Taken together, these results are remarkable because the visual features defining the object span just a few photoreceptors, yet the eye’s own motion spreads these features over many photoreceptors within the presumed temporal integration window of downstream cortical neurons. Surprisingly, although subjects are aware of the incongruent motion of the stimulus, their task performance is the same as the natural condition in which there is no perception of motion. In a third condition, the stimulus moves on the retina with the same statistics as natural eye motion, but incongruent (uncorrelated) with the eye’s true motion. In a second condition, the image of the E is stabilized on the retina by a real-time eye tracker with cone-level precision. The stimulus size is chosen to challenge the subject to the point that the orientation is discriminated correctly 40% to 60% of the time.

Subjects are shown a diffraction-limited letter E in one of four orientations (strokes pointing up, down, left, or right) during natural drift movements of the eye, and are asked to report the letter’s orientation. Recent experiments demonstrate the benefit of these movements for the discrimination of a small letter whose stroke spacing is near the sampling limit of the cone photoreceptor array ( Ratnam, Domdei, Harmening, & Roorda, 2017). During visual fixation, humans have a stable, high-acuity perception of the world despite substantial drifting movements of the eyes.

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