Life-span changes in visuo-spatial short term memory
Several experiments are presented to evaluate the development of visuo-spatial short term memory from childhood to old age (from five-year-olds to about 70-year-olds). Visuospatial short term memory was assessed through transformational imagery tasks. The first set of experiments (chapters 3, 4 and 5) concerned the development of mental rotation abilities. A review of the literature suggested that young children (specifically so-called preoperational children) and elderly people are poor at rotating a mental image of a visual pattern. However, as some mental rotation abilities have been reported while using Shepard's paradigm, attention was focussed on the role of the first steps necessarily taken while performing a mental rotation task, specifically the maintenance of a visual pattern in STM. The second set of experiments (chapter 6) considered another imagery subsystem, namely "mental scanning". Like mental rotation, it requires the maintenance of a visual pattern in short term memory. Image maintenance ability has been assessed in reference to Kosslyn's (1994) model although Baddeley's (1986) working memory model- specifically, Logie's (1995) revision of the VSSP - has been sometimes considered while interpreting the data. These two different theoretical models suggest the existence of two related but different subsystems for sorting visual and spatial information. Most of the data presented in this thesis suggest that young children and the elderly have some difficulties maintaining spatial characteristics of a visual pattern in short term memory, i.e. the orientation of the stimulus in the mental rotation tasks and the location of targets in the mental scanning tasks. These results tend to provide some developmental evidence for a dissociation between the dorsal and ventral subsystems. It seems that the two subsystems develop at different speeds. The ventral subsystem might be better developed earlier than the dorsal subsystem. Similarly, some data suggest that the same ventral system is not yet affected by ageing when the dorsal subsystem has already begun to deteriorate.