Differences between Relative size and size constancy?

[hawks08]

I am a bit stuck, i need 3 differemces. Thanks

[Tashi]

Ummm... they're completely different things aren't they? I'm not sure.

[Chromeo33]

Size constancy denotes a visual constancy whereby we perceive an object's size to be unchanging in reality (despite the changing retinal image's size).

The concept of relative size and its purpose is for us to perceive depth. Though they are somewhat related in that they rely on objects maintaining their sizes in reality, relative size compares the retinal sizes of the objects TO PERCEIVE DEPTH.
The purpose of size constancy is to HELP US PERCEIVE AN OBJECT AS RETAINING ITS SIZE in reality.

They differ in the purposes of which they were conceived for. Though how they go about fulfilling their purposes is somewhat similar.

=]

[lolbox]

There two different things, you will never be asked to compare or contrast them. Size constancy is a visual constancy... which has to be with out ability to see the world (in this case the size of an object_ as stable despite changes occuring in our retinal image. EG - Seeing a bus from the distance, on our retina there will only be a tiny spec but we will realise its a bus and are aware of its actual size

Relative size is a completely different part of visual perception and comes under pictorial depth cues. These are pretty much just cues which explain how we can percieve distance in art. An example to help you understand relative size (might aswell stick with the buses) is two similar buses in the same image which cast different retinal images. One is small on the retina, therefore we know it is further away.

Sorry if I confused you more, typed in a hurry