Joint population coding and temporal coherence link an attended talker’s voice and location features in naturalistic multi-talker scenes
Authors: van der Heijden Kiki , Patel Prachi , Bickel Stephan , Herrero Jose L. , Mehta Ashesh D. , Mesgarani Nima 
Published: May 2024

Listeners effortlessly extract multidimensional auditory objects, such as a localized talker, from complex acoustic scenes. However, the neural mechanisms that enable simultaneous encoding and linking of distinct sound features—such as a talker’s voice and location—are not fully understood. Using invasive intracranial recordings in neurosurgical patients, we investigated how the human auditory cortex processes and integrates these features during naturalistic multi-talker scenes. We found that cortical sites exhibit a gradient of feature sensitivity, ranging from single-feature sensitive sites (responsive primarily to voice or location) to dual-feature sensitive sites (responsive to both features). At the population level, neural response patterns from both single- and dual-feature sensitive sites jointly encoded the attended talker’s voice and location. Notably, single-feature sensitive sites encoded their primary feature with greater precision but also represented coarse information about the secondary feature. Sites selectively tracking a single, attended speech stream concurrently encoded both voice and location features, demonstrating a link between selective attention and feature integration. Additionally, attention selectively enhanced temporal coherence between voice- and location-sensitive sites, suggesting that temporal synchronization serves as a mechanism for linking these features. Our findings highlight two complementary neural mechanisms—joint population coding and temporal coherence— that enable the integration of voice and location features in the auditory cortex. These results provide new insights into the distributed, multidimensional nature of auditory object formation during active listening in complex environments.

SIGNIFICANCE STATEMENT

In everyday life, listeners effortlessly extract individual sound sources from complex acoustic scenes which contain multiple sound sources. Yet, how the brain links the different features of a particular sound source to each other – such as a talker’s voice characteristics and location - is poorly understood. Here, we show that two neural mechanisms contribute to encoding and integrating voice and location features in multi-talker sound scenes: (1) some neuronal sites are sensitive to both voice and location and their activity patterns encode these features jointly; (2) the responses of neuronal sites that process only one sound feature – that is, location or voice – align temporally to form a stream that is segregated from the other talker.

HIGHLIGHTS

Auditory cortex exhibits a gradient of feature sensitivity, with some sites encoding only voice or location features, while others encode both simultaneously (dual-feature sensitive sites).

Dual-feature sensitive sites integrate voice and location features of an attended talker with equal accuracy, providing a unified representation in multi-talker scenes.

Single-feature sensitive sites primarily encode their preferred feature with high precision but also represent coarse information about other features, contributing to population-level integration.

Temporal coherence selectively enhances synchronization between voice- and location-sensitive sites, providing another mechanism for integrating an auditory object’s features.

Multi-dimensional auditory object formation relies on complementary neural mechanisms: joint population coding and temporal coherence.