Demystifying neurotourism: An interdisciplinary approach and research agenda

The academic discourse surrounding tourism's interdisciplinary approach has long piqued the interest of the scholarly community. More recently, attention has pivoted towards the intersection of neuroscience and neuromarketing within the realm of tourism, giving rise to the concept of “neurotourism”. This emergence requires a comprehensive elucidation of the relevance of neuromarketing and neuroscience to the field of tourism, thereby addressing the imperative to bridge existing knowledge gaps. In light of this, the present paper endeavours to fulfil this objective by synthesizing global research in this domain. The study adopts an interdisciplinary approach, employing a hybrid systematic review methodology that encompasses a literature review encompassing nine key indicators and a bibliometric analysis through co-word analysis of author keywords. In total, our investigation unearthed 45 papers from Scopus, each exploring the application of neuroscience and neuromarketing theories and methods within the context of tourism. Among these, three papers delve into the concept of neurotourism. In this paper, we underscore the deep connection between neuroscience, neuroscientific methodologies, and neuromarketing within the realm of tourism research. The outcomes of this research significantly enhance our comprehension of the current state of neurotourism research, revealing both existing voids and emerging areas of interest. Furthermore, this study introduces a pioneering methodological approach, fusing Scival topic prominence and hybrid systematic review techniques into bibliometric analysis. Ultimately, our findings illuminate a notable research lacuna, presenting a fertile terrain for prospective investigations. Additionally, we deliberate on current trends and propose directions for future research within the neurotourism landscape.


Introduction 1.The multidisciplinary realm of tourism and the interdisciplinary of neuroscience
Tourism is considered a multidisciplinary field (Marcano Anés, 2020).Tourism encompasses a wide range of interconnected aspects, including economics, geography, sociology, psychology, marketing, environmental science, and more.Researchers and practitioners in the field of tourism draw upon knowledge and methodologies from these diverse disciplines to gain a comprehensive understanding of the various facets of tourism.Therefore, tourism is currently understood as a multidisciplinary area (Marcano Anés, 2020).However, recently researchers have been pleading for more than a multidisciplinary approach, and urging for interdisciplinary approach (Okumus et al., 2018).Oviedo-García (2016) argues that only through such an approach can tourism be conceived as a common scientific object, in which knowledge is co-produced.
One of the recent knowledge domains that have been incorporated into tourism studies is neuroscience.Neuroscience studies the nervous system through the manifestations of intellectual activity, allowing researchers to understand emotions, feelings, and affections (Bear et al., 2015).Originated within the field of health sciences, this discipline gained great notoriety throughout the last century.Neuroscience is an interdisciplinary field that encompasses the study of the nervous system, including the brain, spinal cord, and peripheral nerves.It draws upon and integrates knowledge and methodologies from various disciplines, such as biology, psychology, chemistry, physics, computer science, and more (Sabbatini & Cardoso, 2002).Within the last decade, neuroscience reinforced its interdisciplinary character; for instance, it has been combined with cognitive science, giving birth to the cognitive neuroscience.This field combines principles and methods from neuroscience, psychology, and sometimes other related disciplines to investigate the neural basis of cognitive processes and behaviour studying the neural substrates of human cognition, attention, memory, emotion, language, motion and so on" (Ma et al., 2014(Ma et al., , p.1637)).Subsequently, neuroscience has been applied to (or combined with) other fields of study, such as psychology -giving rise to neuropsychology -and economics -giving rise to neuroeconomics.These new disciplines applied neuroscientific methods to better understand the processes behind human behaviour and decisions, as did the social sciences (Lehmann, 2020;Xu & Wu, 2018).These integrations have strengthened an interdisciplinary nature to the neuroscience field.

The interdisciplinary nature of neuromarketing and neuroscience
Neuromarketing is a specialized branch of marketing that leverages findings from neuroscience to better understand consumer behaviour and improve marketing strategies.Neuromarketing is an interdisciplinary field that aims to understand consumers' preferences, motivations, expectations, behaviour, and decision-making process, through the study of brain mechanisms (Pourfakhimi et al., 2019;Lew, 2020;Scott, 2020;Singh, 2020;Li et al., 2022).It focuses on the study of how marketing stimuli affect the brain, and subsequently, consumer behaviour (Alsakaa et al., 2019).In this context, neuromarketing studies attempt to explain, for instance, the success factors of advertising campaigns, and thereby seeks to improve marketing strategies (Santos, Moutinho et al., 2012;Santos, Seixas et al., 2012).Furthermore, according to Lim (2018, p. 205), the potential of neuromarketing as a research field is substantial, as its discoveries can establish fresh foundations for the creation of new marketing theories or enhance existing theories within marketing and related disciplines (Liu et al., 2023).
A particularly promising subfield of neuromarketing is consumer neuroscience, refers to the application of neuroscience principles and methods and involves the application of neuroscientific methods to understand how the brain responds to marketing incentives.Consumer neuroscience is an interdisciplinary field, a branch of neuroscience that applies neuroscientific methods to study consumer behaviour, decision-making, and preferences in the context of marketing and consumer research (Cardoso et al., 2022).These methods include tools and techniques to record, map and measure brain and neural activity during a certain behaviour, and in response to certain stimuli (Lopes et al., 2017).Lim (2018) classifies these methods into three broad categories: 1. neuroscientific tools and techniques that record neural activity inside the brain (which include those that record electromagnetic activity, such as electroencephalography (EEG), and those that measure metabolic activity, such as functional magnetic resonance (fMRI), 2. neuroscientific tools and techniques that record neural activity outside the brain (e.g., electrocardiography, eye-tracking (ET), etc.); and 3. neuroscientific methods that manipulate neural activity (e.g., transcranial magnetic stimulation (TMS).
The physiological signals observed by these methods, in turn, are divided by Chanel et al. (2006) into two categories: those originating from the peripheral nervous system (e.g., heart rate (HR), ElectroMyogram (EMG), Galvanic Skin Response (GSR), and those originating from the central nervous system (e.g., neural electroactivity, which is observed by EEGs).Recent studies, such as Singh et al. (2019), Alsakaa et al. (2019) and Cardoso et al. (2022), reveal that the most frequently used neuroscience methods in neuromarketing research are neuroimaging and psychophysiological measures, such as functional magnetic resonance imaging (fMRI) and eye tracking (ET).

