Maternal perception of infant emotion expressions

Transcription

1 Maternal perception of infant emotion expressions Martin Krippl Department Technical Informatics, Otto-von-Guericke-University of Magdeburg, Germany Stephanie Ast-Scheitenberger Institute of Psychology, University of Erlangen-Nuremberg, Germany Ina Bovenschen Institute of Psychology, University of Erlangen-Nuremberg, Germany Gottfried Spangler Institute of Psychology, University of Erlangen-Nuremberg, Germany Running Head: Maternal perception of infant emotion expressions Address of Corresponding Author: Martin Krippl Department Technical Informatics, Otto-von-Guericke-University of Magdeburg, Universitätsplatz 2, Magdeburg, Germany Tel.: Additional Corresponding author on the publication: Gottfried Spangler Institute of Psychology, University of Erlangen-Nuremberg Bismarckstr. 6, D Erlangen, Germany Tel , Fax:

2 Maternal Perception of Infant Emotion 2 Abstract Considering Langs differentiation of the aversive and the approach system, and assumptions from attachment theory, this study aims to further investigate the role of the approach or caregiving system for processing of infant emotional stimuli by comparing IAPS pictures, infant pictures and videos. IAPS pictures, infant pictures and infant videos of positive, neutral or negative content were presented to 69 mothers, accompanied by randomized startle probes. The assessment of emotional responses included subjective ratings of valence and arousal, Corrugator activity, the startle amplitude, and electrodermal activity. In line with Langs original conception, the typical startle response pattern was found for IAPS pictures, whereas no startle modulation was observed, for infant pictures. Moreover, the startle amplitudes during negative video scenes depicting crying infants were even reduced. The results are discussed with respect to several theoretical and methodological considerations, including Langs theory, emotion regulation, opponent process theory and the parental caregiving system. Keywords: maternal emotion perception, IAPS pictures, infant pictures and videos, startle response, Corrugator, SCR

3 Maternal Perception of Infant Emotion 3 Maternal perception of infant emotion expressions: The role of the Approach System for startle modulation The meaning of emotional expression in infancy During the first months of life, infants emotional expression is the most important way for infant communication with the caregivers and, thus, is essential for the infant-caregiver relationship. Especially the expression of negative emotions is important to inform the caregiver about the infants needs in order to get his/her help and support for behavioral regulation. From the perspective of attachment theory, infant fussing and crying or, in general, negative emotional expression has a social or relational function (Campos et al., 1989). At least in infancy, it represents one of the most important attachment behaviors and, as such, by signaling the caregiver the need for proximity and support, serves the specific function to activate the caregiving system in the parent. Thus, an appropriate function of dyadic regulation in infants depends on the behavior of the infant as well as the caregiver. Infants must be able to communicate their needs through vocal or facial emotional expression whereas the caregiver must be able to perceive the infants' signals and to interpret them appropriately. Consequently, parental perception and interpretation of infants emotional signals is of substantial importance for infant social-emotional development. Approaches in the study of parental perception of infant emotion Several approaches were used in the study of parental perception of infant emotions. Within attachment research appropriate perception and interpretation of infant signals is a substantial component of Ainsworth s concept of maternal sensitivity which has been proved to be a reliable predictor of attachment security in infancy (DeWolff & van Ijzendoorn, 1997) and which would be assessed by observation in natural contexts. Similar judgments found across different studies highlight the function of facial expressions as a universally interpretable language of preverbal communication in infancy (Emde et al., 1993: Infant facial expression of emotion from looking at pictures; IFEELpictures). Thus, infant facial expressions convey reliable information and may provide essential cues

4 Maternal Perception of Infant Emotion 4 for effective care-taking. Finally, several experimental studies have focused on adult responses to infant crying including behavioral as well as physiological responses (e.g. Gustafson & Green, 1989; Zeskind et al. 1992; Leger et al., 1996; Lester et al., 1992). Studies investigating heart rate responses found heart rate decelerations suggesting orienting responses (Donovan, Leavitt, & Balling, 1978) as well as heart rate accelerations indicating activation or defensive responses (Bleichfield & Moely, 1984; Wiesenfeld, Malatesta, & DeLoach, 1981). Frodi, Lamb, Leavitt and Donovan (1978) showed that videos including crying infants as compared to smiling infants induced an increase in skin conductance response and diastolic blood pressure. Crowe and Zeskind (1992) found that hyper phonated cries induce higher SCL and heart rate to infant cries than normal phonated. Similar findings were reported by Frodi, Lamb, Leavitt, Donovan, Neff and Sherry (1978) for cries of premature infants as compared to normal infants. In sum, the bulk of research has focused almost exclusively on either subjective evaluations on a conscious level (e.g., IFEEL) or on psychophysiological responses to more intense, acoustic stimuli like smiling or crying. However, Spangler and colleagues (Spangler et al., 2001; Spangler et al., 2005) used a multi-level approach integrating three different levels of assessment, the subjective evaluation level, the expression level (Corrugator), and the psychophysiological arousal level (SCR and startle response). Responses on the autonomic-physiological level being excluded from conscious control can be assessed by sub-cortically controlled processes or reflexes using the startle paradigm (e.g. Lang et al.,, 1990). According to Lang's (1995) biphasic emotion theory, emotional responses are modulated by the emotional valence of the context or foreground stimulus. Thus, for example, the magnitude of the eyelid reflex to an acoustic startle probe, which is a protective response against an aversive stimulation, would be augmented if the actual emotional context was negative and would be inhibited if the actual valence was positive. Within the last years, considerable empirical evidence for this assumption has been accumulated, mainly based on the presentation of emotional pictures derived from the International Affective Picture System (IAPS; Center for the Study of Emotion and Attention, 1994;

