Organisms often have some sort of internal clock that regulates their behaviour. There is a tendency, for example, for leaves of leguminous plants to alter their position so that they lie in one position by day and in another position by night. This tendency persists if the plant is in artificial light that is kept constant, though it can be modified to other periodicities (e.g., to a six-hour instead of a 24-hour rhythm) by suitably regulating the periods of artificial light and darkness. In animals, similar daily rhythms are usually acquired, but in experimental conditions animals nevertheless tend to adapt better to a 24-hour rhythm than to any other. Sea anemones expand and contract to the rhythm of the tides, and this periodic behaviour will persist for some time even when the sea anemone is placed in a tank. Bees can be trained to come for food at fixed periods (e.g., every 21 hours), and this demonstrates that they possess some sort of internal clock. Similarly, humans themselves have some power to estimate time in the absence of clocks and other sensory cues. This fact refutes the contention of the 17th-century English philosopher John Locke (and of other philosophers in the empiricist tradition) that time is perceived only as a relation between successive sensations. The U.S. mathematician Norbert Wiener has speculated on the possibility that the human time sense depends on the α-rhythm of electrical oscillation in the brain.

Temporal rhythms in both plants and animals (including humans) are dependent on temperature, and experiments on human subjects have shown that, if their temperature is raised, they underestimate the time between events.

Despite these facts, the Lockean notion that the estimation of time depends on the succession of sensations is still to some degree true. People who take the drugs hashish and mescaline, for example, may feel their sensations following one another much more rapidly. Because there are so many more sensations than normal in a given interval of time, time seems to drag, so that a minute may feel like an hour. Similar illusions about the spans of time occur in dreams.

It is unclear whether most discussions of so-called biological and psychological time have much significance for metaphysics. As far as the distorted experiences of time that arise through drugs (and in schizophrenia) are concerned, it can be argued that there is nothing surprising in the fact that pathological states can make people misestimate periods of time, and so it can be claimed that facts of this sort do not shed any more light on the philosophy of time than facts about mountains looking near after rainstorms and looking far after duststorms shed on the philosophy of space.

The idea that psychological studies of temporal experience are philosophically important is probably connected with the sort of empiricism that was characteristic of Locke and still more of George Berkeley and David Hume and their successors. The idea of time had somehow to be constructed out of the primitive experience of ideas succeeding one another. Nowadays, concept formation is thought of as more of a social phenomenon involved in the “picking up” of a language, and, thus, contemporary philosophers have tended to see the problem differently: humans do not have to construct their concepts from their own immediate sensations. Even so, the learning of temporal concepts surely does at least involve an immediate apprehension of the relation of “earlier” and “later.” A mere succession of sensations, however, will go no way toward yielding the idea of time: if one sensation has vanished entirely before the other is in consciousness, one cannot be immediately aware of the succession of sensations.

What empiricism needs, therefore, as a basis for constructing the idea of time is an experience of succession as opposed to a succession of experiences. Hence, two or more ideas that are related by “earlier than” must be experienced in one single act of awareness. William James, a U.S. pragmatist philosopher and also a pioneer psychologist, popularized the term specious present for the span of time covered by a single act of awareness. His idea was that at a given moment of time a person is aware of events a short time before that time. (Sometimes he spoke of the specious present as a saddleback looking slightly into the future as well as slightly into the past, but this was inconsistent with his idea that the specious present depended on lingering short-term memory processes in the brain.) He referred to experiments by the German psychologist Wilhelm Wundt that showed that the longest group of arbitrary sounds that a person could identify without error lasted about six seconds. Other criteria perhaps involving other sense modalities might lead to slightly different spans of time, but the interesting point is that, if there is such a specious present, it cannot be explained solely by ordinary memory traces: if one hears a “ticktock” of a clock, the “tick” is not remembered in the way in which a “ticktock” 10 minutes ago is remembered. The specious present is perhaps not really specious: the idea that it was specious depended on an idea that the real (nonspecious) present had to be instantaneous. If perception is considered as a certain reliable way of being caused to have true beliefs about the environment by sensory stimulation, there is no need to suppose that these true beliefs have to be about an instantaneous state of the world. It can therefore be questioned whether the term specious is a happy one.

Two matters discussed earlier in connection with the philosophy of physics have implications for the philosophy of mind: (1) the integration of space and time in the theory of relativity makes it harder to conceive of immaterial minds that exist in time but are not even localizable in space; (2) the statistical explanation of temporal asymmetry explains why the brain has memory traces of the past but not of the future and, hence, helps to explain the unidirectional nature of temporal consciousness. It also gives reasons for skepticism about the claims of parapsychologists to have experimental evidence for precognition, or it shows, at least, that if these phenomena do exist, they are not able to be fitted into a cosmology based on physics as it exists today.