Our perception (or sense) of time differs considerably at different
ages, and under different circumstances. When we are bored, tired,
etc., time seems to move slowly; when we are interested or excited, it
flits by rapidly, etc. A certain span of time always seems shorter to
old people than to young ones. A year is an enormous period to a child;
whereas an old man will often exclaim: “How the years have flown!” Time
which is busily occupied seems short, but it seems a long period, when
looked back upon. A waiting period, on the other hand, in which nothing
is accomplished, seems interminable during its passage; but it seems
extremely brief, when viewed in retrospect. This is probably due to the
fact that many actions _seem_ to occupy a long period of time, whereas
a span in which nothing of importance happens _seems_ to have taken-up
no time at all.
The shortest period of time which we can appreciate is about 1/500 of
a second. Exner recognized two electric sparks to be successive when
the second followed the first at that interval. On the other hand, the
longest period of time which we can accurately distinguish from longer
or shorter bits of time, according to Wundt, is 12 seconds. We probably
have no sense of “empty” time; but of the flow of events _in_ time.
It has been suggested that the pulse may be a sort of natural clock,
enabling us to appreciate time as it flows (for instance in sleep),
but this hardly serves to explain many such cases. The same may be
said of the idea that some unknown, but constant, feature in the brain
activities is the source of our perceiving time at all.
When we become unconscious, time is obliterated altogether; the sense
of time is also seriously impaired under the influence of certain
drugs (_e. g._, hasheesh), so that a second may appear to consume
hours, and _vice versa_. It has been proved by experiment that subjects
under hypnosis, and some natural somnambules, have a remarkable sense
of time, and can reckon it with uncanny accuracy. Our conscious mind
is notoriously bad at this sort of thing. The subconscious mind is
the “ready reckoner,” therefore, which must be added to its other
accomplishments!