## 6 Discussion and Conclusions
Similarly, in [PERSON]'s Dissertation [48] participants identified on average about 16 rhythm icons under no workload, after about three 20 min sessions for four weeks and one week without any exposure to haptic icons. Regarding haptic stimuli not including rhythm, in [PERSON] et al. [32], users were able to distinguish between 36 non-thyrthmical different stimuli but, as highlighted in [PERSON] et al. [39], \"distinguishability is not the same as the ability to independently recognise and identify individual items\". However, in [PERSON] et al., users had to sort stimuli that they could \"feel\" as many times as desired to classify them into different groups, in our work, after the familiarisation and training phases (that lasted less than 5 min) users were asynchronously presented with random haptic icons that they could \"feel\" just once and had to recognise and identify them. Despite the limited number of subjects of our experiments, results showed significant differences when using the haptic tuning fork. A disadvantage, however, is that the inclusion of the haptic tuning fork lengthens the duration of the haptic signal. In subsequent work, we intend to apply this technique to attach haptic icons to filiform structures in two different domains in which we are already working: the development of a tool for visually-impaired people to explore, analyse, and comprehend electrical circuits [49] and the visualisation of neuroscientific abstract data on the topology of neurons of the neurons. Regarding the latter example, performing a deep topological analysis of neural columns is a complex task due to the large number of neurons and their intricate structure of connections. The column structure can be seen as a filiform set of linked elements and its visual exploration often presents cluttering issues. Previous works have propose different techniques to navigate through connected filiform data sets [8; 50], giving additional clues to understand the topology. We plan to test the use of haptic textures to incorporate additional information and alleviate the visual cluttering problem. The following are available at [[https://www.mdpi.com/article/10.3390/app11188772/s1](https://www.mdpi.com/article/10.3390/app11188772/s1)]([https://www.mdpi.com/article/10.3390/app11188772/s1](https://www.mdpi.com/article/10.3390/app11188772/s1)): Table S1: Summary of experiments, Table S2: Entropy of the faithfully transmitted information (\(H_{T}\)), Table S3: Sent information entropy (\(H_{S}\)), Table S4: User response entropy (\(H_{R}\)), and Table S5: Stimulus-response entropy (\(H_{SR}\)). Conceptualization, L.R., M.G.-L. and S.B. ; Formal analysis, S.B., L.R., M.G.-L. and S.A.B. ; Funding acquisition, M.G.-L. and S.B. ; Methodology, L.R., M.G.-L. and S.B. ; Software, L.R., S.A.B. and M.G.-L.; Supervision, M.G.-L. and S.B. ; Validation, S.B., L.R., S.A.B. and M.G.-L.; Writing--Original draft, L.R., M.G.-L. and S.B. ; Writing--Review & editing, L.R., M.G.-L. and S.B. All authors have read and agreed to the published version of the manuscript. The research leading to these results has received funding from the following entities: Spanish Ministry of Economy and Competitiveness under grant TIN2017-83132-C2-1-R (VINA), as well as from the European Union's Horizon 2020 Framework Programme for Research and Innovation under the Specific Grant Agreements No. 785907 (Human Brain Project SGA2) and 945539 (Human Brain Project SGA3). Not applicable. This research is exempt from Ethics Committee approval, since the tests were performed on healthy subjects and did not involve the application of invasive procedures, the use of drugs, the use of biological samples or the use of sensitive personal data. The performance of the tests in no way compromised the mental or physical health of the participants. Recruitment of subjects was voluntary, unpaid, and did not include students.