Well, can you?
Which red circle is bigger?
The Lipps Illusion ~ 1897
Intersections and Dots Illusions
Are you seeing spots before the eyes yet? - The Hermann Grid
The intersection you look at won't change colour, but the others will !!
The Hermann Grid was named after Ludimar Hermann who first described it in 1870 in his "A Phenomenon of Simultaneous Contrast".
It is thought that this type of optical illusions is caused by a neural process called lateral inhibition. The intensity at a point in the visual system is not simply the result of a single receptor, but the result of a group of receptors which respond to the presentation of stimuli in what is called a receptive field.
The center of a on-center receptive field consists of individual photoreceptors which excite the ganglion cell when they detect increased luminance; the photoreceptors in the surrounding area inhibit the ganglion cell.
The Scintillation Grid - A variation of the Hermann Grid
The Scintillation Grid illusion was discovered by E. and B. Lingelbach and M. Schrauf in 1994. It is constructed by superimposing white discs on the intersections of the grey bars on a black background. Dark dots seem to appear and disappear rapidly at random intersections. When a person keeps their eyes directly on a single intersection, the dark dot does not appear. The dark dots disappear if one is too close to or too far from the image.
The image does not just need to be square, grey or sharp for the illusion to work:
A coloured scintillation grid
Warped Grid by Lesha Porche
The above illusion was created by Florida graphic artist Lesha Porche in December 2021. She was designing a courtyard for a game and created the above image. The Warped Grid Illusion is a Hybrid Image illusion. In this type of illusion, two superimposed images—one containing fine and the other containing coarse visual details, also known as high and low spatial frequencies result in competing perceptions. The former is best experienced at close range, and the latter from afar or out of the corner of one's eye.
The high spatial frequencies arise from the rectilinear grid, and the low spatial frequencies from the designs formed by cobblestones of like colors. Observed directly, the high spatial frequencies from the grid itself dominate, making its lines look straight. In the visual periphery, the low spatial frequencies from the cobblestone sets take over, warping the grid design
What happens when you stare at the center of this image?
What about the stripes in the circles? Sure?
What is going on here?
Thiery's figure
The Zollner Illusion - The longer lines really are parallel!
How many triangles can you see in each of these 4 pictures
1, 2 or none?
If you see an upside-down triangle in these pictures, what happens to its shape in the bottom right picture?
Kanizsa figures
Twisted Cord Illusions
The false spiral or twisted cord illusions were first described by psychologist Sir James Fraser (1863-1936) in 1908 when he was Deputy Medical Superintendent of the Central London Sick Asylum. He described the illusion in a paper, "A new visual illusion of direction", in the British Journal of Psychology; Volume 2, Issue 3, (Jan 1, 1908).
The illusion is produced by combining a regular line pattern (the circles) with misaligned parts (the differently colored strands). A sequence of tilted elements causes the eye to perceive phantom twists and deviations
James Fraser's Twisted Cord illusion
Life ~ Another of James Frasers twisted cord illusions
Are the letters really crooked?
Twisted cord illusion
Are you certain you can see a spiral?
What about this one ? A spiral or concentric circles ? Sure ?