5 Maternal Perception of Infant Emotion 5 e.g., Vrana et al., 1988; Bradley et al., 1988; Hamm et al., 1990; Hamm & Vaitl, 1993). Positive evaluation of infant emotional expression by adults. Using the multi-level approach, Spangler et al. (2001) investigated responses of adults to infant facial expression of different valence as compared to control non-infant pictures from the IAPS. The findings indicated a positive bias in the evaluation of infant pictures. Whereas typical valence differences were found for both types of pictures in the subjective ratings, infant pictures in general were rated more positively than the IAPS pictures. On the facial level, the findings indicated lower Corrugator activity in infant pictures, in particular for negative ones, as compared to the control pictures. Finally, while the startle responses to the IAPS pictures revealed the typical pattern of an augmentation of the startle amplitude during negative pictures, this augmentation was not found for infant pictures with negative emotional expression. The missing augmentation of the startle response was replicated in another study with parents (Spangler et al., 2005). Altogether, infant negative emotions, although perceived negative on the subjective level by parents, seem to be evaluated more positively on the sub-cortical level. Several theoretical perspectives can be used to explain this phenomenon: First according to Lorenz s (1971) phylogenetic approach, decisive features of juvenility trigger the innate releasing mechanisms for affecting and nurturing in adults called the Kindchenschema. Thus, infant faces provide a positive stimulus to adults. Second, within Lang s (1995) theory there may be stimuli activating simultaneously the appetitive and the aversive motivational system. Specifically, this coactivation may particularly be found in emotional stimuli not only expressing a certain quality of emotion but additionally possessing a specific social function (c.f. Balaban & Taussig, 1994; Ito, Cacioppo & Lang, 1998), e.g. infant negative emotions. More precisely, by expressing negative emotions, infants would not only express their negative emotional state, which may lead to activation of the aversive motivational system which could be expressed in an augmentation of the startle response. Rather, they also communicate their need for comfort and regulation and, thus, elicit the approach system in the parent which, then, would

6 Maternal Perception of Infant Emotion 6 lead to startle inhibition. In line with this, the failure to find potentiation of startle responses to negative infant pictures by Spangler and colleagues indicates a predominance of the appetitive system over the aversive system in the parents. A similar interpretation can be provided by attachment theory. Adopting a phylogenetic view, Bowlby (1969) assumed that the infant attachment system is biologically pre-adapted to the caregiving system on the parents side. Emotional expression representing an essential component of attachment behavior has the specific function of activating the parents' approach or caregiving behavior in order to gain comfort and support for emotional regulation (e.g. Spangler et al., 1994). If the infant cries, the caregiver would approach the infant to provide support rather than withdraw or flee. Parental information processing, providing a positive or avoiding a negative evaluation of infant negative emotional signals may support the optimal function of the parents' caregiving system. Such processes may be reflected in an inhibition of the startle response in persons confronted with negative infant emotions. The specificity of infant emotional expression Taken together, recent research suggests that infant emotional expressions differ from other emotional stimuli in regard to the underlying information processes. However, recent studies exclusively focused on static pictures containing solely visual information. Assuming that the magnitude of the activation of the approach system corresponds to the intensity of the infant stimulus, the predominance of the appetitive system may be much higher in response to more realistic infant stimuli not only including visual but also auditive information. This could be accomplished by using real life video scenes which contain more information than pictures, as they provide dynamic instead of static information in the visual domain and, most profoundly, acoustic information. Accordingly, we assumed that infant crying activates the approach system in parents stronger than the negative facial expression as well as complex neutral or positive behavior, and, thus, a lower startle response should be expected after presentation of infant crying. A reduced startle response can be explained by a high activation of the approach system as well

7 Maternal Perception of Infant Emotion 7 as a low activation of the aversive system. Thus, for the investigation of startle modulation, additional response parameters on different levels should be included confirming the assumed negative quality of the stimuli used. First of all, on the level of subjective evaluation, the negative quality of a stimulus should be expressed in low valence and high arousal ratings. Second, on the facial-expressive level, negative stimuli should be accompanied by a high activation of the facial muscles, indicative of negative emotion. This has been shown by several studies reporting larger Corrugator activity during presentation of unpleasant as compared to pleasant or neutral pictures (Bradley, Lang & Cuthbert, 1993, Cacioppo et al., 1992). Dimberg (1997) found that the perception of happiness pictures was followed by an activation of the zygomaticus major muscle, whereas anger pictures were followed by an activation of the Corrugator muscle, indicating a mirroring or imitation effect or emotional contagion (Hatfield et al., 1992). Additionally, in the study of Wild et al. (2001), this pattern of emotional contagion was not only found on the facial level but also on the level of subjective experience. Finally, on the physiological level, electrodermal activity can be used as a parameter for sympathetic arousal (Cacioppo et al., 1992). The skin conductance has been shown to be raised by both pleasant and unpleasant pictures in a similar way (Bradley et al., 1988). In contrast, Bradley et al. (1993) found higher skin conductance responses (SCR) for unpleasant as compared to pleasant stimuli. Lang et al. (1993) reported a linear association between SCR and arousal ratings. This was also found by Johnsen et al. (1995) using pictures of facial affect by Ekman and Friesen (1976). In sum, in case of low startle responses during presentation of negative stimuli, both rating and physiological measures of valence as well as arousal can be used as indications for the negative quality. Objectives The main question of the study was, how negative emotional expression in infants are evaluated by parents. Specifically, by presenting different kinds of infant emotional stimuli, i.e. emotion pictures and video scenes, and comparing them to standard IAPS pictures, we wanted to show the influence of

