How can we explain perceptual illusions? Are they glitches in the Matrix, or do they reveal adaptive features of our cognitive system?

So far, we’ve established that, experientially, we tend to perceive as real what we perceive through our senses. However, there are countless instances where perception misleads us. Our perception is not always credible. Consider the following example:

Hollow Mask Illusion

You’re looking at a rotating mask with a protruding, convex outside half and the hollow, concave inside half. As the mask rotates, the hollow side should appear sunken in. But When you see this Hollow Mask Illusion for the first time, your brain automatically interprets both halves of the mask as a normal, outward-facing face, even though the inside is actually hollow and curving inward. This happens because our brains are so accustomed to seeing faces that they ‘correct’ what we see to match that expectation.

Illusions like this demonstrate that (1) perception does not always reflect the outside world as it physically exists, and (2) perception is not a passive recording of reality, but an active interpretation, shaped by prior experiences and expectations. Since every face we typically encounter is convex, our brain automatically imposes this expectation – even when it directly contradicts raw sensory input.

In such cases, our perception tells us one thing – the apparent – while our knowledge tells us something else – the credible. This tension allows us to critically assess how much we trust our perceptual experience.

Thus, we can distinguish yet another sense of reality: credible reality versus mere appearance. In this case, it is not the immediate perception of the rotating mask that we consider real, but our understanding of its physical structure. The apparent reality itself, though vivid and convincing, constitutes a misinterpretation of sensory input – hence, we recognize it as an illusion.

Fourth Sense of Reality: The Credible

real4	unreal4
credible	apparent

This ability to critically reflect our perceptual experiences marks the shift from assuming that perception directly reflects reality to recognizing that perception is an interpretive process that is shaped by cognitive and developmental constraints. In epistemology, this shift is what separates naïve realism – the belief that perception is a direct reflection of reality – from critical realism, which acknowledges both an objective world and the limitations of human perception.

Naive and critical realism

Critical realism provides a balanced epistemological framework, integrating both an objective world and the cognitive constraints that shape perception. But this alone does not explain how our perceptual and cognitive systems came to be. To answer why we perceive reality the way we do, we must look at how perception and cognition have evolved over our developmental history – in other words, we must turn to evolution.

The epistemological stance that frames cognition as a product of biological evolution is known as evolutionary epistemology. This perspective asserts that the way we perceive and interpret the world – our cognitive architecture – has been and is shaped by our developmental history.

Author: Fabian Müller