## 4 Discussion and Conclusions
This is reflected in the evolution between the periods established in this study, where between 1997 and 2015, the theme with the greatest bibliometric indicators was \"virtual environments\" (Works = 12; h-index = 7; g-index = 9; hg-index = 7.94; q2-index = 18.52; citations = 492), while between 2016 and 2019, \"higher education\" (Works = 68; h-index = 8; g-index = 16; hg-index = 11.31; q2-index = 11.31; citations = 294) occupied the top spot. In addition, the same themes are rarely repeated between the two periods. If the motor themes of both periods are analyzed, the above postulation is confirmed; there is a thematic amalgam in both analyzed periods (\"development\", \"tailored optical fibers\", \"mixed reality\", \"pedagogy\", \"instruction\", \"virtual environments\", \"3d modeling\", \"gamification\", \"context aware\", \"pattern recognition\", \"usability\" and \"systems\" in the first period; \"technology acceptance\", \"framework\", \"university\", \"instruction\", \"improve\", \"mobile\", \"higher education\", \"anatomy\", \"usability\", \"attitude\", \"blended learning\", \"internet of things\" in the second period), whose relationship strength is weak. This shows that ARHE is generating an amplitude both in the field of knowledge and in the various branches of research, as well as conceptual gaps between the established periods. Only, a continuity has been found between \"usability\" and \"instruction\" that is repeated in both periods. These results are consistent with those other studies that have found there to be a great variety of research, highlighting the conceptualization of this phenomenon, the development of new RA methodologies, motivation and the attitude, special relocation, academic achievement, and the subjects in which the RA is studied [32; 38]. The realization of this study helps to offer the scientific community the most relevant research fields in which ARHE is currently focused, in order to consolidate, in a diachronic manner, the research foundations upon which this emerging technology is based. Therefore, the analysis techniques used in this work provide an expanded and novel vision of the state of ARHE in WoS. Therefore, this study allows an increase in the knowledge about the use of ARHE because it shows the scientific community where the state of the question about this emerging technology in said educational stage currently. In this way, the research trend so far on this area is shown, enabling researchers who want to study ARHE can select the topics considered relevant in this study and go to the most relevant bibliographic sources on the state of the matter. The limitations of the study include the location of the references in which the WoS was not determined by keywords, in many cases hindering its localization process. Also, the low volume of scientific papers based on bibliometric analysis made it difficult to discuss the findings obtained in this study with those reported in the literature. This causes the results achieved in this investigation to acquire an exploratory character. This determines the existence of new findings in scientific research on ARHE. In this work, only the main findings obtained from the perspective of the WoS have been presented. For future research, we propose to carry out an investigation with the same structure on other databases, such as Scopus and Google Scholar. Conceptualization, S.P.S. and J.A.L.N. ; methodology, J.L.B. and A.-J.M.-G; software, A.-J.M.-G; formal analysis, J.L.B. and A.-J.M.-G.; investigation, J.L.B., A.-J.M.-G., J.A.L.N., and S.P.S. ; data curation, S.P.S. ; writing--original draft preparation, J.L.B. and S.P.S. ; writing--review and editing, J.L.B. and A.-J.M.-G.; visualization, J.A.L.N. and S.P.S. ; supervision, J.L.B and J.A.L.N. This research received no external funding.