Spatial Bias Induced by Simple Addition and Subtraction: From Eye Movement Evidence.

The associations between number and space have been intensively investigated. Recent studies indicated that this association could extend to more complex tasks, such as mental arithmetic. However, the mechanism of arithmetic-space associations in mental arithmetic was still a topic of debate. Thus, in the current study, we adopted an eye-tracking technology to investigate whether spatial bias induced by mental arithmetic was related with spatial attention shifts on the mental number line or with semantic link between the operator and space. In Experiment 1, participants moved their eyes to the corresponding response area according to the cues after solving addition and subtraction problems. The results showed that the participants moved their eyes faster to the leftward space after solving subtraction problems and faster to the right after solving addition problems. However, there was no spatial bias observed when the second operand was zero in the same time window, which indicated that the emergence of spatial bias may be associated with spatial attention shifts on the mental number line. In Experiment 2, participants responded to the operator (operation plus and operation minus) with their eyes. The results showed that mere presentation of operator did not cause spatial bias. Therefore, the arithmetic-space associations might be related with the movement along the mental number line.