Cognitive Psychology And Its Implications, Ch. 4

4

Mental Imagery

Try answering these two questions:

• How many windows are in your house? • How many nouns are in the American Pledge of Allegiance?

Most people who answer these questions have the same experience. For the first

question they imagine themselves walking around their house and counting windows.

For the second question, if they do not actually say the Pledge of Alliance out loud,

they imagine themselves saying the Pledge of Allegiance. In both cases they are creating

mental images of what they would have perceived had they actually walked around

the house or said the Pledge of Allegiance.

Use of visual imagery is particularly important. As a result of our primate heritage,

a large portion of our brain functions to process visual information. Therefore, we use

these brain structures as much as we can, even in the absence of a visual signal from

the outside world, by creating mental images in our heads. Some of humankind’s most

creative acts involve visual imagery. For instance, Einstein claimed he discovered the

theory of relativity by imagining himself traveling beside a beam of light.

A major debate in this field of research has been the degree to which the processes

behind visual imagery are the same as the perceptual and attentional processes that we

considered in the previous two chapters. Some researchers (e.g., Pylyshyn, 1973, in an

article sarcastically titled “What the mind’s eye tells the mind’s brain”) have argued that

the perceptual experience that we have while doing an activity such as picturing the

windows in our house is an epiphenomenon; that is, it is a mental experience that does

not have any functional role in information processing. The philosopher Daniel Dennett

(1969) also argued that mental images are epiphenomenal—that is, that the perceptual

components of mental images are not really functional in any way:

Consider the Tiger and his Stripes. I can dream, imagine or see a striped tiger, but

must the tiger I experience have a particular number of stripes? If seeing or imagining

is having a mental image, then the image of the tiger must—obeying the rules of

images in general—reveal a definite number of stripes showing, and one should be

able to pin this down with such questions as “more than ten?”, “less than twenty?”

(p. 136)

Anderson7e_Chapter_04.qxd 8/20/09 9:42 AM Page 92

Verbal Imagery versus Visual Imagery | 93

Dennett’s argument is that if we are actually seeing a tiger in a mental image, we

should be able to count its stripes just like we could if we actually saw a tiger.

Because we cannot count the stripes in a mental image of a tiger, we are not having

a real perceptual experience. This argument is not considered decisive, but it does

illustrate the discomfort some people have with the claim that mental images are

actually perceptual in character.

This chapter will review some of the experimental evidence showing the ways that

mental imagery does play a role in information processing. We will define mental

imagery broadly as the processing of perceptual-like information in the absence of an

external source for the perceptual information. We will consider the following questions: • How do we process the information in a mental image? • How is imaginal processing related to perceptual processing? • What brain areas are involved in mental imagery? • How do we develop mental images of our environment and use these

to navigate through the environment?

•Verbal Imagery versus Visual Imagery

There is increasing evidence from cognitive neuroscience that several different

brain regions are involved in imagery. This evidence has come both from studies

of patients suffering damage to various brain regions and from studies of the

brain activation of normal individuals as they engage in various imagery tasks.

In one of the early studies of brain activation patterns during imagery, Roland

and Friberg (1985) identified many of the brain regions that have been investigated

in subsequent research. They had participants either mentally rehearse a

word jingle or mentally rehearse finding their way around streets in their neighborhoods.

The investigators measured changes in blood flow in various parts of

the cortex. Figure 4.1 illustrates the principal areas they identified.When participants

engaged in the verbal jingle task, there was activation in the prefrontal cortex

near Broca’s area and in the parietal-temporal region of the posterior cortex

R

R

R

R

J

J

FIGURE 4.1 Results from

Roland and Friberg’s (1985)

study of brain activation

patterns during mental imagery.

Regions of the left cortex

showed increased blood flow

when participants imagined

a verbal jingle (J) or a spatial

route (R).

