Auditory neural tracking reflects target enhancement but not distractor suppression in a psychophysically augmented continuous-speech paradigm

In recent years, neuroscientists have collected conclusive evidence that selective attention to one of the most relevant signals in human environments i.e., continuous speech modulates neural phase-locked responses in auditory cortical regions (neural tracking). To test whether the human brain enhances targets or suppresses distraction when attending to speech, we here employed a psychophysically augmented speech-tracking paradigm with target, distractor and neutral streams. We demonstrate target enhancement to be behaviourally separable from distractor suppression, but no evidence for neural, below-baseline suppressive responses to distractors. A speech stimulus that was never task-relevant served as a neutral baseline, against which processing of concurrent target speech (relevant on present trial) and distractor speech (relevant on previous trial) was contrasted. Listeners (N = 19; male and female) had to detect short repeats in the target, which enabled us to contrast whether neural responses to target, neutral, or distractor speech would independently explain trial-by-trial variation in attention performance. Feasibility of the neutral baseline was evidenced by enhanced behavioural sensitivity when separating target-versus-distractor compared with target-versus-neutral speech. Temporal response functions revealed enhanced target speech tracking relative to neutral speech but no suppression of distraction below the neutral baseline. The amplitude of neural responses to target speech, but not to neutral or distractor speech, explained accuracy in behavioural repeat detection. Results indicate a necessary revision of the presumed role of enhanced phase-locked neural responses to speech to account for a specific sub-process of selective attention, that is, the enhancement of targets rather than the suppression of distraction. ### Competing Interest Statement The authors have declared no competing interest.