The intersection of neuroscience and neuromarketing, both interdisciplinary fields, within the multidisciplinary realm of tourism.
With neuromarketing research techniques increasingly available and affordable, tourism scholars also started adopting them.In tourism studies, neuroscientific methods have a particularly promising potential.One of the main advantages of studying consumers' behaviours and decisions through the direct observation of their biometric signals, rather than by self-report methods (i.e., asking how they feel, how they would act, etc.), is overcoming the limitations of the latter.Human behaviour is affected by subjective, and often unconscious variables, which generate potential biases on marketing research methods that solely rely on what participants say about their own motivations, impressions, associations, images, etc.This is especially true in tourism research, as the tourism product, as an experience provided by an amalgam of more specific products, services, and non-industrial elements (Middleton et al., 2009), is particularly subjective.Moreover, a trip is usually a high involvement consumption decision, as it not only comprises many other smaller decisions (regarding accommodation, transport, attractions, etc.), but also a relatively high financial and time investment (Ritchie & Crouch, 2003).Therefore, tourists' choices are amongst the most complex, subjective, and emotional consumption decisions.Consequently, it could be argued that the mechanisms that explain the effectiveness of destinations' and tourism services' marketing efforts are equally complex and subjective, which further limits the possibilities of fully understanding them through self-report methods.
This complexity is further increased when considering that the potential stimuli that affect destination image and travel decisions are not limited to the places' official initiatives but include everything from the news to popular media (Cardoso et al., 2019;Iwashita, 2008;Kim & Richardson, 2003).In this context, neuroscientific techniques allow tourism researchers to better understand how tourists make decisions, why they behave in certain ways and how they react to stimuli related to destinations and tourism products.The creation and induction of tourism product images, as well as the image of the tourism destination, are areas of marketing research, just as the decision-making processes of tourists and the processing of information in the tourist's memory also fall within the domain of marketing (Cardoso et al., 2019).In this scenario, the application of neuroscientific methods falls within the purview of interdisciplinary fields such as cognitive neuroscience within the broader domain of neuroscience, as well as consumer neuroscience within the scope of neuromarketing.These fields amalgamate principles and techniques from neuroscience, psychology, marketing, and related disciplines.So, these two interconnected interdisciplinary fields, neurosciences and neuromarketing, cannot be separated in the case of tourism with a multidisciplinary domain.
Within the last decade, several studies have combined tourism research problems with neuroscience theories or methods (Halkiopoulos et al., 2022), aiming to understand the behaviour and choices of travel consumers (Astolfi et al., 2009;Smidts et al., 2014).The bibliometric study carried out by Cardoso et al. (2022) in neuromarketing field reveals that consumer neuroscience is applied to tourism studies on, among other areas (e.g., product branding, cinema, journalism, and television), consumer research within the hotel industry.In this context, neuroscientific methods are employed to examine aspects of hotel experience such as human-robot interaction (Chung et al., 2020).They are also employed to understand the effectiveness of marketing efforts, such as subliminal messaging in hotel advertising (Hsu & Chen, 2020).This application of neuroscientific methods to tourism research and practice has been referred to as neurotourism.When we contemplate the concept of neurotourism and grasp the full extent of its interdisciplinary nature, we empower the adoption of a deliberate and purposeful interdisciplinary approach to the study of tourism.This approach aligns with the perspective defended by Okumus et al. (2018) and Oviedo-García (2016), the interdisciplinary approach in tourism.

The absence of uniformity regarding the concept of neurotourism
The word "neurotourism" was introduced by Ma et al. (2014), according to whom, "Neurotourism mainly explores the neural mechanism underlying the tourists' behaviours when they are travelling" (p.1638).The authors' overriding idea is that tourism management should exploit the advantages of neuroscience to make more informed marketing decisions.In a more academic perspective, authors like Tosun et al. (2016, p.19) describe neurotourism as "a discipline that neuroscience and tourism establish through working together".Similar definitions are provided by other theoretical studies (e.g., Giudici et al. 2017).Panyık and Gonçalvez (2017, p.321), on the other hand, are the first authors to argue that neurotourism "goes beyond being merely an applied neuroscience tool in tourism management (…) as Augmented Reality and Virtual Reality technologies, using wearables, are likely to be only transitional in the delivery of the tourist experience".In this sense, the authors argue that neuroscientific methods are increasingly being used in the delivery of the tourist experience itself, that virtual and augmented reality will be each time more ingrained in such experiences, and even that scenarios like totally artificially created memories are in the realm of possibilities.
It should be noted that although Panyık and Gonçalvez (2017) adopt the premise that virtual and augmented reality are neuroscientific methods, considering the extant literature on the topic, they are not.They are technologies that can be used together with neuroscience techniques, either to deliver experiences for its own sake, or to induce experiences as part of an experimental study.Another instance can be found in the systematic review conducted by Al-Nafjan et al. (2023).In their attempt to explore the neurotourism concept by searching for keywords in the WoS Core Collection related to neuroscientific methods applied to tourism, they include the term "artificial intelligence (AI)".Nevertheless, it's important to note that AI is not a neuroscientific method.AI aids neuroscience in processing extensive and intricate datasets, such as the results generated by neuroscientific techniques, to discern patterns, as argued by Savage (2019).This misconception highlights the broader issue of imprecise definitions and the scarcity of academic research in the field of neurotourism.