Brain Structures

Anderson7e_Chapter_04.qxd 8/20/09 9:42 AM Page 93

near Wernicke’s area. As discussed in Chapter 1, patients with damage to these

regions show deficits in language processing. When participants engaged in the

visual task, there was activation in the parietal cortex, occipital cortex, and temporal

cortex. All these areas are involved in visual perception and attention, as

we saw in Chapters 2 and 3.When people process imagery of language or visual

information, some of the same areas are active as when they process actual

speech or visual information.

An experiment by Santa (1977) demonstrated the functional consequence

of representing information in a visual image versus representing it in a verbal

image. The two conditions of Santa’s experiment are shown in Figure 4.2. In

the geometric condition (Figure 4.2a), participants studied an array of three

geometric objects, arranged with one object centered below the other two.

This array had a facelike property—without much effort, we can see eyes and a

mouth. After participants studied the array, it was removed, and they had to

hold the information in their minds. They were presented with one of several

different test arrays. The participants’ task was to verify that the test array contained

the same elements as the study array, although not necessarily in the same

94 | Mental Imagery

Study

array

arrays

Test

Test

arrays

Study

array

Identical,

same configuration

Same elements,

linear configuration

Different elements,

same configuration

Different elements,

linear configuration

Triangle Circle

Square

Triangle Circle

Square

Triangle Circle Square

Triangle Circle

Arrow

Triangle Circle Arrow

Identical,

same configuration

Same word,

linear configuration

Different words,

same configuration

Different words,

linear configuration

(a) Geometric condition

(b) Verbal condition

FIGURE 4.2 The procedure followed in Santa’s (1977) experiment demonstrating that visual

and verbal information is represented differently in mental images. Participants studied an initial

array of objects or words and then had to decide whether a test array contained the same

elements. Geometric shapes were used in (a), words for the shapes in (b).

Anderson7e_Chapter_04.qxd 8/20/09 9:42 AM Page 94

spatial configuration. Thus, participants should

have responded positively to the first two test

arrays and negatively to the last two. Santa was

interested in the contrast between the two positive

test arrays. The first was identical to the

study array (same-configuration condition). In

the second array, the elements were displayed

in a line (linear-configuration condition). Santa

predicted that participants would make a positive

identification more quickly in the first case,

where the configuration was identical—because,

he hypothesized, the mental image for the study

stimulus would preserve spatial information. The

results for the geometric condition are shown in

Figure 4.3. As you can see, Santa’s predictions were confirmed. Participants were

faster in their judgments when the geometric test array preserved the configuration

information in the study array.

The results from the geometric condition are more impressive when contrasted

with the results from the verbal condition, illustrated in Figure 4.2b.

Here, participants studied words arranged exactly as the objects in the geometric

condition were arranged. Because it involved words, however, the study stimulus

did not suggest a face or have any pictorial properties. Santa speculated that participants

would read the array left to right and top down and encode a verbal

image with the information. So, given the study array, participants would encode

it as “triangle, circle, square.” After they studied the initial array, one of the test

arrays was presented. Participants had to judge whether the words were identical.

All the test stimuli involved words, but otherwise they presented the same

possibilities as the test stimuli in the geometric condition. The two positive stimuli

exemplify the same-configuration condition and the linear-configuration

condition. Note that the order of words in the linear array was the same as it

was in the study stimulus. Santa predicted that, unlike the geometric condition,

because participants had encoded the words into a linearly ordered verbal image,

they would be fastest when the test array was linear. As Figure 4.3 illustrates,

his predictions were again confirmed.

Different parts of the brain are involved in verbal and visual imagery,

and they represent and process information differently.

•Visual Imagery

Most of the research on mental imagery has involved visual imagery, and this

will be the principal focus of this chapter. One function of mental imagery is to

anticipate how objects will look from different perspectives. People often have

the impression that they rotate objects mentally to achieve perspective. Roger

Shepard and his colleagues have been involved in a long series of experiments

Visual Imagery | 95

Geometric

Verbal

Reaction time (s)

1.25

1.15

Same

configuration

Linear

configuration