*4.1. Participants*

Ten students were recruited as participants of the experiment. The gender split of the participants was five males and five females, and the average age was 22.5 years (minimum 20 years old, maximum 25 years old). While participating in this experiment, repeated auditory stimulation may have caused side effects such as headaches, and if physical or mental discomfort was felt, participants were informed in advance that they could request to stop the experiment at any time. All participants used their own cell phones and earphones for the experiment. Five participants used the six-color wheel codes, and the other five participants used the eight-color wheel codes.

The experimental evaluation was performed in three stages: learning phase, tests, and feedback. During the learning phase, experiment participants learned and became familiarized with the sound codes through explanations, schematic, and sample audio. Test part divided into color, color + lightness, color + lightness + depth to be tested separately. In the test part, the participants were asked to perceive color, lightness, and depth through sound alone without looking at pictures such as the color wheel. After that, the participants evaluated the workload assessment and usability test.
