prosody identification [15] employed full sentences with much longer duration, giving participants more time to identify the conveyed emotion. Thus, lower task difficulty in the latter study [15] could explain why alexithymia-related differences were not detected at the behavioral level. Taken together, our behavioral findings are in line with previous reports of difficulty in the identification of visually displayed emotion in alexithymia [13–15] and indicate that such emotion identification problems extend to the auditory domain. However, our finding of worse performance only during disgusted prosody identification points toward a rather subtle deficit in emotional prosody identification. This seems not surprising considering that individuals scoring high on alexithymia are, despite their interpersonal problems, generally high-functioning, socially adapted individuals. The pursuit of social conformity is a characteristic feature of alexithymia [2] and implies learning to interpret emotional signals during social communication to the best of one’s ability. Unattended processing of emotional prosody Alexithymia was found to affect amplitudes of the eMMN during unattended processing of emotional prosody (task 1). We observed a left-hemisphere bias during early acoustic encoding (as indexed by a faster left-hemispheric eMMN) with increasing scores on the identifying and verbalizing subscale of the cognitive alexithymia dimension for all deviants in emotional prosody (happy, angry, sad, and disgusted), which was additionally paired with a tendency toward a delayed response of the right hemi- sphere. Difficulty identifying feelings was further associated with overall delayed eMMN latencies to disgusted prosody. These findings are particularly interesting considering that amplitudes of the neuromagnetic equivalent of the MMN in response to changes in emotional prosody have recently been found to be larger in the right hemisphere in healthy individuals [76], and that the right hemisphere has long been assumed to play an important role in processing emotional prosody [77,78]. However, the question of right hemisphere predominance for emotional aspects of speech is still under debate and may constitute a relative rather than an absolute dominance [43,79,80]. In any case, our finding of a left-hemisphere bias during early acoustic processing of emotional prosody in cognitive alexithymia is in line with the hypothesis of a hyperactive left hemisphere during emotional processing in this personality trait [32], and suggests that decreased abilities in identifying and verbalizing one’s feelings are linked to a hyper-reliance on the left hemisphere, normally specialized for cognitive analyses rather than emotional processing [81]. Attended processing of emotional prosody Early processing. During attended processing of emotional speech (task 2), the two alexithymia dimensions modulated early (,300 ms) electrophysiological responses to emotional speech in a qualitatively different fashion. Cognitive alexithymia was associated with larger N1 amplitudes in response to detected deviants, an association that was driven only by the subscale difficulty analyzing feelings. Larger N1 amplitudes were also reported in a previous study on auditory emotion perception in alexithymia in response to aversive white noise [42]. Given that the N1 reflects the extraction of acoustic cues during early acoustic processing and that its amplitude increases with attention [48], this may suggest that individuals with difficulty analyzing feelings need to devote more attention to acoustic cues in order to detect changes in emotional prosody. Difficulty analyzing feelings was further associated with reduced frontal P2 amplitudes. The The Sound of Feelings affective alexithymia dimension did not modulate the N1 but was also associated with reduced frontal P2 amplitudes, an association driven only by the fantasizing subscale. The P2 has previously been shown to be sensitive to the emotional qualities of speech and is thought to reflect initial emotional salience detection [50,51]. Our finding of reduced frontal P2 amplitudes in individuals with difficulty analyzing feelings (cognitive dimension) and impaired abilities to fantasize (affective dimension) could thus represent a reduced initial detection of emotional speech salience, i.e. attenuated basic emotional processing as previously suggested by Pollatos and Gramann [38]. Taken together, these results suggest that alexithymia modulates both the unattended as well as the early attended processing of emotional prosody, with a qualitatively different impact of the two alexithymia dimensions: Only the cognitive dimension was associated with a left hemisphere preference during the un- attended acoustic encoding of variations in emotional speech, and with a higher amount of attention devoted to the extraction of acoustic cues when detecting emotional prosodic deviants. An effect of the affective dimension was only found starting at approximately 150 ms (P2 time-window) reflected in reduced frontal P2 amplitudes, which were also observed in relation to the cognitive dimension. These results confirm previous reports of early perceptual differences in emotional processing as a function of alexithymia [35,38], and extend these findings by suggesting that such early perceptual modulations may be predominantly associated with the cognitive alexithymia dimension, whereas its affective dimension may be related to differences at later stages of emotional appraisal. In addition, our observation of a faster left-hemispheric response and a tendency toward a delayed right-hemispheric response during the early acoustic encoding of unattended emotional speech is in line with the hypotheses of a left hemisphere preference during emotional processing [26,32] and a hypoactive right hemisphere associated with alexithymia [30,82]. However, according to our findings such a left-hemisphere bias and hemispheric dissociation seems predominantly evident in the cognitive dimension of alexithymia. It would be worthwhile to further investigate in future studies whether a left-hemisphere preference and right hemisphere hypoactivity during emotional processing may be a characteristic of particularly the cognitive alexithymia dimension. Late processing. Our results further demonstrated that alexithymia is associated with reduced amplitudes of the later (.300 ms) occurring P3, a component reflecting conscious stimulus evaluation. Amplitudes of this component have been shown to be sensitive to the ascribed importance to a stimulus (the higher the subjective importance, the higher the P3 amplitude). The P3 is also related to the emotional valence assigned to a stimulus in such a way that higher emotional valence is reflected in larger P3 amplitudes [83,84]. Our finding of reduced P3 amplitudes in response to emotional prosody corroborates and extends the findings of previous studies, which reported reductions in P3 amplitudes during emotional picture processing in alexithymia [36,38]. In addition, our results indicate differential effects of the two alexithymia dimensions on P3 amplitudes. The cognitive di- mension was related to generally smaller P3 amplitudes in response to changes in emotional prosody, an association driven by the subscales difficulty identifying and verbalizing feelings. Difficulty verbalizing feelings was additionally related to reduced P3 amplitudes particularly to disgusted prosody. In contrast, the affective dimension was found to be sensitive to the intensity with which emotional speech was pronounced, reflected in even PLoS ONE | www.plosone.org 11 May 2012 | Volume 7 | Issue 5 | e36951