Contextual blending of ingroup/outgroup face stimuli and word valence: LPP modulation and convergence of measures

Abstract

Background: Several event related potential (ERP) studies have investigated the time course of different aspects of evaluative processing in social bias research. Various reports suggest that the late positive potential (LPP) is modulated by basic evaluative processes, and some reports suggest that in-/outgroup relative position affects ERP responses. In order to study possible LPP blending between facial race processing and semantic valence (positive or negative words), we recorded ERPs while indigenous and non-indigenous participants who were matched by age and gender performed an implicit association test (IAT). The task involved categorizing faces (ingroup and outgroup) and words (positive and negative). Since our paradigm implies an evaluative task with positive and negative valence association, a frontal distribution of LPPs similar to that found in previous reports was expected. At the same time, we predicted that LPP valence lateralization would be modulated not only by positive/negative associations but also by particular combinations of valence, face stimuli and participant relative position.

Results: Results showed that, during an IAT, indigenous participants with greater behavioral ingroup bias displayed a frontal LPP that was modulated in terms of complex contextual associations involving ethnic group and valence. The LPP was lateralized to the right for negative valence stimuli and to the left for positive valence stimuli. This valence lateralization was influenced by the combination of valence and membership type relevant to compatibility with prejudice toward a minority. Behavioral data from the IAT and an explicit attitudes questionnaire were used to clarify this finding and showed that ingroup bias plays an important role. Both ingroup favoritism and indigenous/non-indigenous differences were consistently present in the data.

Conclusion: Our results suggest that frontal LPP is elicited by contextual blending of evaluative judgments of in-/outgroup information and positive vs. negative valence association and confirm recent research relating in-/outgroup ERP modulation and frontal LPP. LPP modulation may cohere with implicit measures of attitudes. The convergence of measures that were observed supports the idea that racial and valence evaluations are strongly influenced by context. This result adds to a growing set of evidence concerning contextual sensitivity of different measures of prejudice.

Figure 1

IAT sequence schematic representation. Face and word trials are presented for a short time, strictly interleaved. Both indigenous and non-indigenous faces, along with words of positive and negative valence, are present in the stimuli set and are presented in a randomized sequence. The subject is required to classify each stimulus to the left or to the right according to labels displayed on top of the screen. Reaction times and EEG signals are recorded in each session. Pictures are used with consent of shown subjects. Eyes are shown pixelized for anonymity, but were shown undistorted during the experiment.

Figure 2

Channel locations for EGI HCGSN128 electrode net. Figure shows a schematic representation of EEG electrode localizations over the scalp for the EGI HCGSN128 net used within this study.

Figure 3

Explicit questions scores by relative social position and valence. The vertical axis shows explicit questions score values. The horizontal axis displays valence: positive and negative for both, outgroup and ingroup relationship of the subject with the question target. Interaction is relevant (F (1, 68) = 10.2805, p = 0.0017). Post-hoc comparison yields significant positive vs. negative differences for outgroup position (p = 0.7567) but not for ingroup (p < 0.0001).

Figure 4

Explicit questions scores by participant group and valence. The vertical axis shows explicit questions score values. The horizontal axis displays valence: positive and negative for both, indigenous and non-indigenous participants. There is an interaction effect (F (1, 68) = 52.8548, p < 0.0001). Post-hoc comparison yields a positive vs. negative difference for indigenous participants (p < 0.0001) but not for non-indigenous (p = 0.9884).

Figure 5

IAT scores with data split by stimulus type. The vertical axis shows IAT scores. The horizontal axis displays participant groups: indigenous and non-indigenous participants in both word and face stimuli categories. Single sample t-tests were performed to test for difference against zero. Only word scores for indigenous participants yielded a significant offset from zero (p = 0.0003).

Figure 6

Indigenous participants LPP ERPs. LPP selected ROIs for face and word stimuli compatible (Blue) vs. incompatible (Red) with prejudice against the indigenous minority. Top: ERPs of Faces. Bottom: ERPs of Words. In agreement with the behavioral results, we found a LPP modulation in the right frontal areas (and a bipolar voltage pattern on left posterior ROI) related to compatible blocks with prejudice to the indigenous only in the Word Condition in Indigenous participants. Abbreviations: LA ROI (Left anterior region of interest); RA ROI (Right anterior region of interest); CZ ROI (Vertex region of interest); LP ROI (Left posterior region of interest); RP ROI (Right posterior region of interest). (* = p < 0.05). (** = p < 0.01).

Figure 7

Non-Indigenous participants LPP ERPs. LPP selected ROIs for face and word stimuli compatible (Blue) vs. incompatible (Red) with prejudice against the indigenous minority. Top: ERPs of Faces. Bottom: ERPs of Words. Abbreviations: LA ROI (Left anterior region of interest); RA ROI (Right anterior region of interest); CZ ROI (Vertex region of interest); LP ROI (Left posterior region of interest); RP ROI (Right posterior region of interest).