Distinct neural systems recruited when speech production is modulated by different masking sounds

Abstract

When talkers speak in masking sounds, their speech undergoes a variety of acoustic and phonetic changes. These changes are known collectively as the Lombard effect. Most behavioural research and neuroimaging research in this area has concentrated on the effect of energetic maskers such as white noise on Lombard speech. Previous fMRI studies have argued that neural responses to speaking in noise are driven by the quality of auditory feedback—that is, the audibility of the speaker's voice over the masker. However, we also frequently produce speech in the presence of informational maskers such as another talker. Here, speakers read sentences over a range of maskers varying in their informational and energetic content: speech, rotated speech, speech modulated noise, and white noise. Subjects also spoke in quiet and listened to the maskers without speaking. When subjects spoke in masking sounds, their vocal intensity increased in line with the energetic content of the masker. However, the opposite pattern was found neurally. In the superior temporal gyrus, activation was most strongly associated with increases in informational, rather than energetic, masking. This suggests that the neural activations associated with speaking in noise are more complex than a simple feedback response.

Understanding rostral–caudal auditory cortex contributions to auditory perception

“…The ascending auditory pathways are essential for forming representations of auditory objects, and their associated spatial locations (BOX 1) and rostral cortical auditory fields appear to be capable of representing multiple parallel auditory objects, only one of which forms the currently attended signal45,46. Studies of ‘masked’ speech, in which a target speech signal is heard against a simultaneous competing sound, indicate that when a competing sound is more speech-like, it elicits a greater neural response in rostral auditory fields47,48. This response occurs in addition to the activation associated with the content of the attended speech47 (which may include self-produced speech48), suggesting that the computational processes taking place in the rostral auditory cortex must be flexible enough to process (and recognize aspects of) multiple unattended auditory objects.…”

“…Studies of ‘masked’ speech, in which a target speech signal is heard against a simultaneous competing sound, indicate that when a competing sound is more speech-like, it elicits a greater neural response in rostral auditory fields47,48. This response occurs in addition to the activation associated with the content of the attended speech47 (which may include self-produced speech48), suggesting that the computational processes taking place in the rostral auditory cortex must be flexible enough to process (and recognize aspects of) multiple unattended auditory objects. This flexibility must permit the processing of multiple parallel sources of auditory information for a wide variety of possible kinds of sound as well as the switching of attentional focus between them.…”

Comprehending auditory speech: previous and potential contributions of functional MRI

“…This may be a useful approach for studying effortful listening, which has previously been shown to engage both domain-general attentional and domain-specific sensory systems (Binder et al, 2004;Evans et al, 2016;Vaden et al, 2013;Wild et al, 2012). Furthermore, the ability to de-mix neural signals into functionally independent networks may be of particular benefit in complex experimental designs in which multiple events occur simultaneously within a trial, for example in "cocktail party listening" or speaking in noise (Braga et al, 2013;Evans et al, 2016;Kamourieh et al, 2015;Meekings et al, 2016). Finally, an additional advantage of ICA is that components from a particular study can be compared to those extracted from large scale studies of resting state networks by correlating the spatial maps (Smith et al, 2009).…”

What Has Replication Ever Done for Us? Insights from Neuroimaging of Speech Perception

“…As well as revealing a broader intelligibility network, these replications raise important questions about non-speech baselines. Rotated speech has proven a useful tool to separate “low level” acoustic from “higher level” linguistic processes (Boebinger et al, 2015 ; Lima et al, 2015 ; McGettigan et al, 2015 ; Evans et al, 2016 ; Meekings et al, 2016 ). However the replications discussed here, unexpectedly, showed that primary auditory cortex could distinguish between rotated and clear speech, and that some neural regions responded selectively to rotation as compared to clear speech.…”