MIT Encyclopedia of the Cognitive Sciences - Cryptome

Neurosciences lvii
immediate objects of the perception of our senses are merely particular states induced
in the nerves, and felt as sensations either by the nerves themselves or by the sensorium”
(Boring 1950). Muller thus sidestepped the ancient problem of the mind's
access to the external world by observing that all it can hope to access is the state of its
sensory nerves. Accordingly, perception of the external world is a consequence of the
stable relationship between external stimuli and nerve activation, and—tailing the
associationist philosophers—meaning is granted by the associative interactions
between nerves carrying different types of information. The concept was elaborated
further by Helmholtz and others to address the different submodalities (e.g., color vs.
visual distance) and qualities (e.g., red vs. green) of information carried by different
fibers, and is a tenet of contemporary sensory neurobiology and cognitive neuroscience.
The further implications of associationism for an understanding of the neuronal
basis of perception—or, more precisely, of functional knowledge of the world—
are profound and, as we shall see, many of the nineteenth-century debates on the topic
are being replayed in the courts of modern single-neuron physiology.
See also GESTALT PSYCHOLOGY; PSYCHOPHYSICS; WUNDT, WILHELM
3 Cognitive Neuroscience Today
And so it was from these ancient but rapidly converging lines of inquiry, with the
blush still on the cheek of a young cognitive science, that the modern era of cognitive
neuroscience began. The field continues to ride a groundswell of optimism borne by
new experimental tools and concepts—particularly single-cell electrophysiology,
functional brain imaging, molecular genetic manipulations, and neuronal computation—and
the access they have offered to neuronal operations underlying cognition.
The current state of the field and its promise of riches untapped can be summarized
through a survey of the processes involved in the acquisition, storage, and use of
information by the nervous system: sensation, perception, decision formation, motor
control, memory, language, emotions, and consciousness.
Sensation
We acquire knowledge of the world through our senses. Not surprisingly, sensory processes
are among the most thoroughly studied in cognitive neuroscience. Systematic
explorations of these processes originated in two domains. The first consisted of
investigations of the physical nature of the sensory stimuli in question, such as the
wave nature of light and sound. Sir Isaac Newton’s (1642–1727) Optiks is an exemplar
of this approach. The second involved studies of the anatomy of the peripheral
sense organs, with attention given to the manner in which anatomical features prepared
the physical stimulus for sensory transduction. Von Bekesy’s beautiful studies
of the structural features of the cochlea and the relation of those features to the neuronal
frequency coding of sound is a classic example (for which he was awarded the
1961 Nobel Prize in physiology and medicine). Our present understanding of the neuronal
bases of sensation was further enabled by three major developments: (1) establishment
of the neuron doctrine, with attendant anatomical and physiological studies
of neurons; (2) systematization of behavioral studies of sensation, made possible
through the development of psychophysics; and (3) advancement of sophisticated theories
of neuronal function, as embodied by the discipline of COMPUTATIONAL NEURO-
SCIENCE. For a variety of reasons, vision has emerged as the model for studies of
sensory processing, although many fundamental principles of sensory processing are
conserved across modalities.
Initial acquisition of information about the world, by all sensory modalities, begins
with a process known as transduction, by which forms of physical energy (e.g., photons)
alter the electrical state of a sensory neuron. In the case of vision, phototransduction
occurs in the RETINA, which is a specialized sheet-like neural network with a
regular repeating structure. In addition to its role in transduction, the retina also functions
in the initial detection of spatial and temporal contrast (Enroth-Cugell and Robson
1966; Kaplan and Shapley 1986) and contains specialized neurons that subserve