Minolta ls 110 luminance meter

For reading speed and visual span tasks, the 26 Courier font letters of the English alphabet were used. For crowding zone task, ten Sloan letters and tumbling ‘E’s with different orientations (0°, 90°, 180°, 270°) were used as the target letter and flankers, respectively. For all tests, letters were black on a uniform gray background (159  cd/m²) with a contrast of 99%. Letter size, defined as x-height, was 0.8°. All stimuli were generated and controlled using MATLAB (version 8.3) and Psychophysics Toolbox extensions^{96 (link), 97 (link)} for Windows 7, running on a PC desktop computer (model: Dell Precision Tower 5810). Stimuli were presented on a liquid crystal display monitor (model: Asus VG278HE; refresh rate: 144 Hz; resolution: 1920 × 1080, subtending 60° × 34° visual angle at a viewing distance of 57 cm) with the mean luminance of the monitor at 159 cd/m². Luminance of the display monitor was made linear using an 8-bit look-up table in conjunction with photometric readings from a MINOLTA LS-110 Luminance Meter (Konica Minolta Inc., Japan).

The stimulus was a low contrast target (i.e., two 2% contrast dots separated by 0.8°) on a gray 50 cd/m² background, as measured by a Konica Minolta LS − 110 luminance meter on a 17-inch monitor (1,024 × 768 pixels,75 Hz refresh rate). From the participant’s perspective, the monitor constituted a 25° vertical, 35° horizontal, and 40° diagonal search space. Contrast sensitivity of participants was measured using the Hamilton-Veale test. During visual exploration, eye position was sampled at 500 Hz by an Eyelink II eye tracker controlled by EYETRACK gaze-contingent functions.¹ A saccade was recorded when eye velocity exceeded 30° s⁻¹, or when eye acceleration exceeded 8,000° s⁻². Periods of eye stability between saccades (as defined) were counted as fixations. The gaze-contingent code drew a background bitmap (i.e., gray screen) and a foreground window bitmap (i.e., target, in a randomly chosen location around imaginary concentric circles on a white screen). As the eye was tracked, the code instantaneously (about 14 ms delay) redrew those parts of the display that changed because of the 5^° × 5^° foveal window’s gaze-contingent movement. From the perspective of participants, the screen was blank unless the invisible moving foveal window overlapped the location of the target. Participants acknowledged finding the target by pressing the computer’s left mouse key.