual plasticity, top-down, and non-auditory factors in sound localization with a distractor.

Localization of a 2-ms-click target was previously shown to be influenced by interleaved localization trials in which the target was preceded by an identical distractor [Kopčo, Best, and Shinn-Cunningham (2007). J. Acoust.

Psychophysics and neuronal bases of sound localization in humans.

Localization of sound sources is a considerable computational challenge for the human brain. Whereas the visual system can process basic spatial information in parallel, the auditory system lacks a straightforward correspondence between external spatial locations and sensory receptive fields. Consequently, the question how different acoustic features supporting spatial hearing are represented in the central nervous system is still open.

Neuronal representations of distance in human auditory cortex.

Neuronal mechanisms of auditory distance perception are poorly understood, largely because contributions of intensity and distance processing are difficult to differentiate. Typically, the received intensity increases when sound sources approach us. However, we can also distinguish between soft-but-nearby and loud-but-distant sounds, indicating that distance processing can also be based on intensity-independent cues.

Effect of stimulus spectrum on distance perception for nearby sources.

The effects of stimulus frequency and bandwidth on distance perception were examined for nearby sources in simulated reverberant space. Sources to the side [containing reverberation-related cues and interaural level difference (ILD) cues] and to the front (without ILDs) were simulated. Listeners judged the distance of noise bursts presented at a randomly roving level from simulated distances ranging from 0.

Localization in speech mixtures by listeners with hearing loss.

The ability of listeners with bilateral sensorineural hearing loss to localize a speech source in a multitalker mixture was measured. Five simultaneous words spoken by different talkers were presented over loudspeakers in a small room, and listeners localized one target word. Errors were significantly larger in this group compared to a control group with normal hearing.

Exploring the benefit of auditory spatial continuity.

Continuity of spatial location was recently shown to improve the ability to identify and recall a sequence of target digits presented in a mixture of confusable maskers [Best et al. (2008). Proc.

Speech localization in a multitalker mixture.

An experiment was performed that measured, for the frontal audio-visual horizon, how accurately listeners could localize a female-voice target amidst four spatially distributed male-voice maskers. To examine whether listeners can make use of a priori knowledge about the configuration of the sources, performance was examined in two conditions: either the masker locations were fixed (in one of five known patterns) or the locations varied from trial to trial. The presence of maskers disrupted speech localization, even after accounting for reduced target detectability.

Reference frame of the ventriloquism aftereffect.

Seeing the image of a newscaster on a television set causes us to think that the sound coming from the loudspeaker is actually coming from the screen. How images capture sounds is mysterious because the brain uses different methods for determining the locations of visual versus auditory stimuli. The retina senses the locations of visual objects with respect to the eyes, whereas differences in sound characteristics across the ears indicate the locations of sound sources referenced to the head.

Influences of modulation and spatial separation on detection of a masked broadband target.

Experiments explored the influence of amplitude modulation and spatial separation on detectability of a broadband noise target masked by an independent broadband noise. Thresholds were measured for all combinations of six spatial configurations of target and masker and five modulation conditions. Masker level was either fixed (Experiment 1) or roved between intervals within a trial to reduce the utility of overall intensity as a cue (Experiment 2).

Object continuity enhances selective auditory attention.

In complex scenes, the identity of an auditory object can build up across seconds. Given that attention operates on perceptual objects, this perceptual buildup may alter the efficacy of selective auditory attention over time. Here, we measured identification of a sequence of spoken target digits presented with distracter digits from other directions to investigate the dynamics of selective attention.