Something to Consider • 41among many neurons. This occurs even for stimuli like faces
that are served by specialized neurons that respond just to
faces. It may not take many neurons to let you know that you
are seeing a face, but it takes a number of neurons working
together to signal the presence of one particular face.THE NEURAL CODE FOR MEMORY
Memories are also represented in the brain, and the same
principles hold for memory as for perception—experiences
are represented by nerve fi ring, with different experiences rep-
resented by different patterns of fi ring. Thus, if a few weeks
after you look at the tree you remember seeing it, perhaps
even visualizing what it looked like, this memory is elicited
by a particular pattern of the fi ring of many neurons in the
brain. There is, however, an important difference between the
neural fi ring caused by perception and the neural fi ring caused
by memory.
The neural fi ring associated with experiencing a per-
ception is caused by stimulation of the sensory receptors.
In contrast, the neural fi ring associated with experiencing a
memory is caused by fi ring in structures that contain infor-
mation about what happened in the past. Thus, while the
fi ring associated with perception is associated with what is
happening as you are looking at the tree, fi ring associated
with memory is associated with information that has been
stored in the brain. We know less about the actual form of
this stored information for memory, but it is likely that the
basic principle of distributed coding also operates for mem-
ory, with specifi c memories being represented by particular
patterns of stored information that result in a particular pat-
tern of nerve fi ring when we experience the memory. We will
discuss the physiological processes involved in memory in
Chapters 5 and 7.Something to Consider
“Mind Reading” by Measuring Brain Activity
The idea that cognitions are represented by distributed activity in the brain raises an
interesting question: Is it possible to determine what a person is seeing, thinking, or
remembering by measuring the activity of the brain? To achieve this, we would have
to know exactly what pattern of activity was associated with every possible object,
thought, or memory, and we are far from being able to do this. However, recent research
using computer programs that can be trained to recognize the patterns of brain activity
associated with seeing and thinking about an object has brought us closer to this goal.
Computer programs have recently been developed that can, with a surprising degree of
accuracy, identify from a group of objects the specifi c object a person is seeing.
We will describe an experiment by Svetlana Shinkareva and coworkers (2008). In
the fi rst part of the experiment, a computer learned the patterns of neural activity that
were associated with different objects. The fi rst step was to have participants look at
a series of pictures like the one in ● Figure 2.23. These pictures are line drawings of
tools and dwellings. The participants’ saw pictures of fi ve different tools and fi ve dif-
ferent dwellings while in a brain scanner, which measured the fMRI response to each● FIGURE 2.22 How faces could be coded by distributed
coding. Each face causes all the neurons to fi re, but the
pattern of fi ring is diff erent for each face. One advantage of
this method of coding is that many faces could be represented
by the fi ring of the three neurons. (Source: B. Goldstein, Sensation
and Perception, 8th ed., Fig. 2.23, p. 38. Copyright © 2010 Wadsworth, a part
of Cengage Learning. Reproduced with permission. http://www.cengage.com/
permissions.)
Stimulus Neuron 1 Neuron 2 Neuron 3(a) Bill(b) Mary(c) Ramon(d) RogerCopyright 2011 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part.