Aging and the effect of background rhythm on selective listening in multiple-source environments

In multi-source environments, rhythmic regularities in both to-be-attended signals (targets), as well as to-be-ignored signals (backgrounds) have been found to influence selective listening across a variety of stimuli and listening conditions. Specifically, regular rhythmic structures facilitate recognition of target signals, and background signals with regular rhythmic structures are more effective maskers than irregular backgrounds. The current study focused on the background rhythm effect and assessed to what degree it depends on the perceptual similarity between the target and background signals, and its dependence on listener age. A novel synthetic-vowel identification paradigm was used, in which young and older listeners were presented with an isochronous (regular) target sequence interleaved with background sequences that were either isochronous or anisochronous (irregular). When the background sequences consisted of a repeating vowel-like stimulus that was easily distinguished from the target vowel sequence, listeners were not sensitive to the rhythmic regularity of the background sequences. However, when the background consisted of vowels that only differed from the target vowels in fundamental frequency, regular backgrounds led to lower vowel identification rates than irregular backgrounds. These findings mirror those obtained with natural speech stimuli. The replication and extension of the background rhythm effect with the current paradigm demonstrates that the background rhythm effect is not attributable to differences in energetic masking (there was no target/background overlap in the current study) and is not restricted to continuous speech stimuli. Further, the background rhythm effect was reduced in older listeners, suggesting that sensitivity to background rhythm in multi-source environments may decrease with age.