How does attentional control modulate the younger and older adults’ dichotic listening of Cantonese tones?

Attentional control is found to modulate speech (i.e., consonants) processing in a forced-attention dichotic listening (FADL) task. A right-ear advantage (REA) in the non-forced condition (NF, baseline: hearing two stimuli simultaneously and identifying the clearer one) is often enhanced when participants are instructed to report the right-ear stimulus (forced-right, FR) or switched to a left-ear advantage (LEA) when instructed to report the left-ear stimulus (forced-left, FL). Different from consonants that are cued by voice onset time, lexical tones are often cued by pitch and found to show an LEA baseline. This study investigates whether younger adults show an effect of attentional control on tone processing and whether their older counterparts exhibit a less pronounced effect due to an age-related decline. We first tested 60 Cantonese-dominant younger participants (18–25 years) with the Cantonese tone FADL task under three conditions (NF, FL, FR) in Experiment 1. They increased the LEA baseline in the FL and showed the opposite REA pattern in the FR, suggesting an effect of attentional control. Experiment 2 tested 64 older participants (59–72 years), who showed an LEA baseline, a similar REA in the FR, but a smaller LEA increase in the FL than younger adults, suggesting a potential decline in attentional control. This decline appeared in one but not both forced conditions, implying tones—with more salient, longer-duration cues than consonants—may partially preserve auditory attentional control in aging.