Consider the following scenario. As part of a project, you wish to find out how lightning storms develop. You look up “lightning” in an encyclopedia and come across the following entry:
Lightning can be defined as the discharge of electricity resulting from the difference in electrical charges between the cloud and the ground.
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 con-denses into water droplets and forms a cloud. The cloud’s top extends above the freezing level. At this altitude, the air tem-perature is well below freezing, 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 currents within the cloud may cause hailstones to form. When downdrafts strike the ground, they spread out in all directions, producing the gusts of cool wind people feel just before the start of the rain.
Within the cloud, the moving air causes electrical charges to build, although scientists do not fully understand how it occurs.
Most believe that the charge results from the collision of the
You read the words carefully, but if you are like most learners my colleagues and I have studied over the past twenty years, you may not understand the passage. In our research, students who read this 500-word passage do not perform very well on tests of retention and transfer, even when we give the tests immediately after students finish reading the passage. When we ask students to write down an expla-nation of how lightning storms develop (i.e., a retention test), students typically can remember fewer than half of the main steps in lightning formation. When we ask them to answer questions that require using what was presented to solve novel problems such as figuring out how
cloud’s light, rising water droplets and tiny pieces of ice against hail and other heavier, falling particles. The negatively charged particles fall to the bottom of the cloud, and most of the posi-tively 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 steps, each of which is about fifty yards long, and lasts for about one millionth of a second. It pauses between steps for about fifty millionths of a second. As the stepped leader nears the ground, positively 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 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 seventy micro-seconds. 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 hundreds of millions of volts.
The air along the lightning channel is heated briefly to a very high temperature. Such intense heating causes the air to expand explo-sively, producing a sound wave we call thunder.
to reduce the intensity of lightning storms (i.e., a transfer test), students typically are unable to generate many useful solutions.
Clearly, the time-honored traditional way of presenting instructional messages – providing an explanation in the form of printed words – does not seem to work so well.
These kinds of results led us to search for ways to make the material more understandable for students. Given our findings of the limitations of verbal forms of presentation, our search led us to the possibilities of visual forms of presentation. Can we help students under-stand better when we add visual representations to verbal ones? What is the best way to combine visual and verbal representations to enhance learning? These are the questions that motivate this book.
The research presented in this book mainly involves two kinds of multimedia learning situations – a book-based environment and a computer-based environment. In a book-based environment, we can focus on the issue of how best to integrate printed text and illustrations.
For example, Figure 2.1 presents a book-based multimedia lesson on lightning formation – what I call annotated illustrations. The lesson consists of a series of illustrations, each depicting a key step in lightning formation, along with corresponding text segments (or annotations) that each describe a key step in lightning formation. The five illustrations are simple line drawings containing only essential elements such as posi-tive and negaposi-tive particles, updrafts and downdrafts, and warm and cold air. The text also focuses mainly on the essential elements and events in lightning formation; the 50 words used in the illustrations are selected verbatim from the 500 words used in the longer passage.
Importantly, the illustrations and text are coordinated so that corre-sponding segments of text and illustrations are presented near each other on the page. We place each of these five annotated illustrations next to the corresponding paragraph in the longer 500-word passage that you just read. This is a multimedia lesson because it includes both words (i.e., printed text) and pictures (i.e., illustrations).
The annotated illustrations presented in Figure 2.1 are based on several general design principles adapted from Levin and Mayer’s (1993) analysis of illustrations in text:
concentrated – The key ideas (i.e., the steps in lightning formation) are highlighted in both the illustrations and the text.
concise – Extraneous descriptions (e.g., stories about people being struck by lightning) are minimized in the text, and extraneous visual features (e.g., unneeded details or colors) are minimized in the illustrations.
Ice crystals
charged particles Branches Stepped leader
Upward-moving leader
Return stroke 1. Warm moist air rises, water vapor condenses and
forms a cloud. 2. Raindrops and ice crystals drag air downward.
3. Negatively charged particles fall to the bottom of the cloud.
5. Positively charged paticles from the ground rush upward along the same path.
4. Two leaders meet, negatively charged particles rush from the cloud to the ground.
+ + +
Figure 2.1. Annotated illustrations for the book-based lightning lesson.
correspondent – Corresponding illustrations and text segments are presented near each other on the page.
concrete – The text and illustrations are presented in ways that allow for easy visualization.
coherent – The presented material has a clear structure (e.g., a cause-and-effect chain).
comprehensible – The text and illustrations are presented in ways that are familiar and allow the learner to apply relevant past experience.
codable – Key terms used in the text and key features of the illustra-tions are used consistently and in ways that make them more memorable.
In short, the annotated illustrations presented in Figure2.1constitute an example of a well-constructed multimedia message.
The same approach can be used to produce a multimedia lesson within a computer-based environment. Figure 2.2 presents selected frames from a computer-based multimedia lesson on lightning for-mation – what I call a narrated anifor-mation. The lesson consists of a 140-second animation, depicting the key steps in lightning formation, along with a corresponding 300-word narration spoken by a male voice, describing each key step in lightning formation. The animation is adapted from the line drawings used in the illustrations, and the narration is a shortened version of the text. The animation uses simple line drawings consisting of only a few essential elements and events, and the narration also focuses on only a few essential elements and events. Importantly, the words and pictures are coor-dinated so that when an action takes place in the animation, the learner is given a verbal description of the action at the same time. In this way, the narrated animation summarized in Figure 2.2 is an example of a well-constructed multimedia message. This is a multi-media lesson because it contains both words (i.e., narration) and pictures (i.e., animation).
