Distal stimulus, proximal stimulus, percept:
To understand what perception does, you must understand the difference between the the proximal (~approximate = close) stimulus and the distal(~ distant) stimulus or object.
- distal stimuli are objects and events out in the world about you.
- proximal stimuli are the patterns of stimuli from these objects and events that actually reach your senses (eyes, ears, etc.)
Most of the time, perception reflects the properties of the distal objects and events very accurately, much more accurately than you might expect from the apparently limited, varying, unstable pattern of proximal stimulation the brain/mind gets. The problem of perception is to understand how the mind/brain extracts accurate stable perceptions of objects and events from such apparently limited, inadequate information.
In vision, light rays from distal objects form a sharply focused array on the retina in back of the eye. But this array continually varies as the eyes move, as the observer gets different views of the same object, as amount of light varies, etc. Although this proximal stimulus array is what actually triggers the neural signals to the brain, we are quite unaware of it or pay little attention to it (most of the time). Instead we are aware of and respond to the distal objects that the proximal stimulus represents. This is completely reasonable: the distal object is what is important.