system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does pushing our eye gently against a closed eye lid make us "see" things?
gpt
In order to process sensory information (light, sound, touch, taste, etc.), it must be input through a receptor. The sensory modality (type) a receptor is most sensitive to (made to interpret) is called the adequate stimulus. 

Photoreceptors (what ultimately turn light into an electrical/neuronal signal which can be then interpreted by the brain) in the eye have light as their adequate stimulus. However, (as you have illustrated) they can be stimulated by things other than light (touch/pressure--mechanoreception, electric current, salt concentration, etc.). 

But there is one problem: photoreceptors are adapted (built/"hooked up") to interpret their adequate stimulus only. This means that any stimulus provided to the photoreceptor will be interpreted *as if* it is light--your brain will interpret it (touch, etc.) as vision.