Abstract
The hybrid model of number magnitude processing suggests that multi-digit numbers are simultaneously processed holistically (whole number magnitudes) and in a decomposed manner (digit magnitudes). Thus, individual tendencies and situational factors may affect which type of processing becomes dominant in a certain individual in a given situation. The unit-decade compatibility effect has been described as indicative of stronger decomposed number processing. This effect occurs during the comparison of two-digit numbers. Compatible items in which the larger number contains the larger unit digit are easier to solve than incompatible items in which the larger number contains the smaller unit digit. We have previously described women show a larger compatibility effect than men. Furthermore, the compatibility effect is modulated by situational factors like the vertical spacing of the presented numbers. However, it has not been addressed whether situational factors and sex affect the unit-decade compatibility effect interactively. We have also demonstrated that the unit-decade compatibility effects relates to global-local processing, which in turn also affects spatial processing strategies. However, a link between spatial processing strategies and the unit-decade compatibility effect has not yet been established. In the present study we investigate, whether sex differences in the unit-decade compatibility effect (i) depend on the vertical spacing between numbers, (ii) are mediated via sex hormone levels of participants, and (iii) relate to sex differences in spatial processing strategies. 42 men and 41 women completed a two-digit number comparison task as well as a spatial navigation task. The number comparison task modulates compatibility and vertical spacing in a 2 × 2 design. The results confirm a larger compatibility effect in women compared to men and with dense compared to sparse spacing. However, no interactive effect was observed, suggesting that these factors modulate number magnitude processing independently. The progesterone/testosterone ratio was related to the compatibility effect, but did not mediate the sex difference in the compatibility effect. Furthermore, spatial processing strategies were related to the compatibility effect and did mediate the sex difference in the compatibility effect. Participants with a stronger focus on landmarks in the spatial navigation task showed a larger compatibility effect.
Highlights
Number magnitude processing has been extensively studied using various versions of number comparison tasks
We demonstrated that the compatibility effect is reduced with larger vertical spacing between numbers, suggesting that this facilitation of decomposed processing by simultaneous presentation is diminished if numbers are not presented close enough to each other to allow for efficient simultaneous processing
We hypothesize a significant interaction between sex and vertical spacing in such a way that the sex difference in the compatibility effect is larger with larger vertical spacing between the numbers
Summary
Number magnitude processing has been extensively studied using various versions of number comparison tasks (for reviews see Dehaene et al, 2003; Ballan, 2012). Tasks differ in whether the numbers to be compared are single or multi-digit numbers, whether numbers are compared to a fixed standard or variable and – relatedly – whether they are presented simultaneously or consecutively (Ballan, 2012) Using any of these versions, it has been well established that the comparison of two numbers becomes harder, the larger they are (problem size effect; for a review see Ashcraft and Guillaume, 2009) and the smaller the numerical distance between them (distance effect; Dehaene, 1989; Reynvoet and Brysbaert, 1999; Nuerk et al, 2001; Huber et al, 2017). Spatial and numerical processing interfere in various tasks and share common neural substrates (Hubbard et al, 2005)
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