how perseption different from sensation?

Answer 1

A perception is a recognition and interpretation of sensory stimuli based chiefly on memory.
While a sensation is a perception associated with stimulation of a sense organ or with a specific body condition involving a indefinite generalized body feeling.
In short, perception involves the mind and thoughts while sensation involves the feeling of what is in ones mind.

Answer 2

In psychology and the cognitive sciences, perception is the process of acquiring, interpreting, selecting, and organizing sensory information. Methods of studying perception range from essentially biological or physiological approaches, through psychological approaches to the often abstract 'thought-experiments' of mental philosophy.
http://en.wikipedia.org/wiki/Perception

In psychology, sensation is the first stage in the chain of biochemical and neurologic events that begins with the impinging of a stimulus upon the receptor cells of a sensory organ, which then leads to perception, the mental state that is reflected in statements like "I see a uniformly blue wall."
http://en.wikipedia.org/wiki/Sensation