Note also that the aftereffect is visible only when the afterimage is in register with the grayscale image (by fixating the dots). This occurs because adaptation reduces sensitivity to the local adapting color and, thus, biases perception toward the complementary color. The illusory colors are opposite to the adapting colors, a “negative aftereffect” typical in adaptation. The grayscale image should briefly appear colored. Stare at the black dot in the upper image for 30 seconds or more and then quickly switch your gaze to the dot in the lower picture. The upper image is a pseudo-negative of the original photograph (with color differences exaggerated and brightness differences reduced). While this review focuses on vision, the findings and principles that have emerged are likely to be general to all of the senses as well as their interactions.Īn example of a perceptual aftereffect, similar to the “Big Spanish Castle” illusion popularized on the internet. Recently, the study of adaptation has been extended to much more complex and naturalistic attributes, and this has revealed both new insights and new questions about sensory coding and the role of adaptation. However, these studies have traditionally focused on simple perceptual properties and, thus, potentially early stages of neural coding. A wide variety of aftereffects have been documented, including classic perceptual illusions, such as a bias in what looks vertical after viewing tilted lines, or a change in what looks stationary after adapting to movement. Studies of adaptation have a very rich history in perceptual science, because the perceptual “aftereffects” of the adaptation can provide clues as to how our senses encode and represent the stimulus. These rapid sensitivity adjustments are known as adaptation (changes in the response properties of neurons induced by the recent stimulus context) and suggest that much of our perceptual experience is relative to the stimuli we have experienced recently. For example, the aromas that lure you into a room (or warn you away!) fade quickly from awareness once you enter, while your perception of color can change dramatically depending on the colors seen previously ( Figure 1). in the lighting or temperature) or to compensate for changes in the observer (e.g. The sensory systems we use to monitor the world around us are not static and instead are continuously recalibrating to adjust for changes in the environment (e.g.

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