Sasanguie, D. 1 , Reynvoet, B. 1 & Goebel, S. M. 2
1 Dept. of Psychology, University of Leuven, Belgium
2 Dept. of Psychology, University of York, UK
Previous studies with Transcranial Magnetic Stimulation (TMS) have shown that stimulation of the parietal cortex can disrupt symbolic number processing. From those experiments alone, however, it cannot be concluded whether the stimulation interfered with representational or decisional stages of number processing as both magnitude processing and response selection have been linked to the parietal cortex. In this study, we conducted a priming task which enabled us to dissociate between representational and decisional effects. Sixteen adults were showed two sequentially presented single digits and had to decide whether they were larger or smaller than five, while being stimulated with repetitive online TMS (rTMS, for 500ms at 10Hz) over the left intraparietal sulcus (LIPS) or the vertex (control site). In addition, the onset of the stimulation was manipulated and was simultaneously administered with either the first or the second digit. The comparison distance effect (i.e. distance between the target and the standard) and the priming distance effect (i.e. distance between sequentially presented targets) were analyzed. Repetitive TMS over the LIPS slowed down the reaction times but the comparison distance effect remained significant. In contrast, the priming distance effect disappeared when the stimulation was administered together with the first stimulus. In general, these results suggest that stimulation over the LIPS interferes with magnitude representations and can delay decisions based on magnitude representations without affecting the decision processes.