Qian L, Liu S, Lei Q. Illusory distance modulates perceived size of afterimage despite the disappearance of depth cues. PLOS ONE. 2016;11(7):e0159228. doi:10.1371/journal.pone.0159228 The chapter on ambiguous impossible pictures is great fun. This is the sort of thing where you look at a picture one way and see one image, or you might see a completely different image with a change in perception. It also has images where lines become ambiguous and trying to count how many of something are in the picture becomes impossible. The sort of impossible Physics in Escher drawings are much like some of these examples. What’s more, new illusions, and variants on old ones are appearing all the time. Vision researchers hold an annual competition, now in its 10th year, to find the best new illusions. One of the judges is visual neuroscientist Susana Martinez-Conde from the Barrow Neurological Institute in Arizona. The contest has a selfish motivation of sorts, she says: she wants to keep an eye out for interesting new illusions that will help her to study the brain.

Powell G, Bompas A, Sumner P. Making the incredible credible: afterimages are modulated by contextual edges more than real stimuli. J Vis. 2012;12(10). doi:10.1167/12.10.17 Sakiyama T., Sasaki A., Gunji YP. Origin of Kanizsa triangle illusion. In: Rhee SY., Park J., Inoue A. (eds) Soft Computing in Machine Learning. Advances in Intelligent Systems and Computing, vol 273. Springer, Cham; 2014. doi:10.1007/978-3-319-05533-6_10 Qian J, Liu S, Lei Q. Illusory distance modulates perceived size of afterimage despite the disappearance of depth cues. PLoS One. 2016;11(7):e0159228. doi:10.1371/journal.pone.0159228 Wagemans J, Elder JH, Kubovy M, et al. A century of Gestalt psychology in visual perception: I. Perceptual grouping and figure-ground organization. Psychol Bull. 2012;138(6):1172–1217. doi:10.1037/a0029333My favorite puzzle is How to Become a Giant. This puzzle shows a man at one end of a hallway with column's and it looks like the man is extremely small in comparison with the column's. The next picture shows the man at the end of the hallway and he looks like a giant in comparison to the columns. The book shows you the illusion and then at the end of the book, it gives you the answer of why this illusion is possible. s winning entry is a novel take on the 19th Century Ebbinghaus Illusion. This new version is dynamic, which makes the effect much stronger. “It’s like the Ebbinghaus effect on steroids,” says Martinez-Conde. Just like the original, the illusion highlights that the brain always perceives the size of objects in the context of those that surround them. But if you continually vary this context, then the effect gets even stronger, she explains. Song S, Liu Y, Zhang J. Decoding the subjective rotation direction of the spinning dancer from fMRI data. Proceedings. 2015;94171. doi:10.1117/12.2081570

Weidner R, Plewan T, Chen Q, Buchner A. The moon illusion and size-distance scaling - evidence for shared neural patterns. Journal of Cognitive Neuroscience. 2014;26(8):1871-1882. doi:10.1162/jocn_a_00590 Bertamini M. Ponzo illusion. In: Programming Visual Illusions for Everyone. Vision, Illusion and Perception, vol 2. Springer, Cham; 2018. doi:10.1007/978-3-319-64066-2_5 While we know that different areas of the brain deal with colour, form, motion and texture, how the brain encodes and combines this information into a coherent picture remains poorly understood. Sometimes we see things that aren't there, and the Hermann Grid illusion is a great example. Notice how the dots at the center of each intersection seem to shift between white and gray? Bachy R, Zaidi Q. Troxler fading, eye movements, and retinal ganglion cell properties. Iperception. 2014;5(7):611-612. doi:10.1068/i0679sasNinio J. Geometrical illusions are not always where you think they are: a review of some classical and less classical illusions, and ways to describe them. Front Hum Neurosci. 2014;8:856. doi:10.3389/fnhum.2014.00856 Like many optical illusions, different theories have been proposed to explain exactly why this happens. Lateral inhibition is often used to explain the Hermann grid illusion, but more recent evidence suggests that this might not be why the illusion happens. This theory suggests that the brightest at the intersections forces retinal cells to adjust the intensity. Lateral inhibition happens when the excitation of surrounding neurons inhibits a neuron's response to a stimulus.