VR technology encompasses a spectrum of differently immersive experiences, from non-immersive to highly immersive environments, offering a versatile range of tools for cognitive rehabilitation [10,20]. At one end of this spectrum are non-immersive setups that typically involve standard computers, tablets, smartphones, and television screens. These setups, while less immersive, still provide valuable cognitive exercises and are accessible for a wide range of users. In this case, the individual is not totally immersed in the virtual environment; he navigates the scene in third person, but may experience both the real world, e.g., his location and the physical boundaries of the room he is working in, as well as the virtual world on the screen. Moving along the spectrum, there are more immersive tools, such as the Cave Automatic Virtual Environments (CAVEs), and headsets [21,22]; in this case, the user navigates the scene in first person. The CAVEs [23] consist of a room-sized cube with projected 3D visuals on multiple walls. However, the most common and accessible form of VR technology for cognitive rehabilitation involves head-mounted displays (HMD), such as Oculus Rift/Quest or HTC Vive. Indeed, in a CAVE, if you look down at yourself, you will see your real body; on the contrary, if you wear an oculus you cannot see your body, but you feel immersed in the virtual environment you are interacting with, knowing for sure it is not so [21]. The HMD utilize high-resolution displays and motion-tracking sensors to transport users into immersive 3D environments, but it is also possible to use less expensive devices, like Samsung Gear VR and a smartphone, to enjoy the virtual contents.

Various types of content can be used in VR to evoke different responses from both psychological and physiological perspectives. These content options range from standard and 360° photos/videos to 3D scenarios [24]. The choice of content also depends on the level of interaction with the virtual environment. For example, when using 360° videos, which are more cost-effective in terms of time and resources [18,25], the user can only change the point of view from which they observe the scene and interact with buttons specially designed for navigating the environment or receiving information. On the other hand, with 3D scenarios, users can also interact with all the enabled 3D objects within the scene.

Input devices like handheld controllers, gloves, or hand-tracking sensors allow users to interact with the virtual world, fostering sensorimotor interactions and cognitive engagement. These VR environments, whether non-immersive or highly immersive, offer a flexible and customizable approach to cognitive rehabilitation, accommodating individual needs and preferences.

Two versions of a memory task utilizing a supermarket scenario, one in full immersion with a head-mounted display and the other with low immersion on a desktop, were administered to both young adults and senior individuals. The purpose was to assess age-related differences in the use of these two platforms. The results indicated that immersive VR proved to be more fatiguing for both groups. Older adults performed better with the desktop system and reported minimal side effects. No differences were found in the preference for one platform over the other [26]. Furthermore, immersive VR was well-received by the senior participants.

VR is grounded in several fundamental principles that underpin its efficacy as a tool for cognitive rehabilitation. These principles are crucial to understanding how VR can create immersive and interactive environments that facilitate cognitive recovery.

Immersion and presence are two fundamental aspects of VR that can profoundly impact the effectiveness of cognitive rehabilitation programs. Immersion is the technological capability of a system to create an illusion of reality for the user’s senses, making them an active part of the 3D environment [27]. A sensory-rich environment is provided, which fosters experiential learning. In VR for cognitive rehabilitation, immersion means that patients are not just spectators but active participants in their therapy. They can interact with virtual objects, practice real-life scenarios, and receive immediate feedback, all of which are invaluable for retraining cognitive functions. For individuals with cognitive impairments, immersion helps to bridge the gap between abstract cognitive exercises and practical, real-world challenges. For instance, a person recovering from a traumatic brain injury might use VR to navigate a virtual supermarket, practicing memory and decision-making skills in a context that closely mirrors their daily life. This kind of immersive, contextually relevant training can enhance the transfer of learned skills to real-world situations, a critical goal in cognitive rehabilitation [28,29]. A subjective correlate of immersion is the illusion of “being there”, or the sense of presence [21,30], which refers to the feeling of being physically and mentally present in the computer-generated environment, despite knowing it is not real. The greater the immersion, the greater the sense of presence [31]. Lo Priore and colleagues [32] developed the V-Store, where typical subjects could complete six sets of tasks involving categorical abstraction, programming, short-term memory, and attention. The study aimed to investigate the sense of presence in both immersive and non-immersive conditions. The results indicated a higher psychophysiological galvanic skin response in the immersive group compared to the non-immersive group.

In the context of cognitive rehabilitation, the sense of presence can be harnessed to engage patients more deeply in their therapeutic activities. When individuals feel immersed in a VR scenario, they are more likely to invest their attention and effort, leading to improved outcomes. For example, a stroke survivor participating in VR-based hand–eye coordination exercises may experience a heightened sense of presence, making them more motivated to complete their rehabilitation tasks. This increased engagement can accelerate the recovery process by encouraging consistent and enthusiastic participation in therapy.

