The General Discussion is organized as follows: We i) briefly summarize and discuss the project findings; ii) present an integrative picture of social referencing as a function of diagnostic group; and, iii) discuss the implications of these findings for the development of the behavioral phenotypes of these syndromes.
Summary of findings
On the Social Referencing task (Study 1), clear differences were observed in children’s behavioral responses both as a function of the experimenter’s emotional display and as a function of diagnostic group. In the Joyful condition, the majority of children in both groups demonstrated responses regarding the stimulus that were consistent with the adult’s response; this was not the case for either diagnostic group in the Fearful condition. Despite the between-group similarity on this variable, clear between-group behavioral response differences were observed in both conditions. In the Joyful condition, the children with DS shifted their attention more between the stimulus and the experimenter than did the children with WS. In addition, significantly more children with DS (75%) than children with WS (40%) produced behaviors acknowledging the joyful display and indicating that they attended to both the experimenter and the stimulus. Finally, a trend was observed for more children with DS (80%) than children with WS (50%) to approach the stimulus in the Joyful condition.
In the Fearful condition, only 25% of children with DS and 10% of children with WS demonstrated a negative response regarding the stimulus. Nonetheless, clear between-group behavioral response differences were observed. The children with DS shifted their attention between the experimenter and the stimulus more than did the children with WS. In addition, 60% of the children with DS acknowledged the experimenter’s fearful display and attended to both the experimenter and stimulus. Still, 40% of the children with DS demonstrated a positive response regarding the stimulus and significantly more children with DS than children with WS approached the stimulus without hesitation. The children with WS, on the other hand, produced very long looks at the experimenter, and significantly more children with WS (40%) than children with DS (10%) superficially imitated the experimenter’s fearful display. Only 35% of children with WS acknowledged the experimenter’s fearful display/attended to both the experimenter and the stimulus and only 25% demonstrated any response regarding the stimulus, with the majority of these children evidencing positive responses.
Taken together, these data suggest that few children in either group used the other person’s fearful response to regulate their own behavior toward an ambiguous stimulus. However, there were clear differences in the patterns of behavioral responses, as a function of diagnostic group. The results of Studies 2 to 4 help to clarify the pattern of findings from Study 1.
Initiating eye contact and gaze following
Children with DS performed significantly better than did children with WS in terms of both initiating eye contact and following another person’s gaze, two of the three abilities theorized to be central to the social referencing process. Both the ability to coordinate attention between a social partner and objects/events of mutual interest (initiating joint attention) and the desire to follow into the focus of another person’s attention (responding to joint attention) have been argued to facilitate social learning [70, 71]. In particular, we would argue that these individual skills support the child’s emergent ability to utilize other people as a source of information about how to navigate the social and physical world. Future research focused on examining whether or not differences in joint attention abilities between children with DS and children with WS translate into group differences in social learning will provide insight into the development of socio-cognitive development in both atypical and typical development. It is also important for future studies to identify other factors that relate to social learning and how these differ between populations (typical and atypical).
Joint attention abilities also have been argued to lay the foundation for the later development of theory of mind [72, 73]. Charman and colleagues  postulate that one possible mechanism for the relation between joint attention and theory of mind is that the child acquires theory of mind because of the experiences gained through initiations of coordinated attention between people and objects. Although there are no studies that directly compare the theory of mind abilities of children with DS and children with WS, significant delays in the development of theory of mind have been documented in both diagnostic groups [74–76]. More research is warranted to determine how the early emergence of the ability to initiate joint attention relates to the later development of theory of mind in children with these syndromes. Given the findings of early differences in joint attention ability between children with DS and children with WS, results from this line of research would contribute to the literature on the emergence of socio-cognitive development in both typical and atypical development. In addition, it is important that future studies further consider the potential long-term effects of early differences in abilities fundamental to the social referencing process on higher order social-cognitive abilities such as perspective talking and successful negotiation of conversations.
Finally, it is important to note that our findings of between-syndrome differences in joint attention favoring the children with DS were obtained even though the children with WS had significantly higher overall intellectual ability and verbal abilities than did the children with DS. These results are not the first to indicate better performance by children with DS on joint-attention related tasks when compared to CA-matched children with WS  despite differences in verbal and intellectual abilities favoring the children with WS . Given prior findings of positive associations between TD children’s joint attention abilities and language acquisition [77–79], this may seem surprising. However, it is important to keep two things in mind. First, caregiver linguistic input provided within supported joint attention episodes is also significantly positively associated with child vocabulary acquisition , offering an important avenue for vocabulary development for both children with WS and DS, as well as for TD children . Second, between-syndrome differences in overall intellectual ability [9, 27] and in verbal short-term memory [81–83], two other factors associated with language acquisition [84, 85], consistently favor children with WS [9, 27, 85–87]. Future studies examining all of these factors in relation to language acquisition by both children with DS and children with WS are needed to elucidate the similarities and differences in their development of language.
