The Contrast Principle, first studied by Robert Cialdini in his 2007 book The Psychology of Persuasion, explores the way in which our perceptions are formed by using comparison techniques. When we experience similar things in succession or simultaneously, we evaluate the lesser or greater value of the second through direct comparison with the first.

This Contrast effect will therefore lead to an enhanced or diminished perception of the second thing dependent on how we viewed the first. For example, when you pick up a heavy box and then a lighter one, the second box will appear lighter than it really is. This Contrast effect is due to the fact that our brain evaluates things based on the mode of comparison that is most easily accessible at that given moment, rather than the most suitable one. In other words, we tend to evaluate by comparison to accessible referencing rather than by using more correct, absolute values, as these aren’t readily available for our brains to utilise, and this leads us to make biased judgements.

The Contrast effect is applied to all manner of judgements we might make on a day-to-day basis. For instance, if at a cocktail party you talk to an unattractive person and are then joined by an average-looking person, you will judge the average-looking person to be more attractive than they really are and than you would have perceived them to be had you seen them on their own before you had this unreliable scale of comparison in mind. In this way, the Contrast effect can affect our judgements in relation to people, products, market values, and the values of many other attributes and characteristics. The contrast principle has many applications in sales and marketing and is often utilised by brands to influence customers’ perceptions of their products. For example, a technique often used by salesman is to offer either a low quality or, in contrast, a luxury overpriced item alongside the one they really want you to buy in order to influence your perception of this target product as being a good value deal in comparison to the other being shown.