Human behavior occurs within a dynamic relationship with the natural environment. Individuals do not passively perceive external stimuli, which are often multimodal and complex; instead, they actively interact with their surroundings. As a result, findings from laboratory settings may exhibit low ecological validity. Additionally, within the field of behavioral neuroscience, such findings may not accurately identify the neural mechanisms underpinning natural behavior. Virtual Reality (VR) could offer a valuable solution to this issue [33], as it allows for a high degree of experimental control while providing environments that closely resemble real-life settings [34]. It is worth noting that immersion and ecological validity are interconnected [33]. However, the ecological validity of VR for cognitive rehabilitation remains a critical point of consideration. While VR environments can be tailored to simulate real-world scenarios and challenges, the extent to which these simulations mimic the complexities of everyday life is a subject of ongoing debate. One of the key strengths of VR lies in its ability to provide controlled and repetitive exposure to stimuli and tasks, facilitating targeted cognitive training. However, the ecological validity of these exercises hinges on the accuracy of the virtual environments in replicating the challenges individuals encounter in their daily lives [35]. For instance, a VR driving simulator can help to retrain cognitive functions related to attention and decision-making, but its effectiveness relies on how closely it mirrors the unpredictability and complexity of actual road conditions. Researchers must strive to strike a balance between controlled training environments and ecologically valid scenarios to ensure that cognitive gains achieved in VR translate effectively into real-world functioning [35,36]. Moreover, assessing the ecological validity of VR-based cognitive rehabilitation necessitates a multifaceted approach. It involves not only the fidelity of the virtual environment but also the individual’s ability to generalize skills and strategies learned in VR to real-world settings. Long-term studies that track patients’ progress and functioning in their daily lives following VR rehabilitation are crucial for evaluating its ecological validity. Additionally, interdisciplinary collaboration between cognitive psychologists, VR developers, and healthcare professionals is vital to fine-tune VR applications, ensuring that they align with rehabilitation goals and the complexities of real-life challenges. While challenges remain, the continuous advancement of VR technology and research holds promise for enhancing the ecological validity of VR-based cognitive rehabilitation, offering individuals with cognitive impairments a more effective pathway toward functional recovery.

Embodiment and multisensory feedback play pivotal roles in the effectiveness of VR for cognitive rehabilitation. Embodiment refers to the sensation of one’s physical presence within a virtual environment [37,38]. In the context of cognitive rehabilitation, embodiment is crucial [27], as it can facilitate a profound connection between the patient and the virtual world. By embodying an avatar or virtual representation of themselves, individuals can engage in rehabilitative activities that closely mimic real-life situations. For example, a patient re-learning how to walk after a stroke can embody an avatar and experience the sensation of walking, allowing them to practice and regain motor skills in a controlled and immersive setting. This embodiment not only enhances motivation but also leverages the brain’s plasticity, potentially accelerating the recovery process [27]. Multisensory feedback is another key element in VR-based cognitive rehabilitation, and elderly people seem to benefit from multisensorial learning [39]. VR technology can provide patients with a rich array of sensory inputs, such as visual, auditory, and haptic feedback, making therapy more engaging and effective. For instance, a patient with cognitive impairments related to spatial awareness can benefit from a VR environment that provides multisensory cues about their surroundings, helping them to re-learn navigation skills. Furthermore, multisensory feedback can offer real-time information and reinforcement during therapy sessions, aiding individuals in understanding their progress and making necessary adjustments. The integration of multiple sensory modalities in VR not only enhances the overall rehabilitation experience but also provides a versatile platform to cater to a wide range of cognitive challenges.

Virtual Reality has been extensively applied in attention rehabilitation for individuals with attention deficits, for example, due to stroke [40] or traumatic brain injury [41]. VR environments, reflecting real routes and landscapes, can be designed to include stimuli and distractors, mimicking real-life situations where the user’s focus is challenged. In these environments, users may be required to perform tasks while ignoring distractions and focusing on targets, gradually improving their attentional control, not only into the VR scenario, but also in real life. For example, it is possible to do an activity where users navigate (or are navigated) through a virtual path along which they name the virtual objects encountered. Another example exercise involves a VR driving simulation, where the user must maintain concentration on the road while ignoring roadside billboards or sudden roadblocks, enhancing sustained attention abilities.