On the task assessing the utilization of emotional reactions (Study 4), the majority of children in both groups demonstrated a response to the stimulus that was consistent with the experimenter’s response in the Joyful condition; this was not the case in the Fearful condition. While some caution should be taken interpreting the results of Study 4 due to the limited sample size, these data, once again, show that few children in either group used the experimenter’s fearful response as a source of information to regulate their own behavior toward an ambiguous stimulus. Given the prior literature documenting the difficulties of older children and adults with DS or WS in interpreting the communicative significance of facial expressions of fear (see the introduction to Study 4), the most likely explanation for the failure of most participants in both groups to use the experimenter’s fearful expression to regulate their behavior is that they did not comprehend the communicative significance of that expression. Alternatively, it is possible that because the children were engaged with a friendly and familiar experimenter, their default assumption was that the situation was not dangerous. If so, they may have reacted with curiosity about the ambiguous stimulus, regardless of the experimenter’s display. However, our finding that across Study 1 and Study 4 only a few children in each diagnostic group communicated any response to the experimenter regarding the stimulus after seeing her fearful display, indicates that at a minimum, the child’s lack of response results in a disruption in the reciprocal communicative process.
Emotional reactions are more than an index of underlying states; they are an integral component of the communicative process used as a tool to guide/influence other people’s behavior . In addition, it is important to remember that social interactions are reciprocal in nature. That is, within a social interaction both people involved are simultaneously trying to communicate with and influence each other. Within these interactions, particularly adult-child interactions, emotions are frequently used to communicate social expectation regarding how to behave as well as to communicate one’s perspective on a situation to another person. As a result, when a person utilizes affective expressions to communicate information to a child, it is expected that the child will recognize this communicative act and respond accordingly. As such, even if the children in the present project disagreed with the adult’s perspective on the situation, there is a pragmatic expectation that the child respond, either verbally or nonverbally, to the adult’s communication; failure to do so presents a disruption to the social interaction. As described in the Results section of Study 1, a few children did indicate their disagreement with the experimenter’s fearful display. However, most participants either did not respond or demonstrated a positive response to the stimulus following the experimenter’s fearful expression, indicating either a failure to comprehend the significance of her expression or a pragmatic failure to communicate disagreement with the adult’s response. The potential long-term impact on emotion processing of difficulty using another person as a source of information about the surrounding world should be explored in future studies.
Social referencing in down syndrome
When framed within the context of the social referencing process, it is plausible that, by initiating looks to the experimenter and following the experimenter’s gaze more often than do children with WS, children with DS are more likely to access the adult’s message and map it to objects and events in the environment than are children with WS. When these abilities are paired with the ability to recognize the communicative significance of a joyful expression, children with DS are able to utilize the adult as a source of information indicating that the ambiguous stimulus is enjoyable and act accordingly.
At the same time, the current findings in conjunction with the existing literature on emotion recognition in children with DS [13, 64–66] indicate that, as a group, children with DS have difficulty recognizing the communicative significance of another person’s fearful reactions. This position offers a plausible explanation as to why many children with DS approached the stimulus in the Fearful condition despite frequently looking between the experimenter and the stimulus. That is, although children with DS are more likely to access the experimenter’s fearful message and map it to the stimulus than are children with WS, the children with DS still approach the fearful stimulus because they do not understand the communicative significance of the experimenter’s fearful expression. Alternatively, children with DS may have recognized the communicative significance of the experimenter’s fearful expression but assumed that the situation was not dangerous given the play context with a friendly and familiar adult. Even if this alternative explanation is correct, our finding that the majority of children with DS acted without sensitivity to the adult’s communication indicates that there are disruptions in the reciprocal communicative process. Either way, the findings from the present study highlight the importance of continued investigation of the development of social referencing by children with DS.
Social referencing in Williams syndrome
An examination of the performance of children with WS, framed within the context of the social referencing process, indicates that it is likely that their decreased frequency of looking at adults in triadic situations and in following the adult’s gaze results in less access to information about the situation at hand and fewer opportunities to identify the source of the adult’s reaction. These disruptions cause increased confusion for the child regarding why the adult is reacting in that manner or even create situations in which the intent of the adult’s communication is completely lost. These outcomes could explain why so many children with WS did not demonstrate a response regarding the stimulus in the Fear condition in Study 1.
As pointed out by Meltzoff , human beings would be difficult to predict and even harder to explain if our understanding of them was restricted to their physical behaviors and movements. It is therefore possible that not identifying the source of the experimenter's reaction could be a contributing reason as to why, in Study 1, children with WS were more likely to produce very long looks to the experimenter and to superficially imitate her emotional reaction than were children with DS. This explanation could also account for why no imitation was observed in Study 4, when the source of the experimenter's reaction was much more obvious. Alternately, the lack of imitation in Study 4 could be due to children being more interested in determining what was in the box than they were in what the experimenter was doing.
