University of Auckland, New Zealand
Title: Auditory divided attention and auditory long term potentiation with cochlear implants: Objective clinical measures
Nathan completed his MSc at the age of 27 years from the University of Auckland, New Zealand and did his undergraduate studies in Physiology and Psychology (BSc double major). He has one pending publication (Seminars in Hearing) from a voluntary project during third year, and that team has plans for three more publications from the project (multiple topic study design). He also plans to further his education in cochlear implants and auditory brain plasticity, either via clincial studies or a research career. In his spare time, Nathan enjoys classic cars, photography and travel.
PURPOSE OF STUDY: Measures of auditory plasticity (long term potentiation; aLTP) over short time periods is investigated (n=12 binaural NH, n=16 monaural NH, n=8 Cochlear Implant [CI]) and whether 13Hz tetanic auditory stimulation can induce aLTP for CI therapy purposes. To investigate the Brief Test of Attention (BTA) as a valid cognition test for CI recipients and establish whether re-standardisation is required for CI populations. METHOD: CI recipients aged 17.49 to 86.26 years (µ=55.70, σ =23.07) were tested. Eight participants had post-linguistic hearing loss onset, whereas six were pre-linguistic (n=4, <2 years) or “peri-linguistic” (n=2, 2-4 years). All received Cochlear™ devices (n=12 Nucleus24; n=2 Nucleus22) post-linguistically; 3 childhood, ten post-40, and one at 21. Clincial EEG used to investigate aLTP [Clapp et al’s (2005) methodology]. Monaural-stimulated control participants (n=8) age- and sex- matched to CI participants (n = 8) , in addition to binaural-monoaural comparison (n = 12 Binaural, n=16 monaural). BTA was conducted for all hearing loss EEG participants as a pilot study, and for six additional CI recipients in an ongoing followup study. RESULTS: No group shows evidence of aLTP. N1 amplitude decreased post-intervention; however, baseline-shift for N1 amplitude is evident for all groups. N1 amplitude was significantly larger for CI than NH, but latency was non-significant. N1 amplitude correlates with speech recognition in noise, for the CI group. BTA scores correlates with length of time using a CI (r=0.708, p=0.049). The CI (n = 16) mean BTA score is 55%±22% (range 25%-95%). Six participants passed published age-standardized scores (percentiles and impairment categories). Of the remaining participants, two were “borderline impaired” (2nd - 9th percentile), and six were below 2nd percentile for their age (“impaired”). BTA scores do not correlate with speech-perception-in-noise scores (50% SRT for sentences) (n=10; r=-0.236; p=.582). Similarly, BTA score against time with CI showed non-significant correlation (n=12; r=0.140; p=.664). CONCLUSIONS: Clapp et al’s (2005) findings were not replicated, nor was aLTP observed with monaural. Passive exposure to tetanizing auditory stimuli did not induce aLTP for people who use CIs. Attending to the tetanizing stimulus, or longer therapy, may be required for aLTP induction. N1 baseline-shift suggests passive learning; which may compromise aLTP detection. Lack of correlation between BTA and speech perception supports a divergent validity hypothesis i.e. the BTA is testing attention, not speech perception. The BTA does not seem to require high speech perception ability, making it a promising test of cognition for CI populations. However further data and subsequent re-standardisation is needed before the BTA could be used as a clinical test or screening tool.