Hibuki therapy combined with other art-therapy methods in group work with school-age children of different inclusive categories during the war in Ukraine

Introduction

Because of the Russian military aggression against Ukraine, the need has risen sharply for effective ways to overcome psychological trauma. The Hibuki therapy method for work with children was introduced into Ukrainian psychotherapeutic practice in 2022. Historically, the method of working with a therapeutic toy called Hibuki (Huggy-Puppy intervention – HPI) was proposed by Dr Sh. Hen-Gal in 2006 in Israel. Hibuki is a fairly large (baby-sized) soft toy resembling a “baby-like” dog with a sad face, big eyes, long ears and paws, and sticky Velcro strips on its upper limbs so that the “paws” can “embrace” a child. Hibuki is not just a toy, but a therapeutic tool. The word “Hibuki” is translated from Hebrew as “hugs”, which is the main for of interactions between a person with this toy. The method was actively implemented for overcoming the psychological consequences of the Second Lebanon War; 100,000 Israeli children participated in that program. A brief psychological intervention when children, who suffered various traumatic events, accepted a role of a toy caregiver showed significantly reduced stress reactions in such children (Sadeh et al. 2008). Later, the technique was also used in work with more than 3 thousand Japanese children during overcoming the consequences of the tsunami in 2011 and in the USA (Sharon Maksimov 2023).
Natural disasters and local wars occur very often in the modern world and their consequences lead to large-scale psychological traumatization of both adults and children. In recent years, there have been more than 36 wars worldwide. Since February 2022, Ukraine has also become a “hot spot”, and its citizens are still going through various traumatic experiences. Both military people and civilians suffer, as well as, unfortunately, children, including the younger ones (Lloyd and Penn 2010). The data from the all-Ukrainian survey organized in the summer of 2022 showed that the older a person is, the better his/her psychophysiological resilience is due to better self-efficacy, personal strengthening, valuing relationships with others and life in general (Kokun 2022). Therefore, children as a fairly vulnerable age group need especially some external psychological support with new creative, easy-to-use tools, programs and models (Lutsenko et al. 2018). Thus, the Hibuki therapy method has become such a tool in Ukraine since the spring of 2022.
During 2022-2023 D. Sharon Maksimov popularized the Hibuki toy in Ukraine, transformed it and developed her own Hibuki therapy technique for working with children’s trauma. Ukrainian psychologists, teachers and art therapists actively supported the method during the war. With the help of Hibuki therapy, they actively began to provide psychological assistance to Ukrainian children in refugee camps and social centres, organized both in Ukraine and abroad, and provided online counselling. The method received an additional impetus in Ukraine when the group work with the Hibuki toy was tested. Also, various methods of art therapy that could be combined with Hibuki therapy became an important component of psychological work. Migrant children who were forced to leave their homes and school-age children with disabilities are vulnerable categories, especially during a war. Usually, the latter study in special educational conditions in groups of children with special needs and contact mostly with members of their families or with adults or peers in inclusive resource centres. Our hypothesis is: the Hibuki therapy method combined with art therapy techniques reduces the traumatic effect of current social events on children’s psyche; and in the conditions of social-psychological group work, this approach creates impulses for personal development and provides social support to school-age children of various inclusive categories.

