There are many different zeitgebers, and their relative influence on an individual at any given time depends on a number of factors, including the presence and operation of other kinds of zeitgebers. For example, Jürgen Aschoff showed that individuals can compensate for the absence of some zeitgebers like natural light by attending to social zeitgebers instead. Specifically, individuals placed in total darkness for four days did not differ on a variety of measures, including body temperature and various psychomotor tasks like time estimation and finger tapping, from individuals placed in an artificial light-dark environment when both groups were given the same strict time schedule.[12] Researchers concluded that social zeitgebers, like meal times and interactions with other people, can entrain biological rhythms in ways similar to those of other common zeitgebers like light.