of 500 Hz, amplified, and off-line digitally low-pass filtered with a cut-off frequency of 30 Hz. Participants were seated in front of a monitor at a distance of approximately 50 cm in a dimly lit, electrically shielded and sound-attenuated cabin. The auditory oddball paradigm was presented via loudspeakers placed at the left and right side of the monitor at approximately 70 dB, while the EEG was recorded. In task 1, participants watched the first 20 minutes of a silent cartoon movie (title: Kiki’s delivery service) and were instructed to focus on the story in the movie while ignoring the sounds. In the oddball paradigm used in task 1, neutral prosody served as standards (960 trials), while happy, angry, sad, and disgusted emotional prosody spoken in low intensity served as deviants (60 trials each). Only stimuli of lower salience (low emotional intensity) were used in this task to prevent participants from directing their attention to the auditory stimuli, which enabled us to measure electrophysiological responses to subtle prosodic changes during unattended processing. The ERP component of interest in this task was the MMN. In task 2, participants were instructed to press a button as fast as possible whenever they heard an emotion different from the standard emotion (irrespective of intensity). They were asked to look at a fixation point in the center of the screen to prevent eye movements. In this oddball paradigm, sad emotional prosody spoken with low and high intensity represented the standards (960 trials), whereas happy, angry, and disgusted emotional prosody (60 trials each) in both intensities served as deviants. Sad emotional prosody instead of neutral intonation was used as standard in this task because the aim of this task was to record ERP responses to actual changes in the perception of one emotional intonation to another as it frequently occurs in real life, rather than a change from a neutral to an emotional intonation. The total duration of task 2 was 32 minutes, and participants could take a break after the first 16 minutes, if needed. The ERP components of interest in this task were the early components N1 and P2, and the late component P3. Task 3 was an off-line task, in which participants were given a list to identify both the emotion a nonsense syllable was spoken in as well as the intensity of the emotion. Fifty-four stimuli were presented at an interstimulus rate of five seconds to give participants sufficient time to mark the identified emotion and intensity on the list. ERP data analysis EEG data were analyzed with Brain Vision Analyzer (version 1.05) by means of peak analyses. Prior to averaging, trials with eye- movement and blink artefacts were excluded from analysis. Criteria for artefact rejection were a maximal voltage step of 50 mV, a maximal difference between two values in a segment of 100 mV, and a minimal and maximal amplitude of 2100 mV and 100 mV, respectively. All averages were aligned to a 100 ms pre- stimulus baseline. In accordance with the MMN literature, MMN parameters were calculated from a difference waveform obtained by subtracting the standard-stimulus ERPs from the deviant- stimulus ERPs. For task 1, a total mean number of 229.5 deviant trials (SD 6.6) in emotional prosody were recorded for each of the 60 participants, with a mean number of 57.4 trials for happy, angry, sad, and disgusted prosodic deviants, respectively. Artefact re- jection excluded a mean percentage of 12.2 percent of all trials, leaving a total mean of 201.5 (SD 8.8) deviant trials for analysis, with a mean number of 50.4 trials per emotional deviant condition. For task 2, a total mean number of 172.9 (SD 5.8) deviant trials in emotional prosody was recorded, with a mean The Sound of Feelings number of 57.6 trials per emotional deviant condition. Artefact rejection excluded a mean percentage of 10.6 percent of all trials, leaving a total mean of 154.6 deviant trials (SD 8.5) for analysis, with a mean number of 51.5 trials per condition for each of the 60 participants. Time-windows for peak detection were time-locked to the onset of standards and deviants. The time-windows were chosen in agreement with the existing literature on the respective ERP component and based on visual inspection of the data. The latter revealed that the MMN during unattended processing of emotional prosody consistently exhibited a double-peak across participants. Thus, two MMN peaks were identified in a time- windows of 50–130 ms post-onset for the first peak (in the following referred to as eMMN) and 130–250 ms post-onset for the second peak (in the following referred to as lMMN). Consequently, separate statistical analyses were conducted for amplitudes and latencies of the detected peaks in the eMMN and the lMMN time-windows. During attended processing of emotional prosody (task 2), peaks were identified in the following time-windows: 90–140 ms post- onset for the N1, 150–250 ms post-onset for the P2, and 310– 550 ms post-onset for the P3. Because the P3 does not always exhibit a clear peak, results of the peak detection procedure were inspected in each subject and trials that did not show a clear peak in the defined time-window (due to multiple peaks) were excluded. Statistical analyses were conducted for amplitudes and latencies of the detected peaks in the N1, P2, and P3 time-windows. In order to obtain symmetrical coverage of the scalp during statistical analysis, five midline electrodes were chosen covering frontal through parietal areas (Fz, FCz, Cz, CPz, Pz) along with their corresponding left (F3, FC3, C3, CP3 and P3) and right (F4, FC4, C4, CP4, P4) counterparts (see figure 1). As the results of task 1 show, alexithymia scores were found to modulate ERP responses to sad prosody, which served as standards in task 2. To exclude the possibility that differences in ERP responses to sad standards confounded ERP responses to deviants in task 2, peak amplitudes in response to deviants were subtracted by peak amplitudes in response to standards taking intensity difference into account (i.e. low intensity standards were subtracted from low intensity deviants, high intensity standards were subtracted from high intensity deviants). This procedure ensured that voltage changes elicited by deviants were measured relative to voltage changes elicited by standards. The procedure further led to better comparability of the results of task 1 and 2, as in both tasks standard-related activity was subtracted from activity elicited by deviants and the resulting difference waves were used in subsequent statistical analyses. Statistical data analysis Behavioral data. Statistical analyses were performed in SPSS version 17.0 (SPSS Inc; Chicago, Illinois). Behavioral data were available from 57 (out of 60) subjects. Two subjects did not complete the behavioral task due to time restrictions as a conse- quence of technical difficulties at the beginning of the session. One subject with an outlier score (67) on the affective dimension of alexithymia was excluded to ensure continuity of scores. Scores of the remaining 57 subjects ranged from 20 to 55 on the affective alexithymia dimension (median: 35, SD: 9.7) and from 27 to 93 on the cognitive alexithymia dimension (median: 52, SD: 17.1). Pearson’s correlations were performed between each alexithymia dimension and error rates as well as RT during prosodic deviant detection (Task 2), and with error rates during emotional prosody identification (Task 3). PLoS ONE | www.plosone.org 5 May 2012 | Volume 7 | Issue 5 | e36951