Different stimuli initiate a variety of psychological processes within the consumer - delight, revulsion, hunger, longing, etc. Psychological scaling is a method of translating these psychological processes into a form that can be measured and then quantified.
Focus groups often struggle to measure psychological attributes. Individuals react in predictable ways to stimuli, but it is unrealistic to expect them to verbalise about processes that are below the level of awareness. However, individuals can usually make order judgements, even when they cannot explain their choices. For example, someone may find it difficult to say what constitutes 'quality' in a car. However, show them two models and they will be able to say almost instantly which has more quality. It follows that the position of a stimulus on a psychological scale can be measured for a number of respondents, with survey results having important implications in marketing terms.