The hypothesis evolved from work by Edward Sapir and Benjamin Lee Whorf, which pointed towards the possibility that grammatical differences reflect differences in the way that speakers of different languages perceive the world. Linguistic relativity was formulated as a testable hypothesis called the Sapir–Whorf hypothesis by Roger Brown and Eric Lenneberg, based on experiments on color perception across language groups. Color perception and naming has been a popular research area, producing studies that have both supported and questioned linguistic relativity's validity. In the mid-20th century, many linguists and psychologists had maintained that human language and cognition is universal and not subject to relativistic effects.