Material and methods

To conduct research in the conditions of the war in Ukraine, a set of methods was used in groups of school-age children of various inclusion categories: social-psychological training and art therapy techniques, including puppet therapy, in particular, Hibuki therapy. Additionally, we applied the methods of observation, questionnaires, data generalization and systematization.
We chose social-psychological group training as the main anti-crisis way of psychological support for the project participants. Social-psychological training (SPT) as a group form of work with children was proposed in the 1930s by S. Slavson (Slavson 1943). SPT is an active group method aimed at improving and developing attitudes, skills and knowledge of interpersonal communication, a means of developing competence in communication. In the national social-psychological practice, SPT is used widely as a form of social-psychological work, including with school-aged children (Zlyvkov and Lukomska 2019). Psychologists have proven that participation in training provides confidence in any future situation, which is a rather important social acquisition during childhood (Panok et al. 2020). In the temporal and spatial conditions proposed by such training, children, through social and personal experimentation, acquire necessary knowledge and form appropriate safe behaviour. In the conditions of a long military conflict, children and families experience mental trauma and need psychological rehabilitation; so, specialists turn to SPT as a psychological-pedagogical form of mass work that covers many children efficiently (Dyregrov 2008). Examples of such programs are: the program “SSET – Support for Students Exposed to Trauma” (Dzheikoks et al. 2015) and the authors’ correctional programs (Panok et al. 2020).
When creating our authors’ training program, we assumed that for successful development of a child’s personality, it is necessary to create a social environment of psychological support and creativity, and a media studio for and with children for social interactions in such an environment (Bryl 2019); additionally, the relevant cross-cultural context should be carefully considered during the selection of psychological tools for overcoming post-traumatic stress (Lloyd and Penn 2010). In general, the concept of “training” in social psychology has several different interpretations, including “learning”, “education”, and “preparation” (Bondar 2019; Zlyvkov and Lukomska 2019). As a part of work with inclusive project participants, we chose for a methodological basis a more general activity – development – that would not limit children within a specific and defined educational result. The essence of psychological training for its participants is an attempt to achieve in space and time precisely positive changes in emotions, motivations, etc. In the conditions of social crises, this aspect of work with children has mostly healing and corrective value (Dzheikoks et al. 2015; Tsarenko et al. 2018; Zamelyuk and Mahdysiuk 2021). The purpose of our psychological rehabilitation activities was to create conditions for children’s personal development. Working with children, we focused attention on the development of their deficient skills, on their values free from aggressiveness, negativism, etc. Therefore, we identified the rehabilitation tasks at all levels of work: behaviour (forming behaviour aimed at cooperation, developing skills of consistency in actions, creative work); emotions (releasing from aggression, its expression, overcoming stiffness, developing empathy); attitudes and values (providing an opportunity to realize simple universal values – love, friendship, care, support, acceptance); self-image and personal identity (awareness and acceptance of oneself, one’s potential).
Various art therapy practices are widely implemented in children’s groups to overcome trauma (Kalka and Kovalchuk 2020). Art therapy gives children with disabilities an opportunity to develop their skills for independent life and social adaptability (Lushyn et al. 2022). But of course, art therapy is not a quick remedy for deep mental disorders. Its main value is that art can offer children another language, non-verbal and symbolic, that helps children express feelings, desires, fears and fantasies (this is a non-verbal aspect of art therapy, a key one in creating positive changes in the psyche) (Waller 2006).
Art therapy as a psychotherapeutic method provides visual stimuli and introduces life experience into development. An art object, which exists in the space between a therapist and a child, allows the child to express what worries him/her. One method of corrective influence is puppet therapy, where the main tool – a doll – becomes an intermediate object for interactions between a child and an adult and helps children express things to which children cannot find words. The goal of puppet therapy is to help a child overcome or correct painful experiences, strengthen mental health, improve social adaptation, develop self-awareness and resolve conflicts (Kalinina 2009).
A Hibuki therapeutic toy became such an art object in our project. Because of the novelty of the Hibuki therapy method, only a few publications exist in the professional scientific literature that analyse its implementation for different categories of children and describe individual components or integrations with other methods of art therapy. Some universities and public organizations have organized educational projects (Khibuky-terapiia 2023; Bondarchuk and Karamushka 2023). D. Sharon Maksimov also organized a specialized “Hibuki therapy” group (with more than 4.4 thousand participants) on Facebook (Khibuky-terapiia 2023). During the last two years, D. Sharon Maksimov has published several scientific articles and a monograph devoted to various socio-psychological aspects of the method (Sharon Maksimov 2023).
Various methods of art therapy are a powerful way of work with trauma; they support psychological health during the war. The definition of “art therapy” has hardly changed since 1938: a process with the goal (not always achievable) to relieve, remove or eliminate symptoms (compensation, stopping) of a disease, pathological conditions or other disturbance of life activities, normalization of life activities and health restoration (Khilia 2017). Modern art therapy in Ukraine is a form of practical psychological work with universal application, used for solving almost all psychological problems, regardless of people’s age, gender and psychological characteristics. Art therapy methods are very ecological and unobtrusive (Pletka and Chaplynskaia 2017). Additionally, we should note that art therapy is quite radical: it develops spontaneity, improves attention, memory, cognitive skills, reveals life experience from an unusual angle, teaches to communicate with visual, motor, and sound means, develops self-expression and social skills (Liebmann 1986); teaches new roles and reveal hidden qualities, helps people observe how changes in one’s own behaviour influence other people, increases self-esteem, develops decision-making skills, relaxes, releases negative thoughts and feelings; and develops creativity through various means (McNiff 2014). Art therapy methods have many significant advantages: they are suitable for many people; can be used for people with language or other limitations; are means of free “insight-oriented” self-expression. Art therapy methods evoke positive emotions, help to motivate, form an active life position and a positive worldview; mobilize an individual’s potential, his/her internal mechanisms of self-regulation and self-mobilization; have a “soft” impact (Kalka and Kovalchuk 2020).
D. Sharon Maksimov emphasizes rehabi-litative effects of the Hibuki toy method in work with trauma (Sharon Maksimov 2023). The main technique offered in individual work with this game tool is intervention. The method components having rehabilitative effects are: a child’s active position toward the toy; shifting the focus of his/her attention; transferring one’s emotional state to Hibuki; improved confidence and self-development. Thus, the goal of the Hibuki therapy is to support and rehabilitate children’s mental health. Such toy “philosophy” correlated with our complex social research concept aimed at a wide target audience, namely school children of different inclusive categories.
So, the Hibuki therapy was used by us in combination with other methods of art therapy in socio-psychological training for school age children of different inclusive categories at the experimental stage of our study. The study results were recorded via observations. These observations were analysed and generalized to make conclusions and recommendations. Additionally, the questionnaire was proposed for parent to reveal and interpret outcomes of the Hibuki therapy and other art practices.

