.. _screen: Screen instructions and notes ----------------------------- The Getting Started guide is available here. :download:`BOLDScreen32_Getting_Started ` More detailed specifications are available `here `_ (Technical Data tab) Windows screen settings ~~~~~~~~~~~~~~~~~~~~~~~ This section assumes that you are presenting visual stimuli using the Windows desktop computer in the MRI control room. By default, the screen in the MRI room should mirror the left-hand-side monitor in the control room, while the right-hand side monitor should not be seen by the participant in the scanner. To achieve this, ensure the following screen settings are set on the Windows desktop computer: - right-click on the desktop and click "Display settings" - in "Rearrange your displays", select display #1, #2 or 1|2 - in "Multiple Displays" at the bottom of the Display settings page: - select "Duplicate desktop on 1 and 2 - check "Make this my main display" - in "Rearrange your displays" at the top, select display #3 - in "Multiple Displays" at the bottom of the Display settings page, select "Extend to this display" Viewing distance and angular size of visual stimuli ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ This section is useful if you need to calculate the angular size of stimuli presented on the screen. The angular size of a stimulus depends on the viewing distance (the distance between the participant's eyes and the screen). Screen distance from participant's eyes *************************************** The viewing distance from the participant's eyes can be estimated as the sum of the following distances: - Distance between screen and rear end of the magnet bore: - When the screen cart is placed on the floor markings, the screen is located **43 cm** away from the rear end of the bore. - When the screen card is placed against the bore, this distance is reduced to **2 cm** - Distance between isocentre and rear end of the bore: **107.5 cm** - Horizontal distance between mirror and isocentre: - Radiographers usually place the participant in such a way that their eyebrows approximately line up with the isocentre. - The distance between the eyes and the eyebrows is approximately 2 cm - Therefore, the horizontal distance between the isocenter and the mirror (at the location where the participant fixates) is also **2 cm** - Vertical distance between the participant's eyes and the center of the mirror: approximately **16 cm** The **total viewing distance** is therefore 43+107.5+2+10 = **168.5 cm** at the floor markings or **127.5 cm** when the screen is placed against the bore. Angular size of stimuli *********************** Given the above distances, **1 cm on the screen** approximately subtends: - **0.34 degrees of visual angle** at the floor markings [:math:`2 \times \arctan(1/168.5/2) / \pi \times 180 = 0.34`] - **0.45 degrees of visual angle** against the bore [:math:`2 \times \arctan(1/127.5/2) / \pi \times 180 = 0.45`] At the default resolution of the screen (1920 x 1080), and given the screen dimensions (69.84 x 39.29 cm), the conversion factor between stimulus size in pixels and stimulus size in degrees of visual angle is (approx.): - **80.85 pixels/degree** at the floor markings [:math:`1920 / 69.84 / \arctan(1/168.5/2) / 2 \times \pi / 180 = 80.85`] - **61.18 pixels/degree** against the bore [:math:`1920 / 69.84 / \arctan(1/127.5/2) / 2 \times \pi / 180 = 61.18`] Maximum eccentricity of the display ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Assuming that the screen is centred on the bore and that the participant fixates the centre of the screen, the maximimum eccentricity in the visual field at which stimuli can be presented on the screen depends on the viewing distance: - When the screen is placed at the floor markings (43 cm away from the rear end of the bore): - The full width of the screen (69.84 cm) approximately fills the entire bore aperture as seen by the participant from the isocentre. So, the maximum eccentricity along the **horizontal** meridian of the visual field (at either side of the screen) is **11.83 degrees** [:math:`2 \times \arctan(69.84/2/168.5/2)/\pi*180 = 11.83`] - The full height of the screen is visible, so the maximum eccentricity along the **vertical** meridian of the visual field is (top or bottom of the screen) is **6.67 degrees** [:math:`2 \times \arctan(39.29/2/168.5/2)/\pi*180 = 6.67`] - When the sceen is placed against the bore: - Only about 59 cm of the screen width is visible to the participant (the diameter of the bore is 58 cm along most of its length, with a slight widening to 67 cm near the end). So, the maximum eccentricity along the **horizontal** meridian of the visual field (at either side of the screen) is **13.20 degrees** [:math:`2 \times \arctan(59/2/127.5/2)/\pi*180 = 13.20`] - The full height of the screen is visible, so the maximum eccentricity along the **vertical** meridian of the visual field is (top or bottom of the screen) is **8.81 degrees** [:math:`2 \times \arctan(39.29/2/127.5/2)/\pi*180 = 8.81`] - When against the bore, additional markings on the floor near the rear end of the bore allow you to horizontally centre the screen with the bore.