*2.1. Temperature-Depth Correlation*

### 2.1.1. Temperature Range Used

Before going forward, it is important to define the range of temperatures that will be used from now on, both for the tests and for the design of the algorithms. Our algorithms are designed to help visually impaired people being aware of depth in a more interactive way through thermal interaction. Therefore, the temperature range to use during the tests and for defining the algorithm needs to be fixed from the start. As stated above, the temperature pain threshold is [15, 45 ◦C] although some research sugges<sup>t</sup> it might be [11, 45 ◦C] [17], so the temperature range needs to be within those extreme limits. In [5], it was experimentally validated that the temperature range of [14, 38 ◦C] was convenient and comfortable for the visually impaired users, so it is also the range used in this work.

### 2.1.2. Temperature-Depth Correlation Test

As has been shown in the background section, temperature-depth correlation has not been extensively researched and only a rough relationship between temperature and the presence or absence of a person has been found. These results give us a glimpse about the possibility of the concepts near/far being somehow correlated to warm/cold temperatures. As a result, our team felt encouraged to figure out whether the hypothesis of depth and distance (near/far) being correlated to temperature might make sense or not.

The test was based, as in [13], on an adjective list for the users to select associations with the warm and cold temperatures. The list had similar adjectives to the ones found in there, with the exception of two added adjectives: the adjectives 'near' and 'far'. The list was made so every adjective had another one with the opposite meaning, creating a list of adjective pairs. The main purpose for having so many adjectives when the research was focused on the depth-temperature relationship was to make the user select adjectives without having any clue that the near/far dichotomy was the one the test was focused on. Two di fferent adjectives lists were prepared: one with all the adjectives ordered randomly (Table 1) and another one with the adjectives ordered in pairs (Table 2). Each one of the lists was used at a di fferent stage during the test, which will be explain next.

The test was performed twice, first with a total of ten users, five women and five men. The users had an average age of 24 years and were volunteer college students. Each test lasted around 25 min. Then, for verifying whether the findings could be applied to visually impaired people, the same test was carried out again with six visually impaired users. The users were an average age of 17 years and all of them were students from Chungju Sungmo School, a Korean school for visually impaired people. Two of them were nine-year-old kids and all of them where totally blind from birth. Each test lasted around 30 min. The temperature actuators consisted on two petlier devices, a fan, and a heat-sink, which were controlled by an Arduino Mega board. Both temperature actuators can be seen in Figure 1. The test was performed according to the following four steps:

**Figure 1.** Thermal devices.
