The implication of short-term memory in numerical magnitude processing: evidence from Turner syndrome

Most studies on early magnitude representation focused on the visual modality with no possibility to disentangle the influence of visuo-spatial skills and short-term memory (STM) abilities on visual quantification processes. In order to specify the influence of visuo-spatial and STM processing on numerical abilities, a series of magnitudes comparison tasks differing on visuo-spatial processing requirement (no/high), on the nature of the magnitude to be processed (continuous/discrete/symbolic magnitude) and on WM demands (simultaneous/sequential presentation) were administred to twenty patients with Turner syndrome (TS), a genetic condition characterized by poor mathematical achievement, low spatial skills and reduced STM abilities. Our results showed a lower acuity than a control group matched on verbal IQ when participants with TS compared the numerical magnitudes of stimuli presented sequentially (low visuo-spatial processing and high STM load: Dot sequence and Sound sequence). No difference was observed in the numerical comparison of sets presented simultaneously or when comparing continuous and symbolic magnitude stimuli. Besides, the group difference in sequential tasks disappeared when controlling for STM abilities. These results highlight the importance of STM abilities to extract numerosity through a sequential presentation and underline the importance of considering the impact of format presentation on magnitude judgments.