Basic principles of judgement

The question of how people judge stimuli is one of the oldest in psychology. Judgement tasks can take many forms, and they can crop up in any branch of psychology. Deciding whether a stimulus is present or absent, similar to or different from a standard, larger or smaller, better or worse – all these are kinds of judgement; so too is the decision that a stimulus belongs to a particular category, or that stimuli within one category resemble each other more than they resemble stimuli within another category. In short, the term ‘judgement’ refers to all those processes whereby any piece of information on perceptual input is compared to some criterion. Theories of judgement essentially try to describe how such processes of comparison operate.

Are the ways we judge ‘social’ stimuli – such as other people and things they say and do – the same as the ways we judge physical objects? This question has received considerable attention since, historically, the tendency has been to take theories developed to account for simple perceptual judgements and to see how well they apply to social judgements. On the whole, this approach has been quite successful. To a remarkable extent, principles that account for how people judge the heaviness of cylindrical weights, or the brightness of lights, have been found to be highly predictive of how people judge the desirability of some outcome, or the extremity of somebody's opinion on some issue.