In the main experiment, we utilized a novel display system with an integrated Shack–Hartmann wavefront sensor (FLIR Grasshopper GS3-U3-15S5M-C, FLIR systems, Wilsonville, OR, USA; coupled with a microlens array MLA150-7AR, Thorlabs Inc., Newton, NJ, USA), focus-adjustable lens (Optotune EL-10-30-TC; Optotune, Dietikon, Switzerland), and DLP projector (Texas Instruments LightCrafter 4710; Texas Instruments, Dallas, TX, USA) (
Figure 3). The wavelength of the infrared light source for the wavefront sensor was 875 nm. The field of view was 12.5
\(^{\circ }\) in diameter. An Optotune EL-10-30-TC focus-adjustable lens with a Comar 63 DN 25 Comar 63 DN 25 (Comar Optics, Linton, Cambridgeshire, UK) achromatic doublet offset lens was placed optically at the pupil-conjugate plane. As such, changes in the power of the adjustable lens did not cause changes in the magnification of the image at the eye. We used the adjustable lens to make fast (
\(\sim\)15 ms) changes in the optical distance to the stimulus. A model eye was used to confirm linear and stable defocus performance of the focus-adjustable lens from –1 to +6D. Stimuli were projected onto a screen by a Texas Instruments DLP LightCrafter 4500 with LED primaries and viewed by the subject’s left eye. The spectra for the three primaries are provided in
Supplementary Figure S8. Resolution was 62 pixels/deg for a Nyquist frequency of 31 cycles/deg. Stimuli were white and black; space-average luminance of the fixation stimulus was 138 cd/m
\(^{2}\).