![green screen snake coiled green screen snake coiled](https://ssl.bigstockimages.com/6/6/4/large1500/4667152.jpg)
To explain: on the hypothesis that the mind is modular, a mental module is a kind of semi-independent department of the mind which deals with particular types of inputs, and gives particular types of outputs, and whose inner workings are not accessible to the conscious awareness of the person – all one can get access to are the relevant outputs. The Rotating Snakes Illusion is also interesting because it is relevant to debates about modularity, cognitive penetration, and the nature of experience. This suggests that blinks and small involuntary movements of the eye called ‘saccades’ may play an important role in triggering the illusion (Otero-Mill et al. A processing latency mechanism is consistent with the fact that the illusion ceases when our gaze is fixed, because in that case the signal from each part of the visual field is fairly constant. If the reverse phi phenomenon explains illusory motion, the reversing patterns explain why some snakes rotate clockwise and others anticlockwise. Looking closely at the figure, you will notice that adjacent ‘snakes’ are patterned so that the colours appear in the opposite order. The illusory motion is then explained as an example of the reverse phi phenomenon first described in Anstis and Rogers (1974): a bright spot appearing and fading at some point in the visual field, subsequently followed by a dark spot appearing and fading at some other point, will create a sense of motion from the dark stimulus toward the light stimulus if this pattern is cycled. (2003) propose that high-contrast areas are processed faster than low-contrast areas, where contrast is defined globally over the entire receptive field of an individual retinal neuron in this case, the regions of highest contrast appear in the outermost ‘coil’ of the snakes. No-one is quite sure as to how the Rotating Snakes illusion works, although there is some consensus that it involves a difference in the processing latency of signals corresponding to different parts of the figure. It is one of a class of peripheral drift illusions whatever part of the figure is in the centre of our visual field appears motionless (as indeed it is), while the parts seen in our peripheral vision appear to move. This particular example was devised by Japanese psychologist and academic Akiyoshi Kitaoka (Kitaoka and Ashida 2003), following previous work by Fraser and Wilcox (1979) and Faubert and Herbert (1999). The Rotating Snakes Illusion evokes a perceptual experience of illusory motion.