There are numerous applications of VR in cognitive–motor rehabilitation, and various studies have demonstrated the significant potential and benefits, including improvements in attention, of the use of VR in patients with MCI. Training activities using games designed for the Xbox 360 Kinect have shown benefits both in the short term and in the long term [42]. Virtual reality-based physical and cognitive (dual-task) training programs have led to significant improvements in dual-task gait performance, which may be attributed to enhancements in executive function [43]. Dual-task applications have improved motivation for rehabilitation and cognitive function [44].

The use of VR has also demonstrated benefits for chronic stroke patients. For instance, it has been observed that attention, spatial awareness, and depressive mood can be positively influenced by employing an Adaptive Conjunctive Cognitive Training (ACCT) in virtual reality [45]. The utilization of the Reh@City v2.0 app, a simulator for daily living activities, has revealed improvements in various cognitive domains in everyday life [22].

VR is a potent tool for memory assessment and rehabilitation, addressing both short-term and long-term memory impairments. For short-term memory deficits, VR tasks might include exercises where users must remember a series of objects or locations in a virtual environment, training their working memory. Long-term memory can be targeted by immersing users in memorable virtual scenarios. For instance, individuals with Alzheimer’s disease can revisit familiar places or events from their past through VR, potentially improving autobiographical memory recall.

Virtual reality can be effectively used for both the assessment of memory impairments and memory rehabilitation. In memory assessment, the use of virtual reality can provide more comprehensive, ecologically valid, and controlled evaluations of memory than standardized tests can offer. It can also more effectively guide rehabilitation efforts tailored to the specific impairments of individual patients. Moreover, VR rehabilitation promotes procedural learning in people with memory impairments, and this improvement carries over to the real world [46,47].

While current VR rehabilitation solutions for aging and neurodegenerative diseases are still in their early stages of development, the ability to engage with body-related information, manipulate objects, receive environmental stimuli, and incorporate multisensory cues makes virtual reality one of the most promising options for spatial memory rehabilitation in aging populations [48]. Furthermore, some studies have shown that VR training, on one hand, can lead to an improvement, or at the very least, the maintenance, of cognitive functions [22,45,49]. On the other hand, it enhances motivation for rehabilitation and cognitive function [44] and is both feasible and well-tolerated by participants [50].

VR-based interventions are particularly effective for rehabilitating EFs, such as problem-solving, planning, and decision making [51]. Users can engage in complex, real-world scenarios that demand strategic thinking. The assessment of Executive Functions (EFs) through VR applications typically involves daily-living skill tasks. Indeed, research has established a specific relationship between EFs and activities in daily living [52,53,54]. The virtual supermarket environment is the most commonly utilized, as shopping is considered an essential skill for everyday life. Supermarket and grocery scenarios [55,56,57,58,59], as well as VR versions of the Multiple Errands Test, were developed for this purpose [60,61]. Furthermore, VR environments replicating city locations, apartments [62,63,64], office scenarios [65], and kitchens for cooking tasks [66] have been created. In these scenarios, individuals must follow recipes, manage time, and make decisions about ingredient quantities, thereby exercising their planning and problem-solving abilities.

Additionally, VR-based neuropsychological tests can assess EFs in a more ecologically valid manner and may complement traditional paper-and-pencil neuropsychological assessments or enhance their psychometric validity [7,55,61,62,66,67,68,69].

Regarding the rehabilitation of executive deficits, most studies have developed scenarios based on real-life situations, in which patients perform daily living skills. A positive correlation between standard cognitive and functional measures was found in a task simulating a fire evacuation, administered to participants with MCI, mild AD, and healthy controls [64]. The use of daily living scenarios appeared to have positive effects in rehabilitating and maintaining cognitive functions in patients with stroke [70], AD [51,71,72], various types of dementia [73], and MCI [71,72,74].

Some studies have explored non-daily living virtual environments. For instance, Huang [75] combined exergaming (Fruit Ninja) with VR. Adults and older individuals (non-clinical groups) participated in a 4-week training program, showing improvements in inhibition and task switching, mediated by the sense of presence. Programs that combine VR-based physical and cognitive training have shown effectiveness not only in cognitive function but also in IADL (Instrumental Activities of Daily Living) standard measures in patients with MCI [9,76]. Another study proposed an exergame platform, the Active Brain Trainer, focused on EFs, and designed for patients with acquired brain injury (ABI) in the chronic phase. This feasibility study found both neuropsychological and functional improvements.

A recent review [11] evaluated the effectiveness of VR programs on EFs in patients with MCI. Fourteen randomized controlled trials (RCTs) were included in the study: seven of them used semi-immersive VR, four used fully immersive VR, and three used non-immersive VR. The authors suggested a positive effect of VR applications on cognitive flexibility (especially with semi-immersive and non-immersive VR), global cognitive function, attention, and short-term memory (especially with non-immersive VR) compared to the control groups.

