Abstract
As a result of the representation of numerosities, more accurate and faster discrimination between two numerosities is observed when the distance between them increases. In previous studies, the comparison and same-different task were most frequently used to investigate this distance effect. Recently, it was questioned whether the non-symbolic distance effects derived from these tasks originate at the same level. In the current study, we examined the behavioral and neural distance effects of the comparison and same-different task to assess potential differences between both tasks. Participants were first year university students. Each participant completed both tasks, while their reaction time, accuracy and brain activity on predefined components was measured. The early N1-P2p transition and the P2p component on temporo-occipital (TO) and inferior parietal (IP) electrode groups were considered, as well as the late P3 component on a central (C) electrode group. The results showed that the behavioral distance effects from both tasks were comparable, although participants' performance was worse on the same-different task. The neural results revealed similar effects of distance on the mean amplitudes for the early components for both tasks (all p′s < 0.02) and an additional effect of task difficulty on the mean amplitudes of these components. Similar as in previous studies, we found a (marginally) significant increase in mean amplitude of the later P3 component with increasing distance for the comparison (p = 0.07), but not for the same-different task. Apparently, the initial stages of number processing are comparable for both tasks, but an additional later stage is only present for the comparison task. The P3 effect would be indicative of this decisional stage, which was previously proposed to underlie the comparison distance effect (CDE).
Highlights
The non-symbolic comparison distance effect (CDE) refers to the more accurate and faster discrimination between two numerosities that are farther apart (e.g., 2 dots and 10 dots) than between two numerosities that are closer to each other (e.g., 2 dots and 4 dots)
Linear contrasts of the mean amplitudes of the different distances in the right hemisphere indicated the presence of an increase in mean amplitude with increasing distance [F(1, 16) = 6.48, p = 0.02]
To conclude, the similarity of the behavioral distance effects and the similar effects of distance on the early neural components in the comparison and same-different task suggest that both tasks are comparable
Summary
The non-symbolic comparison distance effect (CDE) refers to the more accurate and faster discrimination between two numerosities that are farther apart (e.g., 2 dots and 10 dots) than between two numerosities that are closer to each other (e.g., 2 dots and 4 dots). This effect is obtained when participants have to indicate the larger of those numerosities (i.e., the comparison task) and is present at different ages (e.g., Buckley and Gillman, 1974; Sasanguie et al, 2012). A larger overlap leads to a lower accuracy rate and a longer reaction time (i.e., the distance effect)
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