Describes a method of detecting a difference between two test samples and, in particular, may be used as: a) a difference test for test samples whose attributes are subject to variation; b) a recognition test for determining whether assessors are able to detect the deviation of an attribute from a known attribute in a test sample; c) a test for recognizing new attributes in addition to those already known; and d) a perception test for determining the sensitivity of an assessor to a particular attribute.