Interaction between Phonological and Semantic Processes in Visual Word Recognition using Electrophysiology

This protocol can help observe the specific interaction between phonological and semantic patterns in Chinese two-character compound recognition, and infer whether the word recognition is a feedforward or an interactive model. The main advantage is the presence of two distinct tasks of the interference paradigm, which is more conducive to exploring whether the interaction between phonology and semantics is task-independent, and how to interact under different tasks. It would be advisable to strictly control the frequency and the semantic relevance of the materials.

In addition, try to minimize the repetition of target words in each block. Begin by instructing the participant to properly clean their scalp and dry their hair in the laboratory. Invite the participants to sit comfortably on a chair in the chamber where the experiment will be conducted.

Instruct them not to move the chair. Use cotton swabs and facial scrubs to clean the skin under the participant’s left eye for attaching the vertical electro-oculographic electrode, near the outer canthus of the right eye for the horizontal electro-oculographic electrode, and around the right and left mastoid bones for TP9 and TP10, which will be used as new offline references. Place the elastic cap on the participant’s head, and make sure that the Cz electrode is at the center of the top of the head.

Fix the electrode cap strap under the chin, with care to ensure that it is not too tight or too loose. Make sure that the cap and amplifier are connected to the recording system. Next, switch the recording software to the impedance monitoring interface.

Ensure that the impedance of all electrodes does not exceed 5 kilo-ohms or 10 kilo-ohms. Starting with the reference and ground electrodes, pass the syringe filled with conductive gel through the small hole of an electrode to the scalp, and push the plunger to inject a small amount of conductive gel into the scalp, while being careful not to cause an overflow. Monitor the display system that displays the impedance in real time until the impedance drops to the threshold.

After the reference and ground electrodes are prepared, reduce the impedance of the other electrodes in the same way. Tape the small holes on one side of the two electro-oculographic electrodes to prevent the injected conductive gel from leaking. Fix the electrodes to the bottom of the left eye and the outer canthus of the right eye, with tape.

After all the electrodes are prepared, instruct the participants to relax and avoid excessive eye blinking and body movement during the experiment. Present the stimulus via the stimulus demonstration program, and let the participants practice in the practice section. Start the formal experiment and record the EEG information.

If an electrode is loose or the resistance exceeds the threshold, refill the electrode when the participant is resting. Monitor the recording system while recording the EEG information. After the experiment is completed, save the EEG signal and turn off the recording system and amplifier.

Then take off the participant’s cap and instruct the participant to wash off the conductive gel from the hair and skin. Finally, reward the participants and thank them for their cooperation. Select semi-automatic ocular correction with independent component analysis.

Compute the event-related potentials from 100 milliseconds to 600 milliseconds after the onset of the target word, with 100 milliseconds as the pre-target baseline. Set the EEG bandpass-filtered offline from 0.05 to 30 Hertz. Discard epochs exceeding plus or minus 80 microvolts by artifact rejection, and eliminate the trials of erroneous responses.

For high-frequency pairs in the 100 to 150 milliseconds period, it was observed that unrelated pairs elicited a significantly more negative waveform than homophone condition. In the 300 to 500 milliseconds time window for the midline electrodes, it was observed that a target primed by homophones elicited significantly less negative amplitude than did the unrelated condition. In the P200 time window, the event-related potential signal was significantly more positive under semantically-related conditions than under unrelated conditions.

In the N400 time window for the midline electrodes, it was observed that the target primed by semantically-related words released a significantly less negative amplitude than unrelated primes. This protocol helps to observe the interaction between phonological and semantic processes in visual word recognition.