– Based on the previous steps and related work we create an abstract secondary task cate- gorisation (3.1.3).
– This categorisation is used in the studies in chapters 4 and 5 in the form of specific tasks that have been derived from it.
3.1.1
Secondary Task Analysis in ADAM
TheADAM(Advanced Driver Attention Metrics, 2001 – 2004) project [17] was originated with the goals to assess driver distraction due to secondary tasks and to verify the guidelines onDriver
Interactions with In-vehicle Information and Communication Systems drafted by the European
Commission in 2000 [31]. In the course of the cooperative project with Daimler-Chrysler and BMW a number of simple assessment methods were developed and evaluated, including the Lane Change Task (cf. 3.2.2).
They chose tasks that cover a wide range of (assumed) task difficulty, represent the con- trol of in-vehicle systems, but also other activities people do while driving, and impose visual, auditory, motoric, and cognitive demand [17]. Table 3.1 shows the final selection of tasks. A classification scheme was established in terms of different demands: visual, visual-motoric, auditory, verbal, motoric left hand, motoric right hand, central processing and memory.
All the named tasks have been evaluated in studies using different methods. Mattes used a newly developed method, the Lane Change Task (cf. 2.1.3, 3.2.2), for evaluation [106]. In the telephone task (TT) the test subjects showed the best dual-task performance, taking coins out of a purse (CO) resulted in the worst performance [106]. Bengler et al. found widely consistent results and a clear main effect of secondary tasks in a driving simulator study analysing the same task set which was mainly caused by manual or manual/visual tasks [7]. However, a real-life field trial which again comprises the tasks listed above could not reproduce these results with the chosen metrics [46]. Yet it could be shown that the test subjects increased their minimum headway when engaging in a secondary task.
3.1.2
Delphi Study on Secondary Task Demands
Since the ADAM tasks do not capture adequately enough the contemporary driver needs and partially covers obsolete tasks (e.g. change cassette), we decided to conduct a study judging task demands by a standardised scale for subjective workload estimation. As an evaluation procedure we decided to use the Delphi method (cf. [76, 101]) that is known for its decisive character. Delphi studies comprise two survey rounds. In the first round, the participants fill out a questionnaire containing questions concerning the object of study. In the second round,
Category Name Abbr. Task
Integrated System “CARIN”
Radio tuning RT Set radio to a certain frequency Sound
adjustment SA Set treble to maximum
Change Cassette CC Change audio cassette and put in case Navigation
speller
NS Enter street name with rotary push button Navigation map NM Set target cross of navigation system to a certain
point on map Other
Tasks
Cell phone CP Enter 4-digit PIN in cellular phone
Sweets SW Unwrap a sweet and put it into the ashtray Talk on
telephone TT
Answer some simple questions in hands free mode
Kleenex KX Unfold a Kleenex and put it onto passenger seat Address Book AB Lookup phone number in small paper address
book
Map book MB Open map book on page X and decide which of two towns Y and Z is further North
Coins CO Get a 20 and a 10 Cent-coin out of a purse, close the purse and place it back onto the passenger seat
Table 3.1: Secondary tasks selection used in the ADAM project (from [17]).
the participants have to answer the same questions, but only those that did not produce an unambiguous result. Additionally, they are shown the aggregated results of the first round. Thus, they are able to rethink their answer to each question and either confirm or thoughtfully revise it.
In our study, we had a sample of 19 participants familiar with in-car interaction involving secondary tasks. We had 13 male and six female test subjects with an average age of 29.47 years (SD=4.94). We created a digital questionnaire with 21 tasks that the participants are to perform during an imaginary, relaxed drive on the motorway. We adopted some of the ADAM tasks, and also added some more. Consistent to the selection in the ADAM project, we chose tasks that are likely to occur while driving, but only those that use in-car technology, e.g. a navigation system. The participants had detailed instructions how to perform each task. An example of a used question is shown in Appendix Fig. A.1, the complete list of tasks is shown in Table 3.2.
1 Destination entry controller 12 Destination entry controller - complex 2 Destination entry speech 13 Activate rear window heating
3 Find target on digital map 14 Climate control 4 Adjust bass settings 15 Watch TV 5 Select mp3 with controller 16 Calculation task 6 Volume control steering wheel 17 Insert CD 7 Select phonebook contact 18 Read e-mail
8 Talk on the phone 19 Texting on mobile phone
9 Volume control 20 Select contact from mobile phone 10 Radio tuning 21 Select mp3 on iPod
11 Adjust bass settings - complex
Table 3.2: List of tasks rating in the Delphi study.
For each task they had to give a rating regarding the demands imposed by this task. As a rating scale we used the approved Driver Activity Load Index (DALI, [128], [127]) that has been derived from the more general workload questionnaire NASA-TLX (Task Load
Index, [74]). The NASA-TLX follows the assumption that workload is influenced by mental
demand, physical demand, temporal demand, performance, frustration level and effort. The DALI assesses seven dimensions of subjective workload during a dual-activity setup (cf. [87]):
1. Effort of attention: Attention required by the activity (think about, decide, choose, look for...)
2. Visual demand: Attention of the visual channel required for the activity 3. Auditory demand: Attention of the auditory channel required for the activity 4. Tactile demand: Attention of the tactile channel required for the activity
5. Temporal demand: Specific constraint due to timing demand when running the activity
6. Interference: Possible disturbance when performing the driving activity simultaneously
with another task
7. Situational stress: Level of constraints while conducting the activity, such as fatigue, irri- tation, discouragement, feeling of overload, etc.
The global attention demand results from
7
∑
n=1
di×20
7 with d∈ {0, ...,5}, which means that all di- mensionsd are rated on a 0 – 5 scale. For the Delphi study we adapted the DALI range to 1 –
5 in order to obtain a balanced scale. The DALI score translates to demand, so a lower rating indicated less demand and is therefore a better result.
Results Texting on a mobile phone resulted in highest cumulated mean score (M=2.30), adjusting the volume on the steering wheel in the lowest (M=.61, cf. Fig. 3.1). The highest attentional demand was imposed by the mental calculation task (M=3.58) and the lowest by manual volume control (M=.53). Watching TV resulted in the highest estimated visual demand (M=3.58), talking on the phone in the lowest (M=.32). The TV task was also judged as the task with the most interference with the driving task (M=3.42), adjusting the volume on the steering wheel with the lowest (M=.47).
S l t 3 iP d Select contact from mobile phone Adjust bass settings ‐complex Destination entry controller Calculation task Radio tuning Insert CD Destination entry speech Select phonebook contact
Adjust bass settings Select mp3 with controller Climate control Activate rear window heating Volume control Volume control steering wheel
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Texting on mobile phone
Watch TV Read e‐mail Find target on digital map Talk on the phone Destination entry controller ‐complex Select mp3 on iPod
Attention Visual Auditory Tactile Temporal Interference Stress
Figure 3.1: Mean results of the final Delphi rating comprising the DALI dimensions for each of the 21 tasks (standard deviation not displayed).