Sensory Processes 51properties of neurons was on. The pioneering studies were
those of Mountcastle and associates at Hopkins on the organi-
zation of the somatic-sensory system (Mountcastle, Davies, &
Berman, 1957), those of Hubel and Wiesel (1959) at Harvard
on the visual system (and Maturana and Lettvin’s work at MIT
on the optic nerve fibers of frogs, see Maturana, Lettrin,
McCulloch, & Pitts, 1960), and those of Rose, Hind, Woolsey,
and associates at Wisconsin on the auditory system (see Hind
et al., 1960).
It was not until many years later that imaging methods
were developed to study the organization and functions of the
normal human brain (see following text). Heroic studies had
been done on human brain functioning much earlier in neuro-
surgical procedures (heroic both for the surgeon and the
patient, e.g., Penfield & Rasmussen, 1950). However, these
patients typically suffered from severe epilepsy. The devel-
opment of PET, fMRI, and other modern techniques is
largely responsible for the explosion of information in the as-
pect of biological psychology termed cognitive neuroscience
(see following and the chapter by Leahey in this volume).
SENSORY PROCESSES
We select two examples of sensory processes, color vision and
pitch detection, that illustrate very well the historical develop-
ment of the study of sensory systems. They are both extraor-
dinary success stories in the field of biological psychology.
Color Vision
Color vision provides an illustrative case history of the de-
velopment of a field in biological psychology with feet in
both physics and physiology. Isaac Newton was perhaps the
first scientist to appreciate the nature of color. The fact that a
prism could break up white light into a rainbow of colors
meant that the light was a mixture that could produce spectral
colors. But Newton recognized that the light rays themselves
had no color; rather, different rays acted on the eye to yield
sensations of colors (1704/1931). Oddly, the great German
literary figure Goethe asserted it was impossible to conceive
of white light as a mixture of colors (1810/1970).
In physics there was an ongoing debate whether light was
particle or wave (we know now it is both). Interestingly,
Newton favored the particle theory. Thomas Young, an
English physicist working a century later, supported the wave
theory. Newton had developed the first color circle showing
that complementary pairs of colors opposite to one another
on the circle would mix to yield white light. Young showed
that it was possible to match any color by selecting three
appropriate colors, red, green, and blue, and suggested there
were three such color receptors in the eye. Helmholtz elabo-
rated and quantified Young’s idea into the Young-Helmholtz
trichromatic theory. Helmholtz, incidentally, studied with
Müller and Du Bois-Reymond. He received his MD in 1842
and published two extraordinary works, the three-volume
Treatis on Physiological Optics(1856–1866/1924) and On
the Sensations of Tone(1863/1954). He was one of the lead-
ing scientists in the nineteenth century and had a profound
impact on early developments in psychology, particularly bi-
ological psychology.
The basic idea in the trichomatic theory is that the three
receptors accounted for sensations of red, green, and blue.
Yellow was said to derive from stimulation of both red and
green receptors, and white was derived from yellow and the
blue receptor. But there were problems. The most common
form of color blindness is red-green. But if yellow is derived
from red and green, how is it that a person with red-green
color blindness can see yellow? In the twentieth century, it
was found that there are four types of receptors in the human
retina: red, green, blue (cones), and light-dark (rods). But
what about yellow?
Hering (1878) developed an alternative view termed the
“opponent-process” theory. He actually studied with Weber
and with Fechner and received his MD just two years after
Wundt in Heidelberg. Interestingly, Hering disagreed with
Fechner about the psychophysical law, arguing that the
relationship should be a power function, thus anticipating
Stevens. Hering proposed that red-green and blue-yellow
acted as opposites, along with white-black. In modern times,
Dorothea Jameson and Leo Hurvich (1955) provided an ele-
gant mathematical formulation of Herring’s theory that ac-
counted very well for the phenomena of color vision.
Russell De Valois, now in the psychology department at
the University of California, Berkeley, provided the physio-
logical evidence to verify the Herring-Jameson-Hurvich
theory, using the monkey (see De Valois, 1960). Ganglion
neurons in the retina that respond to color show “opponent”
processes. One cell might respond to red and be inhibited by
green, another will respond to green and be inhibited by red,
yet another will respond to blue and be inhibited by yellow,
and the last type will respond to yellow and be inhibited by
blue. The same is true for neurons in the visual thalamus.
De Valois’s work provided an elegant physiological basis for
the opponent-process theory of color vision. But Young and
Helmholtz were also correct in proposing that there are three
color receptors in the retina. It is the neural interactions in the
retina that convert actions of the three color receptors into
the opponent processes in the ganglion cells. It is remark-
able that nineteenth-century scientists, working only with the