Mizuki, a 9-year-old female chimpanzee (Pan troglodytes) living in the Great Ape Research Institute, Hayashibara Biochemical Laboratories, Inc., Japan, was the participant. When interacting with human carers and experimenters, she had been called by her name from just after birth.
Three types of vocal stimuli and one non-vocal stimulus were presented. The three vocal stimuli consisted of the subject's own name (‘Mi-zu-ki,’ SON), a familiar name of another group member (‘Tsu-ba-ki,’ FN) and an unfamiliar name (‘A-su-ka,’ UN). The non-vocal stimulus (NV) was white noise that had been adjusted to resemble the sound construction of the SON stimulus. All four stimuli had identical root-mean-square amplitude and similar sound constructions, with an accented sound at the first mora. The duration of all stimuli was 450 ms. The sound intensity measured at the chimpanzee's position averaged 83 dB HL, which was within her audible range (Kojima 1990
Mizuki participated in four recording sessions, each consisting of four to five blocks. During each block, four types of sound stimuli were presented 80 times, with 1500 ms stimulus onset asynchrony, in pseudo-random order with no consecutive repetition of the same stimulus.
The EEG was recorded at five scalp positions (Fz, Cz, Pz, C3 and C4) according to the International 10–20 system for humans. From EEG recording, the peaks of two types of ERP components were identified in the grand average data. The peak of the P3-like component was defined as the most positive peak in the period 200–450 ms following stimulus onset, and the Nc-like component was defined as the most negative peak in the period 450–600 ms following stimulus onset. The peak amplitudes were calculated separately for each stimulus and electrode. Among the five electrodes, the electrode with the largest positive/negative peak amplitude was selected, and the peak latency of that electrode was used for the following calculations. At the respective peak latencies, the amplitude for each epoch was analysed by two-way analysis of variance with factors of stimulus type and electrode, and then by post hoc test corrected for multiple comparisons. We first examined the differences among the stimuli and/or channels, and we then investigated the specificity of SON among the detected differences. For further details, refer to the electronic supplementary material.