Time perception is a field of study within psychology and neuroscience that refers to the subjective experience of time, which is measured by someone's own perception of the duration of the indefinite and continuous unfolding of events. The perceived time interval between two successive events is referred to as perceived duration. Another person's perception of time cannot be directly experienced or understood, but it can be objectively studied and inferred through a number of scientific experiments. Time perception is a construction of the brain that is manipulable and distortable under certain circumstances. These temporal illusions help to expose the underlying neural mechanisms of time perception.Pioneering work, emphasizing species-specific differences, was conducted by Karl Ernst von Baer. Experimental work began under the influence of the psycho-physical notions of Gustav Theodor Fechner with studies of the relationship between perceived and measured time.