How can we assess what someone learns from multimedia pre-sentations such as those depicted in Figures 2.1 and 2.2? The tra-ditional measures of learning are retention and transfer. Retention refers to being able to remember what was presented. For example, the top portion of Table 2.1 shows that as a retention test for the lightning lesson we can ask learners to write down an explanation of how lightning storms develop. In our studies, we typically allow students six minutes to write their answers for the retention
“Cool moist air moves over a warmer surface and becomes heated.”
“Warmed moist air near the earth’s surface rises rapidly.”
“As the air in this updraft cools, water vapor condenses into water droplets and forms a cloud.”
“Eventually, the water droplets and ice crystals become too large to be suspended by the updrafts.”
“When downdrafts strike the ground, they spread out in all directions, producing the gusts of cool wind people feel just before the start of the rain.”
“The cloud’s top extends above the freezing level, so the upper portion of the cloud is composed of tiny ice crystals.”
“As raindrops and ice crystals fall through the cloud, they drag some of the air in the cloud downward, producing downdrafts.”
“Within the cloud, the rising and falling air currents cause electrical charges to build.”
(Continues) Figure 2.2. Frames from the narrated animation for the computer-based lightning lesson.
“The charge results from the collision of the cloud’s rising water droplets against heavier, falling pieces of ice.”
“A stepped leader of negative charges moves downward in a series of steps. It nears the ground.”
“The two leaders generally meet about 165-feet above the ground.”
“As the leaser stroke 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. It produces the bright light that people notice as a flash of lighning.”
“Negatively charged particles then rush from the cloud to the ground along the path created by the leaders. It is not very bright.”
“A positively charged leader travels up from such objects as trees and buildings.”
“The negatively charged particles fall to the bottom of the cloud, and most of the positively charged particles rise to the top.”
Figure 2.2. Continued.
test. Some of the key steps in lightning formation, based on our presentation, are:
1. air rises
2. water condenses 3. water and crystals fall 4. wind is dragged downward
5. negative charges fall to the bottom of the cloud 6. the leaders meet
7. negative charges rush down 8. positive charges rush up
To compute a retention score for a learner, I can examine what the learner writes – i.e., the learner’s recall protocol – and then judge which of the eight main steps are included. In making this judgment, I focus on the meaning of the learner’s answer rather than the exact wording.
Thus, if the learner wrote “negative parts move to the cloud’s bottom”
the learner would get credit for idea “5” even though the wording is not exact. To make sure the scoring is objective, the recall protocol is scored by two independent scorers who do not know which instructional message the learner received. In general, there are few disagreements, but all disagreements are resolved by consensus.
Thus, the retention performance of each learner is expressed as a percentage – that is, the number of idea units remembered divided by the total possible (i.e., eight).
Although retention measures are important, I am most interested in measures of transfer. I not only want students to be able to remember what was presented, I also want them to be able to use what they have learned to solve problems in new situations. Thus, I did not stop with measuring how much is remembered; in fact, the main focus of my Table 2.1. Retention and Transfer Questions for the Lightning Lesson Retention Test
Please write down an explanation of how lightning works.
Transfer Test
What could you do to decrease the intensity of lightning?
Suppose you see clouds in the sky, but no lightning. Why not?
What does air temperature have to do with lightning?
What causes lightning?
research is on measuring students’ understanding by measuring their transfer performance.
The bottom portion of Table2.1lists some transfer questions for the lightning lesson. The first question is a redesign question – asking the learner to modify the system to accomplish some function; the second question is a troubleshooting question – asking the learner to diagnose why the system might fail; the third question is a prediction question – asking the learner to describe the role of a particular element or event in the system; and the fourth question is a conceptual question – asking the learner to uncover an underlying principle (such as
“opposite charges attract”). The student is given the questions one at a time on a sheet of paper, and allowed 2.5 minutes to write as many acceptable answers as possible. After 2.5 minutes, the question sheet is collected and the next question sheet is handed out.
To compute a transfer score for each learner, I count how many acceptable answers the learner wrote across all the transfer questions.
To help in scoring, I construct an answer key, listing the acceptable answers for each question. For example, acceptable answers to the first question about decreasing the intensity of a lightning storm include removing positive particles from the earth’s surface or placing positive particles near the cloud; acceptable answers to the second question about lack of lightning include that the top of the cloud may not be above the freezing level or that no ice crystals form;
acceptable answers to the third question about the role of tempera-ture include that the earth’s surface is warm and the oncoming air is cool or that the top of the cloud is above the freezing level and the bottom of the cloud is below the freezing level; acceptable answers to the fourth question about the causes of lightning include a difference in electrical charge within the cloud and a difference in air temper-ature within the cloud. Answers based on common knowledge, such as using a lightning rod or not standing under a tree, were not counted as acceptable answers. Students receive credit for a partic-ular answer if they express the idea in their written answer regard-less of their writing style or use of terminology. For example, students would receive credit for the fourth question if they wrote
“separation of minus and plus charges in the cloud” rather than
“separation of negatively charged and positively charged particles.”
As with the retention test, answers to the transfer test are scored by two raters who do not know which lesson the learner received.
Disagreements are rare and are settled by consensus. Overall, there were twelve possible acceptable answers across the four questions, so each learner’s transfer performance can be expressed as a
percentage – the number of acceptable answers generated divided by the total possible (i.e., twelve).