Gestalt psychologists attempted to discover refinements of the law of "Prägnanz", and this involved writing down laws that, hypothetically, allow us to predict the interpretation of sensation, what are often called "gestalt laws". Wertheimer defined a few principles that explain the ways humans perceive objects. Those principles were based on similarity, proximity, continuity. The Gestalt concept is based on perceiving reality in its simplest form. The various laws are called "laws" or "principles", depending on the paper where they appear—but for simplicity's sake, this article uses the term "laws". These laws took several forms, such as the grouping of similar, or proximate, objects together, within this global process. These laws deal with the sensory modality of vision. However, there are analogous laws for other sensory modalities including auditory, tactile, gustatory and olfactory (Bregman – GP). The visual Gestalt principles of grouping were introduced in Wertheimer (1923). Through the 1930s and '40s Wertheimer, Kohler and Koffka formulated many of the laws of grouping through the study of visual perception.