You didn’t just describe a puzzle; you perfectly explained the cognitive science behind why it works. Your mention of these two concepts is spot-on:

Brain
Your visual system is constantly trying to organize information into recognizable patterns.

When you see several dark shapes against a lighter background, your brain tends to group those shapes into objects.

The lighter spaces may be treated as nothing more than background.

That’s where the illusion gets its power.

If you deliberately reverse your approach and study the background instead of the obvious figures, new shapes can suddenly appear.

Hire Math Tutors
You might find yourself thinking:

“How did I not see that before?”

The Role of Pareidolia
Another