3.2 Experiment 1—Participants Asking Questions
In the first experiment, participants completed mobility tasks using only their cane. There were four tasks: find the front entrance of a particular building, walk on the sidewalk toward the next intersection, exit a plaza and cross a street (with traffic lights but without an audible signal), and find and enter the train station. Participants were brought to a starting position in the vicinity of their task objective (i.e., approximately 300 m from their destination). Each task took about 5– 10 min, and experiment 1 lasted approximately 30 min.
During the four tasks, the participants were accompanied by a sighted experimenter, who did not guide the participants. The investigator only intervened in potentially dangerous situations. The participants were instructed to request any information they needed, in the form of questions. In turn, the sighted experimenter would answer these questions, as asked. Participants were fitted with a microphone to record their questions and answers during the experiment.
All tasks were performed in environments unfamiliar to the participants and conducted around the same time of day (noon). However, conditions for each participant varied slightly, due to the dynamic nature of the urban environment, which resulted in varying levels of background noise due to traffic and construction, and a different number of potential obstacles like pedestrians and parked vehicles. One participant was not able to complete this experiment and was therefore excluded from the analysis.
3.3 Experiment 2—Participants Rating of Experimenter Descriptions
The second experiment was conducted right after the first experiment with the same 13 participants. In this experiment, the participant was assigned a single mobility task: get to the entrance of a particular building in downtown Boston, which involved a 15-minute walk from the starting point. During this task the sighted experimenter provided information to the participant who rated the information on a usefulness scale from 0 (not useful), 1 (slightly useful), to 5 (extremely useful). The sighted experimenter described 20 predefined subjects along the route. These included 18 objects, such as a pole or a building, route instructions, and a general description of the participant's current location (Figure
1 and Table
2). Route instructions and a general description of the current location were included to test how this type of navigation and orientation information is rated and prioritized compared to the object descriptions. The selection of objects was made based on systems proposed in prior research [
20–
26], expressed information preferences [
32,
33], and based on objects in the environment in which the experiment took place. Two criteria were considered:
•
Information from both a low and intermediate level of abstraction (as described in Reference [
52]) was represented in the selection.
•
Two instances of each object occurred along the route.
Each object was described using five sentences on average and were rated by the participants as independent pieces of information. The different sentences described various aspects of the object such as the appearance, dimensions, and location.
We exclusively refer here to the 18 objects and not to information about the Route and Current Location, as these could not be described similarly. In the remainder of this work, we make the distinction between subjects (i.e., all 20 subjects described to participants) and objects (a subset of 18 objects of the 20 subjects).
Information about the route and location descriptions were provided at two levels of precision: imprecise and precise. For the route, the descriptions were formulated as in the following examples: “walk to the end of the block, and take a right” (imprecise), “walk 100 feet toward 11 o'clock, then continue toward 9 o'clock” (precise). The Location descriptions were formulated as in the following examples: “there is a building on your left, close” (imprecise), “there is a building at 9 o'clock, 10 feet away” (precise). All descriptions were formulated from the participant's point of view, since blind people use “person-oriented” descriptions while describing familiar routes [
38,
47].
Each subject type was discussed twice during the experiment, which accumulated to a total of 40 subjects that were discussed over eight stops (in groups of five per stop). During a stop the participant was asked to imagine the following scenario “you are alone, walking toward the direction you are facing and have access to the following pieces of information…” Then, the sighted experimenter presented five different subjects (e.g., Figures
1 and
3). Two instances of the same subject were never presented during a single stop. Descriptions were pre-prepared and read from a script.
As an introduction to each object and to check for answer consistency across the two instances, the experimenter always started describing an object with a detect sentence (e.g., instance 1—description 1: there is a building; instance 2—description 1: there is a building). In case of more dynamic objects such as a car or pedestrian, a virtual instance of such an object was described to make sure all participants received the same information. Participants were not informed of this, because we did not want to risk a bias in the scoring of these objects. None of the participants remarked missing audio cues in cases where virtual objects were described. This might be due to the background noise at the city center.
For the objects, the two instances were described at a different relative position in terms of distance and angle (e.g., position 1—there is a building, at 3 o'clock, 100 feet away; position 2—there is a building, at 2 o'clock 30 feet away). In this comparison, we only considered the scores for the
location (precise) sentences. The objects were divided into 3 groups based on the characteristics of the difference in relative position of the two instances (Figure
2). The difference in relative position of objects in each group is summarized in Table
3. We hypothesized that participants would score as more useful the description of objects that are closer but at a similar relative angle (
distance only), at the similar distance but more in the prospective path of the participant (
angle only), or both closer and more in the prospective path of the participant (
combined). In the analysis, we excluded objects with an opposing effect of relative distance and angle. For example, position 1—there is a building, 12 o'clock, 200 feet away; position 2—there is a building, 9 o'clock, 20 feet away. The experiment was not designed to investigate this effect; hence, we do not have enough data to examine this relationship. We consider this combination of a potential positive score effect due to a decreased relative distance, versus a potential negative score effect due to increased relative angle, to be too complex to be adequately evaluated and interpreted.
After a subject was described and the descriptions were scored for their usefulness, participants were asked to rank order the described aspects in terms of priority. We included this rank order task to examine which information needs to be prioritized. Subsequently, participants were asked if it is useful to talk about a certain object and to explain why information about this object is or is not useful to them. After all five subjects at a stop were discussed using this procedure, the participants were asked to rank order the subjects in terms of priority for the task performance (Figure
3). The duration of each stop was 10–15 min, and experiment 2 lasted a total of 120 min.