Acclimatization Tasks

The subjects are also trained in two additional tasks. These are only used for acclimatiza-tion to the measurement methods (e.g., occlusion setting, dual-task driving setup, DRT setup). The data of these tasks are not gathered and the tasks are not modeled. On the touchscreen, the test persons are trained to open the calculator and enter a calculation.

For the rotary knob, the subjects are trained to go into the radio menu and change from one preset to another.

4.3. Test Subjects and Procedure

The age of the subjects was 20–26 years (median 23 years). All drivers had a driving license; for Germany very typically issued at the age of 17–18. Therefore, the years of driver experience had a median of 5.5 years. The annual mileage can be seen in Figure 4.14

Figure 4.14.: Mileage

Out of the 24 subjects, 13 were male (54%). Two persons drove with contact lenses and five drove with glasses; no one had a known red-green blindness. Three subjects were left-handed. The simulated vehicle had automatic gears; 12 persons had no previous experience with an automatic car. A driving simulation had not been driven before by 17 people. One person was classified as an extensive simulation driver (eight experiments).

The frequency of touchscreen usage for different devices is queried with a five-point Lik-ert scale (never–often). Most experience stems from mobile phones; 21 persons chose the rightmost option, one person one scale point below. One person had no experience with touchscreen devices. For one person, the usage questionnaire was incidentally omitted.

Ten persons had no previous experience with a rotary knob.

Test subjects who participated in the previous experiment (subtask experiment to con-struct the prediction tool) were not intended to participate again. This was checked by asking the persons before inviting them to the experiment. Unfortunately, when anonymiz-ing the folders of both experiments, it became clear that two subjects from the first experiment also participated in the second experiment (consent signature). This was de-tected after the anonymizing (scrambling), therefore it was not possible to exclude the two datasets. Therefore, the evaluation inadvertently includes an 8% retest (two persons).

The participation was voluntary, with compensation of 15 Euro.

Procedure

Subjects signed a consent form regarding voluntary participation. They were informed that they could quit at any time without any justification and that the eye-tracking sys-tem records video and audio. Also a stasys-tement clarified that the subject is not judged and only that the system and situations would be assessed. Printed instructions were presented at the beginning (cf. Appendix B). The subjects drove the driving simulation for at least two minutes or until feeling comfortable. The examiner gave feedback about the vehicle-to-vehicle distance. The subjects then drove another 2.5 minutes without any

secondary task. The last 90 s of this measurement were later used to calculate some base-line driving metrics.

The examiner demonstrated the tasks (Section 4.2) for each subject. After this in-struction, the subjects executed the tasks alone when the examiner announced a task via microphone. This also trained the later experimental situation. The task and the timing began when the examiner ended the instructions. Always the wording‘... und bitte’ (start please) was used. When the final state of the task was reached, the subjects ended the task with the announcement ‘fertig’ (done). On these two key words (please and done), the examiner operates time taking or trigger remote controls. The task training is ended by operating the two acclimatization tasks (touchscreen calculator and changing a radio preset with a rotary knob) while driving to give the test subjects the opportunity to gain an initial understanding of dual-task settings.

Task Training AAM or DRT Baseline(unoccluded) AAM or DRT

or Occlusion Baseline(unoccluded) or Occlusion

Figure 4.15.: Experimental Procedure

The experiment itself has four sections (Figure 4.15), similar to the subtask experiment before (see Section 3.4)

∙ AAM. Operating the application while driving (with eye-tracking)

∙ Baseline. Operating the application without driving. The measured Total Task on Time is, e.g., required in occlusion calculations

∙ Occlusion. Operating the application with occlusion glasses

∙ DRT. Operating the application while driving and with a Detection Response Task The six touch tasks and the four rotary knob tasks were grouped within these sections.

The order of these two task groups (touchscreen or rotary knob) was randomized. Also, within the groups, the tasks were operated in random order. The AAM and DRT sections were randomly the first or the last section within an experiment. This was intentional in order to obtain eye-tracking results for the radio-tuning task at the beginning, and to assess training effects near the end, of each session. In the middle, Baseline and Occlusion sections changed order randomly.

For all sections, the tasks were performed twice directly after one another.

AAM

In this condition, the application was operated while driving. The glance behavior was recorded with the head-mounted eye-tracking.

Baseline

This is the most obvious condition, without driving, DRT or occlusion Occlusion

The participants were instructed for the occlusion (Appendix B). Before the section, per-sons were accommodated to the occlusion setup with accommodation tasks.

DRT

In addition to the setup in the AAM condition (including the eye-tracking), the condition used a Tactile-DRT setup. The subjects were instructed for the DRT (Appendix B).

To assess possible training effects (Issue 5 – Section 4.4), the radio-tuning task was performed additionally before the actual DRT section without DRT measurement.

A baseline reaction time without driving was recorded for one minute (about 15 stimuli), subsequently termed the static DRT baseline. This is a single-task setting (TDRT only).

For another minute, a second baseline was recorded while driving: dynamic DRT baseline.

This can be seen as a dual-task setup (driving and TDRT). Acclimatization tasks were used to accommodate the test persons to the triple-task setting (driving, secondary task and TDRT).

The ten tasks were then recorded with DRT (including the radio-tuning task).

Whenever one of the telephone tasks (Chapter 4.2, Task 3,4 and 5) had been carried out by the test subjects, the examiner verbally asked (after the second trail) verbally for a subjective rating of this interaction. For easy rating, the German school rating scheme with six numbers was used (1–6; very good – insufficient).

The duration of the experiment per person was approximately 90 minutes.