Event-related potentials

ERPs to different conditions were quantified by mean amplitude measures in the time segments 110-140, 170-200, 200-300, 300-500 and 500-800 ms. The first segment was chosen to correspond to the occipital P1, the second segment corresponded to the

occipito-2 Methods 19

temporal N170 peak in the waveforms, the 300-500 time segment roughly corresponded to the central-parietal P3. The other segments were chosen upon visual inspection. All amplitude measures were taken relative to a 200-ms baseline preceding the target stimulus and recalculated to average reference.

For every time segment, ANOVAs were then performed with repeated measures on type of composite (LL- vs. RR-composite), type of expression (anger vs. fear vs. happiness vs.

sadness), level of intensity (100% vs. 50%) and the additional repeated measurement factor electrode site (32 levels). Where appropriate, epsilon corrections for heterogeneity of covariance with the Huynh- Feldt method (Huynh & Feldt, 1976) were performed throughout.

Further analysis was carried out for effects that turned out significant in the global analysis applying ANOVAs for selected time segments for different regions of interest, being prefrontal/ lateral frontal (FP1, FP2, F7, F8, FT9, FT10, F9, F10, F9’, F10’), frontal (F3, F4, Fz), central-parietal (C3, C4, P3, P4, Cz, Pz), temporal (T7, T8, P7, P8, P9, P10, TP9, TP10) and occipital (O1, O2,

Iz, PO1, PO2) with repeated measures on type of composite (LL- vs. RR-composite), type of expression (anger vs. fear vs. happiness vs. sadness), level of intensity (100% vs. 50%) and the additional factor hemisphere (left vs. right) for regions of interest that did not include a midline electrode (prefrontal/lateral frontal and temporal region of interest). Regions of interest were defined by pooling electrodes that were roughly showing a similar pattern of ERP response, irrespective of experimental condition being investigated.

Individual electrodes within the above described regions of interest were not included as a separate factor for the ANOVAs, since regions of interest were considered to be homogenous.

Defined regions of interest that were kept consistent across all different experimental conditions. Where appropriate, epsilon corrections for heterogeneity of covariance with the Huynh- Feldt method (Huynh & Feldt, 1976) were performed throughout.

Interactions with factor type of expression that turned out significant within the defined regions of interest for a specific time segments were further analysed. Post-hoc comparisons using Tukey hsd were made to determine the significance of differences.

3 Results 20

3 Results

3.1 Intensity task

- Percentage of LL- vs. RR-composites being chosen

Percentage of LL- and RR-composites being chosen were submitted to an analysis of variance (ANOVA) with repeated measures on type of composite (LL- vs. RR-composite), type of expression (anger vs. disgust vs. fear vs. happiness vs. sadness vs. surprise) and level of intensity (100% vs. 50%). Where appropriate, epsilon corrections for heterogeneity of covariance with the Huynh-Feldt method (Huynh & Feldt, 1976) were performed throughout.

The ANOVA revealed a significant effect of type of composite, F(1,23)= 1.5, p<.001, with RR-composites overall being chosen in about 65.3% as more expressive (see Table 1). In addition to this main effect of composite, there was a significant interaction between expression and composite, F(5,115)=4.4, p<.01. Thus the contrast in terms of perceived intensity between LL- and RR-composites was different for individual expressions, although it was present for each expression (see Fig .1). Furthermore, there was a significant three- way interaction between composite, expression and intensity, F(5,115)=5.0, p<.001 (see Fig. 2).

LL/ RR-composites Level of

intensity

overall anger disgust fear happiness sadness surprise

overall ^34.7/

Table 1. Percentage of LL- vs. RR- composites being chosen; overall and separately per level of intensity;

overall and separately for each individual expression

3 Results 21

Figure 1. Percentage of LL-vs. RR- composites being chosen; overall and separately for each individual expression.

Examining individual expressions, an analysis of variance (ANOVA) with repeated measures on type of composite (LL- vs. RR-composite) and level of intensity (50% vs. 100%) revealed a significant main effect of type of composite, F(1,23)=33.8, p<.001, for anger, with RR-composites overall being perceived as more intensive in about 64.9%. Moreover, there was a significant interaction between type of composite and level of intensity, F(1,23)=7.7, p<.05, indicating that the difference in perceived intensity between LL- and RR-composites varied for different levels of intensity. Post- hoc testing with Bonferroni- corrected pairwise comparisons revealed that the effect for RR-composites was significant at each level of intensity, (LL 100%- RR 100%, F(1,23)=15.36, p<.001; LL 50%- RR 50%, F(1,23)=34.83, p<.001; α=. 025).

RR-composites of disgust were overall perceived as being more intensive in about 66.0%, as reflected by a significant main effect of type of composite in an analysis of variance (ANOVA) with repeated measures on type of composite and level of intensity, F(1,23)=42.5, p<.001. Furthermore, there was a significant interaction between type of composite and level

% of LL-vs. RR-composites being chosen

overall anger disgust fear happiness sadness surprise

%

3 Results 22

of intensity, F(1,23)=8.7, p<.01, indicating that the difference in perceived intensity between LL- and RR-composites varied for different levels of intensity. Post- hoc testing with Bonferroni- corrected pairwise comparisons revealed that the effect for RR-composites was significant at each level of intensity (LL 100%- RR 100%, F(1,23)=8.94, p<.01: LL 50%- RR 50%, F(1,23)= 89,81, p<.001; α=.025.

RR-composites of fear were perceived as being more intensive in 71.4% as reflected by a significant main effect of type of composite in an analysis of variance (ANOVA) with repeated measures on type of composite and level of intensity, F(1,23)=72.1, p<.001.

RR-composites of happiness perceived as being more intensive in 66.3% as reflected by a significant main effect of type of composite in an analysis of variance (ANOVA) with repeated measures on type of composite and level of intensity, F(1,23)=58.8, p<.001.

RR-composites of sadness were perceived as being more intensive in 58.7% as reflected by a significant main effect of type of composite in an analysis of variance (ANOVA) with repeated measures on type of composite and level of intensity, F(1,23)=10.8, p<.01. There was a trend towards an interaction between composite and level of intensity, F(1,23)=3.15, p<.09, indicating that the difference in perceived intensity between LL- and RR-composites varied for different levels of intensity. Post-hoc testing with Bonferroni- corrected pairwise comparisons revealed that the difference in perceived intensity between LL- and RR-composites was only significant when shown in 50% intensity (LL 100%- RR 100%, F(1, 23)=2.88, p<.10; LL 50%- RR 50%, F(1,23)=16.8, p<.001; α=.025).

RR-composites of surprise were perceived as being more intensive in 64.7% as reflected by a significant main effect of type of composite in an analysis of variance (ANOVA) with repeated measures on type of composite and level of intensity, F(1,23)=52.5, p<.001. There was trend towards an interaction between composite and level of intensity, F(1,23)=3.3, p<.082, indicating that the difference in perceived intensity between LL- and RR-composites varied for different levels of intensity. Post- hoc testing with Bonferroni- corrected pairwise comparisons revealed that the difference in intensity between LL- and RR-composites was significant at each level of intensity (LL 100%- RR 100%, F(1,23)=47.98, p<.001; LL 50%- RR 50%, F(1,23)=13.49, p<.001; α=.025).

3 Results 23

Figure 1. Percentage of LL- vs. RR- composites being chosen per level of intensity and separately 3.2 Efficiency task

Figure 2. Percentage of LL- vs. RR- composites being chosen per level of intensity and separately for each individual expression

3.2. Efficiency task