Semantic Stimuli

The purpose of this experiment is to find the most suitable sound variables to express depth. To obtain the association of sound variables and depth, this paper used the explicit association + implicit association test. That is, the explicit association is used first for match detection, and if no match can be made, the implicit association test is performed to match implicitly with other adjective pairs. Osgood [57] simplified the semantic space of the relative adjectives into three aspects, which are (1) evaluation (like–dislike), (2) potency (strong–weak), and (3) activity (fast–slow). The adjectives adopted in this research are pairs of adjectives with which people are familiar, such as emotion, shape, location, activity, texture, contrast, temperature, sound characteristics, etc. Thus, the simplified concept pairs of adjectives are chosen per aspect, shown in Table 5. Note that 11 pairs among them are related to sound attributes, as shown in Table 6.

This paper used sound variables such as loudness (Small~Loud), pitch (Low~High), velocity (Fast~Slow), length (Short~Long), and attack/decay (Decay~Attack) for this test. For each sound variable, participants received several audio segments with different levels of variability. Participants in the experiment used this audio file to recognize sound variables and evaluate how well those sound variables matched adjectives. In each of these 11 pairs of concepts, the score for the feeling conveyed by the sound attribute stimulus is 2 points when chosen as most positively consistent with the feeling of depth, −2 points when chosen as most negatively consistent with the feeling of depth, and 0 when chosen

as least consistent with the feeling of depth. These score points were computed for each subject for each of the 11 sound-attribute stimuli.



**Table 6.** The adjective pairs used in the experiments.


Experiment Participants and Results

Seven members of Sungkyunkwan University were recruited as experiment participants. The gender split of the participants was 4 men and 3 women, and the average age was 22.29 years old (minimum 21 years old, maximum 24 years old). When participating in the experiment, side effects such as headaches could occur due to repeated auditory stimulation, and if they felt physical or mental discomfort; the experiment was conducted only after notifying the participants in advance that they could request to stop the experiment at any time.

Test results are shown in Table 7 and Figure 4. For each of the 11 pairs of adjective concepts in Table 7, the scores for the sense of depth transmitted by the sound stimulus are between −1 and 1. In other words, the absolute value of 1 is given when the sound stimulus feels the most consistent with the sense of depth, and 0 points are given when the sound stimulus is the most inconsistent with the sense of depth. By matching the results of sound variables with adjective pairs and matching results of sound variables with depth, this paper can conclude that there is a strong correlation between sound intensity and depth. That is, when the sound is loud it is associated with proximity, while when the sound intensity is small it is associated with depth.

### 3.2.2. Sound Representations of Color and Depth

With the results of the previous experiments, this study used the sound size variation to represent the sense of depth. To deepen the sense of depth, the paper added a reverberation effect while changing the sound size to make the sound depth more obvious. To make it easier to recognize the depth information expressed in velocity, only 3 distance levels (far, mid, and near) were used. The near level was set to the normal sound speed. The mid-level was set to 80% dry, 50% reverberation, and 10% early. The far level was set to 30% dry, 15% reverberation, and 10% early. The reverb setting was 1415 ms decay time,

57 ms pre-decay time, 880 ms diffusion, 22 perception, 1375 m<sup>3</sup> room size, 1.56 dimensions, 13.6% left/right location, and 80 Hz high pass cutoff.


**Table 7.** Matching results of sound variables with adjective pairs.

**Figure 4.** Matching results of sound variables with depth (Near~Far).