8 Maternal Perception of Infant Emotion 8 the approach system on the startle response. IAPS pictures were chosen as comparison, because we wanted to know, whether reactions of mothers to infant emotions could be generalized to emotional stimuli in general. Based on previous findings (Spangler et al., 2001, 2005), we expected (1) a positive bias in the evaluation of the infant stimuli expressed by a generally positive pattern of facial responses and a missing augmentation of the startle response during negative infant stimuli and (2), a specifically decreased startle response to more dynamic and intense infant emotional stimuli like video scenes, due to the influence of a parent approach system. At the same time the negative quality of infant negative expression should be obvious in affective judgments and in other responses on the expressive-facial level as well as in different arousal systems. Specifically, the hypotheses were the following: (1) On the level of subjective judgement of valence, the ratings for all types of stimuli are in line with the a priori valence, while arousal ratings are highest for negative stimuli and lowest for neutral ones, with the positive stimuli lying in-between. (2) Similarly, facial responses of the corrugator muscle vary according to the a priori valence of the stimuli, with highest activity for negative stimuli and lowest activity for positive ones. In addition, corrugator activity, in general, is lower for infant stimuli than for IAPS pictures. (3) While there should be the typical startle response pattern for IAPS pictures, no or a reduced augmentation of the startle response was expected during presentation of negative infant pictures. Moreover, assuming that intense and vivid negative infant stimuli like infant crying strongly activate the parents approach system, we expected a startle modulation with a reduced startle amplitude for negative infant videos. (4) At the same time, the typical arousal pattern induced by negative stimuli can be oberved for infant crying not only on the level of subjective evaluation but also on the level of electrodermal activity. Method Subjects The subjects were 69 mothers (age: 25 to 47 years, M = 36.1 SD = 4.46) from different social background and educational level. The sample consisted of two groups with high vs. low risk for

9 Maternal Perception of Infant Emotion 9 child-abuse assessed by the German version of the Child Abuse Potential Inventory (CAPI, Milner, 1986, German Version by Globisch & Spangler, 2000) and matched for education level, age and number of children. As there were no significant differences between high and low risk mothers with respect to the parameters of this study, these groups were not differentiated for the following analyses. For recruitment mothers were contacted in local preschools. Invitations to participation in the study were distributed to the parents and, after having given informed consent, they were asked to fill in the CAPI. The participants with the 20 % highest and with the 20 % lowest CAPI scores of the sample were selected for further data assessment. The educational level of the mothers was mixed. 57 % had the Abitur (possibility to study at a university), 31 % had Mittlere Reife (middle school certificate), 10 % the Hauptschulabschluss (lowest school certificate). 2 % of the subjects were without any school certificate. Sixty % of the mothers were employed and 40% were caring for the children at home. The number of children was 1 in 38 % of the mothers, 2 in 52 % of the mothers, and 3 to 5 in 10 % of the mothers. 79 % of the mothers were married. Stimulus material The stimulus material consisted of two different picture sets as well as one video set. The fist picture set contains 48 pictures chosen from the IAPS, based on the German normative valence and arousal ratings reported by Hamm and Vaitl (1993). The pictures varied widely in content and affective tone regarding valence (from unpleasant to pleasant), as well as arousal (calm to arousing). According to normative ratings of the IAPS, 16 pleasant, 16 neutral and 16 unpleasant pictures were used 1. The infant stimulus material was derived from videotaped everyday at home activities of ten 9- month-old infants (5 boys, 5 girls). From these videotapes, 80 pictures and 24 video scenes (lasting between 8 and 13 s) were extracted in which the infants exhibited positive, (e.g. smile), neutral or 1 Pleasant/positive pictures used were: IAPS #159, #161, #162, #215, #251, #452, #461, #465, #468, #560, #575, #576, #582, #808, #812 and #819. Neutral pictures used were: #166, #220, #221, #288, #551, #552, #700, #7009, #701, #705, #708, #709, #715, #717, #750 and #751. Unpleasant/negative pictures used were: #120, #122, #130, #212, #301, #303, #312, #620, #661, #690, #900, #904, #905, #914, #916, #918.

