The Art & Neuroscience of Optical Illusion Sketching
Drawing is essentially the art of tricking the human brain. Since paper is a flat, two-dimensional coordinate space, every line we lay down is a code that the visual cortex must translate into three dimensions. By mastering how to draw optical illusions step by step, you are learning how to exploit the biological processing assumptions of your own eyes.
The visual brain relies on specific shortcut rules. For instance, when you sketch easy optical illusions to draw like the Necker Cube, your brain struggles with a lack of depth cues. Because all angles are parallel, the brain alternates between two equally valid 3D hypotheses. This phenomenon, known as bistable perception, occurs in the early stages of visual parsing (V1 and V2 regions of the occipital lobe).
When working on optical illusions drawings that involve motion (such as Tutorial 6), the trick lies in contrasting high-frequency borders. By placing alternating diagonal dashes between straight lines, the orientation-selective cells (simple and complex cells in primary visual cortex) are misdirected. They miscalculate the slope, causing straight lines to appear tilted.
Similarly, learning how to draw moving optical illusions like the Fraser Spiral uses diagonal alignment angles. Each circle is independent, but because the dashes lean inwards, the eye integrates the local vectors globally, interpreting a spiral shape that does not actually exist.