The overall goal of this experimental procedure is to analyze visual perception of media content by the quantification of spontaneous eye blink rates with the help of electroencelographic and electromyographic recordings. Here we are going to pay attention to eye blink rates of participants while watching movies in a screen. The main functions of the eye blinks is to protect the cornea from mechanical and chemical insults and also to maintain it wet and protect it from foreign debris.
This type of eye blinks can be produced by different type of eyelid movements. For example, we have the corneal reflex that is produced by the activation of the mechanical or chemical or painful receptors and they can be found in the cornea and also in the skin. The stimulation of these receptors is stimulating in the same way the trigeminal neurons:first the trigeminal nerve and then the trigeminal neurons and these are activating the motor neurons that they are placed in the facial nucleus.
But there is another not so well-known function of the eye blink which is related to the cognition process of visual input. And this is usually for what, in fact, is happening every time along the visual period of the day because of those spontaneous eye blinks, the visual perception is refreshed during the blink. So the blink on one side is modifying slightly our visual perception of reality.
We are not conscious of that. In fact, we are not conscious that during those spontaneous blinks that last about 100-200 milliseconds, we have the certainty perception that we still see, but this is impossible because the pupil is covered by the lid, the upper lid, for this period of time. The advantage of using EG/MG measurements for analyzing visual perception of media content is the high temporary solution of the data over other thirty cases such as FMRI.
With the use of EG/MG we have access to brain and eyelid activities at different frequencies. The advantage of this procedure is to have a high synchronized response of electrical brain activity to the presentation of the selected visual stimuli. It's important to control all variables and parameters of media content and visual perception.
For that reason is desirable to create your own video movies. In this regard, own content can be created with a video camera by the lab or by a media center for this purpose. Participant selection is also very important.
Multiple investigations have proven different perceptive patterns between subjects during or looking to a visual task. For that reason, it is needed to pay attention to participant selection. For instance, in this experiment, the spontaneous eye blink rates performed by media versus non-media professionals are compared.
In this case, media professionals were selected with some concrete criteria. They had to have a minimum of six years of experience making decisions related to media editing or audio cuts in their everyday work. The specific criteria for the selection of the subjects should be written in the methods part of the publication.
Create a proper scenario for the presentation of your video movie. Any distracting element can annoy your experiment participant. In our case, two black structures were created to define a flexible space.
One black structure as a backdrop for the live play stimulus. And the second black structure with the same dimensions and a hole in the middle to feed a screen for the presentation of the video stimuli. It is important to create a comfortable space for performing your experimental procedure.
Here we are presenting a fragment of the three movies with the same content and duration presented to participants. One was a one-shot movie with an open shot and no camera movements. Another was a Hollywood-style movie with 33 shots and an average shot length of 5.9 seconds and continuity throughout shots, with relationships of content, rhythm, space, and time.
Finally, the third video was an MTV-style movie with 79 shots and an average shot length of 2.4 seconds. Here there was discontinuity of content, rhythm, space, and time between the shots. To begin an EEG/EMG session you have to prepare the following materials:The cap, the control box device, the electrodes, the conductive gel, a syringe, a meter for making the measurements of participants'head, and other basic products.
Now begin by setting the EEG cap to the subject's head. Clean the surface of the skin to remove any sign of dirt, of hair products. Measure the head of the participant.
Measure the distance between the nasion and the inion and mark the half-way point as the vertex. Prepare the electrodes in the EEG cap using the 10-20 system. Put the cap to the subject following the mark, so that the vertex matches the central zero point of the cap.
Apply the conductive gel with the help of a syringe to electrodes, and make sure the cap is properly adjusted. Next, place the reference electrode and the electooculography in the subject's head. Ask the experiment subject whether he or she is comfortable and prepared for the session.
Check that the control box is properly connected to the computer that registers the data. Check that the signal of every electrode is correct, otherwise check the electrode. While recording the EEG/EMG activity, it is desirable that you check that these electrical signals are properly being recorded with the software provided by the manufacturer or any other developed for the experiment.
Confirm the appropriate conductants of EEG/EMG signals and change any parameter of the session if necessary. Once everything is checked, you can start the recording session. Store EEG/EMG data in your files and import them for software analysis.
Eye blinks are usually considered as artifacts in EEG recordings. Thus any software protocol should have a good detector of eye blinks. As used here, it is a good procedure to use specific EEG and EMG electrodes, and to filter the respective bands at the most appropriate frequencies.
Select and filter your data, and apply an appropriate eye blink filter to determine how many and when those eye blinks took place. A good way to triangle your results is to record your participants'eyes with an HD video camera. This will allow you to check eye movements whenever you have any doubts of an eyelid response detected by the software.
In this participant example, we identified several eye blinks while watching at one of the presented stimuli. Those were detected in FP1, FP2, and the EOG electrodes. This figure shows the comparison of the spontaneous eye blink rate in non-media and media professionals while watching different editing styles.
According to our results, media professionalization and media edition affect viewers'eye blink rate. Using EEG or EMG recordings for analyzing subjects'visual perception, the researchers can access to different brain activity in multiple frequency bands. In this experiment, we pay attention to the eye blink rate, but multiple analysis can be now done to the EEG data acquired during the sessions.
This is the first study to report different brain and muscular activities related to media vision styles and to media professionalization. In comparison with other media reception techniques, EG/MG recordings can help to determine brain and muscle activities during the perception of media content.
