Cognitive load in switching between egocentric and allocentric spatial frames of reference: a pupillometry study.

Every day we combine and switch between body-centered (egocentric) and object-centered (allocentric) spatial representations. Several studies so far have reported a greater difficulty to switch from an allocentric reference frame to an egocentric one than vice-versa. To clarify this effect, the present work measured the cognitive load underlying switching vs. non-switching processes between reference frames through cognitive pupillometry. Participants performed a custom-designed visuo-spatial memory task, while pupil dilation variations were measured with eye-tracking. After memorizing triads of objects, participants provided judgments of relative distance in non-switching (only-egocentric, only-allocentric) and switching (from-ego-to-allo, from-allo-to-ego) conditions. The results showed a larger pupil dilation in switching judgments from-allocentric-to-egocentric reference frames than from-egocentric-to-allocentric ones. Moreover, pupil evoked-responses were also larger in allocentric- than egocentric-based non-switching conditions. Overall, the results showed that, for both non-switching and switching visuo-spatial processes, starting from an allocentric-based representation elicits a higher cognitive load than starting from an egocentric-based one. Thus, the disproportional effort in visuo-spatial switching processes seems to be determined by the first reference frame adopted that, in turn, contaminates also the following one.