Research gap and objective
A brief overview of the literature on neurotourism shows that the concept is not yet sufficiently well defined.There is a lack of consistency in definitions and, as concluded by a recent literature review (Moral-Moral, 2021), the extant literature is limited.Moreover, despite the initial efforts found in the extant literature, much is still to be done and a systematic interdisciplinary approach in tourism field is still in its early days.This also applies to the general research on the neuroscience-tourism nexus (which does not necessarily call it "neurotourism").
Regarding the inconsistency in definitions, as previously discussed, some authors narrowly define neurotourism as an academic discipline (e.g., Tosun et al., 2016;Giudici et al., 2017), while others envision it as the future of tourism experiences (Panyık & Gonçalvez, 2017).Some argue that it should encompass not only the study of tourism consumers' emotions and decisions but also those of tourism stakeholders (Araújo, Kastenholz, & Santos, 2017), a dimension not explored in any known study by the authors.In the literature on neuromarketing applied to tourism, studies often simplify it as a tool for destination marketing (Palmatier et al., 2017) or marketing research (Šerić et al., 2015).
Concerning the limited research, as addressed in more detail in this study's results, not only very few studies address the topic, but must of them are literature reviews.The most recent study by Li et al. (2023a), is the first literature review that discusses and adopts an interdisciplinary view of neuroscience and neuromarketing applied to tourism presenting methods (including neuroscientific methods), theories and concepts.However, most of the studies included in this literature review, although they derive from psychology, marketing, neuromarketing, neuroscience, among other scientific areas, are not yet empirically applied to tourism.The great contribution of this study lies in bringing together theories and methods from various scientific areas that can be applied to tourism.Actually, the works that employ such theories to empirical tourism research are rare, and those that employ neuroscience methods per se, are limited to a few.This scenario is exacerbated by the multidisciplinary nature of the neurotourism concept Giudici et al., (2017), and by the evolving nature of both neuroscience and tourism bodies of literature.This results in a lack of standardised metrics, which in turn further increase inconsistencies regarding the concept and the phenomena it addresses.
Moreover, although an increase in the number of studies that relate tourism and neuromarketing to other areas of knowledge has been noticed (Halkiopoulos et al., 2022), the interdisciplinary aspect of such studies has not yet been well defined.This state-of-the-art on neuroscience and tourism reinforces Sop's (2021) urge for further research, namely descriptive studies with a focus on neurotourism or neuroscientific studies, to explore research gaps, current perspectives, and emerging trends.It also reinforces the need identified by Leiper (2000), Koseoglu et al. (2016), and Wang et al. (2020), who call for a truly multidisciplinary approach on tourism and neurosciences.
Furthermore, considering the novelty of this research domain, it is crucial to identify emerging themes and prospective research avenues stemming from empirical inquiries.In this context, performing a systematic literature review becomes essential, and the identification of emerging subjects is most effectively achieved through the utilization of Scival topic prominence -a dependable metric, as detailed by Cardoso et al. (2020).As posited by this author, bibliometric studies that amalgamate systematic and conventional literature reviews are well-suited for mapping emerging topics.In this context, Koseoglu (2016) also contends that bibliometric studies illuminate previously unrecognized patterns within research fields or disciplines, assisting researchers in formulating theories and examining hypotheses.To our knowledge, the study conducted by Al-Nafjan et al. (2023) is the sole instance of a systematic review applied to the field of neurotourism.Nonetheless, the keyword search parameters revolved around "tourism", "neuroscience", and "artificial intelligence", with the substitution of "neuroscience, neuromarketing, and neuroscientific" by terms like "eye tracking", "skin conductance", "EEG", "electroencephalography", "heart rate", "fMRI", and "emotion" or "affective computing".So, this process unveils an incongruity.On one hand, it arises from the fact that artificial intelligence does not qualify as a neuroscientific method, and on the other hand, the omission of neuroscience and neuromarketing prevents the holistic interdisciplinary nature of the neurotourism concept from emerging.To address this methodological research gap, our strategy encompasses a hybrid systematic review employing a comprehensive set of search keywords within Scopus.In order to demystify neurotourism, the primary objective of this paper is to assess the present state of neurotourism and the integration of neuroscience and neuromarketing within the domain of tourism research, with a specific focus on the multidisciplinary aspect of the available literature.In this context, the study seeks to answer the following research questions: "What is the extent and scope of the concept of neurotourism?"and" "What is the relationship of neurotourism with neuroscience and neuromarketing?".To answer these questions, a hybrid systematic review, comprising a variableoriented literature review and relational bibliometric co-word analysis was employed, relying on the body of literature available on the Scopus database.The methodological steps are described in more detail in the next chapter.

Research methodology
To address research questions, the present study adopted a hybrid review approach, which includes bibliometric and qualitative methods.Bibliometric methods were employed because they are an effective tool to highlight unknown patterns in specific research fields (Koseoglu et al., 2016), and in doing so, describe their development and identify predominant themes over time (Rojas-Lamorena et al., 2022).Additionally, analogous to other research fields, this sort of analysis has been employed in recent tourism and neuromarketing studies, where it has been growing in importance (Cardoso et al., 2020;Hall et al., 2004).However, when used alone, bibliometric analysis can lead to excessively datadriven approaches, leading researchers to miss more nuanced aspects of the analysed literature.More specifically, Paul and Criado (2020) argue that purely bibliometric studies can lead to concentration on authors and keywords rather than on theories and methods.To mitigate this risk, the bibliometric analysis was employed in conjunction with the variable-oriented qualitative literature review.
Literature reviews encompass several variations.In this context, Koseoglu et al. (2016) and Cardoso et al. (2022) state that review techniques include structured literature reviews, systematic literature review, and meta-analyses/reviews, all of which are called traditional review methods.Systematic reviews, in particular, can be domain-based, theory-based, method-based (Palmatier et al., 2018), metaanalytical (Paul & Criado, 2020), or meta-systematic (Lim & Weissmann, 2023).The present review, naturally, falls under the first category, as it concentrates on the state-of-the art of an area of study, namely, neurotourism, neuroscience and neuromarketing applied to tourism, hospitality, and travel.Domain-based reviews, however, also include a variety of sub-forms, which according to Paul and Criado (2000), include: structured reviews (e.g., Canabal & White III, 2008), framework-based reviews (e.g., Lim et al., 2021), bibliometric reviews (e.g., Hall et al., 2004), hybrid or integrated reviews (e.g., Chakma et al., 2021), and reviews aiming for theory development (Paul & Mas, 2019).Amongst those, the present study can be classified as a hybrid bibliometric study, as it integrates a bibliometric review and a systematic variable-orientated review.In addition, the relational bibliometric technique of coword analysis is also used.This combination of review approaches helped mitigate the issues normally associated with purely bibliometric reviews and allowed the achievement of more nuanced and rich results.

Research protocol and systematic review procedures
Considering the problematics and approach of this study (i.e., the lack of a consistent definition for neurotourism, and the lack of knowledge on the interdisciplinarity between neurotourism, neuroscience and neuromarketing applied to the tourism sector) the following specific objectives were adopted: 1) To determine the extent and scope of the neurotourism concept.
2) To identify the most prominent topics within neurotourism, and neuroscience and neuromarketing applied to tourism, hospitality, and travel.3) To determine the structure and dynamics of neurotourism, neuroscience and neuromarketing applied to tourism, hospitality, and travel.

