Distinct mechanisms control contrast adaptation over different timescales

Abstract

Changes to the visual environment can happen at many timescales, from very transient to semi-permanent. To adapt optimally, the visual system also adjusts at different timescales, with longer-lasting environmental changes producing longer-lasting effects, but how the visual system adapts in this way remains unknown. Here, we show that contrast adaptation-the most-studied form of visual adaptation-has multiple controllers, each operating over a different time scale. In a series of experiments, subjects completed either a contrast matching, contrast detection, or tilt adjustment task, while adapting to contrast at one orientation. Following a relatively longer period (5 min) of adaptation to high contrast, subjects were "deadapted" for a shorter period (e.g., 40 s) to a lower contrast. Deadaptation eliminated perceptual aftereffects of adaptation, but continued testing in a neutral environment revealed their striking recovery. These results suggest the following account: Adaptation was controlled by at least two mechanisms, with initial adaptation affecting a longer-term one and deadaptation affecting a shorter-term one in the opposite direction. Immediately following deadaptation, the effects of the two mechanisms cancelled each other, but the short-term effects rapidly decayed, revealing ongoing longer-term adaptation. A single controlling mechanism cannot account for the observed recovery of effects, since once deadaptation cancels the initial longer-term adaptation, no trace of it remains. Combined with previous results at very long adaptation durations, the present results suggest that contrast adaptation is possibly controlled by a continuum of mechanisms acting over a large range of timescales.

What we see changes how we see : analyzing the plasticity of the horizontal effect.

“…Similar studies have also determined that long-term adaptation effects follow a 'duration scaling' law wherein the effects of adaptation get stronger and longer lasting as the adaptation duration lengthens (Bao & Engel, 2012;Bao et al, 2013). As revealed in Experiment 1, the relationship between duration of adaptation and magnitude of perceptual effects found here is not linear; while effects increased monotonically from 5-60 minutes of adaptation, the perceptual change began to plateau after 2 hours.…”

“…Indeed, the prolonged time it takes subjects to return to baseline levels in these experiments indicates that the typical perceptual whitening imposed by being continually adapted to natural scene statistics is not retained. However, these results are at odds with the findings that re-adapting subjects to previously experienced environments can reinstate adaptation effects more quickly (Bao et al, 2013). It will be interesting in the future to more explicitly examine the relationship between fast and slow adaptation and determine how long after deadaptation re-adaptation can be implemented to recover sensory advantaged gained during adaptation.…”

“…Perhaps even more relevant to the current results, long-term adaptation has also been studied using similar orientation decrements across different adaptation durations, but with a narrowband orientation perception task (TAE: see Introduction, Bao & Engel, 2012;Bao, Fast, Mesik, & Engel, 2013;Haak et al, 2014;Zhang et al, 2009). These studies have provided evidence for two distinct processes explaining perceptual effects after short and long-term adaptation.…”

“…These studies have provided evidence for two distinct processes explaining perceptual effects after short and long-term adaptation. The strongest evidence for the two mechanism theory has come from studies wherein de-adapting and re-adapting to previously adapted stimuli show spontaneous recovery of adaptation effects (Bao et al, 2013). That is, once subjects were no longer exhibiting perceptual effects of long-term adaptation, such effects could be reinstated much more quickly than before (after only a few minutes of experience; see Introduction and Bao et al, 2013).…”

“…The strongest evidence for the two mechanism theory has come from studies wherein de-adapting and re-adapting to previously adapted stimuli show spontaneous recovery of adaptation effects (Bao et al, 2013). That is, once subjects were no longer exhibiting perceptual effects of long-term adaptation, such effects could be reinstated much more quickly than before (after only a few minutes of experience; see Introduction and Bao et al, 2013). Presumably, the results reported here are also effects of adapting a long-term, cortical mechanism and should thus show spontaneous recovery as well as intraocular transfer if tested in the future.…”