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EEG experiment

The term EEG stands for electroencephalography, which is an experimental method in medicine and neuroscience. The procedure is non-invasive and completely harmless.

The EEG method allows us to record the changes of the brain’s neuro-electric activity at the scalp in response to stimuli. Small electrodes—which are hollow, like tiny doughnuts—are mounted on an electrode cap which resembles a bathing cap. These electrodes conduct the voltage changes that are produced by the brain and are measureable on the scalp. These electrical charges are called brain potentials.

Good conductivity between the electrode and the scalp is necessary to get a viable EEG recording. The participant might therefore need to wash her hair in advance of the experiment, to get rid of oils and cosmetic products. Contact between the electrode and the scalp is established by means of a gel that is injected into the hollow electrodes. While the cap is being fitted and the gel applied, the participant reads the experiment instructions, and has the opportunity to ask questions. Next there is a practice run so that the participant gets used to the experiment, and after that the actual experiment begins.

During the recording, participants read or listen to short texts. After each text, they carry out a task (such as a judgement or comprehension question). Our professional laboratory and medical-technical assistants are always on hand to explain the procedure.

The electrodes are attached to an electrode cap to ensure that they sit close to the scalp. The electrodes, which are attached to colorful wires, are simply clipped into the plastic rings in the cap. Once the cap is on the participant’s head, a gel containing electrolytes, fine sand and water is injected into the space between the electrode and the scalp. The gel bridges the gap between scalp and electrode, allowing the electrical signal to be picked up.
While the laboratory and medical-technical assistants prepare, the participants can watch their own brain activity on the assistant’s computer screen. Because of the sensitiveness of the EEG method, we want our participants to relax and feel comfortable. The participants are required to sit as still as possible, because of the sensitive nature of the EEG measurement. The language-related electrical signals we are interested in are much weaker than the signals that come from other sources such as muscle movements. Muscle movements such as eye blinks, chewing and head shaking can mask the language related signals.
The electrical brain potentials are transmitted through an electrode box to an amplifier and then ultimately to a computer where they are visualized and stored.
Our technical assistants Claudia Kilter (in the photo) and Brita Rietdorf supervise the EEG experiments, during which they offer refreshments and generally ensure that the experimental session runs smoothly.