Finally, the findings from Study 4, in conjunction with the existing literature [13, 65, 67, 69], suggest that children with WS have difficulty comprehending the communicative significance of another person’s fearful expressions. As suggested above, the difficulties of children with WS in recognizing the communicative significance of emotional expressions may be impacted by their difficulties with joint attention; and even if they did understand the communicative significance of fearful expressions, our finding that most children with WS acted without sensitivity to the adult’s communication suggests that there are clear disruptions in the reciprocal communicative process for children with WS. If these hypotheses are correct, it is easy to see how breakdowns in interactions for the children with WS can occur.
It is important to note that not only does the lack of shifting attention and the reduced rate of gaze-following in triadic situations demonstrated by children with WS limit their understanding of the social interaction, but it may also influence their communicative partner’s understanding. For example, both the research assistants who coded the videotapes for this project and the experimenters who interacted with the children frequently reported that it was easier to interpret the behavioral responses of the children with DS than those of the children with WS, as the children with DS gave the adult "more information." Interestingly, this impression was obtained even though the children with WS had considerably more advanced language skills than did the children with DS, many of whom produced only a few single words or manual signs. In contrast, the coders and experimenters often said that the interactions with the children with WS were "weird" and that they were not entirely sure what was happening except that clearly something had gone wrong. Given these findings, it is important to continue the investigation of the development of social referencing in children with WS and to consider the impact of the social referencing process on the development of the phenotype.
Impact on behavioral phenotypes
The findings obtained regarding the social referencing process and the patterns of strengths and weaknesses across the associated component abilities provide new insight into the development of the social cognitive phenotypes for these two groups of children. For children with DS, while the ability to shift attention between people and objects and the ability to follow another person’s gaze are delayed relative to TD children, these abilities are well established at a younger age than for children with WS. These abilities likely are important contributors to the social strengths demonstrated by children and adolescents with DS, and in particular to the success that children with DS have in establishing and maintaining friendships and the success that adults with DS have in securing and maintaining employment. Despite the social strengths that children with DS demonstrate, it is likely that at least young children have difficulty utilizing fearful expressions as a source of information about their environments. This pattern of being able to recognize an object as a topic of focus but not being able to utilize a communicative partner’s fearful expression could result in children inadvertently putting themselves in dangerous situations.
For children with WS, difficulties shifting attention and following the attention of others paired with a difficulty recognizing the significance of fearful expressions may help explain why very young children with WS spend so much time attending to faces . Impairments in recognizing that facial expressions communicate information “about something” likely make it difficult for children with WS to make sense of human behavior in terms of underlying mental states. Basic skills such as initiating eye contact and gaze following are pivotal foundations for the development of higher order skills such as perspective taking, which are necessary to navigate the social world successfully. Accordingly, these early impairments likely alter the experiences children with WS have within their social environment, leading to significant pragmatic impairments , which likely lead to later difficulty establishing and maintaining friendships [20, 21] and difficulty with employment [89, 90] despite relative strengths in concrete vocabulary and structural language and a desire to be around other people.
It will be important to examine the development of the regulatory function of social referencing longitudinally. In addition, future studies considering the influence of other characteristics that likely differ between the DS and WS behavioral phenotypes, such as executive functioning abilities (both behavior regulation and metacognition) and temperament, on the social referencing process would be valuable.
Neural underpinnings of social referencing
To date, no studies have systematically evaluated the neural correlates of social referencing. There are, however, some data from the literature on TD individuals elucidating the neural substrates of the abilities central to the social referencing process. Joint attention has been associated with activity in the ventromedial frontal cortex, the superior frontal gyrus, the cingulate cortex, and the caudate nuclei . The anterior insula, rostral anterior cingulate cortex and the amygdala, have been associated with observing/understanding other people’s emotions [92, 93].
Few studies have focused on the structure or function of any of these brain areas in individuals with DS or WS. Research on individuals with DS in comparison to CA-matched TD controls has indicated, relative to total brain gray-matter volume, no significant differences in bilateral amygdala gray-matter volume [94, 95] but significantly increased gray-matter volume for bilateral caudate nucleus, bilateral frontal superior gyrus and bilateral insula . Findings from studies of individuals with WS have indicated that, relative to total brain gray-matter volume, the gray matter volume of the amygdalae was significantly larger bilaterally for individuals with WS who had ID than for CA-matched TD controls [97–99], but did not differ significantly from TD CA-matched controls for individuals with WS who had low average or average IQ . Structural findings for the insula have been inconsistent, with some studies of individuals with WS who had ID indicating bilateral increase [98, 101] and others indicating bilateral reduction  relative to total brain gray-matter volume. More complex findings were reported for individuals with WS who had low average to average IQs, with bilateral reduction in dorsal anterior insula but increase in the right ventral anterior insula . For individuals with WS who had low average or average IQ, the white-matter connectivity of the amygdala to the orbitofrontal cortex via the insula was compromised , as was the functional connectivity of the amygdala to the orbitofrontal cortex during emotional processing tasks . Alteration in amygdala functioning and regulation was also found for individuals with WS who had ID . Research documenting similarities and differences in the neuropathology associated with DS and with WS that is focused on brain regions and pathways hypothesized to play a role in social referencing is needed to provide further information regarding the neuropathology underlying social referencing for these two syndromes.