Optical illusions persistently fool us, and not just for fun they reveal how our brains are wired for speed, efficiency, and survival. Because the visual world is complex and information often incomplete or ambiguous, our brains use shortcuts (heuristics) and predictions to make sense of what we see. These include filling in missing details, assuming consistency, and interpreting shadows, light, and perspectives based on past experience.

Also important is the distinction between bottom-up data (what our eyes detect: edges, contrast, colour) and top-down processing (our brain’s expectations, context, memory). Optical illusions exploit mismatches or tensions between these processes. For example, ambiguous images can be seen in different ways depending on what your brain expects. Certain illusions overload our visual system (e.g. repeated patterns, strong contrasts), causing it to misinterpret or “fill in” incorrectly.

Another factor is that perception is not passive our brain doesn’t simply record what the eye sees. It constructs visual experience making best guesses. So even after you know an illusion is an illusion, those automatic processes (prediction, expectation, filtering) continue to operate, which is why the trick doesn’t vanish.

Studying illusions helps scientists understand perception, brain processing, and even how errors arise. It shows that perception isn't always objective reality but a dynamically constructed version of it, shaped by biology, cognition, and environment.