"Visual urban monotony has been cited by psychologists as being a major factor in undermining mental well-being. It is proposed that this is the result of two characteristics of the system of perception, involving the mechanics of memory and retrieval. The first is that perception of familiar environment may be progressively achieved on a subliminal level. This involves a secondary "primitive" perceptual system which can discriminate and evaluate. Such evaluation may be conditioned by primitive criteria. The second concerns the physiological change which takes place each time a memory pattern is activated, lowering the threshold of activation, tending towards simplification of schemas of memory, and progressive blindness to detail. Towns can contribute towards a remedy by expressing the principle of dynamic urbanism i.e. creating situations which challenge existing schemas with unfamiliarity and variability, as well as offering incentives to discovery, problem-solving and imagebuilding."