Cannons Central Theory

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Theories of Emotion
Polygraph tests are not foolproof, though
they may intimidate people who believe
that they are. In one small town where
the police could not afford a polygraph, a
guilty suspect confessed his crime when a
“lie detector” consisting of a kitchen
colander was placed on his head and
attached by wires to a copy machine
(Shepherd, Kohut, & Sweet, 1989).
SEARCHING FOR THE TRUTH
Most people do have emotional responses when they lie, but statistics about the
accuracy of polygraphs are difficult to obtain. Estimates vary widely, from those suggesting that polygraphs detect 90 percent of guilty, lying individuals (Honts & Quick,
1995; Kircher, Horowitz, & Raskin, 1988; Raskin, 1986) to those suggesting that polygraphs mislabel as many as 40 percent of truthful, innocent persons as guilty liars (BenShakhar & Furedy, 1990; Saxe & Ben-Shakhar, 1999). Obviously, the results of a polygraph test are not determined entirely by whether a person is telling the truth. What
people think about the act of lying and about the value of the test can also influence
the accuracy of its results. For example, people who believe that lying is acceptable and
who don’t believe in the power of polygraphs are not likely to display emotion-linked
physiological responses while lying during the test. However, an innocent person who
believes in such tests and who thinks that “everything always goes wrong” might show
a large fear response when asked about a crime, thus wrongly indicating “guilt” (Lykken,
1998).
Polygraphs can catch some liars, but most researchers agree that a guilty person can
“fool” a polygraph lie detector and that some innocent people can be mislabeled as
guilty (Ruscio, 2005). After reviewing the relevant research literature, a panel of distinguished psychologists and other scientists in the United States expressed serious
reservations about the value of polygraph tests in detecting deception and argued
against their use as evidence in court or in employee screening and selection (Committee to Review the Scientific Evidence on the Polygraph, 2003). Scientists are working on other lie-detecting techniques that focus on brain activity and other measures
that do not depend on a link between deception and autonomic nervous system
responses (Gronau, Ben-Shakhar, & Cohen, 2005; Kozel, Padgett, & George, 2004;
Langleben et al., 2005).
Cannon’s Central Theory
James said that the experience of emotion depends on feedback from physiological
responses occurring outside the brain, but Walter Cannon disagreed (Cannon,
1927/1987). According to Cannon, you feel fear at the sight of a wild bear even before
you start to run because emotional experience starts in the brain—specifically, in the
thalamus, the brain structure that relays information from most sense organs to the
cortex.
According to Cannon’s central theory of emotion (called the Cannon-Bard theory, in
recognition of Philip Bard’s contribution), information about emotional situations goes
first to the thalamus. The thalamus then sends signals to the autonomic nervous system and—at the same time—to the cerebral cortex, where the emotion becomes conscious. So when you see a bear, the brain receives sensory information about it, interprets that information as a bear, and instantly creates the experience of fear while at
the same time sending messages to your heart, lungs, and legs to get you out of the situation. According to Cannon’s theory, then, there is a direct, central-nervous-system
experience of emotion, whether or not the brain receives feedback about responses in
other parts of the body (see Figure 8.8).
Later research indicates that the thalamus is not the
“seat” of emotion, as Cannon had suggested. Still, the thalamus is indeed involved in
some aspects of emotional processing (Lang, 1995). For example, studies of humans
and laboratory animals show that the emotion of fear is generated by connections from
the thalamus to the amygdala (Anderson & Phelps, 2000; LeDoux, 1995). The implication is that strong emotions can sometimes bypass the cortex without requiring conscious thought to activate them. This process helps to explain why people find it so difficult to overcome an intense fear, or phobia, even though they may consciously know
the fear is irrational.
An updated version of Cannon’s theory suggests that activity in specific brain areas
produces the feelings of pleasure or discomfort associated with emotion. This idea arose
when researchers found that rats kept returning to the place in their cage at which
Updating Cannon’s Theory