SPAR-4-SLR protocol -Stage 1: Assembling
The first step consisted of defining the research domain -neurotourism and neuroscience and neuromarketing applied to tourism -the research questions and the research objectives.Next, Scopus database was chosen as a data source, as it is the largest top-quality abstract and citation dataset of peer reviewed literature (Alsharif et al., 2020;Cardoso et al., 2020).Regarding the research mechanism, the material acquisition, the period and keywords search, a two-step approach was adopted.In this context, before advancing to the Scopus database, the keywords were fine-tuned using the Elicit platform (https://elicit.org).The platform was selected because it performs a semantic search for words, which allow researchers to eliminate the screening conflicts and more accurately determine the search keywords.The two co-authors involved in this step both adopted the strategy of carrying out the first search with "neurotourism and neuro-tourism", followed by the search with "neuromarketing and neuroscience applied to tourism".This initial search generated a set of works related to "neuropsychology, hotel, hospitality, destination, and travel".So, this first search was confirmed by the literature review.The term "neurotourism" is also written as "neuro-tourism", and thus, we have included both spellings in our search in Scopus.The word "Neuropsy*" aims to establish a connection between psychology (a branch of neuroscience), neuroscience, and neuromarketing.This connection is warranted for two main reasons.Firstly, it encompasses neuropsychological methods and data utilized in neuroscience research.Secondly, it holds relevance in the context of neuromarketing, where it finds applications in understanding consumer behaviour, assessing the effectiveness of advertising, and enhancing product design.In the application of neuroscientific methods, Galvanic Skin Response (GSR), which is also referred to as Electrodermal Activity (EDA) or Skin Conductance Response (SCR), was employed in all three variations to minimize potential bias in the screening process.The keywords used in the search in Scopus are identified in Figure 2.
The data collection procedures took place on September 26 th , 2023.The Scopus search was conducted in English by two experts in systematic review analysis.The adopted parameters were: Keyword AND (LIMIT-TO (EXACTEDKEYWORD) + IN TITLE OR ABSTRACT OR KEYWORDS + ONLY ARTICLES.The database containing the retrieved articles was downloaded in Bibtex format from Scopus, then R Studio software version 1.2.5042 was used to eliminate duplicates and create a unified file.Upon the finalisation of the first review cycle, a total of 909 articles were downloaded.
The next step consisted of a second screening procedure, performed through a qualitative approach, in which each paper was reviewed by the two researchers involved.Namely, the researchers scanned the titles, abstracts, and authors' keywords, which allowed them to exclude 864 papers that were unrelated to the topics of interest.The excluded articles were related to neurological diseases, memory disorders, automotive industry, and the majority of those that included the word "destination" were related to the destination memory of Alzheimer's disease patients.In the majority of instances, the term "travel" was associated with mental travel and emotion mental travel, while "emotions" were linked to time travel and episodic memory, with additional connections to Alzheimer's disease and pharmaceutical use.Conversely, the term "hotel" primarily pertained to lodging arrangements within the context of neuroscience or neuropsychology events.Excluded from consideration were papers related to technology (including virtual reality and machine learning), neurology, brain function, and brain regions.
Finally, the database was later exported to R Bibliometrix 4.3.1, which was used for the network analysis, as previously done by Cardoso's et al. (2021;2022).The final database includes 45 articles, published from 2009 to September 2023.As mentioned by Paul et al. (2021), if a small volume of articles is found and they do not include any systematic literature review, the domain is suitable to the subjected to such analysis.Therefore, the results of the screening process indicate that the topic is indeed suitable for this analysis.

SPAR-4-SLR protocol -Stage 2: Arranging
In the first sub-stage of Stage 2, organisation, the 45 articles of the database were homogenized, and an excel file was created.Moreover, the Scival topic prominence and prominence percentile (SciPP) data were retrieved manually from Scopus database as previously done by Cardoso's et al. (2021;2022) andLima Santos´s, et al. (2020), as Scopus does not provide this data in the output.In the second sub-stage of Stage 2, Purification, analysis method criteria were defined for each of the research objectives within the hybrid review approach, following the method proposed by Cardoso et al. (2022).

SPAR-4-SLR protocol -Stage 3: Accessing
Regarding the first sub-stage of Stage 3, evaluation, the procedures employed to achieve each specific objective are summarised in Figure 3.The two first objectives were achieved through the authors' keyword analysis, in which their network structure was performed considering 5-419 nodes with a minimum of two edges.To fulfil the third objective, to determine the structure and dynamics of neurotourism, neuroscience, and neuromarketing applied to tourism and travel, a qualitative approach was adopted, which involved carefully and integrally reading each of the 27 articles within the database.Analogous to previous studies (Cardoso et al., 2022;Mudarra-Fernández et al., 2018;Snyder, 2019), a variable-oriented literature review with nine indicators was employed.This technique was selected because, as argued by Snyder (2019, p.334), "it aims to identify all empirical evidence that fits prespecified inclusion criteria to answer a particular research question or hypothesis", which fits the purposes of the present study.The nine variables used in the variable-oriented literature review were based on the study carried out by Cardoso et al. (2022), which aimed to map the scientific performance of neuromarketing and identifying research gaps and emerging topics within the field.

Figure 3. Summary of research objectives, indicators and bibliometric technics used
Regarding the reporting, presentation and discussion sub-stage, the authors' key-word analysis is graphically represented in Figure 4, and the results of the variable-oriented literature review are exhaustively described in Appendix A. In the next section, these results are discussed in detail.

Neurotourism's scope, prominent topics, and applications of neuroscience and neuromarketing
To determine the extent and scope of the key areas of interest in the domain of neuroscience and neuromarketing as applied to research in tourism, hospitality, and travel spanning from 2009 to October 2023, an analysis of the author-keywords network structure was conducted.This analysis involved the consideration of 50 words, clustering them into 5 groups, and applying 3 labels with a label size of 0.3, utilizing the Louvain Clustering Algorithm.
In relation to the initial and second aims of this study, which involve identifying the prevailing themes in the realms of neurotourism, neuroscience, and neuromarketing as they relate to tourism, hospitality, and travel, the analysis reveals the emergence of two primary clusters linked to the field of tourism, as illustrated in Figure 4.
The cluster with the most substantial presence is "neuromarketing", which is linked to "neuroscience".This is followed by "psychology", which is associated with "eye tracking".Notably, both the "neuromarketing" and "neuroscience" clusters exhibit direct connections with the field of tourism.The "neuromarketing" cluster is directly linked to consumer neuroscience, eye-tracking, electroencephalography, psychology, consumer behaviour, attention, and advertising.The "psychology" cluster establishes a direct connection with "neuroscience", encompassing concepts such as the "prospect theory" and the "decoy effect", both rooted in the fields of marketing and the psychology of pricing.These theories were introduced by Boz et al. (2017) and subsequently applied to the domains of tourism and hospitality.Specifically, they utilized "eye tracking" to assess the pricing of tourism-related products.The "prospect theory" is associated with considerations of profits and losses, often referred to as the "loss-aversion" theory.Meanwhile, the "decoy effect", also known as the "attraction effect", explores how tourists exhibit a distinct change in preference between two options when a third option is introduced asymmetrically.

