Investigating the orgins of the space-number association

Numbers are one of the most common elements in our day-to-day life. The main aim of this thesis is to investigate one of the most intriguing and debated issues in the field of numerical cognition, which is the relation between the representation of numerical magnitudes and the representation of spatial information. The strongest empirical evidence for the interaction between number and space is, undoubtedly, the Spatial-Numerical Association of Response Codes effect (SNARC effect, Dehaene et al., 1993). Authors observed that in tasks requiring the choice between left and right motor responses to judge the parity (e.g. odd or even?) or the magnitude (e.g. higher or lower than 5?) of Arabic numbers presented at central fixation, participants showed faster manual responses when left responses were associated to small numerical magnitudes and right responses to large numerical magnitudes rather than vice versa. The present thesis will provide evidences on different experimental conditions underlying the Space-Number Association (SNA). In particular, the main theoretical hypothesis of the present work recalls the conclusions of Aiello et al. (2012): the left-to-right disposition of numerical magnitudes is not automatic and inherent in the very concept of number, but it is rather elicited by the use of left/right response or conceptual codes. In order to support this hypothesis: • Study 1 highlights how, in absence of a task-relevant association between conceptual or response codes and numerical magnitude, no SNAs will be present. • Study 2 attempts to “reconstruct” the experimental conditions under which numerical magnitudes interact significantly with conceptual spatial codes. • Study 3 investigates more thoroughly the nature of this interaction, under the hypothesis that SNAs are semantically mediated. • Study 4 shows how, in the presence of manual response codes associated with numbers, the SNA is stable and significantly present regardless of the degree of explication of the conceptual association between numerical magnitudes and spatial codes. Study 1 The aim of this study is to evaluate the consistency and reliability of the Attentional-SNARC effect (a behavioural effect indicating an automatic SNA) through a re-analysis of data gathered from different investigations performed with similar procedure and stimuli in a sample of 174 participants. Results highlighted that an automatic and implicit SNA appears to be non-existent in behavioural conditions where the use of spatial response codes is not required. Given the absence of this association, an intriguing interrogative remains without an answer: what is the origin of reliable SNAs? Study 2 To clarify the origins of the SNA, two questions must be addressed: • do contrasting spatial codes used in isolation inherently evoke the conceptual left-to-right representation of number magnitudes? • do contrasting number-magnitude codes used in isolation inherently evoke the conceptual activation of contrasting left/right spatial codes? Results from Go/No-Go tasks highlighted that a reliable association between space and numbers requires the joint use of numerical codes and spatial codes, and that SNAs are not observed when task instructions only ask for the isolated use of one of the two codes. Study 3 Starting from the conclusions of the previous study, one crucial question remains open and regards the depth of the link that reading habits create between space and numbers. This Study shows that the more left/right spatial codes and small/large magnitude codes are jointly and concurrently employed during the processing of numbers, the more the association between number and space representations is stable and reliable. Study 4 The main hypothesis of this study is that, in SNARC-like tasks, the left-to-right arrangement of competing motor responses might act as a powerful trigger for the temporary association between space and number representations and the arrangement of numerical magnitudes on a left-to-right oriented MNL regardless of the degree of the semantical explication of used codes. Results confirmed the main hypothesis of this study. In particular, compared with the purely conceptual contrast between left and right spatial codes that regulates unimanual Go/No-Go choices, the motor contrast between a left-hand and right-hand choice in SNARC tasks is more powerful, and therefore sufficient, in triggering the left-to-right mental spatialization of number stimuli regardless of the degree of the semantical explication of codes. Taken together, results highlighted in the present thesis provided further evidences of a contextual, rather than innate, interaction between numerical magnitudes and spatial information. For this reason, these results confirm the hypothesis of Aiello and colleagues (2012), as these authors consider the SNA as the result of a temporary and flexible association between spatial and numerical representations. Experimental evidences summarised in this thesis highlight that different cognitive contexts and mechanisms can determine the generation of space-number association: providing an exhaustive description and understanding of these contexts is one major challenge for future investigations.