Results

During the four months in 2023, the public Internet-television-radio channel for children VESELKA TV in Kyiv implemented the cultural-artistic project DIM (Home): Children’s Inclusive Media Studio, which was supported by the Ukrainian Cultural Fund (Veselka TV 2023). The aim of the project was to create a socially inclusive creative space to strengthen the mental health of children participating in the project and to organize a series of psychological training sessions using the Hibuki therapy method in combination with various art therapy practices. Creating an inclusive creative space, we assumed that art therapy work could be conducted with children having various disabilities, in particular with those who had developmental problems: preservation of intelligence or its impairment (Kalinina 2009).
The project participants were 120 school-age children of different inclusive categories (from 6 to 17 years old), including those who had hearing, vision impairments, cerebral palsy, Down syndrome, disorders of the autistic spectrum or musculoskeletal system, mental disorders, Williams syndrome, diabetes, and attention deficit hyperactivity disorder. These children also often had traumatic experience – displaced children from the temporarily occupied territories of Ukraine, from the areas of military (combat) operations. As part of the work of the media studio, in addition to the socio-psychological component, children had an opportunity to try themselves in new social roles, performing the functions of various creative professions: TV and radio presenters, animators, bloggers, etc. As a result of the project, cultural products were created where all project participants starred; these products were translated into sign language (Veselka TV 2023).
Sixteen Hibuki toys were used in the project; they were brought to three centres participating in the project (in Vasylkiv and Kyiv). The project participants included children from children’s care organizations (“With warmth in the heart”, “SunWay”) and pupils of specialized schools for children with hearing impairments (Veselka TV 2023). The methodological approach of child-centrism (Bondar et al. 2019) was used in the work. The children were divided into 8 temporary groups (from 10 to 15 people in each of them); each psychological session lasted for 30 minutes, taking into account the different nosologies of the participating children. During the project, each participant attended up to 5 sessions in different weeks. At the same time, all children interacted with their Hibuki during group sessions.

