Tracking the sensory and cognitive processes of shifts of spatial attention induced by numbers: an ERPs study

The relationship between space and number has become a focus of intensive investigation (Hubbard et al., 2005; Walsh, 2003). The present paper aims to explore the nature of attentional shifts induced by the perception of irrelevant numbers as it was shown by Fischer et al. (2003). We measured the event related potentials induced by the perception of visual lateralized targets cued by numbers that differed in their magnitude. Congruent trials were defined as those where a target presented in the Right Visual Field (RVF) followed a large number and those where a target presented in the Left Visual Field (LVF) followed a small number. Numbers generate a modulation of evoked potentials on targets as soon as 80 msec after the presentation of the target: congruency of the target determined the amplitude on perceptual P100 and cognitive P300 in both sides of presentation of the target. Although a typical distribution of the components was found, effects of congruency were distributed around anterior and Centro-Parietal sites. Due to the functional properties of the mentioned components, the present data suggest that, in fact, perception of numbers does affect the location of attention to external space. Moreover, the distribution of the congruency effect signals so that the representational nature of numbers makes a difference with respect to the stimuli classically used in cueing studies of visual attention to location. The role of top-down control generated by numbers is discussed.