10 Maternal Perception of Infant Emotion 10 negative (e.g. crying) emotional expressions. On the basis of the video material, two different observers tried to identify a series of frames where the infants clearly expressed either positive or negative emotions or were neutral. Criteria for positive valence were happy expression or smiling/ laughing indicated by open mouth and laughter lines around the eyes. Crying, tears, contorted mouth, screwed-up face or reddish eyes and face were criteria for negative valence. Criterion for neutral pictures was the absence of any positive and negative signs. In order to draw the participants attention to the infant s emotional expression, the central focus of each picture was the child s face in front view - or at least half-profile - with the face conferring a significant part of the whole picture area. Criteria for positive valence were happy expression or smiling/laughing indicated by open mouth and crow feet wrinkles whereas crying, tears, contorted mouths, screwed-up faces or reddish eyes and face were indices of negative emotional expression. Finally, criteria for neutral valence were the absence of any positive or negative sign. Then, these pictures and scenes were rated by 25 psychology students with respect to valence and arousal using the 9-point Self-assessment-manikin (SAM). Based on these ratings 16 positive, 16 neutral and 16 negative pictures and 8 positive, 8 neutral and 8 negative video scenes were selected which had valence and arousal ratings optimally corresponding to the specific valence categories. Two positive, two neutral and two negative pictures as well as one positive, one neutral and one negative film scene were selected from 8 of the infants. A further criterion of selection criteria for infant pictures and videos has been the clarity and unambiguousness of emotional value. The stimulus material was presented on a computer monitor in a distance of about 1 m in front of the subject s eyes. The size of the visible pictures and videos was cm. The startle stimulus (a 50 ms 95 db (A) sound of white noise) was presented binaurally through stereo-headphones during the picture presentation (3.5 to 4.5 s after begin) or in the interstimulus intervals (5 to 10 s after begin) for the IAPS and infant pictures. For the video scenes, it was presented during the imagination phase (2.5, 3.0 or 3.5 s after the end of the videos) or in the interstimulus interval (5 to 9 s after beginning of the videos). Regarding the videos, the startle probes were applied during the imagination interval (2500, 3000 or 3500 ms after the offset of video presentation) to exclude any influence of the video

11 Maternal Perception of Infant Emotion 11 sound track on the startle response like prepulse inhibition (Blumenthal, 1999). During the presentation of pictures 32 startles (during two third of the presentations) were presented altogether (one during one picture presentation) and 19 during the interstimulus interval. During the imagination phase of the videos 15 startle probes were presented (also two third of the cases) and ten during interstimulus intervals. Apparatus and physiological response measurement Electrophysiological responses during the experiment were assessed by a Varioport system (Becker Meditec Gmbh). Marquete Hellige electrodes were applied (baby electrodes for EMG) and the skin was cleaned by rubbing it with alcohol before the placement. The startle reflex was measured by a bipolar EMG recording of the activity of the m. orbicularis oculi underneath the left eye. Regarding the facial expression, the EMG activity of the Corrugator supercilii (frown muscle) was assessed. All facial EMG data were collected by using electrode placements suggested by Fridlund and Cacioppo (1986). Physiological signals were continuously sampled with a sample rate of 512 Hz. Electrodermal activity was assessed by hypothenary placed electrodes with a sample rate of 16 Hz. Design and Procedure There were two experimental groups differing with respect to the type of stimulus they were presented. While for each group videos were shown, they were confronted with different types of pictures. This was done because if every subject would have had to watch every stimulus (both types of pictures and videos), the experimental session would have been too long to get reliable and valid answers (reduction of compliance). For one group (n=36) IAPS pictures were presented and for the other (n=34) infant pictures were presented. The order of the pictures and of the video scenes as well as the order of valence was pseudo-randomized with three different orders. The three valences were counterbalanced across the time course of the presentation. For each subject, pictures and videos were presented twice: the first time to assess psychophysiological reactions, the second time to assess the subjective ratings of the participants.

12 Maternal Perception of Infant Emotion 12 Participants were tested individually in one session. After arriving at the laboratory, the subjects were informed about the procedure and all subjects consented. They were then seated in a chair and the recording electrodes were attached. After presenting two pictures to familiarize the participants with the procedure, the experiment trials began. Stimuli were balanced across valences. Each picture was presented for 6 s, followed by a ca s interstimulus interval with a black screen and a red cross in the middle. The psychophysiological assessment electrodes were then removed and the second phase for the assessment of the ratings began, in which the subjects had to rate the valence and arousal of the stimuli on the 9-point SAM. Physiological measures Regarding the startle analysis, the highest scores of the rectified and filtered (hardware filter 64 Hz high pass) EMG (512 Hz sampling rate) curve of the orbicularis oculi between 20 and 150 ms after the startle probe were compared to a baseline assessment calculated from mean of the rectified and filtered signal between -40 and -20 ms before the startle probe presentation. Trials were excluded from the data analysis if the raw EMG curve had scores higher than 20 µv or lower than -20 µv in the prestimulus baseline interval in order to avoid a possible influence of pre-stimulus activation of the orbicularis oculi. The magnitude of the eye-blink response to the startle probe was calculated by subtracting the baseline from the highest response score. Negative values were set to zero. To control for outliers, measures were ln-transformed (ln(x) + 1) 2. Regarding the Corrugator analysis, the raw Corrugator signal (32 Hz sampling rate) was initially rectified. To assess the Corrugator muscle response to picture presentation, change scores were calculated by subtracting the mean activity during 1 s preceding picture onset baseline from the average response during the presentation picture and video interval. Electrodermal data were collected with a sampling rate of 16 Hz and a low pass filter of 0.5 Hz. 2 Data were also analyzed without any transformation. Results remained the same for all valence and stimulus comparisons.

