Effects of Orientation-Specific Visual Deprivation Induced with Altered Reality

Abstract

What happens to neurons in visual cortex when they are deprived of their preferred stimuli? Long-term deprivation during development, spanning weeks, reduces the number of neurons selective for the deprived orientation [1-4]. In contrast, short-term deprivation in adults, for periods of seconds, can increase neural sensitivity relative to a stimulated baseline [5]. Effects over intermediate timescales remain largely unexplored, however. Here we introduce a new method for manipulating the visual environment of adult humans and report effects of four hours of orientation-specific deprivation. Subjects wore a head-mounted video camera that fed into a laptop computer that drove a head-mounted display. Software filtered the video stream in real time, allowing subjects to interact with the world while being deprived of visual input at a specified orientation. Four hours in this environment increased sensitivity to the deprived orientation, which likely reflected an increase in responsiveness of neurons in early visual cortex. Our results help distinguish between two theories of neural adaptation: the response increase optimized the responses of individual neurons, rather than increasing the efficiency of the population code. Our method should be able to produce a wide range of environmental manipulations useful for studying many topics in perception.

Distinct mechanism for long-term contrast adaptation

“…Depriving subjects of vertical produced a positive TAE, indicating that the two component gratings of the test pattern appeared to be tilted toward vertical. Adaptation likely increased the responsiveness (gain) of neurons tuned to vertical, causing the population response to diagonal gratings to be biased toward vertical (9). Note that these results are the opposite of the traditional TAE, where exposure to a high contrast vertical grating causes diagonal gratings to appear tilted away from vertical, interpreted as arising from a decrease in gain of vertical neurons.…”

“…The use of a plaid greatly eases the task for subjects and does not affect measures of TAE amplitude compared with more traditional measures (39). Our prior work also reported relatively longlasting aftereffects (at least 20 min) by using a detection task (9).…”

“…Subjects viewed the natural world with most vertical energy removed for 1, 4, or 8 h; this contrast deprivation was achieved by using a novel display comprised of a head-mounted video camera that fed into a laptop computer that, in turn, drove a head-mounted display (9). Real-time image processing on the laptop removed most first-order vertical information ( Fig.…”

“…The altered reality system is comprised of a camera connected to a laptop computer that feeds into a head-mounted display (9). Camera images were filtered in real-time by multiplying a second-order Butterworth filter with the captured image in the Fourier domain, and the inverse FFT of the resultant was displayed (9). Fig.…”

Sensory adaptation as optimal resource allocation

“…However, some studies of visual adaptation appear to contradict this expectation. Many procedures have been used to imitate environmental change (13)(14)(15)(16)(17)(18)(19). Though some studies found that behavioral and neuronal visual performance improved for stimuli prevailing in the new ("adapting") environment (20)(21)(22)(23), other studies found that performance did not change or it declined where it was expected to improve (16,20,23), or the changes occurred for stimuli very different from the adapting ones (20,23).…”