Autism spectrum disorder (ASD) is a lifelong complex neurodevelopmental disorder that significantly impairs individuals’ verbal and nonverbal communication, social interactions, and behaviours (i.e., exhibition of restricted interests, repetitive and unusual sensory–motor behaviours) [1]. Prevalence estimates of ASD have increased over time, and a recent systematic review [2] reported a median global prevalence (ranging within and across regions) of 100/10,000. ASD presents a striking sex difference, as males are more likely to be affected relative to females (3:1 ratio) [3]. The ASD aetiology is suggested to be multifactorial, as both genetic and non-genetic factors (e.g., prenatal/perinatal) may play a crucial role in the manifestation of the disorder (see [4] for a review). In contrast to its first description, ASD is now regarded as a spectrum that spans from very mild to severe [5], as symptoms manifest differently in each individual based on their functionality level (level 1—requiring support; level 2—requiring substantial support; level 3—requiring very substantial support). Nevertheless, several individuals with ASD (not all) require some kind of support throughout their life [5]. Even individuals with high-functioning ASD, similar to other individuals at the mild and lower end of the spectrum, present social skill deficits across the lifespan (up to adulthood). Adults with ASD are likely to experience problems in social and everyday life functioning due to a lack of ecological training and intervention programmes during childhood and adolescence [6].

Adults with ASD have been found to experience social isolation, loneliness, and social anxiety (e.g., [7]) due to their deficient social skills, such as atypical gaze/poor eye contact, less conversational involvement, inappropriate affect, reduced verbal fluency (e.g., [8,9]), poor understanding of social cues, and difficulties in initiating and maintaining social conversation/communication [10]. The social skill deficits in individuals with high-functioning ASD are mainly attributed to impairments in cognitive components such as executive functions (EFs) (e.g., [11]) or cognitive processing speed (e.g., [12]). Indeed, impaired EF, which refers to high-order, goal-directed cognitive processes that control behaviour, thought, and emotions, is another salient characteristic of the spectrum [13]. The EF construct is seen as an umbrella term that includes abilities such as inhibition, working memory, and planning (not an exhaustive list; see [14,15] for a more detailed EF discussion). Two recent meta-analyses [16,17] demonstrated broad EF impairment in ASD, as deficits have been consistently found in several EF aspects (e.g., inhibition, working memory, cognitive flexibility, and planning) across the lifespan.

To implement effective interventions, research over the last decade has aimed to identify which EF aspects contribute to the manifestation of social skills in ASD [11,18], as it is suggested that higher-order cognitive regulation is required for social interactions [19]. EFs have been proposed to support the processing and manipulation of information from one’s and others’ perspectives to facilitate social interaction and communication skills [20]. Such associations are understudied in adulthood in ASD. Limited evidence from childhood and adolescence has shown that performance-based measures of EF (e.g., auditory attention and inhibition/switching) are related to social deficits in ASD (e.g., [21,22]), while ratings-based EFs such as initiation, cognitive flexibility, and working memory were found to be related to adaptive social skills in ASD [23,24]. A recent study [18] also demonstrated significant associations between ratings-based EFs (self-monitoring) and selective social skills (social inferencing and social knowledge) in ASD. It should be noted, though, that none of the aforementioned studies, despite their findings, used in vivo measures of social functioning or a naturalistic context of assessment. Social skills have been theoretically proposed to also depend on social cognition aspects such as mental state/emotion recognition [25], but as these aspects are not consistently associated with social impairment in ASD [26], the extent to which socio-cognitive abilities are associated with the social difficulties in ASD has been debated over the years. Given these potential associations among social cognition and social skills, EFs and social skills, and EFs and social cognition (e.g., [27,28,29]), it has been suggested that EFs may contribute to social skills both directly and indirectly [30]. Social cognition aspects are likely to partially mediate the association between EFs and social skills; perhaps no single cognitive mechanism in ASD can explain the various social difficulties, as previously argued [31], as there may be several factors potentially contributing to social skills (e.g., poor emotion regulation) that could also explain the social and behavioural problems in ASD (e.g., [32]).

The assessment of ASD impairments is critical for identifying potential difficulties and weaknesses when implementing interventions. For example, widely used measures of social functioning include the Social Responsiveness Scale (a measure of general social ability [33,34]), Reading the Mind in the Eyes test (a measure of mental state/emotion recognition [35]), and the Autism Diagnostic Observation Schedule (a measure of social interaction, communication, and play [36,37]). Taking into consideration the tremendous impact of the aforementioned cognitive and social impairments on the everyday lives of individuals with ASD, suitable intervention and training programmes are needed [38]. Targeting cognitive deficits, cognitive training exercises in adults with ASD are usually implemented to enhance performance through repeated practice on EF tasks (e.g., [39,40]). Cognitive training exercises encompass various intervention methods, such as pen-and-paper tasks, downloadable tools, and logical games. Given the EF contribution to several aspects of social functioning, targeting specific EF aspects is thought to improve the effectiveness of training interventions in ASD [41]. However, it should be noted that cognitive training studies in ASD have been designed only in recent years, and thus, their limited and mixed results as well as their lack of ecological validity are the subject of ongoing discussion (e.g., [42,43,44]).

