Abstract
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.
Significance statement Is selective attention implemented along the central auditory pathway primarily via enhancement (i.e., neural gain) of behaviourally relevant targets, or by active (i.e., below-baseline) suppression of potential distractors, or both? Most current studies reporting attentional effects in the neural and behavioural response do not allow us to distinguish between such competing explanations of target enhancement versus distractor suppression. In a psychophysically augmented continuous-speech paradigm with three concurrently active sound locations, we show that selective attention to speech is implemented primarily via an enhancement of attended speech and not via suppression of distracting speech in the brain. These results suggest that the presumed role of neural responses to speech primarily reflects a specific sub process of selective attention, namely, target enhancement.
Competing Interest Statement
The authors have declared no competing interest.
