Isolating observer-based reference directions in human spatial memory: head, body, and the self-to-array axis

Abstract

Several lines of research have suggested the importance of egocentric reference systems for determining how the spatial properties of one's environment are mentally organized. Yet relatively little is known about the bases for egocentric reference systems in human spatial memory. In three experiments, we examine the relative importance of observer-based reference directions in human memory by controlling the orientation of head and body during acquisition. Experiment 1 suggests that spatial memory is organized by a head-aligned reference direction; however, Experiment 2 shows that a body-aligned reference direction can be more influential than a head-aligned direction when the axis defined by the relative positions of the observer and the learned environment (the "self-to-array" axis) is properly controlled. A third experiment shows that the self-to-array axis is distinct from - and can dominate - retina, head, and body-based egocentric reference systems.

Figure 1

Depiction of the stimulus layout and learning conditions in Experiment 1. Participants in the Stay Misaligned group learned by standing in front of the array (depicted with open circles) with their head facing the array. The direction of their head (dashed arrow) and body (dotted line) were misaligned by 72° . Participants in the Walk Misaligned group (not shown) also learned with head and body misaligned, but in addition, walked in the direction that their body faced, starting from the solid arrow and repeating the circuit indicated by the dotted line. A third group (Stay Aligned) is not shown.

Figure 2

Mean difficulty (defined in the text) of imagining various headings in the learned array among the three groups in Experiment 1. Error bars represent standard errors.

Figure 3

Depiction of the stimulus layout and learning condition in Experiment 2. The facing directions of participants’ body (dotted arrow) and head (solid arrow) were each separated by 36° from the self-to-array axis (dashed arrow).

Figure 4

Mean difficulty (defined in the text) of imaging various headings in the learned array in Experiment 2. Imagined headings that were aligned with the body and head during learning are indicated with a B and H, respectively. Error bars represent standard errors.

Figure 5

Schematic plan view of the stimulus layout and learning condition in Experiment 3. Participants looked into a video camera while learning the positions of three objects on a table next to them. The relative directions among objects were aligned with either the self-to-array axis (e.g., A and B) or the egocentric axes (e.g., A and C). Participants learned both an acute (left) and obtuse (right) arrangement of objects.

Figure 6

Circular histograms of the directions of the objects in the acute (left) and obtuse (right) arrays constructed by participants in Experiment 3. In general, the object aligned with the position axis during learning (represented for each participant by the solid circles) was more closely aligned with the vertical axis of participants’ maps than the object that was aligned with the retinal axis (represented by the open circles.) Also depicted are the direction (m) and length (r) of the mean vector (see Batschelet, 1981) as well as its 95% confidence interval.