Figure4.1presents a short lesson on how lightning storms develop – including illustrations depicting the major steps and corresponding text describing the major steps. It is a multimedia presentation because
Freezing level Ice crystals
Water droplets
Updrafts
Warm moist air
Warm moist air rises, water vapor condenses and forms a
cloud.
Raindrops and ice crystals drag air downward.
When the surface of the earth is warm, moist air near the earth's surface becomes heated and rises rapidly, producing an updraft. As the air in these updraft cools, water vapor condenses into water droplets and forms a cloud. The cloud's top extends above the freezing level.
At this altitude, the air temperature is well below freez-ing, so the upper portion of the cloud is composed of tiny ice crystals.
Eventually, the water droplets and ice crystals in the cloud become too large to be suspended by updrafts.
As raindrops and ice crystals fall through the cloud, they drag some of the air from the cloud downward, producing downdrafts. The rising and falling air cur-rents within the cloud may cause hailstones to form.
When downdrafts strike the ground, they spread out in all directions, producing gusts of cool wind people feel just before the start of the rain.
(Continues) Figure 4.1. A portion of a multimedia lesson on lightning.
the explanation is presented in both words and pictures. The lesson is consistent with many of the design principles suggested in this book because it combines words and pictures in an integrated way. What can you do to improve on this lesson – so that students will be able to use it to solve problems?
Positively charged particles
Negatively charged particles
Negatively charged particles fall to the bottom of the cloud.
Branches Stepped leader
Upward-moving leader Two leaders meet, negatively charged particles rush from the
cloud to the ground.
Return stroke
Positively charged particles from the ground rush upward along the
same path.
Within the cloud, the moving air causes electrical charges to build, although scientists do not fully under-stand how it occurs. Most believe that the charge results from the collision of the cloud's light, rising water droplets and tiny pieces of ice against hail and other heavier, falling particles. The negatively charged part-icles fall to the bottom of the cloud, and most of the positively charged particles rise to the top.
The first stroke of a cloud-to-ground lightning flash is started by a stepped leader. Many scientists believe that it is triggered by a spark between the areas of positive and negative charges within the cloud. A stepped leader moves downward in a series of steps, each of which is about 50-yards long, and lasts for about 1 millionth of a second. It pauses between steps for about 50 millionths of a second. As the stepped leader nears the ground, posi-tively charged upward-moving leaders travel up from such objects as trees and buildings, to meet the negative charges. Usually, the upward moving leader from the tallest object is the first to meet the stepped leader and complete a path between the cloud and earth. The two leaders generally meet about 165-feet above the ground.
Negatively charged particles then rush from the cloud to the ground along the path created by the leaders. It is not very bright and usually has many branches.
As the stepped leader nears the ground, it induces an opposite charge, so positively charged particles from the ground rush upward along the same path. This upward motion of the current is the return stroke and it reaches the cloud in about 70 microseconds. The return stroke produces the bright light that people notice in a flash of lightning, but the current moves so quickly that its upward motion cannot be perceived. The lightning flash usually consists of an electrical potential of hun-dreds of millions of volts. The air along the lightning channel is heated briefly to a very high temperature.
Such intensse heating causes the air to expand explo-sively, producing a sound wave we call thunder.
Figure 4.1. Continued.
One seemingly reasonable suggestion is to spice up the lesson by adding some text and pictures intended to make the lesson more interesting. For example, let’s add a short story about a high school football player who was struck by lightning during football practice, and show a picture of the hole it produced in his helmet and uniform.
Also, let’s add a description of what happens when lightning strikes a swimming pool and show a picture of swimmers as “sitting ducks.”
Figure 4.2shows some interesting material that can be added to the lesson – including sentences and pictures.
