Counting Is Easier while Experiencing a Congruent Motion

We calculate during each phase of our lives: we try to understand what happens when we invest our money, when we try to keep time and when we have to go home taking the right bus at the right time. All these everyday activities involve numbers and the relation between numbers and their magnitude, which means counting. Different researches have consistently suggested that numerical magnitude is linked with the processing of spatial information[1],[2], to the extent that it has been postulated a common cortical metrics of time, space, and quantity[3]. A straightforward demonstration of the strong association between numbers and space can be found in the so-called SNARC (Spatial Numerical Association of Response Codes) effect[4]. In this task, participants are typically faced with numbers ranging from 1 to 9 and asked to make a parity judgment by pressing a left or right key. Results show better performances when responding with the left key to small numbers (e. g., 2) and with the right key to large numbers (e. g., 7), with respect to the opposite instructions. This evidence led Dehaene and authors-authors to postulate the existence of an horizontal mental number line (MNL) where numbers are progressively located from left to right according to their magnitude (see[5],[6],[7], see also[8]for a different account). The existence of an horizontal MNL has gathered support by several evidence so far, while few studies have found a SNARC effect also for vertical number arrangements (i. e., a facilitation for upward or downward responses to large and small numbers, respectively) across different response modalities, such as key-presses[9]and eye movements[10]. Recently, Holmes and Lourenco[11]focused on the relative strength of the horizontal and vertical mental number organization and found that the vertical axis would be only triggered when numbers are conceptualized as magnitudes that elicit an orientation (e. g., 1st floor from surface, 2nd floor from surface, etc).

Despite the majority of the SNARC studies focused on the influence that number representation has on spatial attention[12],[13],[14], several researches have shown that numerical magnitude can also modulate action-related processes[15],[16],[17],[18],[19],[20]. Further studies demonstrated a bidirectional relation between numbers processing and action-related processes (i. e., motor-to-semantic effect,[21],[23]). More specifically, the motor-to-semantic effect revealed a facilitation, in terms of response latencies, when participants observed a closing grip posture of a biological hand and had to generate small numbers. Badets et al.[21]claimed that the “motor-to-semantic effect is assumed to come from the action system of the participant who either actively performs an action or passively experience a motion and generates a number after” (ibidem, p. 2). Other studies have investigated the influence of the specific body parts' movements, such as head positions[24]or ocular saccades[25], on the generation of small numbers.

In our study we assess whether and to what extent motions experienced with the whole body can influence arithmetical calculations of addition and subtraction. We hypothesize, thus, that these calculations, both leading to numerical magnitudes, can be conceptualized along an upward and downward orientation for additions and subtractions, respectively. A study by Knops, Viarouge, and Dehaene[26]demonstrated that arithmetical calculations bias corresponding spatial location over others: participants tended to select the numerosity displayed in the upper right location for additions, and in the upper left location for subtractions (Space-Operation Association of Responses: SOAR). Differently from Knops and colleagues, we ask participants: (a) to keep adding or subtracting the same quantity (i. e., 3) from a starting number (e. g., 578) in a set period of time (22 seconds); (b) to report the result of each calculation aloud, so that they could be more focused on the calculation process which was occurring on-line and progressively; (c) to experience ascending and descending motions with the whole body, either in a passive (going up and down taking an elevator) or in an active (walking up and down the stairs) mode.

To summarize, we predict a congruency effect between the direction of the experienced motion and the spatial orientation inferred by the type of calculation made. More specifically, we hypothesize a facilitation for the congruent conditions (i. e., ascending body motion/upward orientation: additions; descending body motion/downward orientation: subtractions) with respect to the incongruent ones (i. e., descending body motion/upward orientation: additions; ascending body motion/downward orientation: subtractions).