Complimentary Work

The work reported in this thesis, as well as the future work presented in the previ- ous sections investigate the limit of conveying tactile information in mid-air using technology such as ultrasonic phased arrays. However, such displays are only able to stimulate the cutaneous part of the somatosensory system. Therefore, it is likely that ultrasonic phased arrays fail to convey all the aspects of touch information.

Nonetheless, it is worth to mention that mid-air haptic displays are unlikely to be used on their own. As stated in the introduction, mid-air haptic displays are born from the necessity to enhance 3D-Display interaction with touch information. Therefore, it is sensible to assume that mid-air tactile stimuli will be used in synergy with stimuli from other modalities. Additionally, it is well-known in the literature, that perception is a joint effort between the different modalities. On a daily basis, one’s brain uses information from the different senses to draw conclusions from one’s surroundings.

For instance, it has been shown that the use of visuals in virtual environments could influence one sensation of compliance (Di Luca et al. [2011]). Similarly, it has been demonstrated that audio stimuli could affect one’s perception of roughness (Jousm¨aki and Hari[1998]).

Therefore, it is likely that results from multisensory interaction could be applied to mid-air tactile patterns. Hence, future work could also explore how to re-enforce mid-air tactile pattern sensation through the design of multisensory stimuli using both visuals and auditory signals, and vice versa.

Ultimately, this Thesis only presents initial work on getting stronger mid-air tac- tile patterns. The future work should be pursuing investigations on how to render stronger mid-air tactile patterns, but also how to render richer patterns. Strength is only one aspect and the technology will only become widely adopted if one man- ages to produce richer stimuli. As presented in this Thesis, the research in mid-air haptic patterns needs to be cross-disciplinary. Only collaboration between experts in different key-fields will allow further progress. Therefore, I not only hope to be able to carry out working on the ideas and work presented here, but also have the chance to collaborate with many experts on those fascinating research questions.

This chapter presented initial investigations on a new research framework to predict the perception of spatiotemporal patterns according to various parameters such as pattern length, repetition rate and device update rate. Even though further

investigations are necessary to validate the approach, the current results provides interesting cues. Indeed, using simple equations, we derived the width of the local pulse signal and determined this width was independent from the number of points per pattern. This observation leads us to refute the suggestion that the number of points per pattern was affecting the signal pulse width and therefore the pattern perception. It is encouraging for the future work, which has the potential to address the remaining suggestions we formulated at the end of chapter 5. This progress has been made possible by considering the haptic signal produced at a specific location on the skin, rather than the haptic signal produced at the focal point centre. We believe that this approach should lead to further breakthroughs in understanding the perception of mid-air haptic patterns in the near future. However, we could not fully explore our suggestions in this thesis. The next and final chapet will summarise our work’s contribution but also highlight its limitations.

Chapter 7

Conclusion

Mid-air haptics is a growing field, which has a great potential to enhance a wide range of interactions such as AR, VR and 3D-displays. As we discussed in chapter 3, the field relies on various technologies, among which ultrasonic phased arrays have a growing popularity amid academia and industry. The work presented in this thesis is essentially focusing on investigating the use of such technology to convey continuous and distributed spatiotemporal tactile feedback. While, in section 3.3, we presented an approach to render spatiotemporal mid-air tactile patterns where patterns are divided into shape and sensation, we focused our work mainly on the former. In other words, our work focused on rendering strong mid-air tactile pattern shapes. In particular, in the work reported here, we looked at exploring and strengthening the relationship between spatiotemporal parameter space and perceptual space, with a focus on perceived pattern strength.

While our work includes a significant contribution to the field, we acknowledge that the results reported in the chapters also have some limitations. This final section first summarizes the contributions and limitations of our work and then identifies future opportunities. We acknowledge that the work presented in this thesis is only a stepping stone towards better spatiotemporal mid-air tactile feedback and does not solve all the problems we have identified at the beginning of this thesis.

7.1

Contributions

The main goal of the work presented in this thesis was to investigate how to con- vey stronger spatially distributed mid-air tactile patterns. To do so, we leveraged the rendering capabilities of a recent modulation technique, namely Spatiotemporal Modulation. While most researchers focused their effort on engineering and algo- rithmic challenges, which lead to the development of spatiotemporal modulation,

little attention has been paid to the relationship between spatiotemporal parame- ters space and its associated perceptual space. In that sense our research is the first step towards a better understanding of the relationship between STM parameter space and STM perceptual space. Our research results are mainly valuable to the mid-air haptic experience designers, who can reuse our contributions within their work. However, our results also provide insights into the perception of spatiotem- poral tactile pattern, which are beneficial to the broader haptic community. The current section summarise our contributions to both communities.