Figure 4. Author keywords -co-word analysis
The cluster with the highest betweenness centrality (53.95) in connection to tourism is "emotions", which is also intertwined with hospitality, affection, and emotional aspects.Additionally, two other clusters are linked to "neuromarketing" applied within the domains of tourism and hospitality: "advertising" and "advertising effectiveness", both having connections with EEG.Noteworthy studies in the realm of advertising include the work of De-Frutos-Arranz and Blasco López (2022), which conducts a bibliometric analysis on the influence of emotions in advertising tourism destinations.Lastly, within the "neuroscience" cluster, there is a notable presence of "consumer neuroscience" linked to EEG and ERP-Event Related Potential (often referred to as a time-locked EEG signal).This aspect has been extensively explored by McInnes and Hooshmand (2023), shedding light on neural responses to marketing stimuli.

The structure and dynamics of neurotourism, neuroscience and neuromarketing applied to tourism
The structure and dynamics of neurotourism, neuroscience and neuromarketing applied to tourism (including hospitality and travel) was determined by the systematic literature review guided by nine indicators that are identified in Appendix A. The two following sub-sections present a discussion on these results.

Research purpose, discussed concepts and application
The articles' research aim discussed concepts and application to tourism vary according to the methods employed, generally fall into one of three categories: literature reviews and systematic reviews, surveybased studies and neuroscience experimental studies.Notably, literature reviews and systematic reviews constitute a significant portion, making up 42% of the scientific output in this area.Among these systematic reviews, it is important to highlight that the term "neurotourism" is only introduced in Al-Nafjan et al.'s (2023) paper.Reinforce, that the Kasperiuniene and Zydziunaite (2019) paper, a systematic review on professional identity construction in social media, does not have any direct application to tourism.The remaining literature reviews and systematic review care classified into three general categories: those aiming to apply cognitive psychology theories to tourism, those that integrate cognitive psychology to tourists' choice processes, those that discuss the integration of cognitive neuroscience to tourism.Examples of the first category are Scott (2020), who provides a personal perspective on the application of psychology theory in tourism studies; Pearce (2020), who discusses tourists' perception of time and the temporal features of their social episodes ;Skavronskaya et. al. (2020), who critically assesses the relationship between novelty and memorable tourism experiences; and studies like Godovykh and Tasci (2021); Bastiaansen et al. (2019) which reviews the literature triangulating EEG, heart rate variability (HRV), skin conductance (SCR) and, facial EMG technique to study the emotions of the tourist experience; Koc and Boz (2014), which all address topics related to emotions in tourists' experiences.
Examples of the second category, studies that integrate cognitive psychology to tourists' choice processes, include Walls et al. (2011), which propose a framework for the tourists' destination decisionmaking process based on the cognition and affect interplay; Fennell (2009), a literature review on pleasure, incorporating knowledge from many knowledge fields; and Bastiaansen et al. (2019), who discusses what constitutes an experience and how it should be measured.
Finally, studies examples of the third category, studies that discuss the integration of cognitive neuroscience to tourism, are Parrinello (2012), whose main purpose is to argue that tourism studies should consider recent developments in neuroscience; Lew (2020), which discusses tourism' role as a vector of global sustainability awareness in an increasing integrated "shrinking world"; and Koc and Boz (2014), who use neuromarketing examples to illustrate how tourists perceive prices ;Li et. al., (2022), who discuss the use of electroencephalography (EEG) in tourism and hospitality research; and Tham et al. (2021) which discusses the ethical issues of applying electrodermal activity (EDA) to ethnographic studies of tourism.
Survey-based studies also include three main categories: those that employ surveys to the study of tourists' behaviour and perceptions, those that measure the emotional dimension of tourist experiences, and those that employ surveys to measure the potential or effectiveness of neuromarketing strategies in tourism businesses.With the first category, examples are Morar et al. (2021), which employed surveys to collect self-reported data on the psychological factors that influenced tourists' behaviour during the Covid-19 crisis; Pozharliev et al. (2021) and who employed surveys to collect data on tourists' emotional response, to interactions with service robots in hotels.
Examples of the second category, that measure the emotional dimension of tourist experiences, include Goggin et al. (2017), which measured the experience dimension and place attachment of visitors to a National Park; and Pearce (2012), which attempts to explain peoples' experiences of visiting places of previous significance The experience of visiting home and familiar places and familiarity in their lives.The last category includes works such as Mojahedi and Hassanpour (2016), who demonstrated, through data collected via questionnaires with a travel agency chain's personnel, that neuromarketing strategies have a significant impact on the company's competitive advantage.
Finally, within the realm of neurotourism research, about 31% of the studies utilize neuroscientific methods.These studies can be classified into five distinct categories, each with its unique application to the field of tourism: 1) Investigations pertaining to the application of neuroscience methods in the context of hotels and restaurants -As an example, Chark and McCartney (2023) conducted a study in which they employed neuroimaging to examine the cognitive processes of hotel employees.Likewise, Pozharliev et al. (2021) utilized neuroimaging techniques within the realm of robot services.In a similar vein, Hsu and Chen (2020) applied EEG technology in the hospitality sector, measuring participants' brain activity to gain insights into how hotel videos, featuring a smiling face emoji as a subliminal message, impact consumers' choices in selecting hotels.2) Studies that focus on understanding the impact of neuroscience on consumers' intention to purchase tourism products - Gunawan et al. (2023)  The Scival topic prominence and prominence percentile were analysed using a combination of qualitative and qualitative variables (see Appendix A).The most relevant result is that 84% of all scientific production on neuroscience and neuromarketing applied to tourism, hospitality and travel is clustered above the 90th Scival prominence percentile, which means it is in the top 10% of all topics in the world.The results also reveal a high level of CiteScore, citation and view counts.This means this is a popular topic amongst researchers, which are both reading and citing works addressing it in significant rates, which in turn, makes it an emerging domain with great funding potential.
The results also demonstrate that the distribution of themes is quite diversified in terms of positioning in the Scival topic prominence clusters, amongst which the most relevant is "Neuromarketing | Neurosciences | Community Participation".Namely, this clusters include the study of Li et al. (2022b), which focuses on the prospects of using electroencephalography (EEG) in tourism and hospitality research.