Discussion

In the conditions of military events, the human psyche must withstand serious psychological stress: people are emotionally tired, and the human body is the first to respond to traumatic events. Tactile methods of intervention at the physical level in such cases can help both the body and the brain find the necessary state of balance, overcome anxiety and panic. Human hugs have significant potential in this sense. It is believed that people usually hug for an average of 3 seconds; but if a hug lasts longer (up to 20 seconds), it has a permanent therapeutic effect because hugs produce the oxytocin hormone, which is released into the nervous system during physical closeness. Oxytocin also helps people overcome social rejection, and hugs as a physical process help reduce the level of cortisol as a “stress hormone”, normalize blood pressure and heart rate, and increase the level of the neurotransmitter dopamine as a “hormone of happiness”. That is, hugging is a form of positive physical contact (Kachmar 2023). Using this idea, we tried in the life-threatening conditions during the war in Ukraine to teach children and teenagers with the help of Hibuki as a huggable toy, which implement the above-mentioned “idea of hugs”, to develop personal stress resistance and the ability to restore oneself and maintain existing productivity.
The Hibuki toy occupied an “honourable place” during psychological training. Its presence at the training had an accompanying character. Its was the main one mainly at the first familiarizing session, when the toy was “introduced” into the space of group work and “met” each child. In the introductory speech, a psychologist-trainer noted an accompanying “co-trainer” and assistant, the Hibuki dog. It will “come” to training sessions and improve everyone’s mood, help children to perform tasks creatively and cheerfully. The trainer paid attention to Hibuki’s external signs (paws, eyes, ears, tail, skin characteristics, pocket). At the first session, children saw the toy, got to know it, contacted it, explored it and with its help, using the psychological mechanism of transfer, had the opportunity to introduce themselves (depending on their diagnosis) to adults (the trainer, children’s assistants) and the group. If a child did not move or speak, such work was helped by the child’s assistant, who knew him/her well and felt his/her needs and desires. This generally increased the positive effect almost always, unmistakably showing what the child would like to do or demonstrate on his/her own. For example, if a séance were held in the morning, the trainer-psychologist while getting to know children (a large enough group was formed of children in wheelchairs, including those with significant speech and intellectual disabilities) offered the children to show what exercise they would recommend Hibuki to do during morning gymnastics. Children’s imagination and fantasy allowed them to find themselves in a conditional state of physical movement, inventing various physical exercises for Hibuki. Having almost no opportunity to do it themselves in practice, the children diligently tried to invent something original, without repeating the previous versions of exercises demonstrated by other children (the presentation was made by everyone in a circle). Most children did not refuse contact with the toy and were happy to look at it, touch it, attach it near the neck, on the back or stomach, less often to the head or waist, sit next to it or attach it to a chair. In our practice, there was only one case of categorical refusal of a toy at 2 training sessions. The toy was rejected by an 11-year-old autistic boy, by the way, with very independent and ‘adult’ behaviour, who usually showed maximum autonomy and refused to perform all exercises together with other participants, demanding separate attention and individual creative tasks. Based on the boy’s interests in construction and papercraft, revealed at a previous session, the trainer proposed him to create a large plane for Hibuki’s travels from a paper poster. The boy completed the proposed task with interest and satisfaction, allowed himself to be photographed with the Hibuki on the airplane, and then took the model airplane home. So, in this case, we found confirmation of the idea that support for children with disabilities depends on children’s needs, and not on their disorders (Sharon Maksimov 2023). Also, according to our observations, older participants had less intense tactile contact with Hibuki during sessions, placing it simply on the table while performing other art therapy tasks.
Another interesting task for children was the exercise called “How would you wear Hibuki?” The exercise was also carried out with a diagnostic purpose, because as noted by D. Sharon Maksimov (2023), the way of Hibuki wearing could also provide additional information to the trainer for organizing effective group work with children. In our practice, some children tossed the Hibuki strongly, twisted it around themselves, twisted or tied the limbs into a knot, which, in our opinion, manifested a surge of quite strong experiences and emotions, as it was already noted in previous studies (Sharon Maksimov 2023). Therefore, it was important for the trainer to choose techniques for group work that would enable children and adolescents to feel and see connections between thoughts and emotions, teach them to note thoughts that could provoke anxiety, and change them to adaptive and positive ones (Dyregrov 2008).
The proposed psychological training was designed according to the classic scheme: introductory, main and final parts (Karpenko 2015). By content, they included the following actions:
