Object and spatial subsystems in mental imagery : behavioral investigations

Abstract

Recent evidence indicates that mental imagery comprises independent object and spatial subsystems. The experiments reported here are behavioral studies of these subsystems. Experiments 1 and 2 used the selective interference paradigm to determine whether these subsystems could be behaviorally dissociated. In Experiment 1, subjects listened to descriptions of spatially arrayed objects as they performed an object or spatial interfering task. Recall of the descriptions was expected to demonstrate selective interference of item names or spatial relations as a function of interfering task, however this result was not found. In Experiment 2, subjects indicated whether sentences read in either a spatial or a non-spatial format were true or false. Sentences required either object, spatial, or no imagery. The spatial presentation differentially slowed verification time for high imagery sentences compared to abstract sentences. The prediction that the spatial format would selectively slow verification time for spatial versus object imagery sentences did not obtain for all subjects, however subjects of lower spatial ability showed this pattern of results. Experiments 3-5 isolated one contribution of spatial imagery to memory: Its ability to preserve the sequential order of events. Pictures were presented either in the same location or in different locations. When items in the spatial condition appeared in consecutive locations (Experiment 3), there was no effect on amount recalled, but subjects made fewer sequencing errors. No benefits of the spatial presentation were found with nonconsecutive locations (Experiment 4), presumably because subjects could not remember the order of locations in which the stimuli appeared. When retrieval cues informed subjects of the sequence of locations in which the stimuli had appeared (Experiment 5), subjects were able to use the nonconsecutive locations to aid in sequencing. These studies are interpreted in terms of the anatomical underpinnings of the spatial and object systems. It is argued that connections between these systems make it difficult to separate them through selective interference. Nevertheless, Experiments 3-5 indicate that spatial imagery functions to maintain temporal order information. The two systems therefore appear to serve different and complementary roles in memory.