Fig. 2.

Photodiode verification of video performance during movie presentation in the XGL (A) and Psychophysics Toolbox (PTB; B) versions of the software. The black trace indicates the voltage recorded from the output of a photodiode circuit with the photodiode sensor affixed to the display screen (near the center of the display). The green and red lines indicate the timing of the stimulus-on and stimulus-off event markers, respectively. The movie consisted of alternating “white” and “black” frames, and frames were played at a rate of 75 Hz. The interval between the green line and 1st upward deflection of the photodiode signal was ∼8.0 ms, which is consistent with the frame rate and the position of the photodiode near the center of the display.