13 Maternal Perception of Infant Emotion 13 The program edr_para (Schäfer 3 ) was used to analyze SCR, with an amplitude criterion of 0.01 µmho for SCR. As a measure for the SCR magnitude the maximal SCR in the post-stimulus interval of 6 and 8 s (for pictures and videos, respectively) was taken. If a SCR could not be identified, the SCR magnitude was set to zero. SCR was range corrected by the formula of Lykken and Venables (1971). In this formula the SCRs are divided by the maximum SCR of each participant. For maximum we used the highest SCR of each participant in our study. Statistical Analyses Because of technical reasons, parts of the measures could not be used or analyzed in some subjects resulting in missing data. Thus, the final sample size ranged between 32 and 34 in the IAPS group (with a total sample size of 36) and between 28 and 32 in the infant picture group (with a total sample size of 34). For each dependant measure, a three-factorial MANOVA was conducted with the picture type as between-subject factor (IAPS vs. infant pictures) and the stimuli valence (positive, neutral, negative) as well as the type of stimulus (picture vs. video) as within-subject factors. Additionally, ANOVAs were computed for testing hypotheses on valence differences within each type of stimulus and t-tests were used for post-hoc paired comparisons. The dependant measures were valence and arousal ratings, magnitude of startle response, Corrugator activity, and SCR. Additional ANOVAS were conducted to test the effect of the startle response on the SCR and Corrugator activity. As a posteriori analyses ANOVAs were done including number of children (of the participating mothers) as an independent factor to check,whether this had a relevant influence on the results. An alpha level of.05 was used for all statistical tests. Effects with p >.10 are not reported in statistical details. Greenhouse-Geisser (1959) corrector of degrees of freedom was used when sphericity was not given. To make the result reports easier to read the partial η 2 are only reported as η 2 without the word partial. 3 Unpublished Computer program.

14 Maternal Perception of Infant Emotion 14 Results Demographic differences between IAPS and infant picture group The IAPS group and the infant picture group did not differ with respect to education of the mothers. However, there were differences with respect to the occupation status of the mothers (chi 2 (1, 70) = 5.652; p =.01) indicating a higher proportion of working mothers in the IAPS group which included 25 working mothers and 10 housewives. In contrast, there were 14 working mothers and 19 housewives in the infant picture group. Effect of startle probe on SCR and Corrugator activity During trials with picture presentation Corrugator activity and SCR may be affected by startle probes (e.g. Vrana, 1995). This could not be the case for video trials, because startle probes were presented after infant video presentation. A picture group (IAPS vs. infant pictures) by valence (positive, neutral, negative) by startle probe (startle vs. no startle probe) mixed MANOVA did not show a significant effect of the startle probe on Corrugator activity. The same type of MANOVA for SCR magnitude showed a main effect of startle probe (F(1, 63) = 17.43, ε =.946, p=.000, η 2 =.217), indicating higher SCR magnitudes during trials with startle presentation. Therefore we included startle probe as an additional factor in our analyses of SCR data. Subjective ratings of valence and arousal Concerning the experienced valence of the stimuli, the MANOVA resulted in main effects for type of stimulus (F(1, 62)= 13.34, p =.001, η 2 =.18), qualified by a two-way interaction between picture group and type of stimulus (F(1, 62)= 16.67, p =.001, η 2 =.22), and in a main effect for valence (F(2, 124)= , ε =.70, p <.001, η 2 =.89), qualified by a two-way interaction between type of stimulus and valence (F(2, 124)= 4.33, p =.05, η 2 =.07) as well as a three-way interaction between picture group, type of stimulus and valence (F(2, 124)= 6.49, ε =.72, p <.01, η 2 =.10).

15 Maternal Perception of Infant Emotion 15 Insert figure 1 about here As depicted in figure 1, infant stimuli were perceived more positively than non-infant stimuli, as higher valence ratings for video stimuli as compared to picture stimuli were only found in the IAPS group (T (32) = 5.23, p <.001) and there was a significant difference between the IAPS pictures and the infant pictures (T (64) = 3.56, p <.001), while the mean valence ratings for infant pictures and videos did not differ significantly. Regarding the valence effect, contrast analyses confirmed clear differences with respect to the a priori valences and, in addition, indicated specific effects for the valence ratings of negative stimuli (p <.01) Post-hoc comparisons showed that negative infant stimuli received higher valence ratings than non-infant stimuli. Thus, the negative IAPS pictures were rated more negative than the negative infant pictures (T (64) = 3.15, p <.002) as well as infant videos (T (32) = 4.77, p <.001), while no significant difference between the negative infant pictures and videos was found. Regarding the experienced arousal, the MANOVA resulted in a main effect for valence (F(2,124)= , ε =.99, p =.000, η 2 =.68) qualified by two-way interactions between valence and stimulus group (F(2, 124)= 3.06, p =.05, η 2 =.05) and valence and type of stimulus (F(2, 124)= 7.27, p =.01, ε =.88, η 2 =.11) and a three-way interaction between picture group, type of stimulus and valence (F(2, 124)= 14.39, ε =.88, p <.001, η 2 =.19). Regarding the valence effect, contrast analyses showed clear differences regarding the a priori valences and, in addition, indicated specific effects for the valence ratings of negative stimuli (p <.01). Post-hoc comparisons showed that negative infant stimuli received lower arousal ratings than non-infant stimuli (see Fig. 1). The arousal ratings of negative IAPS pictures were higher than those of negative infant pictures (T (64) = 3.54, p <.001) and infant videos (T (32) = 4.41, p <.001), while no significant difference between negative infant pictures and videos was found. Startle response The analyses of the startle responses revealed a significant main effect for valence (F(2, 116 ) =

