Brain potentials with old/new distinction of non-words and geometric figures.

Event-related potentials (ERPs) were recorded in a continuous memory recognition task. Readable non-words and abstract geometric figures were presented in an alternating manner with an inter-stimulus interval of 2.1 s. Probability of item repetition was 0.25, a lag of one item lay between initial presentation and repetition. OLD/NEW distinction was indicated by the subject's motor response. Using linked-mastoid electrodes for reference, material-specific hemispheric asymmetries of ERPs started 150 ms after stimulus onset in temporo-lateral and parietal recordings with ERPs elicited by non-words being lateralized to the left and those by figures to the right. Clear OLD/NEW ERP effects were found with non-words: Starting about 200-250 ms after stimulus presentation, ERPs of formerly presented (OLD) items were more positive-going in recordings over the midline than ERPs of items that were new and to be repeated (NEW). In contrast, no local OLD/NEW ERP-difference was found with figures. In some brain regions, OLD/NEW ERP-differences were larger over the left hemisphere compared to the right. This finding, however, did not differ between non-words and figures.