Elsevier

Biological Psychology

Volume 76, Issues 1–2, September 2007, Pages 109-115
Biological Psychology

Event-related potential responses to love-related facial stimuli

https://doi.org/10.1016/j.biopsycho.2007.06.007Get rights and content

Abstract

In event-related potential (ERPs) studies, emotional stimuli usually elicit an enhanced late positive potential (LPP), which is assumed to reflect motivated attention. However, whether a stimulus elicits emotional responses may depend on the individual's state, such as experiencing romantic love. It has been suggested that stimuli that are related to someone's beloved will elicit increased attention in that infatuated individual. In this study, participants who were in love viewed faces of their beloved, their friend, and of an unknown, beautiful person. The friend was included to control for familiarity, and the unknown person for perceived beauty. As expected, the LPP was larger in response to the face of the beloved than to the other two emotionally significant faces. Interpreting the LPP as reflecting motivated attention, this implies that romantic love is accompanied by increased attention for the face of one's beloved.

Introduction

Almost everybody has been deeply in love sometime and therefore knows that love is accompanied by physical symptoms, such as trembling, palpitations, and reduced hunger. Recently, scientists have started to investigate the biological and neural basis of romantic love, for example using functional magnetic resonance imaging (Bartels and Zeki, 2000, Aron et al., 2005). Event-related potentials (ERPs), however, have not yet been employed to investigate romantic love, although they have extensively been used to study other emotions and motivations.1 In previous studies, emotional stimuli have consistently been found to elicit enlarged late (emerging around 300–400 ms after stimulus onset), positive components of the ERP waveform compared to neutral stimuli. These late positive components have a centro-parietal distribution and a parietal maximum. The positivity from about 400 ms after stimulus onset has inconsistently been labeled late positive potential (LPP) (e.g. Schupp et al., 2004a), late positive component (LPC) (e.g. Ashley et al., 2004), and positive slow wave (PSW) (e.g. Amrhein et al., 2004). Here the term LPP will be used to describe this late positivity. The LPP has been found to be greater for emotional words (Dietrich et al., 2000), emotional pictures (Amrhein et al., 2004, Cuthbert et al., 2000, Dolcos and Cabeza, 2002, Pollatos et al., 2005), and faces with emotional expressions (Eimer and Holmes, 2002, Johansson et al., 2004, Schupp et al., 2004b) than for neutral stimuli. Because the LPP is enhanced for both unpleasant and pleasant stimuli, it is generally assumed to be sensitive to arousal rather than to valence (Schupp et al., 2006).

The LPP is also enhanced for emotionally neutral, but task-relevant stimuli. Target stimuli that occur infrequently among distractor stimuli, for example, elicit larger LPPs than the distractor stimuli do (Picton, 1992). Therefore, it is assumed that the LPP reflects attentional processes. This, combined with the fact that emotional stimuli tend to demand allocation of attention (Compton, 2003) because they signal important information regarding reproduction and survival (LeDoux, 1996), has led to the suggestion that the enlarged LPP in response to emotional stimuli also reflects an attentional process. This attentional process has been called motivated attention, since it is evoked by stimuli that trigger motivational processes such as approach or avoidance (Schupp et al., 2004a). The results of a study by Schupp et al. (2007) are in line with the idea that the increased LPP to emotional stimuli reflects attention. In that study, participants had to count either the pleasant, neutral or the unpleasant pictures, which all occurred with equal probability. The LPP appeared larger for both target and emotional pictures, and moreover, these effects augmented each other. This implies that the LPP reflects task-induced as well as motivated attention.

While a picture of a wounded person or the word “rape” will elicit emotional arousal and motivated attention in the large majority of people, other stimuli will elicit emotional responses in certain individuals only. Spider-related words, for example, capture attention more than neutral words especially in spider-phobics (e.g. Lipp and Waters, 2007). Similarly, Fisher, 1998, Fisher, 2000 has suggested that someone who is in love will allocate more attention to his or her beloved than to another person, whereas both persons would be equally interesting to an outsider. Fisher et al. (2002) further proposed that this increased attention for the beloved would contribute to the fact that infatuated people feel that their beloved is unique, that they focus their attention on the positive qualities of the beloved and that people are in love with one person at a time only. It is reasonable to assume that stimuli related to the object of one's romantic feelings, like other motivational and emotional stimuli, would elicit motivated attention because they play an important role in the evolutionary process of reproduction (Fisher, 1998, Fisher, 2000, Fisher, 2004).

Indeed, the personal significance of a certain stimulus has been found to influence the LPP amplitude in response to that stimulus. Heroin and alcohol dependent participants, for example, showed an increased LPP in response to heroin and alcohol-related pictures, respectively, while non-dependent participants did not (Franken et al., 2003, Namkoong et al., 2004). Moreover, in a study by Johnston and Oliver-Rodríguez (1997) with facial stimuli, the LPP amplitude was correlated with the perceived beauty of the faces. Interestingly, the dopaminergic reward system has been found to be activated when participants viewed beautiful faces (Senior, 2003), as well as when infatuated participants viewed the face of their beloved (Aron et al., 2005, Fisher et al., 2002, Fisher et al., 2005). Similarly, dopamine has been implicated in drug craving elicited by drug-related cues (Franken et al., 2005). Thus, the neurotransmitter dopamine could play a role in the signaling of personal salience of these positively valenced and rewarding stimuli.

The present study investigated event-related potentials in response to love-related facial stimuli. Considering the above-mentioned findings, it can be expected that the LPP will be augmented in response to a photograph of the face of the participant's beloved compared to a photograph of an unfamiliar face. However, this comparison between the face of a beloved and the face of another arbitrary person will be confounded by variables such as familiarity and perceived beauty. In order to control for these variables, we compared the ERP response to the face of the participant's beloved with ERP responses to photographs of the participant's friend and of an unknown, beautiful person. It was expected that the photograph of the beloved would elicit a greater LPP than the photographs of the friend and unknown person. This because, in accordance with Fisher, 1998, Fisher, 2000, we expected that the face of the beloved would capture more attention than the faces of the friend and unknown person, which are not associated with romantic love but merely with familiarity or beauty.

Section snippets

Participants

Participants were recruited by means of a poster at the university campus. Eighteen students (9 men, 9 women; mean age 21.5, range 18–34) volunteered to participate and gave informed consent prior to testing. Only participants who were in love with someone of the opposite sex were included. Other inclusion criteria were normal or corrected-to-normal vision, no medical diagnosis and no medication use. Furthermore, all participants were right-handed as determined by a hand preference

Questionnaire and behavioral data

The mean duration of the participants’ romantic love was 12.6 months (S.D. = 10.1, range 2.5–36 months). All participants, except one female, were involved in a romantic relationship with their beloved. Mean duration of these relationships was 12.1 (S.D. = 9.4) months. The participants’ score on the PLS was 7.8 (S.D. = 0.5, range 7.0–8.5, Cronbach's alpha = 0.78). The mean AIM score was 3.8 (S.D. = 0.5, range 2.9–4.5, Cronbach's alpha = 0.88) and this score was not correlated with the PLS score, r = 0.13, p = 

Discussion

The goal of this study was to examine the effect of love-related facial stimuli on event-related potentials. The LPP was of greatest interest, since this potential has previously been found to be amplified for emotional stimuli and is thought to index motivated attention (e.g. Cuthbert et al., 2000, Polich, 2003, Schupp et al., 2004a, Stormark et al., 1995). As discussed in the introduction, the term motivated attention reflects the finding that more attention is allocated to emotional than to

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