Literature Review

By Sofia Fischel for Neurotech@Davis

The abstraction pieces and definitions of the previous section are vital information to understand before planning a recording session, though forming the whole puzzle takes them a step further. It is somewhat difficult to fully encapsulate the intermediate step between the two: there is more nuance and minutiae than is able to be neatly summarized in one section, and a great deal of specificity is lost when staying in the realm of the general, as these sections have mainly focused. It is difficult too to forewarn of every potential issue teams may face when project types vary widely (monitoring ERP signals vs alpha waves, for example). As a result, it is imperative that a detailed literature review occurs. There’s no need to reinvent the wheel. Particularly with long established EEG paradigms – P300, N400, etc. – there are countless studies that can provide excellent resources; note common themes in electrode placement, stimulus, type, trial length, etc. Other UC neurotech clubs are often useful resources for the notable reason of using the same equipment (OpenBCI Cyton boards). Research studies too are important in finding the information above, though they often have more advanced technology at their disposal, so note if they are using EEG caps, EMG monitors, etc. It may be required to accommodate accordingly.

Spend a substantial amount of time doing research; much like good experimental design, investing time now saves effort down the road.

Example

Read through the following taken from the following paper: “EEG Correlates of Involuntary Cognitions in the Reflexive Imagery Task”$^{10}$. Notice the level of specificity. (Click Figure 1 for the schematic description of the trial sequence and Appendix for the stimuli).

This is the level of detail to strive for during project proposals. Remember: imagine someone is given only your experimental design and is tasked with running the setup exactly as you have imagined; are they given enough detail to do so? Where might there be some confusion?

Abstract of study: “The Reflexive Imagery Task (RIT) reveals that the activation of sets can result in involuntary cognitions that are triggered by external stimuli. In the basic RIT, subjects are presented with an image of an object (e.g., CAT) and instructed to not think of the name of the object. Involuntary subvocalizations of the name (the RIT effect) arise on roughly 80% of the trials. We conducted an electroencephalography (EEG) study to explore the neural correlates of the RIT effect. Subjects were presented with one object at a time in one condition and two objects simultaneously in another condition. Five regions were defined by electrode sites: frontal (F3–F4), parietal (P3–P4), temporal (T3–T4), right hemisphere (F4–P4), and left hemisphere (F3–P3). We focused on the alpha (8–13 Hz), beta (13–30 Hz), delta (0.01–4 Hz), and theta (4–8 Hz) frequencies.”

Instructions were presented on a 56 cm monitor using a Dell Optiplex 980 computer with a viewing distance of approximately 60 cm. Stimulus presentation and behavioral data were controlled by SuperLab version 5 (Cedrus Corporation) software. Instructions were presented in black 48-point Helvetica font on a light gray background. In the One-Object block, the stimuli consisted of 37 well-known visual objects (e.g., a key; Figure 1; Appendix) that were displayed at a centered viewing angle of 4.22°× 6.49° (4.42 cm × 6.80 cm). In the Two-Object block, the stimuli consisted of 72 visual objects (e.g., a fire and a cake; Appendix) that were not part of the stimulus set in the One-Object block. On each trial, two visual objects were presented side by side with a fixation-cross (+) between the visual objects (Figure 1). The array of stimuli, which was composed of both visual objects, was presented on the screen with a subtended visual angle of 17.76°× 5.96° (15 cm × 5 cm). Each object occupied the visual angle of 6.56°× 5.96° (5.5 cm × 5 cm). All the stimuli were used successfully in previous research

Procedures

Subjects were run individually, with the experimenter present, in a sound attenuated and electrically shielded room. The experimenter read all instructions aloud to the subject and verified that the subject understood the instructions before proceeding to the critical trials. Before each block, the subject completed a practice trial that resembled the critical trials. Importantly, the stimuli (HARP, for the One-Object block, and FORK and UMBRELLA, for the Two-Object block) to which the subject responded in the practice trials were not included in any of the critical trials. For the purposes of EEG recording, prior to receiving instructions for the critical trials in each block, the subject completed a baseline trial in which he or she gazed at a fixation-cross presented for 1 min.

The funneled debriefing included general questions to assess whether (a) the subject was aware of the purpose of the study, (b) the subject had any strategies for completing the task, (c) anything interfered with his or her performance on the task, (d) there were any objects of which the subject did not know the name, (e) the subject often named both objects during trials in which he or she happened to think of the name of either object, (f) the subject ever thought of the name of the object in a language other than English, (g) he or she pressed the spacebar or “z” key and “/” key in such a situation, and (h) he or she had a strategy for completing the task if he or she happened to think of the name of the object in more than one language. From 25 subjects, the data from all subjects were included in the analysis.