Fusion and identification of vowels in the free field

Binaural fusion occurs when signals arriving separately at the two ears are perceived as one sound. Previously, Reiss and Molis (2021) showed that listeners with normal or impaired hearing fused and perceptually averaged dichotic vowels presented through headphones, especially vowels with the same fundamental frequency. To extend these findings to a more real-world listening context, the current study investigated if vowel fusion and averaging would replicate in the free field. Stimuli were good exemplars of /æ/, /a/, /u/ or /i/ synthesized with fundamental frequencies of 106.9, 151.2, or 201.8 Hz. On each trial, vowels were presented simultaneously via speakers located on the left and the right at ±60°. On test trials, vowels presented from the left and right were different; fundamental frequencies could be the same or different. On catch trials, identical non-exemplar vowels were presented from both speakers; these trials reduced the likelihood listeners would notice that different categories were presented on test trials. Listeners indicated which single vowel or two vowels they heard. Preliminary findings from normal-hearing listeners suggest there are fewer single vowel responses—fusion is decreased—in free field compared with headphone presentation. As demonstrated with headphones, vowels with the same fundamental frequency are more often fused. Results indicate that vowel fusion patterns previously observed with headphones can also be observed in the free field. [Work supported by NIH R01DC013307 and CSULA SPROUTS program.]