External and body-centered frames of reference in spatial memory: evidence from touch

The study reports independent effects of external and body-centered reference cues on spatial coding of an irregular sequence of haptic locations. The aim was to investigate the nature of spatial coding by using a modality that does not provide distal cues routinely. Our method isolates and combines body-centered and external spatial reference cues for irregularly placed locations, scanned along a raised-line route. Disrupting body-centered reference for the locations, by orienting the map differently to the body in the test phase than in the presentation phase, doubled errors in positioning the locations along the route in recall. Adding external reference, by giving instructions to use a surrounding frame for reference when body-centered coding was disrupted, reduced errors to near baseline (no-rotation) levels. Adding external reference cues to intact (not displaced) body-centered reference halved errors, as compared with the baseline. The results are consistent with the hypothesis that accurate spatial coding is determined by the congruence of potential reference cues from diverse sources. The new findings suggest that external and body-centered reference cues have independent additive effects on spatial coding. The sequence of locations had a significant effect in all the reference conditions, suggesting the additional use of fortuitous but distinctive local touch cues on the route. The discussion considers theoretical and practical implications of the results.