Interventions

We devised three conditions, two of which conveyed different concepts in speech, in a between-subject design. Participants in the Elevation Language group were told that each contour line represents one value of elevation, and to consider that the concept of elevation implies that as contour lines are closer together, elevation changes more quickly. Participants in the Shape Language group were encouraged to focus on the shape of the contour lines, and imagine how they might look in three dimensions. In both conditions, participants imitated the gestures made by the experimenter, and then answered questions about a set of practice maps using their own gestures. Participants in a third, no instruction condition received no instructions on how to interpret the maps, but saw the same stimuli, and were asked open-ended questions about each map. Gesturing by the participant was neither encouraged nor discouraged. Condition assignment was pseudo-randomized and counter-balanced for map experience based on reports of experience with topographic maps (participants’ response to “Rate your experience with topographic maps” on the Map Experience Survey).

The language interventions consisted of two parts: an experimenter-led script, followed by open-ended questions. For the experimenter-led script: the experimenter guided participants of the Elevation Language group through a series of sample topographic maps, describing how the lines provided information on how to analyze the maps and determine the elevation of specific contour lines; the experimenter guided participants of the Shape Language group through a the same sample topographic maps, describing how the lines provided information on how to analyze the maps and how the shape of the lines would allow them to visualize the three-dimensional shape of the terrain surface. The experimenter-led script for both the Elevation Language group and the Shape Language group is provided in Appendix B.

The experimenter read from a script while the participant looked at the maps being described. Throughout the reading of the script, the experimenter gestured on the maps by pointing out various features and tracing the contour lines. For the experimenter-led portion of the intervention, the maps and gestures were identical for the Elevation Language group and the Shape Language group. The script itself was created by adapting the script used with the Pointing and Tracing group in Experiment 1 to emphasize elevation information. An analogous script for shape was then generated by revising each sentence of the script to emphasize shape information, specifically emphasizing transitioning from a two-dimensional pattern to a three-dimensional shape. The two resulting scripts were then matched in structure as closely possible. Both scripts include definitions, examples, and comparisons of either elevation or shape. The Elevation Language group’s script mentions the word elevation 31 times, whereas the Shape Language group’s script mentions the word shape 32 times.

The second part of the intervention, the practice problems, was also adapted from Experiment 1. The questions were designed to focus the participant’s attention on how the contour lines provided information about that condition’s concept. The Elevation Language group’s questions focused on two elevation-related concepts: (a) that each line depicts one level of elevation, and (b) that elevation changes as you move across and between contour lines. The Shape Language group’s questions focused on two three-dimensional shape-related concepts: (a) that the shapes of the lines in two dimensions could be used to predict the shape of the surface in three dimensions, and (b) that the three-dimensional shape of the surface changes as a function of the change in the shape of the lines. The Elevation Language group’s questions mention the word elevation seven times, while the Shape Language group’s questions mention the word shape six times.

The Open-ended group saw the same topographic maps as the two speech groups, and the participants were simply asked to describe what they saw on the maps with requests such as “Take a look at this topographic map, and describe in as much detail as possible what you think the terrain it represents looks like.” When presented with maps 2 and 3 and terrains 2 and 3 (shown in Fig. 7), the participants were asked to compare and contrast both maps and the terrains represented by the maps. When participants were presented with maps 4 and 5 and terrains 4 and 5 (shown in Fig. 7), again, they were asked to compare and contrast the maps and the terrains they represented. The experimenter prompted participants by saying, “Is there anything else you notice about the map(s)?” The complete script for the experimenter-led portion of the experiment is provided in Appendix B. After completing these tasks, participants in the Open-ended group also completed open-ended questions using the same practice maps as those presented to the intervention groups. For the open-ended questions, instead of focusing on a particular type of information, participants were asked to describe each topographic map and were only prompted to give more detail.