Deafferentation theory proposes that loss of sensory input plays a role in Charles Bonnet hallucinations.

Predictive processing suggests that learned expectations influence the form taken by hallucinations.

Learned expectations may sculpt bursts of neural activity into persistent hallucinations.

People whose sight loss is the result of damage to incoming sensory pathways to the brain may develop the visual hallucinations of Charles Bonnet Syndrome (CBS). The primary feature of CBS is complex visual hallucinations: fully formed animate or inanimate objects that are unrelated to serious psychiatric disorders (Altieri & Battaglini, 2026; Pang, 2016). In fact, people with CBS typically show full or partial “insight into the unreality of their hallucinations.”

For about two years after the onset of my blindness, I hallucinated people, bicycles, pillows, and plants. The hallucinations that intrigued me most were those that occurred repeatedly when I performed certain activities. For instance, when I was learning to use a white cane, I sometimes found myself in the middle of a crowd of hallucinated white-cane learners. And for a time, I hallucinated a keyboard in front of me whenever I used my laptop.

Why did I repeatedly have those particular hallucinations? And why do I no longer have them? In this post, I will discuss current thinking in vision science to explore possible answers to those questions.

How the Visual System Works

Visual perception in sighted people begins when light activates sensory receptors in the eyes. The activated receptors produce neural signals that are transmitted to visual areas in the cerebral cortex—the large outer layer of the brain (Mars et al., 2025).

The brain’s visual system is organized hierarchically (Powers et al., 2016). The “early visual cortex” (i.e., the first areas receiving sensory input from the eyes) specialize in processing basic features of incoming sensory signals. The “later visual cortex” (i.e., visual areas in upper levels of the hierarchy) specialize in processing increasingly abstract and complex features of sensory input. For example, Dominic Ffytche and colleagues (1998) showed that the........

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