Facilitation and inhibition of return using numbers as attentional cues

Behavioural studies have shown a relation between numbers and space (DeHevia et al., 2008). Fischer and colleagues (2003) showed that digits can act as central spatial cues in a target detection task, resulting in shorter reaction times (RT) for left-sided targets when preceded by small numbers and for right-sided targets when preceded by large numbers. This facilitation effect indicates that numbers orient visuo-spatial attention to the left or right hemifield, depending on their magnitude. To date no studies investigated whether this facilitation is followed by inhibition of return at longer intervals, as could be expected with visuo-spatial attention shifts. To this aim, we designed an analogous paradigm to Fischer et al.’s, introducing additional longer intervals. Participants (n=25) were presented a task irrelevant digit (1,2 vs. 8,9) for 400ms and had to detect a brief (100ms) lateral target appearing after a variable interval (100, 250, 500, 750, 1000, 1250ms). A 2x6 repeated measures ANOVA of mean RT, with congruency and interval as within-subject variables yielded a significant interaction (F(5,24)=2.3, p<0.05). As expected, targets were detected faster when appearing in the congruent (small-left, large-right) hemifield after 250ms. Using the regression method proposed by Lorch and Myers (1990), the slope at this interval was significantly negative (t(24)=1.70, p=0.05); indicating a facilitation for the detection of targets in the congruent hemifield) (cf. Fischer et al., 2003). At the 1250ms interval, targets were detected significantly slower when they appeared in the congruent compared to the incongruent hemifield (yielding significantly positive slopes at 1250ms: t(24)=2.68, p=0.007). These findings provide the first evidence that digits not only produce facilitation effects at shorter intervals, but also induce inhibitory effects at longer intervals, confirming the visuo-spatial nature of the attention shifts associated with Arabic digits.