Electrophysiological responses to emotional prosody perception in cochlear implant users

Abstract

The present electroencephalographic (EEG) study investigated the ability of cochlear implant (CI) users to recognize emotional prosody. Two CI speech-processing strategies were compared: the ACE (Advance Combination Encoder) and the newly developed MP3000. Semantically neutral sentences spoken in three different emotional prosodies (neutral, angry, happy) were presented to 20 post-lingually deafened CI users and age-matched normal-hearing controls. Event related potentials (ERPs) were recorded to study the N100 and the P200 responses. In addition, event-related spectral power modulations were calculated to study the brain activity corresponding to the recognition of prosody in earlier (0-400) as well as later (600-1200) part of the stimuli where the prosodic features differed maximally. CI users with MP3000 strategy showed a higher proportion of correctly recognized prosodic information compared to the ACE strategy users. Our ERP results demonstrated that emotional prosody elicited significant N100 and P200 peaks. Furthermore, the P200 amplitude in response to happy prosodic information was significantly more positive for the MP3000 strategy compared to the ACE strategy. On spectral power analysis, two typical gamma activities were observed in the MP3000 users only: (1) an early gamma activity in the 100-250 ms time window reflecting bottom-up attention regulation; and (2) a late gamma activity between 900 and 1100 ms post-stimulus onset, probably reflecting top-down cognitive control. Our study suggests that the MP3000 strategy is better than ACE in regard to happy prosody perception. Furthermore, we show that EEG is a useful tool that, in combination with behavioral analysis, can reveal differences between two CI processing strategies for coding of prosody-specific features of language.

Keywords: Cochlear implants; ERP; Emotional prosody; Gamma band power; P200.

Fig. 1

Pitch contours of the three prosodies. Praat generated pitch contours of neutral (dotted line), angry (solid line) and happy prosody (dashed line) for the original (unsimulated) sentence: “Sie hat die Zeitung gelesen”. The maximum difference in pitch across emotions can be seen between 200 and 1200 ms from the starting of the sentence.

Fig. 2

Accuracy rate and reaction time. Top (A): accuracy rate for NH controls vs. CI, ACE users vs. MP3000 users for neutral, angry and happy emotional prosody recognition in percentage. Bottom (B): post offset reaction time for emotional prosody recognition in seconds. The significance is indicated with asterisk with p < 0.05.

Fig. 3

ERP waveforms for three emotional prosodies for NH controls, ACE and MP3000 users. Average ERP waveforms recorded at the Cz electrode for NH controls (black), ACE users (red) and MP3000 users (blue) for all three emotional [neutral, angry and happy] stimuli from100 ms before onset to 600 ms after the onset of the sentences with respective scalp topographies at N100 and P200 peak (X-axis: latency in milliseconds, Y-axis: amplitude in μV). Top left: N100-P200 waveform for neutral, Middle: waveform for angry and right for happy prosody. Bottom left scale topography of NH controls, middle: ACE users, right: MP3000 users for N100 and P200 respectively.

Fig. 4

Induce gamma power plots for ACE and MP3000 users. The average gamma power computed at Cz electrode for ACE users and MP3000 users for all three emotional prosodies (neutral, angry and happy) for (− 200–1500) time window in range of 25 to 70 Hz. Highlighted area along with scalp plots represent induced gamma power in early (0–400 ms) and in late (600–1200 ms) time windows at significance (p < 0.01).