Common Brain Substrates Underlying Auditory Speech Priming and Perceived Spatial Separation

Under a “cocktail party” environment, listeners can utilize prior knowledge of the content and voice of the target speech [i.e., auditory speech priming (ASP)] and perceived spatial separation to improve recognition of the target speech among masking speech. Previous studies suggest that these two unmasking cues are not processed independently. However, it is unclear whether the unmasking effects of these two cues are supported by common neural bases. In the current study, we aimed to first confirm that ASP and perceived spatial separation contribute to the improvement of speech recognition interactively in a multitalker condition and further investigate whether there exist intersectant brain substrates underlying both unmasking effects, by introducing these two unmasking cues in a unified paradigm and using functional magnetic resonance imaging. The results showed that neural activations by the unmasking effects of ASP and perceived separation partly overlapped in brain areas: the left pars triangularis (TriIFG) and orbitalis of the inferior frontal gyrus, left inferior parietal lobule, left supramarginal gyrus, and bilateral putamen, all of which are involved in the sensorimotor integration and the speech production. The activations of the left TriIFG were correlated with behavioral improvements caused by ASP and perceived separation. Meanwhile, ASP and perceived separation also enhanced the functional connectivity between the left IFG and brain areas related to the suppression of distractive speech signals: the anterior cingulate cortex and the left middle frontal gyrus, respectively. Therefore, these findings suggest that the motor representation of speech is important for both the unmasking effects of ASP and perceived separation and highlight the critical role of the left IFG in these unmasking effects in “cocktail party” environments.

Spatial Release from Masking Using Clinical Corpora: Sentence Recognition in a Colocated or Spatially Separated Speech Masker

Background Speech recognition in complex multisource environments is challenging, particularly for listeners with hearing loss. One source of difficulty is the reduced ability of listeners with hearing loss to benefit from spatial separation of the target and masker, an effect called spatial release from masking (SRM). Despite the prevalence of complex multisource environments in everyday life, SRM is not routinely evaluated in the audiology clinic. Purpose The purpose of this study was to demonstrate the feasibility of assessing SRM in adults using widely available tests of speech-in-speech recognition that can be conducted using standard clinical equipment. Research Design Participants were 22 young adults with normal hearing. The task was masked sentence recognition, using each of five clinically available corpora with speech maskers. The target always sounded like it originated from directly in front of the listener, and the masker either sounded like it originated from the front (colocated with the target) or from the side (separated from the target). In the real spatial manipulation conditions, source location was manipulated by routing the target and masker to either a single speaker or to two speakers: one directly in front of the participant, and one mounted in an adjacent corner, 90° to the right. In the perceived spatial separation conditions, the target and masker were presented from both speakers with delays that made them sound as if they were either colocated or separated. Results With real spatial manipulations, the mean SRM ranged from 7.1 to 11.4 dB, depending on the speech corpus. With perceived spatial manipulations, the mean SRM ranged from 1.8 to 3.1 dB. Whereas real separation improves the signal-to-noise ratio in the ear contralateral to the masker, SRM in the perceived spatial separation conditions is based solely on interaural timing cues. Conclusions The finding of robust SRM with widely available speech corpora supports the feasibility of measuring this important aspect of hearing in the audiology clinic. The finding of a small but significant SRM in the perceived spatial separation conditions suggests that modified materials could be used to evaluate the use of interaural timing cues specifically.

Spatial Release From Masking Using Clinical Corpora: Sentence Recognition In a Colocated or Spatially Separated Speech Masker

Background: Speech recognition in complex multisource environments is challenging, particularly forlisteners with hearing loss. One source of difficulty is the reduced ability of listeners with hearing loss tobenefit from spatial separation of the target and masker, an effect called spatial release from masking(SRM). Despite the prevalence of complex multisource environments in everyday life, SRM is not routinelyevaluated in the audiology clinic.<br />Purpose: The purpose of this study was to demonstrate the feasibility of assessing SRM in adults usingwidely available tests of speech-in-speech recognition that can be conducted using standard clinicalequipment.<br />Research Design: Participants were 22 young adults with normal hearing. The task was masked sentencerecognition, using each of five clinically available corpora with speech maskers. The target alwayssounded like it originated from directly in front of the listener, and the masker either sounded like it originatedfrom the front (colocated with the target) or from the side (separated from the target). In the realspatial manipulation conditions, source location was manipulated by routing the target and masker toeither a single speaker or to two speakers: one directly in front of the participant, and one mountedin an adjacent corner, 90° to the right. In the perceived spatial separation conditions, the target andmasker were presented from both speakers with delays that made them sound as if they were eithercolocated or separated.<br />Results: With real spatial manipulations, the mean SRM ranged from 7.1 to 11.4 dB, depending on thespeech corpus. With perceived spatial manipulations, the mean SRM ranged from 1.8 to 3.1 dB. Whereasreal separation improves the signal-to-noise ratio in the ear contralateral to the masker, SRM in the perceivedspatial separation conditions is based solely on interaural timing cues.<br />Conclusions: The finding of robust SRM with widely available speech corpora supports the feasibility ofmeasuring this important aspect of hearing in the audiology clinic. The finding of a small but significantSRM in the perceived spatial separation conditions suggests that modified materials could be used toevaluate the use of interaural timing cues specifically.<br />

Brain substrates of perceived spatial separation between speech sources under simulated reverberant listening conditions in schizophrenia

BackgroundPeople with schizophrenia recognize speech poorly under multiple-people-talking (informational masking) conditions. In reverberant environments, direct-wave signals from a speech source are perceptually integrated with the source reflections (the precedence effect), forming perceived spatial separation (PSS) between different sources and consequently improving target-speech recognition against informational masking. However, the brain substrates underlying the schizophrenia-related vulnerability to informational masking and whether schizophrenia affects the unmasking effect of PSS are largely unknown.MethodUsing psychoacoustic testing and functional magnetic resonance imaging, respectively, the speech recognition under either the PSS or perceived spatial co-location (PSC) condition and the underlying brain substrates were examined in 20 patients with schizophrenia and 16 healthy controls.ResultsSpeech recognition was worse in patients than controls. Under the PSS (but not PSC) condition, speech recognition was correlated with activation of the superior parietal lobule (SPL), and target speech-induced activation of the SPL, precuneus, middle cingulate cortex and caudate significantly declined in patients. Moreover, the separation (PSS)-against-co-location (PSC) contrast revealed (1) activation of the SPL, precuneus and anterior cingulate cortex in controls, (2) suppression of the SPL and precuneus in patients, (3) activation of the pars triangularis of the inferior frontal gyrus and middle frontal gyrus in both controls and patients, (4) activation of the medial superior frontal gyrus in patients, and (5) impaired functional connectivity of the SPL in patients.ConclusionsIntroducing the PSS listening condition efficiently reveals both the brain substrates underlying schizophrenia-related speech-recognition deficits against informational masking and the schizophrenia-related neural compensatory strategy for impaired SPL functions.