Altering the rhythm of target and background talkers differentially affects speech understanding

Three experiments investigated listeners' ability to use speech rhythm to attend selectively to a single target talker presented in multi-talker babble (Experiments 1 and 2) and in speech-shaped noise (Experiment 3). Participants listened to spoken sentences of the form "Ready [Call sign] go to [Color] [Number] now" and reported the Color and Number spoken by a target talker (cued by the Call sign "Baron"). Experiment 1 altered the natural rhythm of the target talker and background talkers for two-talker and six-talker backgrounds. Experiment 2 considered parametric rhythm alterations over a wider range, altering the rhythm of either the target or the background talkers. Experiments 1 and 2 revealed that altering the rhythm of the target talker, while keeping the rhythm of the background intact, reduced listeners' ability to report the Color and Number spoken by the target talker. Conversely, altering the rhythm of the background talkers, while keeping the target rhythm intact, improved listeners ability to report the Color and Number spoken by the target talker. Experiment 3, which embedded the target talker in speech-shaped noise rather than multi-talker babble, similarly reduced recognition of the target sentence with increased alteration of the target rhythm. This pattern of results favors a dynamic-attending theory-based selective-entrainment hypothesis over a disparity-based segregation hypothesis and an increased salience hypothesis.