The Effects of Auditory Experience on Psychophysical Tuning Curves in Pediatric and Adult Cochlear Implant Listeners

The development of the auditory system may be affected by the type and quality of input. Individuals with early deafness receive degraded acoustic input (depending on the degree of loss), whereas those who receive cochlear implants (CIs) receive degraded electrical input. In animal models of congenital or early deafness, substantial neural degeneration occurred in the ascending auditory pathway. However, in some studies, animals listening to electrical stimuli through a CI showed some retention of neural integrity. In humans, little is known about auditory development in individuals with congenital deafness who wear CIs. In addition to the number/density of surviving auditory neurons, the effects of early implantation on spatial selectivity is currently unknown. The present study investigated the specificity of CI stimulation in congenitally-deafened children who received a cochlear implant early in life, and adults who were either early-or late-deafened. The hearing histories of these listeners spans a wide range of chronological age, duration of deafness, etiology, and CI listening experience. Psychophysical tuning curves (PTCs) were evaluated on one electrode to quantify the spatial specificity of CI channels (or channel interaction). PTCs were measured using a forward masking paradigm for 13 children, 8 of whom were sequentially, bilaterally implanted (21 ears). PTCs were also measured in 13 unilaterally implanted adults (3 early-, 10 late-deafened). The equivalent rectangular bandwidth (ERB) was used to quantify the PTC bandwidth. Although there were no statistically significant differences in the ERB distributions for the various groups in this study, the median ERB for children was 5.0 mm for the first implanted ear and 6.3 mm for the second ear, and 4.6 mm in adults. There was no correlation between PTC ERB and age at implantation for the children. The results with this small data set are inconclusive about the role of early acoustic versus electric hearing on spatial selectivity of CI stimulation as measured by psychophysical tuning curve bandwidths. However, the results demonstrate the tremendous variability in PTC bandwidth in early- implanted children. (C) 2018 The Author(s). Published by S. Hirzel Verlag.EAA.