Large Manual Pointing Errors, but Accurate Verbal Reports, for Indications of Target Azimuth

Abstract

Many tasks have been used to probe human directional knowledge, but relatively little is known about the comparative merits of different means of indicating target azimuth. Few studies have compared action-based versus non-action-based judgments for targets encircling the observer. This comparison promises to illuminate not only the perception of azimuths in the front and rear hemispaces, but also the frames of reference underlying various azimuth judgments, and ultimately their neural underpinnings. We compared a response in which participants aimed a pointer at a nearby target, with verbal azimuth estimates. Target locations were distributed between 20° and 340°. Non-visual pointing responses exhibited large constant errors (up to −32°) that tended to increase with target eccentricity. Pointing with eyes open also showed large errors (up to −21°). In striking contrast, verbal reports were highly accurate, with constant errors rarely exceeding ±5°. Under our testing conditions, these results are not likely to stem from differences in perception-based versus action-based responses, but instead reflect the frames of reference underlying the pointing and verbal responses. When participants used the pointer to match the egocentric target azimuth rather than the exocentric target azimuth relative to the pointer, errors were reduced.