16 Maternal Perception of Infant Emotion , ε =.95, p <.001, η 2 =.18), qualified by significant interaction between valence and stimulus groups (F(2, 116) =3.10, ε =.95, p <.05, η 2 =.05) as well as between valence and type of stimulus (F(2, 116) =36.23, ε =.95, p <.001, η 2 =.38) and a three-way interaction between valence, type of stimulus and stimulus group (F(2, 116) =5.75, ε =.96, p <.01, η 2 =.09). Insert figure 2 about here Simple main effect analyses conducted separately for pictures and videos revealed significant valence effects for infant videos in both stimulus groups (F (2, 116) =16.32 and 19.97, p <.001). According to post-hoc t-tests, the startle amplitude during negative infant videos was lower than during positive and neutral ones (T (59) = 8.66 and 6.66, p <.001), while the amplitudes during positive and neutral ones did not differ (see Fig. 2). Concerning the pictures, simple main effect analyses for a priori valence resulted in a main effect for IAPS pictures (F(2, 122) =18.27, p <.001), but not for the infant pictures. According to post-hoc t-tests, the startle amplitude during positive IAPS pictures was lower than during neutral and negative ones (T (32) = 5.18 and 6.80, p <.001), while the amplitudes during positive and neutral ones did not differ. No startle differences depending on the valence of the stimuli were found for infant pictures. The finding of no effect in the startle response during infant picture presentation is a replication of Spangler, Emmlinger, Meinhardt & Hamm (2001). To eliminate that the finding in that study, was due to low power of the study, we computed a post-hoc power analyses of the Spangler, Emmlinger, Meinhardt & Hamm (2001) study. It revealed a power (1 - beta) of.89. The power analyses for a repeated-measures MANOVA with within and between interaction was computed with G-power (Faul, Erdfelder, Lang & Buchner, 2007) with the scores F =.60; alpha =.05, n = 46, number of groups = 3 and repetitions 12. The power score of.89 is generally regarded as adequate. Corrugator activity Regarding the Corrugator response, the MANOVA revealed a significant main effect for valence (F (2, 122) = 26.81, ε =.57 p <.001, η 2 =.31) qualified by an interaction between valence

17 Maternal Perception of Infant Emotion 17 and type of stimulus (F (2, 122) = 4.10, ε =.77 p <.05, η 2 =.06). Insert figure 3 about here Contrast analyses for the valence affect confirmed clear differences with respect to the a priori valences, but indicated interaction effects for positive stimuli depending on type of stimulus and stimulus group (p <.05). Post-hoc comparisons indicated a decrease of Corrugator activity in response to positive infant stimuli as compared to non-infant stimuli (see Fig. 3). More precisely, the Corrugator activity during the presentation of positive IAPS pictures was higher than during presentation of positive infant pictures (T (63) = 2.31, p <.05) and of infant videos (T (31) = 3.88, p <.001). Additionally, the Corrugator activity during infant videos was even higher than during infant pictures. This difference, however, only approached significance (T (30) = 1.83, p <.10). Skin conductance magnitude With respect to the skin conductance response (SCR) the MANOVA revealed significant main effects for type of stimulus (F(1, 60) = 57.27, p <.001, η 2 =.49) and valence (F (2, 120) = 28.86, ε =.99, p <.001, η 2 =.33) qualified by a significant interaction between valence and stimulus group (F(2, 120) = 5.40, ε =.99, p <.01, η 2 =.08) and between valence and type of stimulus (F(2, 120) = 7.05, ε =.90, p <.01, η 2 =.11) as well as between valence and stimulus group and type of stimulus (F(2, 120) = 3.42, ε =.90, p <.05, η 2 =.05). Insert figure 4 about here Simple main effect analyses for a priori valence revealed a significant effect for the IAPS pictures (F (2, 128) = 14.61, p <.001) and the infant videos (F (2, 122) = and 5.96, p <.01), but not for infant pictures. Post-hoc-analyses showed that the SCR during presentation of the IAPS pictures was higher for negative than for neutral and positive pictures (T (32) = 3.64 and 4.23, p <.001; see Fig. 4). SCR was also higher for negative infant videos than for neutral ones in both stimulus

