Visuospatial priming of the mental number line Ivilin Stoianov * , Peter Kramer, Carlo Umilta `, Marco Zorzi Dipartimento di Psicologia Generale, Universita ` di Padova, Via Venezia 8, 35131 Padova, Italy Received 5 October 2006; revised 17 April 2007; accepted 20 April 2007 Abstract It has been argued that numbers are spatially organized along a ‘‘mental number line’’ that facilitates left-hand responses to small numbers, and right-hand responses to large numbers. We hypothesized that whenever the representations of visual and numerical space are concur- rently activated, interactions can occur between them, before response selection. A spatial prime is processed faster than a numerical target, and consistent with our hypothesis, we found that such a spatial prime affects non-spatial, verbal responses more when the prime fol- lows a numerical target (backward priming) then when it precedes it (forward priming). This finding emerged both in a number-comparison and a parity judgment task, and cannot be ascribed to a ‘‘Spatial–Numerical Association of Response Codes’’ (SNARC). Contrary to some earlier claims, we therefore conclude that visuospatial–numerical interactions do occur, even before response selection. Ó 2007 Elsevier B.V. All rights reserved. Keywords: Number line; SNARC; Magnitude; Backward priming; Attentional shift 1. Introduction A few decades ago, it was suggested that the representation of numbers could be spatially organized along a mental number line (Restle, 1970). That this mental num- 0010-0277/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.cognition.2007.04.013 * Corresponding author. Tel.: +39 049 827 6642; fax: +39 049 827 6600. E-mail address: ivilin.stoianov@unipd.it (I. Stoianov). www.elsevier.com/locate/COGNIT Cognition 106 (2008) 770–779