Distinct mechanism for long-term contrast adaptation

Abstract

To optimize perception, neurons in the visual system adapt to the current environment. What determines the durability of this plasticity? Longer exposures to an environment produce longer-lasting effects, which could be due to either (i) a single mechanism controlling adaptation that gains strength over time, or (ii) long-term mechanisms that become active after long-term exposure. Using recently developed technology, we tested adaptation durations an order of magnitude greater that those tested previously, and used a "deadaptation" procedure to reveal effects of a unique long-term mechanism in the longest adaptation periods. After 4 h of contrast adaptation, human observers were exposed to natural images for 15 min, which completely cancelled perceptual aftereffects of adaptation. Strikingly, during continued testing this deadaptation faded, and the original adaptation effects reappeared. This pattern strongly suggests that adaptation was maintained in a distinct long-term mechanism, whereas deadaptation affected a short-term mechanism.orientation | deprivation | adult neuroplasticity T he visual system continually adapts to the current environment to improve its function. Neurons in the retina and visual cortex, for example, decrease their sensitivity after prolonged exposure to a high contrast environment (for reviews, see refs. 1 and 2). Such adaptation is hypothesized to increase the efficiency of neural coding by bringing responses down from ceiling levels and allowing neurons to respond differentially to the high contrast values that are the most likely stimuli in that environment. Because adaptation effects are both large and common in the natural world, understanding them is a key component of any account of visual function (3).Effects of contrast adaptation are evident almost immediately after onset of an adapting stimulus but get stronger and longerlasting as the adaptation period grows in duration. This duration scaling law has been observed for both firing rates of retinal ganglion cells and contrast detection measurements of human observers (4, 5).How the visual system produces these temporal dynamics remains the subject of debate (Fig. 1). One theory proposes that a single neural mechanism controls contrast adaptation at multiple time-scales (putting aside extremely rapid effects that occur within 100-200 ms; refs. 5 and 6). As the adapting period grows longer, this mechanism increases its confidence in its estimates of the current environment. Increased confidence, in turn, produces stronger adaptation effects and also increases the evidence required to convince the system that the environment has changed back to its original state, yielding longer-lasting aftereffects.Alternatively, contrast adaptation might be controlled by multiple neural mechanisms, each tuned to a different preferred timescale (7,8). As the adapting period grows longer, mechanisms tuned to longer timescales exert increased control over adaptation. The dynamics of such mechanisms would most naturally operate at similar long t...

Hour-long adaptation in the awake early visual system

“…Here, we show that the effect of prolonged visual stimulation can last for Ͼ1 h in the thalamus. Moreover, psychophysical studies have described a relationship between stimulus duration and recovery time from adaptive effects, termed the duration-scaling law (Bao and Engel 2012;Greenlee et al 1991;Greenlee and Magnussen 1987;Leopold et al 2005), which is consistent with our measurements from thalamic neurons (Fig. 1E).…”

“…However, psychophysical studies have also shown a number of adaptations and afterimage effects that can last for hours to months following induction (Bao and Engel 2012;Jones and Holding 1975;McCollough 1965). Here, we show that the effect of prolonged visual stimulation can last for Ͼ1 h in the thalamus.…”

Human Yaw Rotation Aftereffects with Brief Duration Rotations Are Inconsistent with Velocity Storage

“…7), even though similar stimulus parameters have been demonstrated to produce perceptual aftereffects with fore-aft translation ) and with roll ). Large differences in the duration of the adapting and test stimuli have also been shown to induce aftereffects in several other sensory stimuli including visual (Hershenson 1993;Leopold et al 2005;Bao and Engel 2012) and auditory motion (Neelon and Jenison 2004). A general theme in sensory aftereffects is that a longer period of adaptation leads to a stronger and longer aftereffect (Taylor 1963;Greenlee et al 1991;Anstis et al 1998;Neelon and Jenison 2004), but the current data presents a rare exception to this, at least when the test stimulus and adapter are different durations.…”

Pulse trains to percepts: the challenge of creating a perceptually intelligible world with sight recovery technologies

“…This suppression (as predicted by the optical cause of his diplopia) varied between his left and right eyes, suggesting a neural locus relatively early in the visual pathway. This plasticity does not seem to be limited to perceptual distortions that occur in early childhood: short-and long-term modulation of contrast sensitivity specific for location and orientation in adulthood have also been noted as a consequence of altered video input over various timescales [79,80], and normally sighted individuals show adaptation to the amount of blur in a sequence of images [81]. Thus, it seems plausible that analogous suppressive mechanisms might minimize the perceptual salience of 'comet' trains resulting from axonal stimulation.…”