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

An Effect of Gaze Direction in Cocktail Party Listening

It is well established that gaze direction can influence auditory spatial perception, but the implications of this interaction for performance in complex listening tasks is unclear. In the current study, we investigated whether there is a measurable effect of gaze direction on speech intelligibility in a "cocktail party" listening situation. We presented sequences of digits from five loudspeakers positioned at 0°,  ±  15°, and ± 30° azimuth, and asked participants to repeat back the digits presented from a designated target loudspeaker. In different blocks of trials, the participant visually fixated on a cue presented at the target location or at a nontarget location. Eye position was tracked continuously to monitor compliance. Performance was best when fixation was on-target (vs. off-target) and the size of this effect depended on the specific configuration. This result demonstrates an influence of gaze direction in multitalker mixtures, even in the absence of visual speech information.

Defining functional spatial boundaries using a spatial release from masking task

The classic spatial release from masking (SRM) task measures speech recognition thresholds for discrete separation angles between a target and masker. Alternatively, this study used a modified SRM task that adaptively measured the spatial-separation angle needed between a continuous male target stream (speech with digits) and two female masker streams to achieve a specific SRM. On average, 20 young normal-hearing listeners needed less spatial separation for 6 dB release than 9 dB release, and the presence of background babble reduced across-listener variability on the paradigm. Future work is needed to better understand the psychometric properties of this adaptive procedure.

Implicit and explicit learning in talker identification

In the real world, listeners seem to implicitly learn talkers' vocal identities during interactions that prioritize attending to the content of talkers' speech. In contrast, most laboratory experiments of talker identification employ training paradigms that require listeners to explicitly practice identifying voices. Here, we investigated whether listeners become familiar with talkers' vocal identities during initial exposures that do not involve explicit talker identification. Participants were assigned to one of three exposure tasks, in which they heard identical stimuli but were differentially required to attend to the talkers' vocal identity or to the verbal content of their speech: (1) matching the talker to a concurrent visual cue (talker-matching); (2) discriminating whether the talker was the same as the prior trial (talker 1-back); or (3) discriminating whether speech content matched the previous trial (verbal 1-back). All participants were then tested on their ability to learn to identify talkers from novel speech content. Critically, we manipulated whether the talkers during this post-test differed from those heard during training. Compared to learning to identify novel talkers, listeners were significantly more accurate learning to identify the talkers they had previously been exposed to in the talker-matching and verbal 1-back tasks, but not the talker 1-back task. The correlation between talker identification test performance and exposure task performance was also greater when the talkers were the same in both tasks. These results suggest that listeners learn talkers' vocal identity implicitly during speech perception, even if they are not explicitly attending to the talkers' identity.

Vocal and semantic cues for the segregation of long concurrent speech stimuli in diotic and dichotic listening-The Long-SWoRD test

It is not always easy to follow a conversation in a noisy environment. To distinguish between two speakers, a listener must mobilize many perceptual and cognitive processes to maintain attention on a target voice and avoid shifting attention to the background noise. The development of an intelligibility task with long stimuli-the Long-SWoRD test-is introduced. This protocol allows participants to fully benefit from the cognitive resources, such as semantic knowledge, to separate two talkers in a realistic listening environment. Moreover, this task also provides the experimenters with a means to infer fluctuations in auditory selective attention. Two experiments document the performance of normal-hearing listeners in situations where the perceptual separability of the competing voices ranges from easy to hard using a combination of voice and binaural cues. The results show a strong effect of voice differences when the voices are presented diotically. In addition, analyzing the influence of the semantic context on the pattern of responses indicates that the semantic information induces a response bias in situations where the competing voices are distinguishable and indistinguishable from one another.

Talker discontinuity disrupts attention to speech: Evidence from EEG and pupillometry

Speech is processed less efficiently from discontinuous, mixed talkers than one consistent talker, but little is known about the neural mechanisms for processing talker variability. Here, we measured psychophysiological responses to talker variability using electroencephalography (EEG) and pupillometry while listeners performed a delayed recall of digit span task. Listeners heard and recalled seven-digit sequences with both talker (single- vs. mixed-talker digits) and temporal (0- vs. 500-ms inter-digit intervals) discontinuities. Talker discontinuity reduced serial recall accuracy. Both talker and temporal discontinuities elicited P3a-like neural evoked response, while rapid processing of mixed-talkers' speech led to increased phasic pupil dilation. Furthermore, mixed-talkers' speech produced less alpha oscillatory power during working memory maintenance, but not during speech encoding. Overall, these results are consistent with an auditory attention and streaming framework in which talker discontinuity leads to involuntary, stimulus-driven attentional reorientation to novel speech sources, resulting in the processing interference classically associated with talker variability.

Perceptual organization and stability of auditory streaming for pure tones and /ba/ stimuli

The dynamics of auditory stream segregation were evaluated using repeating triplets composed of pure tones or the syllable /ba/. Stimuli differed in frequency (tones) or fundamental frequency (speech) by 4, 6, 8, or 10 semitones, and the standard frequency was either 250 Hz (tones and speech) or 400 Hz (tones). Twenty normal-hearing adults participated. For both tones and speech, a two-stream percept became more likely as frequency separation increased. Perceptual organization for speech tended to be more integrated and less stable compared to tones. Results suggest that prior data patterns observed with tones in this paradigm may generalize to speech stimuli.

Attention capture in birds performing an auditory streaming task

Numerous animal models have been used to investigate the neural mechanisms of auditory processing in complex acoustic environments, but it is unclear whether an animal’s auditory attention is functionally similar to a human’s in processing competing auditory scenes. Here we investigated the effects of attention capture in birds performing an objective auditory streaming paradigm. The classical ABAB… patterned pure tone sequences were modified and used for the task. We trained the birds to selectively attend to a target stream and only respond to the deviant appearing in the target stream, even though their attention may be captured by a deviant in the background stream. When no deviant appeared in the background stream, the birds experience the buildup of streaming process in a qualitatively similar way as they did in a subjective paradigm. Although the birds were trained to selectively attend to the target stream, they failed to avoid the involuntary attention switch caused by the background deviant, especially when the background deviant was sequentially unpredictable. Their global performance deteriorated more with increasingly salient background deviants, where the buildup process was reset by the background distractor. Moreover, sequential predictability of the background deviant facilitated the recovery of the buildup process after attention capture. This is the first study that addresses the perceptual consequences of the joint effects of top-down and bottom-up attention in behaving animals.