the cortices.These individualized patterns lacked invariance with respect
to the stimuli that triggered them (Freeman 1992).They were not eidetic
or derived images.Instead,they reflected the experiences,contexts,and
significances of stimuli,in a word,the meaningsof the stimuli for indi-
viduals.Our evidence from other sensory cortices indicated that this
principle holds for all senses in all animals,including humans.The con-
clusion is that the only knowledge that animals and humans can have of
the world outside themselves is what they construct within their own
brains.
This finding could not have been obtained by introspection,because
the process of observation contains within it some well-known opera-
tions that compensate for accidental changes in appearances of objects
owing to variations in perspective,context,and so forth (Smythies 1994).
We are drenched in perceptual constancies as a necessary condition for
daily living.No one can tell from one’s own experience or from the con-
stant response R of someone else to a repeated stimulus S that an appar-
ently invariant S-R relation is mediated by inconstant patterns of brain
activity.I explain the lack of invariance as owing to the unity of individ-
ual experience (Freeman 1995),because every perception is influenced
by all past experience.Each exposure to a stimulus changes the
brain’s synaptic structure so that it cannot respond identically over time,
although it may appear subjectively to be so.As Heraclitus remarked,
one cannot step twice in the same river.Biological Isolation of Brains from Each Other
These findings can be summarized by saying that a form of solipsism
isolates each brain from all others.The word as it is commonly used is
applied to an individual who is so self-centered that he or she believes
that all others are mere projections of their own imaginations.That is
metaphysical solipsism,by which everything that exists is the projection
of a brain.That would lead to the absurd conclusion that all of us are the
fantasy of a dreaming rabbit.I am proposing a less common use of the
word to mean epistemological solipsism,which holds that all knowledge
is created within the brains of individuals.Each mind constructs its world
view under the realization that other minds must exist.Knowledge is not
instilled by indoctrination,as held by programmers who feed informa-
tion into their computers.It is encouraged to grow by exhortation and
example,as held by educators and insightful parents.
Solipsistic views have been held in some degree by many philosophers
since Descartes,but they pose difficulties.It is impossible for minds to
disprove metaphysical solipsism by logic alone,so how can a mind really414 Walter Freeman