The representational space of numerical magnitude: Illusions of length

In recent years, a growing amount of evidence concerning the relationships between numerical and spatial representations has been interpreted, by and large, in favour of the mental number line hypothesis—namely, the analogue continuum where numbers are spatially represented (Dehaene, 1992 Dehaene, S. 1992. Varieties of numerical abilities. Cognition, 44: 1–42. [Crossref], [PubMed], [Web of Science ®] , [Google Scholar]; Dehaene, Piazza, Pinel, & Cohen, 2003 Dehaene, S., Piazza, M., Pinel, P. and Cohen, L. 2003. Three parietal circuits of number processing. Cognitive Neuropsychology, 20: 487–506. [Taylor & Francis Online], [Web of Science ®] , [Google Scholar]). This numerical representation is considered the core of number meaning and, accordingly, needs to be accessed whenever numbers are semantically processed. The present study explored, by means of a length reproduction task, whether besides the activation of lateralized spatial codes, numerical processing modulates the mental representation of a horizontal spatial extension. Mis-estimations of length induced by Arabic numbers are interpreted in terms of a cognitive illusion, according to which the elaboration of magnitude information brings about an expansion or compression of the mental representation of spatial extension. These results support the hypothesis that visuo-spatial resources are involved in the representation of numerical magnitude.