Garner and her colleagues coined the term seductive details to refer to interesting but irrelevant material that is added to a passage in order to spice it up (Garner, Brown, Sanders, & Menke,1992; Garner, Gilling-ham, & White,1989). In order to distinguish between the use of words and pictures, Harp and Mayer (1997,1998) used the term seductive text to refer to interesting but irrelevant text that is added to a passage and the term seductive illustrations to refer to interesting but irrelevant illustrations that are added to a passage. The seductive text and seductive illustrations in Figure4.2are interesting because readers rate them as entertaining and interesting. The seductive text and seductive illustrations in Figure4.2are irrelevant because they are not related to the cause-and-effect explanation of how lightning works.
The Case for Adding Interesting Words and Pictures
The major theoretical justification for adding seductive details (such as the seductive text and seductive illustrations in Figure 4.2) is arousal theory – the idea that students learn better when they are emotionally aroused by the material. Weiner (1990,1992) has shown how arousal theories have dominated the field of motivation in the past, and Kintsch (1980) refers to the idea as emotional interest. According to arousal theory, adding interesting but irrelevant material energizes learners so that they pay more attention and learn more overall. In this case emotion affects cognition, that is, a high level of enjoyment induced by the seductive details causes the learner to pay more attention and encode more material from the lesson. We can predict that students who learn from lessons containing seductive details will perform better on tests of transfer than students who learn without seductive details.
What’s wrong with arousal theory? In spite of its commonsense approach, arousal theory is based on an outmoded view of learning as knowledge transmission – the idea that learning involves taking infor-mation from the teacher and putting it into the learner. By contrast, the
Freezing levelIce crystals Water droplets Updrafts Warm moist air Warm moist air rises, water vapor condenses and forms a cloud.Metal airplanes conduct lightning, sustain little damage.
Actual picture of airplane being struck by lightning
When the surface of the earth is warm, moist air near the earth’s surface becomes heated and rises rapidly, producing an updraft. As the air in these updrafts cools, water vapor condenses into water droplets and forms a cloud. When flying through updrafts, an airplane ride can become bumpy. Metal airplanes conduct lightning very well, but they sustain little damage because the bolt, meeting no resistance, passes right through. The cloud’s top extends above the freezing level. At this altitude, the air temperature is well below freezing, so the upper portion of the cloud is composed of tiny ice crystals. Figure4.2.Aportionofamultimedialessononlightningwithinterestingbutirrelevantwordsandpicturesadded.
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cognitive theory of multimedia learning is based on the view of learning as knowledge construction – the idea that learners actively build mental representations based on what is presented and what they already know. It follows that seductive details may interfere with the process of knowledge construction – an idea that is spelled out in the next section.
The Case Against Adding Interesting Words and Pictures
In his classic book Interest and Effort in Education, Dewey (1913) argued against viewing interest as an ingredient that could be added to spice up an otherwise boring lesson. In particular, Dewey noted: “When things have to be made interesting, it is because interest itself is wanting. Moreover, the phrase is a misnomer. The thing, the object, is no more interesting than it was before” (Dewey,1913, p. 11–12). More recently, Kintsch (1980) used the term cognitive interest to refer to the idea that students enjoy lessons that they can understand. According to this view, cognition affects emotion – that is, when students can make sense out of a lesson they tend to enjoy the lesson.
In contrast to arousal theory, the cognitive theory of multimedia learning suggests that adding seductive details can interfere with the process of knowledge construction in several ways – involving selecting relevant information, organizing the information into a coherent struc-ture, and integrating material with existing knowledge. First, the pres-ence of seductive details may direct the learner’s attention away from the relevant material about the steps in lightning formation. Second, the insertion of seductive details within the explanation may disrupt the learner’s ability to build a cause-and-effect chain among the main steps in lightning formation. Third, the learners may assume that the theme of the passage comes from the seductive details – such as stories about people being injured by lightning – and therefore try to integrate all incoming information into a general framework about lightning inju-ries. Harp and Mayer (1998) provide some evidence favoring the third hypothesis, but additional research is needed. According to the cogni-tive theory of multimedia learning, adding seduccogni-tive details will result in poorer performance on tests of transfer.