1. Introductory part: greetings (to demonstrate the toy and create a general positive emotional mood, for example, physical movement with the trainer’s commentary, poem reciting with accompanying movements, etc.). In our case, the introductory part required some preparation for work with the toy in a group: the children were not supposed to see the Hibuki right away. At first, the trainer suggested “warming up” physically. It could be fairly small exercises with movements, reciting poems with movements, tapping, using Kruger hooks or Aliyev key, etc. At this stage, all Hibuki toys could be hidden behind a screen or with some other method; then, toys would be handed over to each child. This moment was important, because if children paid attention to the toy in advance (before the beginning of work) this could later affect the planned course of the training.
2. The main part: a) establishing contact with Hibuki; b) a practical stage (performance of psychological tasks, “camouflaged” as a creative one). The first contact with Hibuki assumed some feedback from each child; the trainer noticed children’s response to direct contact with the huggable Hibuki toy. The questions could be: “What is the name of your Hibuki toy? What can he/she do?”. The game went around the circle. A “snowball” exercise could be used when the trainer repeated the names and actions of previous participants. If this game was difficult to organize in a particular group, children were simply asked the to call their Hibuki toy by name and with the toy to show what they could do (physical exercises, emotional reactions, different actions – sleep, run, eat, study, read, etc.). An interesting collective technique (it could be done even while sitting at the tables) was the “Hibuki bracelet” – a circle was created by intertwinement of Hibuki legs, so the participating children were united into a common circle.
After the more physically active first stage, at the next one, tasks were proposed using various means of art therapy, during which the Hibuki was always close to the children. Some children placed the Hibuki on themselves, others placed it on the table they were working on or attached it to the chair they were sitting on. At this stage, the Hibuki performed the role of “psychological support” – becoming a friend, observer, adviser and still an active participant in the creative-therapeutic process. The main methods applied in group work during the second stage within the implemented Hibuki therapy were drawing, games, metaphors and active imagination during creative tasks (Bondar et al. 2019; Kalka and Kovalchuk 2020; Pletka and Chaplynskaia 2017). Here are some examples of proposed tasks with some author’s modifications:
– colouring – a pre-prepared template of a picture with a dog similar to the Hibuki for colouring. “Colour your Hibuki” exercise: children were asked to colour a picture with a Hibuki toy and sign his/her name. It was important to do this at the first meeting, because Hibuki toys were left in the playroom, so the psychologist’s comment was as follows: “The Hibuki toy stays in our room, and you can take the picture with you as a memory of meeting Hibuki”; this was perceived well by the majority of children;
– doodles – the trainer offered children to draw any doodles on a sheet for 1 minute (alternatives: with closed eyes, during another specified time). In most groups, we limited the time but did not ask children to close their eyes, because the children had different diagnoses. Then the psychologist set the task: “What did Hibuki see in this picture? Look at it, colour it in, finish it”;
– handout cards for work (Roiz 2022) – a game with colouring and making a product with the idea of “hugs”. All cards had pictures and “instructions” how different animals could hug. These cards were distributed to children. Then the drawn hugs were demonstrated to the Hibuki dog or another participant to teach others with new hugs. After that, children were offered to make a clipping, to colour and cut the picture. At the end, the cut-out instructions for hugging were “sent” home; so the task also had a delayed therapeutic effect for children and their families: children would show their parents how to hug. Children were also asked to invent their original ways of hugging;
– drawing palms – drawing a line around a child’s palm and the Hibuki’s palm and creating a fairy tale story about how they met. In this exercise, the therapeutic effect was achieved thanks to “control” over the palm: developing self-control, the ability to contact another person. The main and often used topic for autistic children is the image of their own body, so this feature should be taken into account when choosing exercises for such children;
– a house for Hibuki – children “as architects” were invited to design and make a house for Hibuki. After work completion, a Hibuki “opening” and show of all Hibuki houses was organised in the group, all works were somehow marked and the most original houses or works were determined;
– Hibuki’s secret letter – crafting a pocket note for Hibuki. The following instruction was proposed: “Every person has some secret that he/she can tell far from everyone. You can tell Hibuki anything or share your wish – write it down on a note. You can write/draw your wish and then hide it in Hibuki’s pocket”. After completing the work and placing wishes into the pockets, Hibuki dogs were shuffled by changing their places on chairs; and the trainer took out the notes from the pockets, read the wishes aloud, and the children could name the child whose wish they thought it was;
– the island where Hibuki stayed – a group exercise when children invented means to save Hibuki, whose ship had got into a difficult situation near a deserted island; children invented the island infrastructure for Hibuki’s safe stay and waiting for help. The exercise united all participants around the task, which greatly affected the cohesion of children; it was given at the end of training sessions;