In a recent study by Araújo et al. [77], the effects of a single session of VR, augmented reality, and neuro-functional physiotherapy on EFs and postural control in individuals with Parkinson’s disease without cognitive impairments were compared. The sessions lasted 50 min each, with a 7-day interval between them. All three intervention modalities improved both EFs and postural control.

Spatial cognition and navigation abilities are vital for everyday tasks, and VR can provide tailored interventions for individuals with deficits in this domain. Users can practice wayfinding in VR environments, like virtual cities or mazes, improving their spatial orientation and navigation skills. The literature on this topic was reviewed with a focus on patients presenting with various neuropsychological diseases. The results underscored the potential of navigation tasks in virtual environments to enhance navigation and orientation skills in patients with spatial memory disorders [78]. For individuals with brain injuries impacting spatial skills, exercises involving map reading, virtual treasure hunts, or even architectural design tasks can promote spatial cognition recovery. Currently, the rehabilitation of navigation ability and spatial orientation after brain damage is generally focused on training within the rehabilitation hospital or in the patient’s home as part of common physiotherapy and occupational therapy sessions.

The development of virtual reality (VR) applications may enable better generalization and the precise assessment and rehabilitation of spatial skills [79,80]. Studies with stroke patients who compared cognitive test results before and after VR training involving navigation and orientation in virtual environments have shown improvements in several cognitive domains (such as executive and visuospatial skills, language, attention, and memory skills) [22,81,82]. A controlled study with community-dwelling chronic stroke and cognitively impaired stroke patients who performed 30 min of daily exercise for 6 weeks showed significant improvements in attention, spatial awareness, and generalized cognitive functioning in the experimental group compared to the control group, who solved standard cognitive tasks at home for an equivalent period of time [45].

In the context of neurodegenerative diseases, a study was conducted with patients at risk of developing Alzheimer’s disease (AD) who performed worse than their age-matched controls, making it a potential tool for diagnosing disease development [83]. Additionally, AD patients showed impairments in VR tasks designed to study navigation skills; however, their performance could not be used to predict the degree of disorientation they might experience in the real world [84]. In one case study, a man at the onset of AD was enrolled in a cognitive treatment program based on spatial navigation in a VR environment. The results showed that the participant learned to navigate perfectly towards the desired goals in the virtual environment over the course of the training program. Furthermore, subjective feedback from his primary caregiver indicated that his ability to orient himself while driving improved significantly, and he appreciated the cognitive improvement in his daily life at home. These findings suggest that VR treatments could benefit other people with AD [85].

VR-based language rehabilitation is beneficial for individuals with aphasia or language impairments. In VR environments, users can engage in interactive conversations with virtual characters, practicing their language comprehension and expression.

Some studies have investigated virtual reality in neurorehabilitation with the aim of analyzing its effects on specific cognitive domains, for example, memory, attention, executive functions, language, and visuospatial abilities [13,86]. The results relating to language are conflicting; in some cases, there were no significant improvements after rehabilitation based on virtual reality [13], and in other studies improvements were observed in specific areas, for example, in verbal fluency [86].

This inhomogeneity of results is confirmed by another study [87], which demonstrated a borderline-positive clinical effect of VR for the severity of the language disorder compared to conventional rehabilitation therapy, while no effects of VR were found on functional communication, word search, and on repetition.

Giachero et al. [89] conducted a study in which thirty-six people with chronic aphasia (PWA) were randomly assigned to two groups. The VR group underwent conversational therapy while observing daily life in VR, while the control group was trained in a conventional environment without VR support. Within-group comparisons showed significant improvement in several language tasks only in the VR group. Significant gains, after the treatment, were also found in the VR group in various psychological dimensions, for example, self-esteem and emotional and mood state.

In a quasi-randomized study on a group of people with aphasia, a platform called Eva Park was tested, which contained a number of functional and fantastic places and allowed for interactive communication between multiple users. After a 5-week training program, significant improvements in functional communication were noted; there was excellent compliance with the intervention, with no participant lost to follow-up [90].

Marshall et al. [91] investigated the possibility of providing group social support to people with aphasia via a multi-user virtual reality platform with the aim of promoting well-being and communication success. The feasibility results showed that the recruitment objective was achieved with excellent participant compliance, while no significant change was observed in any of the outcome measures (well-being, communication, social connection and quality of life). Overall, however, the data suggested that a broader trial of remote group support, using virtual reality, would be worthwhile.