The application of theoretical models in the selected papers
The analysed papers employ or propose a variety of theoretical models.Amongst survey-based and experimental studies, Pozharliev et al. (2021) presents a conceptual model of human versus robot type service.Namely, the authors observe how working model differences -in terms in of social behaviouramong consumers affect their automatic emotional reactions when interacting with robots in a hospitality context.Within the literature reviews, Bastiaansen et al. (2019) proposes a conceptual model of the experience construct.Namely, the authors' framework seeks to explain how memorable experiences are formed, viewing emotions as their building blocks.Still in this group, Walls et al. (2011) presents an affective-cognitive model of vacation decision making, and Fennell (2009) adapts of model of the temporal frames of pleasure to theoretically discuss the concept building on knowledge fields such as philosophy, psychology, marketing and tourism.

Neuroscience and neuromarketing technologies employed
The neuroscientific technologies (also called neurotechnology, neuroscientific methods, or biometric technologies, in the neuromarketing domain) applied to tourism, vary according to the studies' objectives.However, they can be generally classified into those the record neural activity in the brain and outsider the brain.
Amongst the methods that record brain activities inside the brain, the most common is electroencephalography (EEG).The method is favoured, for instance, to assess potential tourists' emotional reactions to promotional films.For instance, by Hsu and Chen (2020) use it to examine the role of subliminal messaging (namely, their impact on hotel choice) in promotional films.EEG is also employed in conjunction with techniques that measure activity outside the brain, such as galvanic skin response (GSR) and eye tracking, also with the purpose of assessing the effectiveness of marketing content through in images and videos, as done by Flores et al. (2022) discussing the role of Eye Tracking in advertising.
As an example of the combination of EEG and GSR, Bastiaansen et al. (2019) employ it to assess the effectiveness of tourist destination marketing content in films.As an example of combining EEG and eye tracking, Ramsøy et al. (2019) employed these two neuroscience methods to test whether direct emotional and cognitive responses to travel destination (through the viewing of images and videos) is indicative of subsequent stated destination preference.Eye tracking on its own is also employed.Chen (2020) all used this method to test whether participants' statements about their preferences or decisions coincide with what their brain activities suggest.

3.3.
Research agenda highlighted within the body of scientific output in the fields of neuroscience, neuroscientific methods, neuromarketing, and tourism domain As detailed in Appendix A, most literature reviews on neurotourism and neuroscience and neuromarketing applied to tourism hospitality and travel urge future studies to integrate more specific psychological concepts, definitions and theoretical relationships from cognitive psychology and neuroscience.Namely, Skavronskaya et al. (2020), who analyses the role of novelty in the creation of memorable tourism experiences through psychology theories, suggests further studies on the connection of novelty with emotions and memories.Other topics suggested for future studies are tourists' perception of time (Pearce, 2020) and the relationships between tourists' emotions, feelings, and moods (Godovykh & Tasci, 2021).These studies also suggest the use of specific neuromarketing technologies by future studies, such as EEG combined with other techniques (Li et al., 2022;Bastiaansen et al., 2019).
Regarding empirical studies employing neuroscience techniques to tourism investigation, these present a valuable contribution to tourism scholars, as well as businesses and destination managers.For decades, consumer research on tourism relied almost exclusively on self-report studies.Although insightful, those studies have clear limitations, especially when attempting to address subjective and, to a great extent, unconscious variables, such as emotions.Therefore, they have a clear potential to help better understand phenomena such as tourists' destination decision-making process and image formation process.They can also help tourism businesses of many types understand what works and what does not when trying to create a pleasant and transformative experience to tourists.Accordingly, they can help destinations communicate more effectively and convey the intended affective image.
Naturally, since this research trend is still very recent, there are several limitations to be tackled by future studies.Before discussing items in the future research agenda for neurotourism, however, one issue must be addressed.As neuroscience technologies assess emotional responses that might be unconscious, and thus, unknown to respondents, the ethics of such procedures becomes a topic of discussion.This problem is addressed by Tham et al. (2021), who argues that ethics must be embedded through increased collaboration and co-creation in the context of applying, preparing and approving research procedures.Therefore, such suggestion must be considered within all further tourism research employing neuroscience techniques.
Regarding specific research objectives that should be pursued, previous studies' limitations point to some possibilities.For instance, studies measuring brain responses to images and videos, like Bastiaansen et al. (2018), only measure short-term changes in emotional responses.Measuring longterm responses is, therefore, an important challenge for future studies in the field.Accordingly, studies analysing tourists' decision-making process are based on evidence from participants' prefrontal cortex.According to Hsu & Chen (2020), while this region is considered the decision-making centre of the brain, neural activities in other regions should also be explored.Moreover, while Ramsoy et al. (2019) found that although emotional responses partially explain tourists' travel preferences, they are not identical to their subjective stated preference, which suggest that other mechanisms might also affect it.Those should also be explored by future studies.Some empirical studies also suggest specific concepts to be addressed.For instance, Pozharliev et al. (2021) calls for further studies on the emotional dynamics of human-robot interaction in hospitality services.Meanwhile, and Goggin et al. (2017), calls for studies on how tourists' experiences change according to the context.Regardless of the specific context or phenomenon being explored, Michael et al. (2019) summarises the main aspect of the research agenda for neurosciences in tourism: considering it as not a special branch, but as a set of tools embedded as a natural part of tourism research.

