reflexes, and we might
begin with either. The introspective psychologists usually start with
sensations, because their great object is to describe consciousness,
and they think of sensations as the chief elements of which
consciousness is composed. The behaviorists would prefer to start with
reflexes, because they conceive of behavior as composed of these
simple motor reactions.

Without caring to attach ourselves exclusively to either
introspectionism or behaviorism, we may take our cue just here from
the behaviorists, because we shall find the facts of motor reaction
more widely useful in our further studies than the facts of sensation,
and because the facts of {22} sensation fit better into the general
scheme of reactions than the facts of reaction fit into any general
scheme based on sensation.

A reaction is a _response_ to a _stimulus_. The response, in the
simplest cases, is a muscular movement, and is called a "motor
response". The stimulus is any force or agent that, acting upon the
individual, arouses a response.

If I start at a sudden noise, the noise is the stimulus, and the
forcible contraction of my muscles is the response. If my old friend's
picture brings tears to my eyes, the picture (or the light reflected
from it) is the stimulus, and the flow of tears is the response, here
a "glandular" instead of a motor response.

The Reaction Time Experiment

One of the earliest experiments to be introduced into psychology was
that on reaction time, conducted as follows: The experimenter tells
his "subject" (the person whose reaction is to be observed) to be
ready to make a certain movement as promptly as possible on receiving
a certain stimulus. The response prescribed is usually a slight
movement of the forefinger, and the stimulus may be a sound, a flash
of light, a touch on the skin, etc. The subject knows in advance
exactly what stimulus is to be given and what response he has to make,
and is given a "Ready!" signal a few seconds before the stimulus. With
so simple a performance, the reaction time is very short, and delicate
apparatus must be employed to measure it. The "chronoscope" or clock
used to measure the reaction time reads to the hundredth or thousandth
of a second, and the time is found to be about .15 sec. in responding
to sound or touch, about .18 sec. in responding to light.

Even the simple reaction time varies, however, from one {23}
individual to another, and from one trial to ano