Regarding the use of VR in the assessment of acquired language disorders, the study by Wall et al. [92] shows preliminary evidence that the VR cognitive assessment app for aphasia is a feasible cognitive assessment for stroke survivors with and without aphasia.

There are currently no VR applications that have been designed to assess or treat cognitive-communication disorders (CCDs) following traumatic brain injury (TBI). A study of Brassel et al. aimed to explore the views of speech–language pathologists (SLPs) who work with people who have a TBI to generate ideas and considerations for using VR in rehabilitation for CCDs [93]. Useful suggestions emerged from the thematic analysis to overcome possible obstacles to the use of VR, and the idea also emerged that VR could be a very useful tool for improving clinical practice.

These interactions can be customized to target specific language deficits, such as naming difficulties. Furthermore, VR environments can simulate real-life scenarios like a grocery store or a restaurant, enabling users to practice functional language skills in context.

VR-based programs have emerged as groundbreaking approaches for improving the activities of daily living (ADL) and the instrumental activities of daily living (IADL) [56,74,94], especially for individuals with various mental disorders such as MCI and AD [72]. These applications can be personalized according to the strengths and weaknesses of the patients, immersing them in realistic virtual environments where they can practice a wide range of tasks, from basic self-care routines to more complex activities like grocery shopping or managing finances. VR therapy not only enhances physical and cognitive skills but also fosters a sense of independence and confidence in individuals striving to regain control over their daily lives.

Only a few studies have developed programs with scenarios for daily living to re-learn specific functional living skills and evaluate the impact that this re-learning has on actual skills in natural environments [28,29,71,95,96,97,98,99]. The results of these studies will be described in Section 4. However, some general indications can be drawn:

• The utility of familiarization training before starting real VR training, especially for older people who are less familiar with even simple technological devices.
• Virtual training (VT) should have a sufficient duration, of at least a few weeks, to allow for the re-learning of functional living skills.
• The development of the virtual application should include not only feedback but also error corrections and prompts to help patients to produce the correct responses.
• VT variable scores and/or standard neuropsychological and quality of life measures should be included, as well as questionnaires on agreement, acceptability, and negative side effects.

In the virtual assessment of everyday functions, a study by Allain et al. [100] used a non-immersive virtual coffee machine for a coffee-making task with patients with AD. The authors aimed to compare virtual and real tasks, as well as to find links between the virtual task and global cognition, executive functions, and IADL (as reported by caregivers). The findings showed correlations between the virtual task and all the cognitive and IADL measures, as well as the ability of the virtual task to predict the actual skill.

VR-based interventions excel in addressing multiple cognitive domains simultaneously. For example, a VR-based shopping scenario can require users to plan their shopping list (EFs), navigate through the store (spatial skills), maintain attention to the task (attention), recall item names (memory), and engage in conversations with store attendants (language). This holistic approach is particularly valuable for individuals with complex cognitive deficits, promoting comprehensive cognitive rehabilitation. VR technology’s adaptability and versatility make it a valuable tool for creating tailored interventions that cater to the specific cognitive needs of each individual, fostering a more inclusive and effective approach to cognitive rehabilitation.

The intersection of VR and human psychology has also been explored. Kim et al. [102] analyzed the stress-alleviating potential of VR by conducting an open randomized crossover trial on individuals experiencing high stress levels. Their findings reveal that exposure to VR not only significantly reduces stress but also induces positive changes in physiological parameters, particularly heart rate variability. The study suggests that immersive VR experiences have promising applications in stress management interventions. Complementing this, Collins et al. [103] contributed to the discourse by proposing a methodology to measure cognitive load and insight in VR learning contexts. By employing a mixed-methods approach, combining self-reporting measures and physiological data, they offer a comprehensive understanding of cognitive processes in VR. This integrated approach sheds light on the intricate relationship between stress reduction, emotional load, and cognitive processes in VR environments, paving the way for more refined and effective applications in areas such as stress management and virtual learning experiences.

Multisensory feedback, particularly in the context of integrating VR with biofeedback mechanisms such as electroencephalogram (EEG) and electrocardiogram (ECG), represents a groundbreaking approach to enhance user experience and therapeutic interventions. Studies exploring the synergy between VR and biofeedback have demonstrated promising outcomes in various fields [104]. For instance, in the realm of rehabilitation, VR coupled with biofeedback can facilitate motor skill development and cognitive rehabilitation by providing immersive and responsive environments [105]. The integration of EEG and ECG data into VR experiences not only enhances the realism and interactivity of virtual environments but also provides valuable insights into users’ cognitive and emotional states. This holistic approach to feedback systems not only elevates the immersive quality of VR but also holds great potential for advancing fields such as healthcare, education, and mental well-being.