Fig. 2: Assessing visibility of stimuli moving over finite amplitudes at high speeds.
From: Lawful kinematics link eye movements to the limits of high-speed perception
a Participants fixated throughout a trial as a vertical Gabor stimulus (100% contrast, 1 cycle/dva, 1/3 dva envelope) appeared on one side of the screen, rapidly moved to the opposite site of fixation, and then disappeared again. The stimulus' path followed a circular arc (height: 15% of the horizontal amplitude) and observers judged the vertical direction in a 2-alternative forced choice (upward vs downward). While the stimulus moved rapidly, strict fixation control at the center of the screen ensured that observers maintained fixation throughout the 500 ms of stimulus presentation. We updated stimulus position at 1440 Hz (i.e., every 0.69 ms) to achieve smooth, continuous motion and reliable timing at all speeds (see Supplementary Methods: Faithful rendering of high-speed motion). b Trajectories of stimulus motion for the five amplitudes tested. c Absolute speed v of the stimulus as a function of time, shown for the peak velocity vp corresponding to each movement amplitude. Movement duration varied as a function of movement amplitude and speed (D = A/v); the stimulus was stationary at its start and end points before and after the movement. d For each movement amplitude (here, 4 dva), we varied the absolute speed in proportion to vp (each line corresponds to one relative movement speed, vrel). Prediction of thresholds expressed for absolute (e) and relative (f) speed when these thresholds are invariant to movement amplitude (dashed white lines) or, alternatively, proportional to the main sequence (solid white lines).
