4.2.2. Methodology

The evaluation was performed at our usability laboratory located within Sungkyunkwan University. Participants were invited into an isolated room and sat in front of a desk. The materials were provided to the participants by the test facilitator. A set of speakers was set at a comfortable volume and placed facing the participants. Capped bottles containing the scents were placed on one side of the table. When necessary, the test facilitator opened the scent bottles and provided them for a couple of seconds to the test participant for olfactory stimuli. The facilitator, observer, and test participants used sanitary face masks during the session. The participants could temporarily remove their masks to facilitate the olfactory stimuli. Between each participant evaluation, the area and scent bottles were sanitized.

**Figure 2.** (**a**) Tactile graphic version of Van Gogh's Starry Night featuring the tactile color patterns described in Reference [32] used during the evaluation. (**b**) Visual sensory substitution prototype that expresses color contents through sound and scent.

The evaluation consisted of two parts. The first was a training session that lasted for 25 min. In this session, the facilitator introduced the purpose and methodology of the evaluation. Then, he explained the theory of color, its dimensions, and the terminology

used. He emphasized the relationship between the hue, light, dark, warm, and cool color dimensions for the composition of a determined color. Participants were encouraged to ask any questions regarding the contents and explanations they received to ensure proper understanding. The second part of the evaluation lasted for about 50 min. There, the facilitator introduced and evaluated the VIVALDI and multi-sensory color codes. The color codes introduction and evaluation order followed a 2 × 2 Latin Square test design to counterbalance practice, fatigue, or order effects. For the VIVALDI color code, the facilitator explained the relationship between the color hue and the different musical instruments' timbre. He also described the relationship between the spring, autumn, and summer melodies selected from Vivaldi's Four Seasons and the saturated, light, and dark color dimensions. During the explanation, the facilitator reproduced the audio files of the VIVALDI color code and highlighted their characteristic features. Then, the facilitator played some of the audio files and asked the participant to identify some of the colors as a warming-up exercise and to verify the participant's understanding of the evaluation procedure. The participant was given ten min to review any of the colors of the VIVALDI color code in preparation for the color identification evaluation. For the multi-sensory color code explanation, the facilitator provided a similar explanation to that of the VIVALDI color code. In addition, he introduced the scents from the multi-sensory color code selected in this work and their relationship with the saturated, light, and dark color dimensions. The participant experienced the audio and scents stimuli during the introduction. A color identification warm-up exercise was also performed. After which, the participant had ten min to review any of the colors in the multi-sensory color code. After each of the color code explanations and reviews, the participant performed a color identification test. The test consisted of eighteen identification tasks. The tasks consisted of experiencing audio or audio and scent stimuli depending on the color code being evaluated and identifying the color it represents. Each task corresponded to a random color from the color code palette. Results were recorded for further analysis, and a short questionnaire was performed after the participant evaluated both color code systems to identify perceived preferences, learnability, and memorability. The results of this evaluation are described in detail in Section 5.1.

#### *4.3. Visual Artwork Color Content Exploration Using a Visual Sensory Substitution Prototype*

This section describes the second evaluation where participants use the visual sensory substitution prototype described in Section 3.4 to explore the color contents of a visual artwork. The participants also explored a tactile graphic equivalent using tactile color patterns. A System Usability Survey was performed for each exploration method to investigate their feasibility, usability, and elicit feedback of the systems.
