Spatial representation of serial order in working memory: a cross-cultural comparison between Japanese and Italian adults

The spontaneous spatialization of serial order in working memory (WM), often reflected by the SPoARC effect, is thought to be influenced by reading/writing habits. However, cross-cultural research comparing the direction of spatial organization in WM remains limited. Here we investigated the spontaneity of this spatialization (its independence from visual-spatial prompts) and its generalizability across different cultural reading systems (Italian vs. Japanese) and spatial axes using a modified SPoARC procedure where visual stimuli are replaced with auditory sequences during encoding, while participants provided manual responses along horizontal (Experiment 1, N = 57) and radial (Experiment 2, N = 49) axes. We predicted a horizontal left-to-right effect in Italians, a potentially different or absent effect in Japanese due to their mixed reading-writing system, and a top-to-bottom radial SPoARC effect in both groups, considering shared downward information flow experiences. Results confirmed an early-left/late-right horizontal SPoARC effect in Italian readers, which extended, albeit significantly smaller, to Japanese readers. In contrast, no reliable radial spatial bias emerged in either group. These findings are consistent with the view, supported by developmental research, that spatial-order associations emerge from the interaction between early maturational constraints on right hemisphere recruitment for visuo-spatial attention and sensorimotor experience from reading/writing habits.