– a profession for Hibuki – the “Profession Compass” set of cards was used (Blynov 2016) for the exercise. The following instruction was given: “Let’s help Hibuki choose a profession”. Children chose different cards with pictures of professions for Hibuki, and with such choices they could tell about their needs, interests and dreams.
During work, it was important to give children opportunities to choose independently materials, colours and compositions, to reduce instructions to a minimum, paying attention to the satisfaction from the task, to be guided by the general principle of non-interference in a child’s work, not to use evaluative comments (Savytska et al. 2022).
3. The final part (demonstration of the participants’ works, farewell to Hibuki and the trainer). An important moment at this stage was the obligatory demonstration of the works done by each participant (presentation, commentary, “opening”, exhibition, etc.) and the ecological “farewell to Hibuki”. During this stage, children were given opportunities to talk about their works, feelings, attitudes to their results, possibly with stimuli-questions from the trainer (Savytska et al. 2022). At this stage, we used the following techniques: after finishing a session, children, saying goodbye, put their Hibuki in the trainer’s hands, saying to them: “Goodbye!”. If there were many children and many toys, this technique looked quite funny and delighted the children and, as a result, did not evoke negative emotions because of separation. It was also important to ensure that after each session, children had some physical things with them – a picture, a craft, a drawing compensating the “absent” Hibuki. Another possible technique was: to organize a scenario where children put each Hibuki toy on a separate chair and invented a way to say goodbye to them. This task was also perceived by the children as a game and helped to “ecologically” get out of the situation of “farewell to Hibuki”. The following session started with the questions: “What was Hibuki doing (Hibuki’s paw touched a child’s hands)?”, “Where did Hibuki go (Hibuki’’s paw touched a child’s feet)?” and “What was Hibuki thinking (Hibuki”s paw touched a child’s head)?” In this way, the trainer conducted “screening” of each child’s mood to make the final decision about the techniques that would be used during the session. In this exercise, children talked about how the last time or day passed, about themselves, describing their latest impressions and their own activities. Additionally, the trainers established contact with children and between children. We should note especially that the trainer must very carefully prepare to work in a group: methodically, morally, psychologically (Bondar 2019; Zhang 2018; Zlyvkov and Lukomska 2019). He/she must be able to integrate, compile various methods, combining them comprehensively and building a sequence, pay attention to all children, which is quite difficult, especially in groups of children with different nosologies.
After the project completion, we asked the parents of the participants to evaluate the effectiveness of the carried out work. The parents were asked whether their children’s behaviour, mood or state had changed after the project. The majority of parents answered positively (97%). As for tasks that children remembered the best, the leader was artistic creation (75.6%) and television filming (53.7%), while psychological training together with acting took the third place (its effectiveness was noted by 31.7% of respondents). Another question was how “getting to know Hibuki” affected children’s behaviour. What changes were observed? 9.2% of parents did not notice changes in their behaviour, while 90.80% noticed a positive effect: a calming effect, tactile contact that improved mood, the range of emotional reactions was as follows: joy, kindness, positivity, curiosity, calmness, care (Fig. 1).
As for the question what the project as a whole has given to children, the majority of respondents answered: confidence (86%), psychological support (53.5%), new friends (46.5%), unforgettable impressions and positive emotions; new types of art, understanding that efforts needed to achieve a result, and even speech development – 2.4% each (7% in total) (Fig. 2).

Conclusions

So, the study showed that the Hibuki therapy method can be used in group work with school-age children of different inclusive categories who have a traumatic experience. The participants of the cultural-artistic project felt they were part of the developing environment and most of them received a personal impulse for changes. The social context of communication in combination with art therapy tools (puppet therapy, drawing, working with metaphorical association cards) allowed children to explore and express feelings that were difficult for them to convey in words by placing them into an object – a toy, drawing, etc., which became a means of communication between an adult and a child. The children’s experience was enriched by the expansion of communication ties, social experience, creative assets, and most importantly, their confidence increased. In our opinion, an inclusive social-creative space created in the groups and acceptance of all children was provided by the introduction of Hibuki therapy methods into game practices as a safe psychological tool helping children explore themselves and adults recognize what support children needed. In the future, we plan to continue to investigate the impact of Hibuki therapy in combination with various art therapy methods on children with disabilities of specific nosologies, to study the use of the Hibuki therapy method within a hybrid model that combines both individual and group approaches and also to focus attention on the development of the authors’ group techniques how to use the Hibuki therapy as an anti-crisis approach.

Disclosure

The authors declare no conflict of interest.

References