Abstract
Depriving adult subjects of visual stimulation at a narrow range of orientations increases sensitivity to the deprived orientation. Here we measured the growth of this effect as a function of adaptation duration. Subjects were deprived of vertical energy for 1, 4, or 8 hours, viewing the world through an “altered reality” system. The system was comprised of a head mounted video camera that fed into an image-processing laptop computer that in turn drove a head-mounted display (HMD). Vertical energy was removed from the video in real time using a simple mask in the Fourier domain. Viewing the filtered video, subjects were able to interact with the world while being deprived of vertical visual input. Prior to and following deprivation, we measured perceived orientation of sinusoidal gratings, using a version of the tilt aftereffect. Subjects viewed a plaid made from two 45 deg gratings, which perceptually resembled a blurred square checkerboard. When the grating components were symmetrically tilted away from 45 degrees, the checks appeared rectangular. Subjects adjusted the tilt of the components from a random initial angle until the checks appeared square, which revealed the physical orientations that appeared to be 45 deg. Subjects adapted to deprivation: Following deprivation, they set the components tilted away from 45 degrees towards horizontal, indicating that they perceived 45 degree gratings tilted towards vertical. Eight hours of adaptation produced reliably larger and longer-lasting effects than four or one hours. The shift in apparent orientation towards vertical suggests that deprivation increased the gain of neurons selective to the deprived orientation. The fact that this effect continues to strengthen over eight hours suggests that relatively low level mechanisms of adaptation can operate over long time scales, which may allow them to contribute to long-term plasticity in the visual system, such as adaptation to retinal disease.