18 Maternal Perception of Infant Emotion 18 groups (T (32) = 6.75, p <.001; T (29) = 2.83, p <.01). In addition, in one of the groups the SCR was increased for positive videos as compared to neutral ones (T (32) = 4.59, p <.001). One of the most prominent effects was that the magnitude of the skin conductance response, at least for positive and negative stimuli, was twice as much than for infant videos as compared to picture stimuli (p <.002). As exposed at the beginning of the results section startle probe presentation has an influence on the SCR magnitude. The influence of startle probing was tested in an extra 2 (type of stimulus) by 2 (startle vs. no startle) by 3 (valence) ANOVA. A significant valence startle probe interaction effect (F(2, 126) = 4.45, ε =.969, p=.015, η 2 =.066) revealed that the difference between trials with and without startle was stronger during negative trials as compared to neutral and positive trials. The ANOVA for IAPS pictures revealed a significant main effect valence (F(2, 64) = 8.963, ε =.862, p =.001, η 2 =.219) a significant main effect startle presentation (F(1, 32) = ,, p =.001, η 2 =.274) and a significant interaction valence startle presentation (F(2, 64) = 7.683, ε =.862, p =.002, η 2 =.194) indicating much higher SCRs during negative trials with startle presentation compared to negative trials without startle presentation and neutral trials with startle presentation as well as all other combinations of startle presentation and valence. The ANOVA of IAPS trials without startle presentation revealed no significant difference between valences. So the valence difference in IAPS trials is only due to startle presentation. The ANOVA of SCRs for infant pictures revealed no significant effect. Influence of the number of children For each dependant variable a 2 (number of children: 1 vs. more than 1) by 2 (type of stimulus) by 2 (picture group) by 3 (valence) mixed ANOVA was done. 4 The ANOVA for the Corrugator activity revealed no significant effects for Number of children and number of children valence (F(2, 118) = 3.96, ε =.576, p =.045, η 2 =.063). The main effect for number of children showed a reduced Corrugator activity for mothers with two or more children. The interaction of number of children and 4 Only effects regarding number of children will be presented in this part of results.

19 Maternal Perception of Infant Emotion 19 valence showed up, that there is only a difference during neutral (simple main effect p <.10) and negative (p <.05) but not during positive trials. The 2 (number of children) by 2 (type of stimulus) by 2 (picture group) by 3 (valence) mixed ANOVA for the startle response revealed significant effects on valence type of stimulus number of children (F(2, 112) = 3.750; p =.028; η 2 =.063. To further analyze this interaction effect, separate ANOVAs for each type of stimulus were done. The ANOVA of IAPS pictures revealed a marginally significant interaction of valence number of children (F(2, 62) = 2.83, ε =.980, p =.068, η 2 =.084). This shows a reduced startle response in mothers with two or more children during positive and negative valenced pictures but no difference between the two groups during neutral material. The ANOVAs of startle response for infant pictures and videos did not show any significant effect. A 2 (number of children) by 2 (type of stimulus) by 2 (picture group) by 3 (valence) mixed ANOVA for the SCR did not reveal any effect for number of children (main effect and interactions). Discussion The most interesting result of this study is the modulation of the startle response to infant negative emotions, in mothers. Possible interpretations like Lang s theory, attachment theory, emotion regulation (Gross, 1999), opponent process (Solomon, 1980) or attentional processes (prepulse inhibition) are described. In general, the affective judgments for the different types of stimuli were as expected, both for the valence and the arousal dimension. This was obvious from strong main effects for the a priori valence of the stimuli. Positive stimuli were rated more positively than the neutral stimuli as well as the neutral ones were rated more positively than the negative ones. Regarding arousal, negative stimuli received the highest values, whereas neutral stimuli were perceived as least arousing and positive stimuli lied in-between. While these patterns were found in general, there were two effects for

20 Maternal Perception of Infant Emotion 20 stimulus type. First, infant stimuli, both pictures and videos, in general, were evaluated slightly more positively than the IAPS pictures. Second, negative infant stimuli were rated less arousing than negative IAPS pictures. There were also strong valence effects for facial activity of the Corrugator muscle. The presentation of negative stimuli, both infant and non-infant ones, lead to a significant increase of the Corrugator activity, in accordance to recent results by Cacioppo et al. (1992) or Bradley et al. (1993). In contrast, there was a deactivation of Corrugator activity during the presentation of positive infant stimuli, in particular during infant video scenes, which was not observed for positive IAPS pictures. In congruence with previous findings (Spangler et al., 2001, 2005), these results indicate a more positive evaluation of positive infant emotional expression on the expressive-physiological level. However in contrast to previous results, this effect was not found for negative expression in the present investigation. According the effects found in SCRs results showed that startle probes had an important influence on it. Startle probes had a generally enhancing effect on SCRs especially for negative trials. Without startle presentation the differences are not significant although the tendency is the same as with trials without startle probes. Unmodified remains the interpretation of SCRs in infant videos because there was no confounding with startle probes. In contrast to SCRs the effects of startle presentation to Corrugator activity are not as strong. Trials without startle presentation revealed also the clear pattern of high activity during negative trials lower during neutral and deactivation during positive trials. Taken together, typical valence-specific response patterns were found for infant as well as noninfant stimuli, on the level of subjective evaluation as well as on the expressive level. However, on both levels, there were indications for a positive bias, i.e. a more positive evaluation of infant stimuli in contrast to other stimuli. It might be the case that the positive bias relates to faces in general rather than only infant faces. This assumption, however, is contradicted by Cacioppo et al. (1992) who did not find differences in ratings and facial responses during the presentation of face as compared to scene pictures. Comparisons of infant vs. adult pictures would be needed for a final clarification.

