Lukas Suveg, Au.D.
Doctoral Candidate, Litovsky Lab, Waisman Center, UW-Madison
Effects of Peripheral Asymmetry on Speech Understanding in Simulations of SSD-CI Listening
Patients with single-sided deafness (SSD) have the greatest possible interaural asymmetry – one ear has clinically normal acoustic hearing while the other has no usable hearing. Since their introduction in the late 2000s, cochlear implant (CI)s have been used increasingly to manage SSD, restoring access to sound in the previously unusable auditory pathway. Although CI recipients with SSD (i.e., “SSD-CI”) can hear through both ears, the ability to integrate acoustic and electric stimulation from the typical and implanted ears, respectively, is highly variable. Given that multiple etiologies can induce SSD, there is variability in how well the implanted ear can encode auditory inputs. This variability is hypothesized to be reflected in the ability of SSD-CI users to fuse speech information arriving at the two ears simultaneously, and to encode speech information presented to the two ears using an inter-ear switching, or alternating pattern.
The first step in this investigation is to simulate various aspects of CI processing to approximate peripheral encoding that varies in precision and spread of excitation across electrical channels using vocoders and to study how normal hearing listeners process these signals. Previous work in this population suggests that at low rates (e.g., 1-2 Hz), participants selectively attend to the ear in which the signal is playing; at high rates (e.g., > 6 Hz), participants can attend to the ear in which the signal is clearer. However, at intermediate (e.g., 3-5 Hz), speech target intelligibility depends on integrating the input from each ear. Our initial data suggest that the low points on the rate-intelligibility functions occur earlier for TH participants listening to unilaterally vocoded speech compared to previous work with this paradigm from our lab among TH participants listening to bilaterally un-processed speech or bilaterally vocoded speech. This may suggest that the qualitative difference across ears induces increased processing difficulty resulting in an inability to maintain attention-switching that occurs earlier than it does when ears are symmetrical.