Discussion of Experiment 2

A. Utility and usability of CROSSFLOW

Excluding the invalid tasks, in the CROSSFLOW condition the participants found the target foam walls among many visually similar walls in a complex indoor environment which contains many small and partitioned spaces using CROSSFLOW with 100% success rate regardless navigation errors. Although they only used vibration cue combing with the fish-flow visual pattern, they were still able to complete the tasks within a reasonable period of time. This result proves the success of CROSSFLOW's user-interface and interaction model and supports our hypothesis that CROSSFLOW could support multiple simultaneous users to perform navigation tasks in an unfamiliar complex indoor

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environment. The result of the navigation task success rate in the CROSSFLOW condition is also a evidence that the designed components of CROSSFLOW including regular cue mapping, abstract public directional information (the projected fish-flow pattern) and private cues (the vibrations from smartphone) can be used for personalized directional information presentation for multiple simultaneous users, and that users are able to identify the correlation between private cues and public directional information corresponding to a target location or object with less than five minutes training, and then reach it successfully.

B. CROSSFLOW in comparison with MAP

Looking at CROSSFLOW in comparison with hand-held paper map case indicates a similar level of navigation task success rate, navigation error, subjective task workload and completion time of two successfully completed navigation tasks (tasks III and IV), because no statistically robust difference was able to be drawn from the data. However, the mean navigation task time in the CROSSFLOW condition is more than which in the MAP condition on all the five navigation tasks, moreover, the participants spent significantly more time in the CROSSFLOW condition than in the MAP condition on completing three out of five navigation tasks. Such results are inconsistent with the results of the Experiment 1 that the task completion time in the CROSSFLOW condition was significantly shorter than which in the MAP condition. This may be on account of the following factors, which were also confirmed in the participants‘ qualitative feedbacks.

1) Increased density of decision points in the experimental area.

Although the size of the experimental area in Experiment 2 is similar to which in Experiment 1, in order to make the navigation tasks more demanding than which in Experiment 1, 28 foam walls partitioned the experimental environment into many dense and small spaces. As a result, in comparison with the environmental area of Experiment 1, much more decision points were densely distributed in this small scale area (at least four decision points between two target locations). In contrast, there were much fewer decision points in Experiment 1 as there were only targets and distractor targets within the experimental area and no obstacles.

When using CROSSFLOW to navigate, the participants have to rely on the directional information provided by CROSSFLOW at each decision point, where they need

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to wait for a private cue so as to identify a direction to a target location, which may take them a whole cycle time. Sometimes they may wait one more cycle time to confirm the identified direction. This was confirmed by six out of the ten participants on the post- experiment questionnaire. Thus more decision points on the way to a target location means more cycle time the participants have to spend.

In comparison with Experiment 1, more and denser decision points were distributed in the navigational environment, thus the participants may also take longer time to learn the map and the environment in the MAP condition, but they may not need to stop or spend time as long as in the CROSSFLOW condition at each decision point during navigation.

Drawing from the analysis above, it can be concluded that the density of decision points in such a small scale experiment area may have a greater impact on the navigation task completion time in the CROSSFLOW condition than in the MAP condition. This inference is supported by the observations of the participants' behaviour in the two conditions. When the participants encountered a decision point after walking every two or three steps, they apparently paused longer and more frequently in the CROSSFLOW condition than in the MAP condition.

Therefore, the worse time performance in the CROSSFLOW condition might be attributed to the increased density of the decision points in the experimental area, which might also be the cause of a complaint about the duration of cycle time of CROSSFLOW. One of the participants complained that the duration of cycle time of CROSSFLOW was too long, which is probably because she stopped and waited for her private cues too frequently.

2) Shadows of the obstacles and participants in the CROSSFLOW condition. In the CROSSFLOW condition, although two projectors had been employed to project the fish-flow pattern to avoid shadows caused by the foam walls and other obstacles within the experimental area. The shadows near some target locations still existed and blocked the projected visual pattern. Moreover, the shadows of the participants themselves could block their views of the projected pattern as well, which may also impair their navigation task performances. The effect of shadows on the participants' task performances was confirmed by one of the ten participants on the questionnaire and other participants in the interview. Although the data relevant to the shadowed target locations was removed

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from the statistical analysis (as mentioned in Section 5.3.3 A. 1)), the participants' task performances may still be impaired due to the shadows.

3) The fish-flow pattern

The worse time performance in the CROSSFLOW condition may also be attributed to the design and configuration of the visual pattern.

The identification of public directional information corresponding to a target is highly related to navigation task performance, which may involve two processes. The first is the integration of the private cue and the visual pattern corresponding to a target; the second is the identification of the public directional information from the visual pattern corresponding to a target. The design and configuration of visual pattern play important role in the second process. If the design and configuration of visual pattern was not satisfactory for indication of different locations or objects in an indoor environment which contains many small and partitioned spaces, the identification of public directional information from the visual pattern would be difficult. As a result, the navigation performance using CROSSFLOW would be worse than using hand-held map in that kind of environment.

The fish-flow pattern was clear and explicit for indication of locations or objects in an open navigational environment like the environment in Experiment 1, which resulted in better performances in the CROSSFLOW condition than the MAP condition on almost all measures. However, on the post-experiment questionnaire of Experiment 2, four of the ten participants (40% of responses) commented that directional information relevant to them was difficult to be identified from the fish-flow pattern, thus the pattern should be re- designed; and four participants (40% of responses) indicated that the indication of different target locations of the fish-flow pattern should be more explicit. These results and the observation of participants' behaviour in Experiment 2 suggested that the fish-flow pattern was not very satisfactory for indication of several different locations or directions in an indoor environment which contains many small and partitioned spaces, in detail, the flowing directions near in time and the convergences of flows indicating target locations near in space were not very clear and explicit.

The results of the comparison of navigation task success rate and navigation error are consistent with the results of Experiment 1, which suggests that using CROSSFLOW to

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perform relative more demanding navigation tasks is still as successful and accurate as using a hand-held map.

The difference of the score of NASA-TLX subjective workload for the CROSSFLOW condition and the MAP condition is not significant (Subjective workload: CROSSFLOW = MAP). This result is inconsistent with the result of Experiment 1 that the scores of NASA-TLX subjective workload for the CROSSFLOW condition is significantly lower than the MAP condition (Subjective workload: CROSSFLOW << MAP). This result may due to the same factors that discussed in the analysis of the results of navigation task time performance above.