## 4 Usability Evaluation by the UTA
### Results  
First, the verbal responses of the participants obtained through the usability test were recorded as written textual data. Then, the textual data were coded according to the procedure of the proposed method. As part of the analysis procedure and the results, Task 1 for one of the participants is shown below as follows:  
(1) Extraction of keywords  
The following words and phrases were extracted as the focus of attention from the speaking (the original textual data were in Japanese): \"doesn't go back\", \"what's this?\", and \"SEEK TRACK\".  
Figure 1: The user interface of the evaluated in-vehicle audio system.  
2. Paraphrasing of keywords The words extracted in (1) were paraphrased as follows, referring to the original text data and the context before and after the paraphrasing: * \"Doesn't go back\" \(\rightarrow\) failure in the selection of CD tracks. * \"What's this?\" \(\rightarrow\) blind operation. * \"SEEK TRACK\" \(\rightarrow\) confirmation of button name. (3) Interpretation using 70 design items The words paraphrased in (2) were interpreted from the viewpoint of 70 design items, referring to the original text data and the context before and after the paraphrased words as follows: * Failure in the selection of CD tracks \(\rightarrow\) mismatch with user's mental model, lack of discrimination. * Blind operation \(\rightarrow\) lack of operation cue. * Confirmation of button name \(\rightarrow\) terms as operation cues. (4) Extraction of problems based on 70 design items The following usability problems in Task 1 were extracted from these step codings and the original text data: * The method of the CD track selection does not match with users' mental model. * The CD selection button is not distinguishable from similar buttons, making it challenging to identify. * There are few clues for CD selection operation, and users become confused. * The English words \"SEEK TRACK\" can be a clue for operation, but it is not clearly understood by Japanese users and is not an appropriate term for Japanese users. (5) Description of other items Through the step coding, the analyst wondered whether Japanese users could understand the meaning of \"repeat\" in the text \"RPT\". This procedure was followed for each of the six participants. As a result, a total of 29 usability problems were extracted. The extracted problems can be roughly classified into four categories. The following is a list of the four categories and the significant problems in each category: (1) Problems related to terminology (nine problems) * Terms are difficult to understand. * Explanation and display are difficult to understand. Example: The term \"TRACK\" is difficult to understand and is not highlighted prominently. (2) Problems related to obtaining information (13 problems) * There are few clues for operation. * Lack of distinguishing features. Example: There are not enough cues and identifiers for the power button. (3) Problems related to the user's mental model (three problems) * Mismatch between the user's mental model and the system. Example: The user does not have a mental model of \"pressing\" the volume button. (4) Problems related to the understanding of button functions (four problems) * There is a lack of explanation, display, and feedback about the button functions. Example: The user cannot understand the button function of the traffic information button with only an icon.