21 Maternal Perception of Infant Emotion 21 The question arises how the findings of this study could be explained by known theories. Additionally it has to be mentioned, that the transposition of startle effect in videos is not due to the number of children of the participating mothers as statistical analyses revealed. Although mothers with two or more children had reduced startle amplitude during positive and negative trials the pattern of results is the same as in mothers with one or no child. Regarding the startle responses, the results indicate a, pattern of modulation according to previous findings and Lang s (1995) theory only for the IAPS pictures. In contrast, startle modulation was not observed during presentation of infant pictures or even reversed concerning the infant videos. While there was no response difference between positive and neutral videos, the magnitude of the startle response considerably decreased during presentation of negative infant videos. Therefore, although prompting a pattern of valence judgments comparable to standard IAPS pictures and leading to valence-specific facial responses, stimuli containing infant emotional expressions obviously did not produce an affective startle modulation comparable to the IAPS pictures. While the missing startle modulation during the presentation of infant pictures has already been found in previous studies (Spangler et al., 2001, 2005), the reverse pattern regarding the infant videos, expressed in strong startle inhibition during negative infant videos, surpasses existing findings, as it is even contradictory to the usual pattern found for the IAPS pictures. In conjunction with Lang s theory, the negative infant stimuli, though experienced as unpleasant, may not activate the aversive system, as they may not provide imminent threat or danger to the observer. So, the arousal potential of infant pictures is rather low and this is known as a core feature of startle facilitating material (Bernat et al., 2006; Bradley et al., 2001; Schupp et al., 2004). Thus, an augmentation of the startle response wouldn t be expected (Lang et al., 1997). However a reduction of the startle response for the negative infant videos would not be expected also, because arousal in negative infant material is still higher than in neutral material.

22 Maternal Perception of Infant Emotion 22 These assumptions are made on the basis of looking at the startle response as a measure of emotional valence. It could also be seen, as a measure of approach and avoidance motivation, which would be most often go parallel to the emotion view (approach equivalent to positive valence), but not always. In this view a negative emotion could exist parallel to approach motivation. Although we support the view that approach motivation happens not only while positive emotions are felt, we think that in this case it is not plausible and not necessary to make this assumption. Other explanations have to be found which are more plausible. At this point the question arises which emotion is associated with the caregiving behaviour respectively is induced during negative infant video presentation? The typical negative emotion which is approach related is anger. The findings of Cook et al. (1991) indicate that anger generally enhances the startle amplitude during imagery. So our startle results in video imagery are an argument against an anger effect. This does not mean that anger did not occur during the presentation of negative valenced videos or other material. It only means that anger did not occur after the presentation of infant videos. The only emotion which is approach-related instead of positive emotions and anger could be compassion. But it is unlikely that it is the reason for the startle transposition because it should have a similar effect as sadness (because it is very similar to it) on the startle response and sadness induced a facilitation of the startle response as anger and fear did it. But if compassion would be the reason, the startle of positive videos should have been reduced in comparison to neutral videos also, because positive emotions should induce approach behavior. Therefore attachment theory can not explain the startle effect in videos. It should be mentioned that the two-factorial arousal theory according Gray (1987) and its adaptation from Fowles (1980) could not explain the results either. The only effect they could explain is the diminished differences in startle response between valences in infant pictures, because infant pictures of all valences induce only low arousal. A pattern like in our study (with reduced startle

23 Maternal Perception of Infant Emotion 23 response for negative stimulus material) has not been found for any high or low BIS or BAS group (Hawk & Kowmas, 2003). Moreover, as in this study startle responses were assessed during imagery immediately after the presentation of the video scenes, it has to be considered that the responses could reflect counterreactions, i.e. reactions to the set-off of the stimuli. Burton (2003) reported the typical startle pattern while assessing startle responses immediately after the end of the presentation (300 ms), but an inverted pattern about 3 seconds afterwards, which is the time-lag used in this study. This indicates that the time of startle application is important. According to Gross (1999), this startle pattern transposition may represent an emotion regulation process, in which the reaction to stimuli of negative valence is being inhibited whereas the reaction to those of positive valence is being enhanced. Findings of Jackson, Malmstadt et al. (2000) suggest that emotion regulation can change the startle amplitude after negative and neutral stimulation. According to Gross (1999), suppression and reappraisal are possible processes of emotion regulation. Reappraisal processes modifying the way a situation is evaluated lead to a decrease or increase of emotional responding but often are not found to be associated with physiological changes (Gross, 1999). Suppression is characterized by reduced emotion-expressive behavior accompanied by raised physiological sympathetic activity, which could be explained by emotional discharge theory (Cacioppo et al., 1992). It does not seem to be reasonable to expect suppression of emotions in the context of this study, because the behavior is not embedded in a social interaction and therefore display rules will not be applied (Ekman, 1988). Another explanation for the low negative startle responses during video imagination could be provided by Solomon s (1980) opponent process theory of acquired motivation. This theory assumes that any unconditioned stimulus, operant reinforcer or innate releaser, which induces an emotional process (the so called a-process ), also induces an opposite working process (the so called bprocess ). First, at the beginning of the stimulus presentation, the b process is weaker than the a process, but increases during the presentation of the stimuli. While the a process immediately stops after the end of the presentation, the b process continues, which can often result in an emotional