Q.Distinguish between sensation and perception, giving one example of each.

Sensation and perception are closely related processes that together form part of what psychologists broadly call cognition, but they refer to two genuinely distinct steps in how we come to know the world. Sensation is the initial, elementary experience produced when a stimulus first registers on a particular sense organ -- it is the basic process through which we detect and encode a physical stimulus, and it corresponds to immediate, low-level experiences of stimulus qualities such as 'hard,' 'warm,' 'loud,' or 'blue,' arising directly from the appropriate stimulation of a sense organ. Sensation, by itself, does not tell us anything about the meaning, identity, or source of the stimulus that produced it -- a flash of light, a burst of sound, or a whiff of fragrance registered purely as sensation carries no information yet about what caused it. Perception is the further process by which this raw sensory material is actively recognised, interpreted, and given meaning, drawing on learning, memory, motivation, emotion, and other psychological processes. Because of this, perception is not merely a neutral, passive 'read-out' of objects and events exactly as they exist in the external (or internal) world; it also involves an active construction of those objects and events, shaped by the particular perceiver's own point of view, motivations, expectations, and past experience. A simple illustration makes the distinction clear: hearing a knock at the door is, at the level of sensation, just a registered pattern of sound; recognising it specifically as 'the milkman's knock' (rather than, say, a neighbour's) is an act of perception, because it involves interpreting the raw sensory information using expectation and past experience, and this interpretation can sometimes turn out to be mistaken even though the underlying sensation was accurately registered. In practice, sensation and perception operate together as part of one continuous, tightly interrelated process, rather than as two cleanly separated stages -- which is exactly why they are often grouped, along with attention, as different elements of the single overarching process of cognition; nevertheless, the conceptual distinction matters, because a defect can, in principle, occur at either stage -- a genuine sensory deficit (such as damage to a receptor or its neural pathway) is a fundamentally different problem from a perceptual error (such as a misleading illusion or an expectation-driven misinterpretation), even though both can result in an inaccurate understanding of the same stimulus.