Conclusions
Given how recent neurotourism and the application of neuroscience to tourism is, as well as the consequent research gaps in this domain, the present paper aimed to assess the state-of-the-art of neurotourism and the application of neuroscience and neuromarketing to tourism research.Namely, the study sought to answer the following research questions: 1. "What is the extent and scope of the concept of neurotourism?". 2. "What is its relationship with neuroscience and neuromarketing?".
The stated questions were answered a systematic literature review carried out through a combination of bibliometric and framework-based analysis, to which the Scopus database was adopted as a main database.The results show that neurotourism and the application of neuroscience and neuromarketing to tourism research is a popular emerging domain.This is evidenced by the results of the Scival topic prominence and prominence percentile, analyses, which show that the domain is above the 90 th percentile and have a high CiteScore.
In terms of the specific research questions, the full extent and scope of the neurotourism concept are still in their early stages of development.Nevertheless, the existing body of literature, although relatively limited, portrays neurotourism as an emerging research domain within the tourism context.While certain studies, exemplified by Pourfakhimi et al. (2023) and Chark et al. (2023), contend that neurotourism encompasses the application of neuroscientific methods to both tourism and hospitality, the prevailing consensus among researchers defines it primarily as the application of neuroscience within the field of tourism.This perspective is shared by scholars such as Al-Nafjan et al. (2023), Ma et al. (2014), andLi et al. (2023).
Certainly, the thematic network analysis conducted in this study highlights a strong interconnection among neuromarketing, neuroscience, and the field of tourism.As Cardoso et al. (2022) have asserted, neuromarketing is situated within the broader realm of neuroscience, encompassing elements of psychology, and it primarily seeks to comprehend various facets of consumer behaviour, motivations, preferences, expectations, and the efficacy of advertising strategies.Furthermore, the dominant themes in this research, which encompass neurotourism, neuroscience, including the neuroscientific methods, and the application of neuromarketing principles to tourism, hospitality, and travel, are prominently represented within the "neuromarketing" cluster.This cluster exhibits close associations with both "neuroscience" and "psychology".Additionally, other notable clusters include "emotions", "advertising", "consumer neuroscience", "EEG (electroencephalography)", "eye-tracking", "behaviour", "attention", and "advertising".These topics are predominantly explored through literature reviews, survey-based studies, and experimental studies, as evidenced by the findings related to the structure and dynamics of the research domain.Among these study types, experimental studies stand out as the ones that truly employ neuroscientific methods and techniques as integral components of their research designs.On the other hand, survey-based studies typically rely on self-report data to measure constructs rooted in psychological and neuroscientific theories.These topics are addressed mostly through literature reviews, survey-based studies and experimental studies as evidenced by the results on the structure and dynamics of the domain.Amongst those, experimental studies are the ones which indeed employ neuroscientific methods/techniques within the research design.Survey-based studies mostly rely on self-report data that measure constructs built on psychology and neuroscience theory.
Furthermore, when considering their applications within the tourism context, neuroscientific methods are predominantly utilized to gain insights into tourists' emotions.These applications encompass understanding how positive emotions contribute to the creation of memorable experiences, examining tourists' emotional responses to interactions with service robots, and evaluating the effectiveness of marketing content for tourism destinations or services, such as hotels.Additionally, these methods are employed to assess the effectiveness of advertising efforts and their impact on destination choices and destination products.Emphasizing the interdisciplinary nature of tourism studies, it's worth reinforcing that the commonly used neuroscientific methods such as EEG, ET, GSR, and HR play a pivotal role.EEG, dedicated to measuring brain electroactivity, and ET, GSR, and HR, dedicated to capturing psychological responses within the body, facilitate a profound connection between the fields of neuroscience and neuropsychology (a branch of neuroscience) within this context.Just as the intersection of neuroscience and psychology gave rise to a new research domain known as neuromarketing, it is evident that the fusion of neuroscience and neuromarketing within the realm of tourism is giving birth to a nascent field of study: neurotourism.Therefore, the findings of this study clearly indicate that "neurotourism" is an expanding research domain that incorporates principles from neuroscience, neuromarketing, and applies neuroscientific methods within the sphere of tourism.
The Scival topic prominence analysis conducted in this study illuminates the nascent stage of neurotourism research, as evidenced by its high topic prominence percentile scores, consistently exceeding the 90th percentile in Scival prominence rankings.This emerging area appears to be dispersed across multiple topic clusters, with its primary association being within the neuromarketing cluster."Topic Prominence" in Scival serves as a valuable metric in this context, as it quantifies the significance and recognition of research topics within specific fields or disciplines.This metric helps researchers and institutions identify which topics are gaining substantial attention and prominence in the academic and research community.Recognizing the importance of neurotourism growth, it is essential to establish a dedicated cluster for "neurotourism" within Scival.By doing so, we can formally acknowledge and track the development of this emerging research area, enabling researchers and institutions to better understand its evolution and significance in the broader landscape of research and academia.

The study's contributions
For researchers in the field of tourism, this study demonstrates that the application of neuroscience, neuroscientific methods, and neuromarketing to the domains of tourism, hospitality, and travel, also as known as "neurotourism", is an emerging and promising area that offers significant potential for publications, citations, and research funding.These results deconstruct the preconceived idea that neuromarketing applied to tourism is an expensive and inaccessible research area and encourage researchers to pursue it.Namely, as demonstrated by the described research agenda, researchers interested in pursuing this area should focus on specific psychological concepts, definitions, and theoretical relationships from cognitive psychology and neuroscience applied to tourism.Concepts like novelty (ad its connection with emotions and memory), tourists' perception of time, feelings and moods are all fertile paths for future research.Accordingly, experimental studies involving specific neuroscientific methods, such as EEG, are also advisable.
Our paper makes several noteworthy contributions to the field of neurotourism.First and foremost, it provides a comprehensive review of the existing literature, amalgamating insights from various sources and fields.This synthesis enhances our comprehension of the interplay among neuroscience, neuroscientific methods, neuromarketing, and tourism, lending neurotourism a distinct interdisciplinary nature.Secondly, the pioneering methodological approach, combining Scival topic prominence and hybrid systematic review techniques, introduces a novel way of assessing research trends and identifying knowledge gaps.Thirdly, by highlighting the substantial research gap we uncovered, our paper provides a roadmap for future investigations, stimulating further research endeavors in neurotourism.Lastly, our discussions on current trends and future research directions offer valuable guidance for scholars and practitioners interested in advancing this burgeoning field.

