UPDATE FROM 2011 CAPITA FOUNDATION AUDITORY RESEARCH GRANT RECIPIENT

Dr. Carol Lee De Filippo
Professor at National Technical
Institute for the Deaf, Rochester, NY

Improving Speech Perception in Prelingually Deaf Adult Listeners: Exploring a Novel Training Concept

Audiologists at the National Technical Institute for the Deaf (NTID) located at Rochester Institute of Technology (RIT), have designed a novel audiovisual speech training strategy for adults born deaf (prelingually deaf adults) who obtained cochlear implants (CI) beyond the critical period for auditory stimulation. The rehabilitative program examines the hypothesis that fading dominant visual speech cues will trigger neuroplasticity by fostering useful sensory integration of the visual and acoustic components of spoken language. Initial findings have implications for the efficacy of the strategy for use with prelingually deaf adults who have not benefitted from traditional auditory training. 

Current CIs can produce dramatic speech perception benefits by restoring hearing and reorganizing audiovisual pathways developed in adults who have lost all or most of their hearing later in life and capitalizing on developmental plasticity in early implanted children. In contrast, prelingually deaf adult CI recipients typically have limited speech recognition skills and continue to be visually dominant, both behaviorally and neurologically.

 “Life-long dependence on lipreading prior to implant may be one reason for the continued use of visual cortex for processing of speech, even post-implant. Thus, typical auditory training (listening only) is often frustrating, resulting in slow progress and highly varied outcomes, although exceptional cases of open-set speech recognition suggest that learning-dependent plasticity is possible”, says Dr. Carol DeFilippo, NTID/RIT professor, PI for the study.

For the study, Dr. De Filippo and colleague Dr. Catherine Clark recruited prelingually deaf adults who perceived inadequate benefit from their CIs and were interested in a new rehabilitative strategy. One older adult and 7 young adults participated. Subjects completed 4-9 blocks of training (3240 -7920 trials) over 3 weeks.  On each trial, they viewed a head-only audiovisual clip of one of 6 talkers speaking a vowel-consonant-vowel syllable (b, d, or g; with ah, ee, or oo) in one of 5 conditions, including the original (no added effects) and 4 edited clips that progressively obscured lipreading cues. Training used a three-alternative forced-choice task (“B”, “D”, or “G”) with feedback. As expected, performance decreased in degraded conditions, indicating that the training materials were effective in requiring attention to auditory cues.  As training increased, all subjects obtained better scores by the last block in the most degraded condition (auditory-only) for at least 2 of the 3 consonants. As a group, they also demonstrated a greater listening advantage on one or all of the consonants, ranging up to a 31% improvement in the clear audiovisual condition by the end of the study. These levels of gain are typically unheard of for prelingually deaf adult listeners, particularly in a short period of time (3 weeks). The ultimate goal of this work is to develop a unique clinical intervention that can evoke beneficial change in prelingually-deaf adult CI users.