Psychophysiological parameters of prosodic discrimination in children with a history of psychosocial deprivation.
During the first several years of life children rapidly acquire basic cognitive and language skills (Rueda, Posner, & Rothbart, 2005). The sensibility and responsiveness of caregiver have been found to facilitate children’s attention (Olson, Bates, Sandy, & Schilling, 2002), cognitive, and language development (Landry, Smith, & Swank, 2006). When caregiver is absent or provides impoverished input, children often exhibit lags in a variety of developmental domains, including cognitive and social-emotional development (Nelson, 2007; Pears, Fisher, Bruce, Kim, & Yoerger, 2010). Institutional environments provide children with suboptimal social and cognitive/linguistic experiences needed to develop basic socio-emotional abilities such as joint attention, face processing, and secure attachment (Плешкова, Мухамедрахимов, 2007). Without these foundational competencies, institutionalized children (IC) have an insufficient basis to acquire more comprehensive and complicated socio-emotional skills such as reading social cues transmitted through voice and face.
The current study is focused on the electrophysiological aspects of prosodic information processing in children with and without history of early psychosocial deprivation and institutionalization. Linguistic Encyclopedic Dictionary defines prosody as a system of phonetic patterns (pitch, volume, tempo and rhythm), realized in the speech at all levels of speech segments (syllable, word, phrase, syntagm, phrase, text). Prosody may reflect various features of the speaker or the utterance: the emotional state of the speaker; the form of the utterance (statement, question, or command); the presence of irony or sarcasm; emphasis, contrast, and focus; or other elements of language that may not be encoded by grammar or by means of vocabulary.
Unlike the voluminous behavioral work on processing facial expressions in infancy (Parker, Nelson, 2005; Moulson, Westerlund, Fox, Zeanah, & Nelson, 2009), studies on infants’ perception of vocal expressions of emotion are scarce, and to the best of our knowledge these abilities have not been examined in children raised in suboptimal caregiving environments.
The body of research on prosodic discrimination in infancy falls into two broad categories depending on the utilized methodology. The first group of methods includes behavioral testing. Habituation paradigm has been frequently used to study prosodic processing in infancy: children are presented with a visual stimulus accompanied by auditory stimulus with prosodic components. After the change of the auditory stimulus, increased looking time to the familiar visual stimulus is taken as evidence of infant’s ability to recognize two different vocal expressions. (Walker-Andrews 1983; 1991; Fernald 1988). Studies show that 5 months-old infants can discriminate between happy, sad, and angry vocal expressions by integrating information from visual and auditory domains (Walker-Andrews and Lennon 1991). 5 months-old infants have also been shown to discriminate between happy and sad vocal expressions, when a matching facial expression was presented (Walker-Andrews & Grolnick 1983). 7-month-old infants dishabituated to a change from happy to angry, and from angry to happy emotions, only when both facial and vocal expressions changed, but not when the facial expression was presented alone (Carons, MacLean 1988). Based on this research ,a developmental pathway has been proposed in which infants learn to discriminate emotional expressions on the basis of multimodal, vocal, and finally, as visual acuity improves, facial cues (Walker-Andrews, 1997).
The second group of studies utilize electroencephalographic (EEG) and ERP (event-related potentials) methods to study prosodic discrimination in infancy. ERP studies revealed that 7-month-old infants show an increase in a negative component that is thought to reflect the allocation of attention when negative facial expression (fearful) is presented (Nelson & de Haan 1996). 4-month-old infants also have been shown to display more negative shifts in electrical activity registered at the scalp in response to the mother’s voice, then in response to the unfamiliar (Purhonen et al. 2004). Words with angry prosody elicited a more negative response in 7-month-old infants’ ERPs than words with happy or neutral prosody, which indicates that emotionally charged words undergo more extensive processing than words with neutral prosody (Tobias Grossmann et al., 2005). 7-month-old infants’ ERPs are characterized by larger negative component in response to incongruent prosody that mismatched facial expression of the speaker. Conversely, the amplitude of the positive component was larger to emotionally congruent words than to incongruent words (Tobias Grossmann et al., 2006). In 6-10-years-old children’s ERPs, N400 component is also attenuated by angry prosody compared to happy and neutral voices (Chronaki et al. 2012). Findings of this study are in line with research conducted with adult participants showing reduced N400 amplitudes to negative compared to neutral emotional stimuli (Kanske & Kotz, 2007).
The brief review of published literature presented above suggests that research on prosodic discrimination in infancy has mainly focused on typically developing children. In our study, we focused our attention on children who are raised in institutional care. To test prosodic discrimination we used modified version of experimental paradigm proposed by Grossmann, Striano, & Friederici, (2005). In this paradigm, children are seated in front of a computer screen on caregiver’s lap and watch pictures of a faces (happy, angry and neutral) that are accompanied by auditory stimuli (pseudoword spoken with a different intonation). In different conditions facial expressions and prosodic characteristics either match or mismatch in emotional tone. EEG signal is recorded using a high-density active electrode setup with actiCHamp EEG system. ERP data was collected from children living in different environments, such as children raised in baby homes (IC) and their peers from biological families (BF) in the age range from 21 to 48 months.
Based on previous research documenting language and socio-emotional deficits in this group, we hypothesize that the ability of children with a history of institutionalization (IC) to discriminate prosodic contour is compromised by impoverished environment of institutional settings and their neural response to prosodic incongruity will be different from that in BF children (raised in biological family). We suggest that the main differences between the IC and BF groups will be found in the processing of negative emotional information. We are currently at the stage of data collection, and will present the preliminary findings at the conference during the talk.