The study's limitations and implications
While this paper contributes valuable insights, it is essential to acknowledge certain limitations.Firstly, the focus on Scopus as the primary source for paper selection may introduce a potential bias, as it excludes papers from other databases.Additionally, this research is contingent on the availability and inclusion of relevant papers in Scopus, which may not encompass the entirety of neurotourism literature.Secondly, the study is not necessarily cross-sectional as the database was acquired using a set of keywords that may not fully encompass the entirety of scientific output in the fields of neuroscience, neuroscientific methods and neuromarketing applied to tourism.For future studies employing a similar methodology, it is advisable to incorporate the concepts and theoretical models outlined in the appendix table of this research as part of the search keywords in Scopus or another database.Thirdly, the hybrid systematic review approach we employed, while innovative, is not immune to subjectivity during the selection and evaluation of papers.Lastly, the concept of neurotourism is still evolving, and the framework we present may require adaptation as the field matures.
The limitations presented by the extant literature also point to additional research paths.These include measuring long-term (rather than only short-term) changes in emotional responses to marketing stimuli, considering neural activity in regions of the brain other than the prefrontal cortex, and considering factors other than emotional responses to explain tourists' stated choices.The most assertive suggestion, however, is increasingly embedding neuroscientific methods as tools for tourism research, rather than considering investigations using them as a special branch.
The implications of this extend to multiple stakeholders.Academically, our paper sets the stage for a more structured and rigorous exploration of neurotourism, encouraging scholars to delve deeper into this interdisciplinary domain.Practically, it offers insights to professionals in the tourism industry by elucidating how neuroscience and neuromarketing approaches can be harnessed to enhance tourism experiences and marketing strategies.Policymakers and destination managers can benefit from our findings by understanding the potential of neurotourism to drive tourism growth and its associated economic implications.Furthermore, our identification of knowledge gaps and emerging areas provides a valuable resource for researchers seeking to address unanswered questions in neurotourism, ultimately contributing to the advancement of knowledge and the potential for practical applications in the tourism sector.
To fulfil these objectives,Paul's et al. (2021)  Scientific Procedures and Rationales for Systematic Literature Reviews (SPAR-4-SLR) protocol was adopted.This protocol involves three stages, each comprising of their respective sub-stages: (1) Assembling (Identification and Acquisition); (2) Arranging (Organization and Purification); and (3) Assessing (Evaluation and Reporting), which have been adapted to the specific circumstances of the present study.The procedures performed at each stage of the SPAR-4-SLR protocol are summarised in figure1and described in detail in the following sections.

Figure 1 .
Figure 1.SPAR-4-SLR systematic review protocol 2.1.1.SPAR-4-SLR protocol -Stage 1: Assembling The first step consisted of defining the research domain -neurotourism and neuroscience and neuromarketing applied to tourism -the research questions and the research objectives.Next, Scopus database was chosen as a data source, as it is the largest top-quality abstract and citation dataset of peer reviewed literature(Alsharif et al., 2020;Cardoso et al., 2020).Regarding the research mechanism, the material acquisition, the period and keywords search, a two-step approach was adopted.In this context, before advancing to the Scopus database, the keywords were fine-tuned using the Elicit platform (https://elicit.org).The platform was selected because it performs a semantic search for words, which allow researchers to eliminate the screening conflicts and more accurately determine the search keywords.The two co-authors involved in this step both adopted the strategy of carrying out the first search with "neurotourism and neuro-tourism", followed by the search with "neuromarketing and neuroscience applied to tourism".This initial search generated a set of works related to "neuropsychology, hotel, hospitality, destination, and travel".So, this first search was confirmed by the literature review.The term "neurotourism" is also written as "neuro-tourism", and thus, we have included both spellings in our search in Scopus.The word "Neuropsy*" aims to establish a connection Li et al. (2023b) explore arousal in destination advertising through EEG, whileBaraybar Fernández et al. (2023) investigate the impacts of emotional stimuli using measurements such as heart rate, EEG, and electrodermal responses.Furthermore,Flores et al. (2022) delved into the role of Eye Tracking in advertising.
employ EEG technology to investigate purchase intention.Additionally,Boz et al. (2017) expand upon existing research in neuroscience and neuromarketing to delve into tourists' perceptions of prices and pricing matters.Their study utilizes EEG, GSR -Galvanic skin response, HR -Heart rate, and ET-Eye tracking in the context of a price psychology model for tourism products, further contributing to the field of neuroscience and neuromarketing.3) Research examining the role of emotions from a neurological perspective within the tourism sector -Mengual-Recuerda et al. (2021), which employ neuromarketing biometrics -assessed through galvanic skin response, eye-tracking and electroencephalography -to analyse tourists' response to the presentation and tasting of dishes and wines in haute cuisine restaurant, and Zhou et al. (2023) -studying emotion and the dynamic functional connectivity of brain regions to perform EEGs.4) Analyses of how advertising stimuli affect the communication in tourism and hospitality tourism -López (2020), which employed eye-tracking to compare the perceived level of visual attractiveness of different hotel websites; Hsu and Chen (2020) compared both participant's choices and their brain waves to assess the impact of subliminal messages in destination promotional videos.Muñoz-Leiva et al. (2019), who crossed eye-tracking and self-report data to analyse advertising effectiveness in social media in terms of customers' visual attention and memory recall.Bastiaansen et al. (2018), the first study to effectively apply neuroscience techniques to tourism research.The authors used EEG to measure Event-related potentials (ERPs) triggered by viewing scenes of destination promotional videos.Lazo et al. (2023) employ eye-tracking (ET) technology to examine the communication related to tourism on the internet.Ramsoy et al. (2019), employed eye-tracking and electroencephalography (EEG) brain monitoring to test the effect of viewing of images and videos about places on tourists' destination choice.Meanwhile, Li et al. (2023b) employed EEG to assess the spillover effects of negative commercials on destination advertising.5) Studies exploring the neurological factors influencing competitiveness and the choice of tourist destinations -Royo Vela and Garzón Paredes (2023) employ EEG to examine the competitiveness of a destination's image.In a similar vein, Ramsoy et al. (2019) analyse emotional and cognitive reactions associated with destination choices, while Michael et al. (2019) utilize both eye-tracking (ET) and EEG technologies to investigate the same aspect.Savelli et al. (2022) conducted a study where they utilized both EEG and ET to investigate the impact of communication signals on tourism destinations' attractiveness.
Muñoz-Leiva et al. (2019), for instance, crossed it with self-report data to analyse advertising effectiveness in social media in terms of customers' visual attention and memory recall.BaraybarFernández et al. (2023) combined EEG with heart rate and electrodermal response to study the effects of emotional stimuli in advertising.Finally, a trend in the application of neuroscience techniques in recent years is its triangulation with self-report data.The mentioned works ofRamsøy et al. (2019), Muñoz-Leiva et al. (2019), and Hsu and