When a car passes you on the road and appears to shrink as it gets farther…

Concept: Perceptual constancy is the tendency of the perceptual system to experience an object's stable properties — its size, shape, brightness and colour — as unchanging, even though the image that object casts on the retina keeps changing as distance, viewing angle and illumination change. Size constancy is the sub-case that applies here: perceived size is computed from retinal image size together with the perceived distance of the object, so a change in one is offset by a change in the other.

Application: Trace what happens as the car drives away from you:

1. The car recedes, so the visual angle it subtends at your eye shrinks and its retinal image becomes smaller.

2. Depth cues along the road — linear perspective, texture gradient, relative size and height in the visual field — register that the car's distance is increasing.

3. The perceptual system scales the shrinking retinal image by the increasing perceived distance; the two changes offset each other, so the physical size you compute stays the same.

Cross-check: The other terms name phenomena from different areas of psychology:

• Self-actualization sits in Maslow's hierarchy of needs and concerns the motive to realise one's own potential — a motivational construct, not a perceptual one.

• Transitivity is the logical relation that if A > B and B > C then A > C; in Piaget's account it is a concrete-operational reasoning skill for ordering objects, and it says nothing about how a changing retinal image is interpreted.

• Similarity is a Gestalt principle of perceptual grouping: elements sharing colour, shape or size are grouped into one set. It explains how parts are organised into groups, not why a single object's size is experienced as stable across distance.

Result: Because size constancy holds, you experience a car of unchanged size moving farther away rather than a car that is physically shrinking. The phenomenon is perceptual constancy.