Neural speech tracking is modulated by voice identity, but not by voice familiarity

The brain tracks incoming speech by aligning the phase of its low-frequency endogenous oscillatory activity to the slow amplitude modulations in the speech signal and is modulated by various bottom-up and top-down factors such as speech acoustics or selective attention. However, it is unclear whether speech tracking can be influenced by voice characteristics such bottom-up driven voice identity or the top-down feature of familiarity with the speaker’s voice. Speech from familiar speakers is more intelligible, so higher speech tracking response can be expected for speech from familiar compared to unfamiliar speakers. To test this, we familiarized 39 young adult listeners with four female voices. We used high-variability training containing sentence stimuli from different speaking styles and audio qualities to ensure listeners can recognize voices reliably across different stimuli types and form more stable voice representations. After this, we recorded EEG while participants listened to sentences from familiar and unfamiliar speakers in quiet and in multitalker babble noise. To quantify neural speech tracking, we computed cross-correlation between the neural response and the amplitude envelopes of the presented sentences. Results revealed that lab-trained familiarity with female voices does not affect neural speech tracking. We also found no differences in sentence comprehension scores for familiar and unfamiliar voices suggesting that lab-trained familiarity does not benefit sentence comprehension. However, we found a significant effect of individual speakers on speech tracking suggesting that neural speech tracking is modulated by voice identity. We also found a relationship between voice recognition and speech tracking: the better a particular speaker was recognized, the higher the speech tracking response was to the respective speaker. Our results further support the notion that voice identity is reflected in early acoustic and later linguistic processing stages in the brain and that linguistic and speaker-specific voice information are processed jointly on the neural level.