As the world population grew, there were multiple people searching for answers to common questions regarding the physical behavior of the universe they are born into.
Life doesn't come with an owners manual. In a quest for knowledge, it's left as an exercise for the individual.
Human life forms are thus totally ignorant of this behavior, not being present when the universe was formed. Their only recourse is speculation in the form of mental constructs that model the physical behavior observed, a representational methodology. This human activity is philosophy, an attempt to acquire an understanding of how the world works.
Study of the human mind has revealed an image oriented organ in conjunction with sensory input via vision. In the course of processing images, the mind searches for patterns that suggest relations among physical entities.
Perception is defined as the act of observation and accompanying analysis.
There is a common misconception in science evident in the use of 'objective vs subjective'. Perception involves the mind, which is primarily biological, which classifies it as chemistry, which is a subclass of physics, involving the interactions occurring within the electron cloud surrounding an atomic nucleus. Note the use of conceptual models (italics). Perception involves real images formed via real neural networks activated by real weak electrical currents, i.e. matter in motion.
Perception's definition can then be extended to 'reality confined to the mind'.
The theory of Relativity reveals, motion alters measurement and perception. This idea was and still is shocking to a society weaned on overly simplistic concepts of instantaneous light speed, universal time, and a deterministic world.