subsequent movements are not suppressed until their proper moment
arrives, but appear in advance of their scheduled time. In writing, for
example, we frequently omit words or add to a word the final letter of
some word that belongs to a subsequent part of the sentence. An error of
this sort could hardly occur so readily in the course of an act that
belongs to the type of the true reflex.

Lest the reader suspect that this is _a priori_ physiology, I may quote
the following from a prominent neurologist: "No simple sensory impulse
can, under ordinary circumstances, reach the cerebral cortex without
first being influenced by subcortical association centers, within which
complex reflex combinations may be effected and various automatisms set
off in accordance with their preformed structure. These subcortical
systems are to some extent modifiable by racial and individual
experience, but their reactions are chiefly of the determinate or
stereotyped character, with a relatively limited range of possible
reaction types for any given stimulus complex.

"It is shown by the lower vertebrates, which lack the cerebral cortex,
that these subcortical mechanisms are adequate for all of the ordinary
simple processes of life, including some degree of associative memory.
But here, when emergencies arise which involve situations too complex to
be resolved by these mechanisms, the animal will pay the inevitable
penalty of failure--perhaps the loss of his dinner, or even of his life.

"In the higher mammals with well-developed cortex the automatisms and
simple associations are likewise performed mainly by the subcortical
apparatus, but the inadequacy of this apparatus in any particular
situation presents not the certainty of failure, but rather a dilemma.
The rapid preformed automatisms fail to give relief, or perhaps the
situation presents so many complex sensory excitations as to cause
mutual interference and inhibition of all reaction. There is a stasis in
the subcortical centers. Meanwhile the higher neural resistance of the
cortical pathways has been overcome by summation of stimuli and the
cortex is excited to function. Here is a mechanism adapted, not for a
limited number of predetermined and immediate responses, but for a much
greater range of combination of the afferent impressions with each other
and with memory vestiges of previous reactions and a much larger range
of possible modes of response to any given set of afferent impr