48 Biological Psychology
and his student Tichener in their attempts to measure the at-
tributes of sensation.
Tichener identified the elements of conscious experience
as quality, intensity, extensity, protensity (duration), and at-
tensity (clearness) (see Tichener, 1898). But for all their at-
tempts at scientific observation, the basic approach of Wundt
and Tichener was introspection, but other observers (e.g.,
Külpe at Bonn) had different introspections. Boring studied
with Tichener and was for many years chair of the psychol-
ogy department at Harvard. He attempted to recast Tichener’s
views in more modern terms (The Physical Dimensions of
Consciousness,1933) by emphasizing that the dimensions
listed earlier related to discrimination of physical stimuli. His
student S. S. Stevens showed that trained observers could re-
liably form judgments of sounds in terms of pitch, loudness,
“volume,” and “density” (see also Boring, 1950).
At Harvard, Stevens later introduced an important new
method of psychophysics termeddirect magnitude estimation.
The subject simply assigned a number to a stimulus, a higher
one to a more intense stimulus and a lower number to one that
was less intense. Somewhat surprisingly this method gave very
reliable results. Using this method, Stevens found that the
proper relationship between stimulus intensity and sensation is
not logarithmic, as Fechner had argued, but rather a power
function: The sensation, that is, sensory magnitude, equaled
the stimulus intensity raised to some power, the exponent rang-
ing from less than to greater than one. This formulation proved
very useful in both psychophysical and physiological studies
of sensory processes (see Stevens, 1975).
The key point of all this work on psychophysics is that it is
not necessary to be concerned at all about subjective experience
or introspection. The observer simply pushes a button or states
a word or number to describe his or her judgment of the stimu-
lus. The more the observer practices, the more reliable the judg-
ments become and the more different observers generate the
same results. Psychophysics had become purely behavioral.
As Hilgard (1987) notes, Fechner was troubled by the ques-
tion of where the transformation between stimulus and judg-
ment occurs. Fechner distinguished between “inner” and
“outer” psychophysics,outerreferring to the relation between
the mind and external stimuli andinnerto the relation between
the mind and excitation of the sensory apparatus. Fechner
opted for a direct correspondence between excitation and sen-
sation, a surprisingly modern view. Indeed, Stevens (1961) ar-
gued with evidence that the psychophysical transformation
occurs at the receptor–first-order neurons, at least for intensity.
We take an example from the elegant studies of Mount-
castle, Poggio, and Werner (1963). Here they recorded the ac-
tion potentials of a neuron in the somatosensory thalamus of
a monkey driven by extension of the contralateral knee. The
relation between degrees of joint angle () and frequency of
neuron discharge (F)isF13.90.42924, where 13.9 and
24 are constants determined by conditions. So the power ex-
ponent is 0.429, within the general range of exponents for
psychophysical judgments of the relation between joint angle
and sensation of movement. In other words, the relationship
is established by ascending sensory neuron activity before
the level of the cerebral cortex, presumably at the receptor–
first-order neuron.
The modern era of psychophysics can perhaps be dated to
a seminal paper by John Swets in 1961: Is there a sensory
threshold?His answer was no. He and David Green devel-
oped the theory and methodology of signal detection theory
(Green & Swets, 1966). There is always noise present with
signals. When one attempts to detect a signal in noise, the cri-
teria used will determine the outcome. This approach has
proved immensely useful in fields ranging from the telephone
to psychophysical studies in animals to detection of structural
failures in aircraft wings to detection of breast cancer. But
where is the mind in decision theory? It has disappeared. The
initial hope that psychophysics could measure the mind has
been reduced to considerations of observer bias. A similar
conclusion led to the downfall of introspection.THE BRAINUntil the nineteenth century, the only method available to
study brain function was the lesion, either in unfortunate hu-
mans with brain damage or brain lesions done in infrahuman
animals. The key intellectual issue throughout the history of
the brain sciences was localization. To state the question in
simplistic terms: Are psychological traits and functions local-
ized to particular regions of the brain or are they widely dis-
tributed in the brain?
The history of ideas about localization of brain function
can be divided roughly into three eras. During the first era,
which spans from antiquity to about the second century A.D.,
debate focused on the location of cognitive function, al-
though the discussion revolved around the issue of the soul,
that is, what part of the body housed the essence of being
and the source of all mental life (for reviews, see Finger,
1994; Gross, 1987; Star, 1989). In an early and particularly
prophetic Greek version of localization of function, the soul
was thought to be housed in several body parts, including the
head, heart, and liver, but the portion of the soul associated
with intellect was located in the head (McHenry, 1969). The
individual whom many historians have viewed as having the
greatest influence during this era was Galen, an anatomist of
Greek origin. Using animals, he performed experiments that