Stimuli were generated on a γ-corrected 21” achromatic CRT monitor (Phillips FIMI MGD-403, pixel resolution 976 × 1028; frame rate 121 Hz, MEH site; Ampronix, Irvine, CA, USA) or a γ-corrected 21” CRT monitor (Sony GDM F500-PST, pixel resolution 700 × 800; frame rate 120 Hz, UUC site; Sony Corp., Tokyo, Japan;) with a stimulus generator (ViSaGe MKII; Cambridge Research Systems, Rochester, UK) and the CRS toolbox (version 1.27) for MATLAB (version R2011a, MathWorks, Inc., Natick, MA, USA). The background luminance of each monitor was 10 cd/m2, with the maximum luminance of stimuli being 366 and 90 cd/m2 for the Phillips and Sony monitors, respectively. The chromaticity coordinates of both the background and stimulus were x = 0.258 and y = 0.257, as measured with a spectrophotometer (ColorCal-II; Cambridge Research Systems, Rochester, UK). Refractive error was determined foveally for the viewing distance using retinoscopy, followed by subjective refinement by an experienced optometrist after pupil dilation (≥7 mm) in the test eye using tropicamide hydrochloride 1%. Full-aperture trial lenses were used where refractive correction was required. During each test, participants placed their chin in a rest and forehead against a bar to view the CRT display at a distance of 60 cm in an otherwise darkened room. Responses were collected with a response pad (Cedrus RB-530; Cedrus Corp., San Pedro, CA, USA).
Temporal summation functions were generated for a stimulus close in size to a GIII stimulus (diameter 0.48°). To achieve this, contrast thresholds were measured for seven stimuli of different duration (1–24 frames, Bridgeman
42 duration: 1.8–191.9 ms), at 8.8° visual field eccentricity along the 45°, 135°, 225°, and 315° meridians.