The effect of age on egocentric and allocentric spatial frames of reference

Abstract

IntroductionLittle is known about the developmental course of spatialmemory, although this topic would be of clinical andtheoretical relevance. Spatial memory plays a fundamentalrole in everyday human activities, like way-finding, local-izing places or grasping objects. The assessment of spatialmemory, that is the pre-requisite of independent mobilityin the environment, is therefore crucial to monitor elderlypeople’s well-being.The purpose of this research is to investigate the effectof ageing on the frames of reference necessary to representspatial information in memory. Frames of reference areusually divided into egocentric and allocentric. Egocentricframes define spatial information with respect to the bodyor its parts, while allocentric frames specify spatial infor-mation on the basis of external objects (Kosslyn 1994).So far, age-related changes in basic visuospatial abili-ties, mental imagery and navigational abilities have beeninvestigated (see Ruggiero et al. 2008; Iachini et al. 2005).Laboratory-based psychometric tasks, such as mentalrotation, and more ecological tasks, such as direction-finding and map learning have been used (Barrash 1994;Wilkniss et al. 1997; Kirasic 1991). The results obtainedare still controversial and it is not yet clear which spatialprocesses decline with normal ageing and which ones arepreserved. Furthermore, deficits in spatial cognition, suchas topographical disorientation (Aguirre and D’Esposito1999), may be symptoms of age-related diseases likeAlzheimer’s disease.As regards the egocentric/allocentric distinction, to thebest of our knowledge the literature on ageing and spatialmemory has not directly addressed this issue. Few attemptsto compare directly these two kinds of processing in youngpeople with behavioural data (Iachini and Ruggiero 2006)and fMRI acquisition (Committeri et al. 2004), and withfocal brain-damaged patients (Iachini et al. 2009a) havebeen made. Parkin et al. (1995) used a spatial discrimina-tion task that involved egocentric spatial memory tocompare healthy elderly and young people. They found nosignificant negative effect of age on the spatial perfor-mance, but only a slight decline. Instead, Hort et al. (2007)compared healthy elderly and patients with mild cognitiveimpairment (MCI) and with Alzheimer’s disease (AD) on anavigational task that involved either egocentric or allo-centric components. Interestingly, they found a significantdeficit in the allocentric component in patients but not inhealthy elderly people.In this research healthy participants aged from 20 to89 years were submitted to a spatial task that compareddirectly the capacitytouseegocentric andallocentricframesofreference.Thiswasachievedbymanipulatingtheframeofreference required to give distance judgements. Further, thetask allowed to investigate the performance in far and nearspaces by varying the distance between the viewer and theobjects. In humans, egocentric frames of reference representthe primary interface between the organism and the envi-ronment (e.g. Millar 1994). For this reason, we expected afaster and more accurate egocentric than allocentric perfor-mance. As regards the effect of ageing, two outcomes arepossible: a negative influence on both spatial components ora selective drop in one of them. In the second case, an ego-centric decrease would be more likely (see Hort et al. 2007).