Dual-coded advisory turn indicators for GPS navigational guidance of surface vehicles: Effects of map orientation

Objective: The aim of the study was to compare the decision times for left-right decisions for a dual-coded advisory turn indicator and a typical spatial-only turn indicator in a GPS navigational map display. Background: Track-up maps are useful for turn decision making but do not facilitate configural knowledge acquisition of an area. North-up maps present a stable orientation for this type of learning, but typical implementations of north-up map displays lead to misaligned and confusing turn information. We compared a typical spatial-only indicator with a dual-coded spatial-plus-verbal indicator, systematically manipulating vehicle heading and measuring reaction time. The new display, the Dual-Coded Advisory Turn Indicator for Maps (DATIM), was based on an assumption of the advantages of concurrent verbal and spatial processing of advisory turn indicators in map displays. Method: The experimental design was a 2 x 2 x 24 mixed design with indicator type as a between-subjects factor and turn direction (left, right) and 24 heading angles (15 degrees intervals) as repeated-measures factors. Participants made turn decisions while viewing static displays of intersections at variably rotated headings. Results: Reaction time for the DATIM display was consistently faster than the typical spatial-only indicator at all heading angles but especially at heading angles beyond +/- 45 degrees (520-ms difference at 180 degrees). Conclusion: The DATIM display produced faster turn decisions at all heading angles. Application: DATIM displays could allow north-up maps to be used for turn-by-turn decision making in GPS navigational systems. Drivers could have the advantages of both the stable orientation to facilitate planning and the easy turn-by-turn guidance. Limitations are discussed.