When it comes to social skills, several different strategies have been used in training and intervention programmes to enhance social functioning (usually social interaction and communication) in adults with ASD. For example, strategies such as social stories and social scripts, behavioural modelling and role-playing demonstrations, video modelling, and self-modelling (e.g., [45]) in the context of didactic lessons to enhance conversational skills, developing friendships, the appropriate use of humour, dating, and handling embarrassing feedback and peer pressure (e.g., [46]) have been used in ASD. Most psychosocial intervention and training programmes in ASD, however, are thought to yield limited benefits [47] because of their limited ecological validity, which does not permit the generalisation of the outcomes to everyday life [48,49]. The limitations of the aforementioned methods are thought to likely arise because of the ASD literature’s tendency to examine social (and/or cognitive) deficits as isolated and individual features without evaluating how they manifest in real-life contexts, in which outcomes are influenced by relational dynamics as well [41,50]. For that reason, computing technology with more naturalistic set-ups and role play is a significantly effective training and intervention medium for individuals with ASD [51].

Ecological validity refers to the verisimilitude (i.e., the likeness to everyday life) and veridicality (i.e., the association between the observed and real-life performance) of a neuropsychological tool, which subsequently allows the generalisation to everyday life [52]. In contrast to paper-and-pencil or computerised approaches, which incorporate static and simplistic testing and training environments and stimuli, immersive virtual reality (VR) facilitates the attainment of enhanced ecological validity and pleasantness [53]. Immersive VR neuropsychological tools may thus contribute to the understanding of everyday functionality (e.g., [54,55]) and improve everyday physical and cognitive functioning (e.g., [56,57,58]). In the context of VR interventions in ASD, immersive VR technology facilitates the creation of simulated environments that can be used to help individuals with ASD improve social skills, communication, and behaviour [59,60,61,62]. These interventions aim to provide individuals with ASD with a safe and controlled environment in which to practice and develop skills, as well as to reduce the anxiety and stress associated with real-world interactions [60]. VR interventions can include activities such as role-playing social scenarios, virtual social skills training, and virtual exposure therapy. However, the effective implementation of immersive VR for research and clinical purposes requires technological competence [63]. An inappropriate conceptualisation of VR training may have negative ramifications and compromise its otherwise beneficial outcomes [62].

Nevertheless, several VR applications have efficaciously been implemented for assessment and intervention purposes. The VR Everyday Assessment Lab assesses everyday memory (prospective and episodic), attention (visuospatial and auditory), and EFs (planning and multitasking) and has been found to be a valid and substantially more pleasant testing experience [53] that is representative of the everyday functionality of adults [54,55]. The ClinicaVR: Classroom-CPT is a VR classroom that examines selective and sustained attention and inhibition, and it has been validated in children and adolescents [64]. Regarding interventions in ASD, there is preliminary evidence postulating its feasibility for being adopted in clinical and educational environments [59,65]. Additionally, the use of social stories in VR has been evaluated by clinicians for implementation in clinical and educational settings for social skills training in children with ASD [66]. Preliminary evidence suggests that VR software may improve the conversational [61], problem-solving, and communication skills of children with ASD [67]. After a VR training protocol, children with ASD showed significant improvements in emotion expression and regulation and socioemotional reciprocity [68]. Comparably, two more studies [69,70] reported a substantial enhancement of social skills in children with ASD after they attended VR-based training sessions. It is important, however, to underline that VR interventions in ASD are still considered an emerging field, and more research is needed to fully understand their efficacy, usability, and the provided user experience, as well as their acceptability by individuals with ASD [59,60,62]. Furthermore, the relationship between performance in VR social scenarios and cognitive functioning has not yet been investigated. Finally, while there are several VR applications used in children and/or adolescents with ASD, none of the aforementioned VR applications was designed for or implemented in adults with ASD.

The VR Enhancement of Social Skills (VRESS) was developed in line with the guidelines for developing VR software for research and clinical applications in the field of psychology [71]; these guidelines have been found to produce VR software that meets the criteria of the American Academy of Clinical Neuropsychology (AACN) and the National Academy of Neuropsychology (NAN) [72]. VRESS incorporates social scenarios that are exemplary of adult activities and common in daily life, such as renewing one’s subscription to the gym, selecting a movie and buying a ticket at the cinema, browsing the available options and purchasing a smartphone at the phone store, attending a seminar class and interacting with the instructor and the co-students, and attending a job interview and responding to the interviewers’ questions. The social scenarios were designed in line with the guidelines of Gray and Garand [73] for providing social stories that provide individuals with ASD (i.e., the learners) a visual representation and a description of a situation or activity to prepare and instruct them on what to expect, as well as the underlying reasons for this matter. Thus, the social scenarios of VRESS are descriptive rather than directive. The social stories were designed for individuals with ASD to comprehend and apply the intricacies of interpersonal communication to interact more appropriately and effectively. The social story approach provides the opportunity for people with ASD to identify the context, discuss their motives, comprehend the amplifiers or the obstacles, and improve their social skills [73,74].