Objective measurement of initial word comprehension after cochlear implantation using evoked potentials

Introduction After cochlear implantation, hearing by the electrical stimulation initially differs largely compared to the acoustic stimulation. Therefore, speech comprehension is usually not possible directly. Longer learning and adaptation processes are required to ensure comprehension. In this study, these processes were investigated by means of objective brain potential measurements.

Method Fifteen postlingual patients with severe bilateral hearing loss who were fitted with a CI on one side participated. There were three measurement time points: T1 (3 days after initial activation), T2 (9 weeks), and T3 (5 months). An N400 paradigm was used in which patients saw a picture on a monitor and simultaneously heard a word that either matched the picture (congruent) or not (incongruent). In another condition, the auditory words were accompanied by a noise. The EEG was recorded with 23 electrodes and subsequently evoked potentials were calculated.

Results For T1, there was a significant difference between congruent and incongruent condition (N400 effect). For T2 & T3, the effect became more stable widely distributed. For words in noise, on the other hand, there was no effect for T1 & T2. Only for T3 was a weak but significant N400 effect observable.

Discussion  The data provide the first objective evidence of neurocognitive processing of speech at a very early stage of CI fitting. The assignment of a spoken word to a given picture is already possible shortly after first fitting. In contrast, the comprehension of words in noise develops later, but overall surprisingly early.

Fa. MED-EL

Publication History

Article published online:
12 May 2023