Analysis of the Variability of Three-Dimensional Spatial Relations in Visual Short-Term Memory

In a laboratory experiment, 13 participants reproduced from memory the position of a sphere relative to a second landmark sphere located on the viewing axis of the observer. The relative location of the second sphere varied both laterally and in depth. The stimuli were generated on a stereoscopic display. The paper focuses on the analysis of the structure of the noise in the reproduced object locations, this structure reflecting the mental representation of the stored spatial relations. The results showed that the spatial location of the landmark sphere affects the variability of the reproduced object locations. In particular, the variability in the frontoparallel plane increases with the length of the depth component of the spatial relation. This finding can be interpreted in two ways. First, spatial acuity in perception decreases, or second, participants encode sensory information by transforming it into a mental spherical coordinate system. Both interpretations are discussed.