Finding a feature on a 3D object through single-digit haptic exploration

Humans use tactile and kinesthetic cues to easily identify the location of an object feature without vision. This preliminary work quantitatively examined the behaviors of 15 individuals locating a target on an object with a single digit (index or thumb). Search methods could be categorized into one of three search strategies, termed ¿scanning,¿ ¿landmark,¿ and ¿direct.¿ The scanning strategy consisted of (1) back and forth scanning and (2) confirmation of the target, and was always utilized in trials in which the target location was unknown. The landmark strategy consisted of (1) contour following, (2) ballistic movement from an edge toward the target, and (3) error correction and confirmation of the target. The direct strategy consisted of (1) ballistic movement from the start position directly to the target, and (2) error correction and confirmation of the target. Follow-up relocalization trials were executed with the landmark strategy 42% and the direct strategy 58% of the time. The landmark strategy was utilized significantly more often by the index finger than by the thumb. Future work to understand how strategy selection depends on the strength of an individual´s internal model of the 3D object and the uncertainty of finger location with respect to the object will inform the development of a computational model of human object exploration.