Event-related potentials (ERPs) were measured in normal young subjects using the paradigm "Cross-modal and delayed response", which is able to improve inattention purity and to avoid the effect of task target on the deviance-related components (DRC) of ERPs. The experiment was conducted under two conditions: one is attending to the visual modality but ignoring the auditory modality, the other is attending to the auditory modality but ignoring the visual modality. A series of five kinds of stimuli were presented to every subject: standard, deviant stimuli and response imperative signal in attended channel; standard and deviant stimuli in unattended channel. The visual and auditory stimuli including verbal and non-verbal stimuli presented in a pseudo-random order. The presentation probability of standard stimuli was 82.5% and deviant stimuli was 17.5%. Every standard or deviant stimulus was followed by a response imperative signal in attended modality. The DRC was obtained by subtracting the ERPs of the standard stimuli from that of the deviant stimuli. The attention components were obtained respectively by subtracting the ERPs of the standard and deviant stimuli in the unattended condition from those of the same standard and deviant stimuli in attended conditions. To clarify present Standpoints that are the central issues of the ERPs research on selective attention，this experiment provided the further evidences and put forward some new ideas.
The main results and conclusions obtained in the present experiment are as follows:
1. The nature of E1ZPs components elicited by the non-verbal stimuli was identical with that found in classical oddball paradigms. For example, the Nl was distributed at the frontal scalp regardless of modality or attention condition. However, the largest Nl peak elicited by spoken words was located at the fronto-central scalp and the Nl elicited y the written words was located at lateral occipital and posterior-temporal area regardless of modality or attention condition. This showed an obvious modality difference and suggested that the Nl elicited by verbal is probably specific index reflecting primary processing of Chinese shape and sound.
2. The Nl elicited using the non-verbal auditory standard, visual standard, and the deviant stimuli at the frontal area is increased under the attention condition than under the unattended condition. Under the verbal attending condition, the Nl yielded by the auditory deviant stimuli was increased at the fronto-central area and thatb by the visual standard, furthermore, the deviant stimuli was increased at the occipital and posterior-temporal areas. This showed that the Nl selective enhancement caused by both verbal and non-verbal attention processing. The present results suggest that the Nl is the outcome of overlapping with the endogenous and exogenous components in view of the dispute whether the Nl is of exogenous or mixed components.
3. Under both attended and strict unattended conditions, an early deviance-related (DRNI) was evoked by using Chinese orthographic and phonological processing. The basic such as peak latency, distribution and attention effects were analogous with the mismatch negativity properties, (MIvIN) except for scalp distribution of DRN1 peak evoked under the unattended condition. In addition, these properties of DRN1 yielded by visual verbal and non-verbal stimuli were also proved as same as auditory MIvIN. Regarding the question as to whether or not visual MIvIN and verbal IvffVtN exists, it can be initially believed that the MIvIN exists in the visual modality and in the language processing process in the current experiment.
4. The auditory and visual MIvIN amplitudes were unaffected by attention while comparing them under attended with unattended condition, The DRN1 amplitudes evoked by verbal were unaffected by attention. The present research suggests that the MIvf1}I amplitude is independent of attention, therefore, it can be looked at as an important index of the reflection of automatic processing process of verbal and non-verbal stimuli in connection with a lasting debate about whether the MNIN is affected by attention.
5. The onset time of early attentive components (Ndl) elicited by non-verbal stimuli was the same as that of N 1如elded under the attention condition but was earlier than that of N1孙elded under the unattended condition. The time sequence of the Chinese orthographic and phonological processing is as follows: the Ndl of relatively pure attention components, the attention N1 of combined with endogenous and exogenous components, and unattention N1 of relatively pure exogenous component. To counter the basic problem of the early or late selection, the present experimental results show that both verbal and non-verbal attention effects first occur before the exogenous components and this provides evidence supporting early selective theory.
6. In the non-verbal task, the largest Ndl elicited by auditory and visual deviant stimuli wasdistributed respectively over their primary sensory projection area, but Ndl evoked by auditory and visual standard stimuli was over the frontal scalp. In the verbal task, the largest Ndl yielded by auditory deviant stimuli were located at the fronto-central area and visual ones were located at the occipital area, however, the Ndl elicited by auditory and visual standard stimuli were located over the occipital area. This suggests that the processing location of cross-modal attention to deviant stimuli is modality-specificity, while standard stimuli use a supramodal mechanism for non-verbal task. In the verbal task, the processing location of selective attention for deviants is different, however, for standards, it is common between modalities. The present research suggests that early- and late- selection probably depends on various conditions for the selective attention, this has been debated for a long time. This means the early-and late-selection of attention has plasticity.
7. According to the characteristics of N350 peak latencies, amplitudes and its scalp distribution, the current results suggest that the N350 is overlapping of N200 and N400, but N400 plays a more important role under the attended condition. On the other hand, the N350 consists mainly of the N200 component under the unattended condition. They are not immutable and this gives an expression that ERPs components reflecting a plasticity of the processing mechanism in the brain.