Abstract: Several theories, such as the post-lexical processing theory and prelexical processing theory, have been proposed to explain the mechanisms of N400. However, there were certain deficits in these theories and in the current paradigm of priming study. Therefore, a new approach and new theories to investigate N400 effects are required. Verification model and interactive activation models were employed in this study to address these problems. The objective was to ascertain which of these theories provides a much better explanation for the mechanisms of N400. The interaction study approach was adopted.
This study adopted a delayed character-matching task to investigate how semantic priming, frequency, and blurredness interact on the N400 components of the Event-Related Potentials (ERPs), which were recorded while participants performed the task. Three Chinese characters were presented in succession in each trial, representing the prime, the target, and the probe stimuli. The prime and the probe were intact characters, whereas the target was blurred one. The materials and procedures in the two experiments were the same, except for the blurredness level of the targets: The targets were slightly blurred in Experiment 1 and were more blurred in Experiment 2. The priming and frequency were manipulated in each experiment with four treatment conditions, namely, primed high frequency, primed low frequency, unprimed high frequency, and unprimed low frequency conditions. Blureedness was manipulated across experiments. The subjects’ task was to press one keyboard if the target and the probe were the same character, and to press another otherwise.
The results of Experiment 1 showed larger N400 amplitudes in unprimed condition than in primed condition for low-frequency target characters, but not for high-frequency target characters. By contrast, Experiment 2 showed N400 priming effects, but no N400 frequency effects. Combining the date from the two experiments, both a three-way interaction among the blurredness, frequency, and priming, and an interaction between blurredness and frequency in unprimed condition were found. An interaction between blurredness and priming under high frequency was observed, whereas interaction between blurredness and priming under low-frequency condition did not occur. These interactions are interpreted to indicate that frequency, blurredness, and priming are involved in the same stage of lexical processing.
In conclusion, the results of the present study are partly expected from the lexical verification explanation constructed based on the verification model, completely expected from the interactive activation model, but completely unexpected from the postlexical theory.

Key words: the verification model, the interactive activation model, N400, blurredness, semantic priming, frequency