As concluded by Grush et al. the results obtained in their study show that color experiences changed in the early stage of application of the rotation gear and became stable, that is, they adapted to color constancy in the late rotation stage, without however consistently showing significant phenomenal adaptation by the end of the test. The investigators leave open a potential explanation of this outcome. The difference between this result and other studies, in which achieving phenomenal adaptation to spatial displacement or luminance inversion was more successful, may suggest that color sensations are special properties of early visual processing relatively difficult to phenomenally adapt as well as more resistant to penetration and manipulation by cognition (Fodor 1983; Pylyshyn 1999; Brogaard & Gatzia forthcoming; but cf. Macpherson 2012; Siegel 2012; Vetter & Newen 2014). At least this seems to be the case for the general population.
Synesthesia, although not considered to be an adaptive plastic phenomenon, may be a case in which some modifications take place, such as cognitive penetration of perception including early sensory processing. Synesthetic colors are frequently modified by cognitive operations, conceptual contents, contextual expectations, linguistic modulation, cultural factors, and other semantic knowledge mechanisms (Dixon et al. 2000; Simner 2007, 2012; Meier 2013; Mroczko et al. 2009; Mroczko-Wąsowicz & Nikolić 2013, 2014). Since synesthetes are able to penetrate this early aspect of vision it would be interesting to investigate whether synesthetically-perceived colors change under rotation. If so, is this in the same or in a different way to non-synesthetic, phenomenally-transparent colors?
Synesthetic colors are in some respects similar to the color experiences of rotation-gear wearers. In both cases, subjects are aware of the fact that what they see is not reliably colored, i.e., that their abnormal color experiences are not actual colors of the surroundings. On the other hand, these color experiences differ remarkably from each other. Whereas rotation gear wearers’ color experiences are able to adapt to fall in line with what the subjects know to be true about colors of the things around them, synesthetes’ color experiences do not display such flexibility. Thus, a theoretically founded hypothesis is that irrespective of the form of color synesthesia to be used in a color rotation experiment (e.g., grapheme-color, sound-color, time unit-color synesthesia) synesthetic colors would not alter.
Admittedly, the sensorimotor theory of color has difficulties explaining many of the features of the phenomenon of synesthesia, but this does not mean it is completely useless in the context of synesthesia. The theory could be used to account for the asymmetry in adaptation capability between those experiencing synesthetic and non-synesthetic colors. From the perspective of the enactive view of color, it could be proposed that the rotation gear interferes with regular color perception, because the equipment introduces a new set of sensorimotor dependencies. This is the reason why after wearing the rotation gear for some time and acclimatizing to the conditions, the rotated colors begin to appear normal, that is, the subjects’ ability to perceive original colors returns—such that phenomenal color adaptation under rotation takes place. Unlike the rotated color perception of non-synesthetes, synesthetic subjects (associators) do not experience their additional colors as attributed to perceived objects but as seen in their “mind’s eye”. Therefore the concurrent colors do not affect their ability for regular color vision. An explanation of why there is no phenomenal color adaptation in synesthesia could be that synesthetic colors just fail to adapt because they do not need to make room for non-synesthetic colors (cf. Ward 2012). Thus, in line with the sensorimotor account, we could interpret the difference between ordinary color perception and color synesthesia as a difference between real and seeming engagement. However, another type of synesthetes, projectors, who see colors as projected onto inducing objects, may require a different explanation. Since this group of synesthetes demonstrates an external frame of reference for their synesthetic colors, projectors’ phenomenal color adaptation under rotation might be comparable to the adaptation of non-synesthetes. A testable empirical prediction here would be that it is possible for projector synesthetes’ colors to adapt after using a rotation equipment specially adjusted to interfere with internally-generated concurrent color experiences. Depending on the outcome of this prospective study, which could be designed in such a way that it would take into account all the differences related to color phenomenology, the sensorimotor theory of color may gain new insights into the threat of synesthesia.
What sensorimotor enactivism can also learn from studies on phenomenal adaptation in various perceptual conditions is that the notion of “phenomenal adaptation” applies to some conditions, but not others. There may also be different senses of the notion, and apart from “adaptation of the sensory sort” a rigorous analysis should consider “adaptation in the cognitive aspects of experience”—an expansive interpretation supported by phenomenal liberalism and cognitive phenomenology. In addition, the extent to which the phenomenon of adaptation may develop varies among various perceptual conditions. No matter the exact magnitude of the adaptive effects discussed, the very existence of phenomenal adaptation to alterations of sensory input, or its general lack, needs to be fully integrated by philosophical theories, especially by sensorimotor enactivist theories of perception that attempt to account for all the dynamics related to perception. This adaptation highlights that perceptual experience is more flexible and variable than usually presumed.
Acknowledgements
I would like to thank the editors and anonymous reviewers for very helpful comments on earlier versions of this commentary.