Bias in spatial memory: a categorical endorsement.

Two experiments investigated how angular estimates reflect bias as a function of response mode, geometric plane of variation, number of implicit categories, memory load and intervening task conditions. In Experiment 1, participants made motor and verbal estimates of incline and azimuth from memory. Estimates in both response modes showed signs of bias predicted by a single-category adaptation of Huttenlocher et al. [Huttenlocher, J., Hedges, L. V., & Duncan, S. (1991). Categories and particulars: Prototype effects in estimating spatial location. Psychological Review, 98, 352-376] category-adjustment model. In Experiment 2, participants made motor estimates of azimuth from memory under a variety of conditions. Stimuli in this experiment were distributed along two contiguous spatial categories. Although increasing levels of cognitive load did not produce a graded effect, participants' estimates were biased and were well described by a multiple-category adaptation of the category-adjustment model. Results from both studies supported an implicit region-based model of bias in spatial memory. These findings were discussed with respect to accounts of spatial memory that propose multiple systems or formats for coding.