Abstract: Event - related potentials were measured on 1 2 normal youth subjects aged 20 - 22 using paradigm " Cross - modal and delayed response" which can improve inattention purity and avoid the effect of task target on the deviant components of ERP.The experi- ment included two conditions: Attend visual modality , ignore auditory modality: At- tend auditory modality , ignore visual modality. The stimulation presented to every subject was the series of five kinds of stimuli, standard, deviant stimuli and response imperative signal in attended modality: standard and deviant stimuli in unattended modality. The vi- sual and auditory sdmuli occurred with a pseudo - random order. The presentation probability of standard stimuli was 82.5 % and deviant stimuli was 1 7. 5 % Every standard or deviant stimulus followed a response imperative signal in attended modality. Different waves were obtained respectively by subtracting ERPs of the standard and deviant sdmuli in unattended condition from those of the same standard and deviant stimuli in attended condition. The present results showed, Under attended condition, there was anenhancement of N1 elicited by deviant stimuli in auditory ,and standard and deviant in visual modality at their own primary sensory area The evidence supported early selection the- ory of attention being provided by the N1 and Nd1 topography, which showed that the Nd 1 onset was earlier than N1 onset in unattended condition rather than that in attended condition. The Nd1 elicited by auditory and visual deviant stimuli were distributed respectively over their primary sensory areas, but Nd1 evoked by auditory and visualstandard stimuli over frontal scalp This result suggested that the processing location of cross-modal attention to deviant stimuli was modality-specificity and to standard stimuli was supramodal mechanism. With regard to the lasting debated problem about selective at - tention, the author suggested that early and late-selection probably changed as a result of various conditions. This means that the early and late - selection of attention has plasticity

Key words: Event-related potentials (ERPs), Negative difference (Nd), Processing Negativity (PN), Selective attention, Cross-modal and delayed response paradigm