Experimental Equipment and Procedures

A Power MAC mini, Intel Core 2 Duo (8 GB memory), including an NVIDIA GeForce 320M Graphic card, running OS X 10.10 (Yosemite), compatible with Psykinematix software (KyberVision, Sendai, Japan, psykinematix.com) was used to generate and run the motion null task, the EEG experimental conditions, and the direction discrimination task. Visual stimuli were presented on a 24" NEC MultiSync PA241W LCD display with a native resolution of 1920 x 1200 and a refresh rate of 60 Hz. The continuous EEG data were recorded using EGI’s Netstation (v4.3) data acquisition software run on an Apple MAC Pro, sampling at 500 Hz (Electrical Geodesics Inc., Eugene, OR). Anti-aliasing filters (0.1-100 Hz band pass) were automatically applied during digitization of the analog recording. EEG data were recorded in a sound-attenuated, electrically shielded room with humidity and ambient temperature controlled.

4.4.1.1 Peripheral equipment. To calibrate the monitor’s luminance, or brightness levels, a Minolta LS 100 photometer and a Spyder Elite 4 colorimeter were used. A Cedrus Response Box RB-730 was used to confirm participant engagement by recording button presses to the appearance of an emoticon during stimulus presentation. A Cedrus Stim Tracker was used to conduct timing tests and provide offset values for data preprocessing. The ambient room lighting was maintained at consistent levels throughout the stimulus calibration, behavioral task, and experimental blocks (18.1 volts—suitable for photopic vision).

4.4.1.2 Electrode nets. EEG data were collected from (130 series) high-density, 128- channel hydrocel Ag/AgC1 electrodes, made of carbon fiber silver chloride and embedded in soft sponges woven into a geodesic array connected to a high-impedance (200 series) amplifier manufactured by EGI (Electrical Geodesics; Tucker, 1993). This system permits the rapid

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and accurate use of numerous electrodes in high-density arrays with minimal time while

maximizing participant comfort and safety. Each net was soaked in a potassium-chloride solution (2 teaspoons potassium chloride, 1 liter of water purified by reverse osmosis, and 3 milliliters of Johnson & Johnson baby shampoo to remove oils from the scalp) for 5 minutes to minimize impedances and ensure optimal conductivity. The high-density hydrocel nets and associated high-impedance amplifiers were designed to accept impedance values ranging as high as 100kΩ, which permits the sensor nets to be used without scalp abrasion, recording paste, or gel (e.g., Ferree, Luu, Russell, & Tucker, 2001; Pizzagali, 2007). Impedances for all electrodes were measured before data collection and between blocks and were kept below 40kΩ.

4.4.2 Participant Lab Visit and Data Collection Overview

Thirty minutes prior to each EEG recording session, the experimental display monitor was turned on to allow the luminance levels to stabilize at 200 cd/m2_{. Amplifier calibration,}

including zero and gain measurements, were conducted prior to each run. Additionally, timing tests to track stimulus offset, which permits identification of the interval between stimulus recoding and stimulus presentation, were conducted for each recording session.

Upon entering the lab, participants were given a tour of the facilities and provided with a full verbal description of the procedures and risks, including an opportunity to ask questions. Further opportunities and encouragement to ask questions were provided throughout the session. Participants signed the consent forms and were reminded that they could withdraw from

participation at any time. Screenings were then conducted, followed by completion of the online handedness survey adapted by BrainMapping.org from the Edinburgh Inventory. A paper-and- pencil questionnaire was also completed by participants. After the initial screenings, the

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sequence of the assessments and EEG recordings was counterbalanced across participants and a break provided between activities.

Regardless of the order of assessment or EEG recording, both were preceded by the motion null calibration and the direction discrimination task. Participants were comfortably seated and instructed to view the monitor. The motion null calibration was explained before and while practicing the task. Participants were given ample practice opportunities and, when ready, completed the task twice. Two values were obtained for each of the two steps of the calibration process and then averaged. The luminance values for both green and red were then used to customize the color stimulus (entered into the Psykinematix graphical user interface by the principal investigator). After completing the task, participants were asked to select a brain- shaped stress ball from a black nylon bag initially containing 20 blue and 20 purple stress balls. The random selection (no replacement based on 20 participants per group) of a ball provided the sequence of experimental conditions (blue/motion and purple/color) during the EEG portion of the session. This brief activity provided a break from the monitor. Participants then completed the direction discrimination task.

For the EEG portion of the experiment, participants were seated in a comfortable wooden chair 46" away from the monitor screen in the EEG chamber. The circumference of each

participant’s head was measured and the vertex of the participant’s head marked to ensure accurate placement of the net. The appropriately-sized electrode net was then soaked in

potassium chloride solution, as previously described, for 5 minutes, and the net was fitted on the participant’s head. Before running the EEG session, impedances (loss of signal between scalp and sensor) were measured by feeding a minute (400 microvolt) electrical field through each electrode, and then having it measured by the acquisition system so that the amount of signal loss

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could be calculated. Once impedances were measured and any problematic electrodes

repositioned, those electrodes exceeding 40kΩ impedances were identified and noted in the run logbook. Before beginning the recording session, participants were shown how their brain data displays on the screen across electrodes and provided with instructions aimed at reducing

movement artifacts. The instructions included a demonstration of the unwanted effects of various body movements (eye blinks and saccades, head turning, foot tapping, etc.) on the EEG

recording, plus an explanation of when during the programmed presentation such movements would have the least impact (when emoticons are presented). Lastly, participants were asked to try to refrain from moving as much as possible and to wait for the appearance of an emoticon to blink or adjust.

Brief online instructions, a repeat of the previous verbal description of the task, were presented on screen at the start of the experimental block. Participants read the instructions and indicated via button press when they were ready to begin the experiment. All participants were continuously monitored by video feed to the data collection station outside the EEG chamber.

When the first condition (motion or color, counterbalanced) was completed, the

experimenter entered the room to check on the participant and confirmed his or her willingness to continue. Electrode impedances were measured and re-established before proceeding with the second and final condition. At the conclusion of the EEG portion of the experiment, the net was removed from the participant’s head.

The assessment portion of the session was completed in a quiet room with minimal distractions. Components of the CTOPP, WRMT-R, TOWRE-2, WAIS-IV were administered as well as the orthographic and homophone choice tasks and nonverbal reasoning/memory task.

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Upon completion of the assessment and EEG portions of the experimental session, remuneration was provided and participants were encouraged to share their impressions of the experience and ask any further questions.

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5. DATA PROCESSING AND ANALYSIS