Purnell & Solman (1991)

Purnell, K. N. et Solman, R. T. (1991). The influence of technical illustrations on students' comprehension in geography. Reading Research Quarterly, 26 (3), 277-299.

Dans cinq expériences, les auteurs étudient la contribution de l'illustration (diagrammes) à la compréhension d'un matériel de lecture technique auprès de lecteurs de l’école secondaire.

Sujets. Soixante-quinze adolescents de 10e et de 11e années (classes de géographie) d'une école secondaire à Sydney, âgés en moyenne de 15 ans et demi, participent à l'expérience. Les adolescents sont répartis en trois groupes de nombre égal et, d'après les résultats de l'année scolaire précédente, de compétence égale en géographie.

Traitement. Les sujets lisent silencieusement un texte de géographie. Le texte est accompagné d'un diagramme de flux (avec étiquettes-mots) qui illustre de façon schématique le cycle de l'eau (voir l’encadré, page suivante).

Titre et paragraphes 1 et 2 (tous les groupes expérimentaux) WHAT IS THE HYDROSPHERE? The hydrosphere is the " water-sphere ". It includes all the water of the earth, whether it be frozen, in liquid form, or as a vapor. The hydrosphere includes the oceans, ice caps, lakes, rivers, swamps, creeks, and water under the ground (groundwater) and in the air (water vapor). Water is constantly moving from place to place. It is also changing from state to state (for example, from a liquid into a gas). The water in the hydrosphere is unevenly distributed. Most of it (97 per cent) is in the liquid state in the oceans. These cover over 70 per cent of the surface of the earth. About 2 per cent is in solid form in the ice caps. Less than 1 per cent is in the form of " fresh " water either on the ground or below the surface.
Paragraphe 3 (groupe 1): The movement of water is best illustrated by the diagram below (figure 1). The water cycle is driven by the radiant energy of the sun and has no beginning or end. There are a number of processes that are important. Precipitation refers to the falling of water in the form of rain, snow, hail or dew. Precipitation can only occur after condensation has taken place. This is the transfer of moisture from a vapor to a liquid. When water reaches the ground it may run over the surface or be absorbed (infiltrate) into the soil. Water may evaporate (turn into a vapor) from any water surface on the earth. It is also transpired from plants and animals into the atmosphere.	Paragraphe 3 (groupes 2 et 3; la première phrase est enlevée dans le cas du groupe 2) The movement of water is best illustrated by the diagram below (figure 1). The water cycle is driven by the radiant energy of the sun and has no beginning or end. There are a number of processes that are important. Precipitation refers to the falling of water in the form of rain, snow, hail or dew. Precipitation can only occur after condensation has taken place. This is the transfer of moisture from a vapor to a liquid. Clouds are the visible result of the process of condensation. Precipitation may occur after clouds have formed and it results in water returning to the earth. When water reaches the ground it may run over the surface (overland flow) or be absorbed (infiltrate) into the soil. Water may be stored on the ground surface in a depression storage. Water infiltrating into the soil may pass through the unsaturated zone in the ground and into the saturated zone. The water table is the dividing line between the unsaturated zone and the saturated zone. The downward movement of water in the saturated zone is called percolation. Water stored under the ground surface is called groundwater. Some of the groundwater may move laterally to return to a water body such as a stream. The flow of water in the unsaturated zone which moves laterally towards a water body such as a stream is called interflow. Some of the water stored in depression storages on the ground surface evaporates while some of this water may infiltrate into the ground. Interception of some precipitation by vegetation may stop some of the precipitation from reaching the ground. Water may evaporate (turn into a vapor) from any water surface on the earth. It is also transpired from plants and animals into the atmosphere.
Diagramme (groupes 1 et 3)
Paragraphe 4 (tous les groupes): The water cycle shows some of the links that exist between the four main components of the biophysical environment. The movement of air in the atmosphere decides where and when precipitation will occur. The layers of rock in the lithosphere will influence the amount and flow of groundwater. The extent of plant cover in the biosphere will affect runoff and transpiration.
Paragraphe 5 (tous les groupes): Once again people have altered this part of the biophysical environment. Runoff can be reduced or increased by certain uses of the land. The water itself can be polluted, even in its vapor state. " Acid rain " is formed from industrial air pollution. This rain has killed forests and water life in many lakes in the northern hemisphere.

Mesure 1. Dix questions à choix multiple portent sur l’information du texte qui ne se rapporte pas au diagramme.

Mesure 2. Dix questions à choix multiple portent sur l’information du diagramme.

Mesure 1. En ce qui concerne l'information du texte, l'écart entre la moyenne des deux versions illustrées et la version non illustrée est non significatif (Var 1.1 et Var 1.3 = Var 1.2).

Mesure 2. En ce qui concerne l'information du diagramme, la version modifiée avec diagramme est significativement mieux réussie que la moyenne des deux autres versions (Var 1.3 > Var 1.1 et Var 1.2).

Sujets. Cent trente adolescents de 10e, de 11e et de 12e années (classes de géographie), âgés en moyenne de 16 ans et demi, participent à l'expérience. Les sujets sont répartis en cinq groupes de nombre égal, et d'après des tests en géographie, ils sont de compétence égale.

Traitement. Le texte de lecture utilisé, différent de celui de l'expérience 1, décrit différentes parties d'un paysage imaginaire à l'aide d'une illustration de coupe en travers (diagramme), les parties étant identifiées à l'aide de mots.

Mesure. D'après les exemples fournis en annexe, il semble que les15 questions à choix multiple portent sur des informations illustrées du texte.

Sujets. Vingt-quatre adolescents de 11e année, âgés de 16:9 ans en moyenne, participent à l'expérience.

Traitement. Le matériel expérimental consiste en quatre thèmes géographiques jugés de difficulté comparable. Deux thèmes sont présentés sous forme de texte, et deux thèmes, sous forme de diagramme (voir l’encadré ci-dessous). Chaque sujet participent aux quatre conditions; celles-ci correspondent à autant de thèmes différents.

Extrait du matériel expérimental utilisé dans l’expérience 3 (thème 1), l’expérience 4 (thème 1) et l’expérience 5

A cross section from Mt. Gerard to Tass Ocean

The horizontal distance covered by this cross section is 1100 meters. The vertical scale goes from 0 to 120 meters. The average gradient is 1:650.

Mt. Gerard is on the left hand side of the cross section and is covered with rainforest. Kennedy Hill is approximately 60 m high and is next to Mt. Gerard. This hill is covered with scattered shrub. Cunthia's bluff has no vegetation on it and is 16 m high and is on the right hand side of Kennedy Hill. At the foot of the bluff is Lake George which is 80 m wide and there is a dam on the right hand side of the lake. To the right of the lake is a corn field on a gentle slope which gives way to Grodd River. Next to the river is the town of Smithston. The town runs down to Palm Beach which is on the shore of Tass Ocean. Cumulus clouds can be seen over the hills and there is a cumulo-nimbus cloud over the town and the coast in this cross section.

Mesure. Le test comprend 80 questions à choix multiple (20 questions par thème). D'après les exemples fournis en annexe, les questions à choix multiple portent sur les informations illustrées du texte.

Sujets. Vingt-cinq adolescents de 10e année d'une école secondaire à Sydney, âgés en moyenne de 16 ans, participent à l'expérience.

Traitement. Quatre des cinq traitements expérimentaux sont identiques à ceux de l'expérience 3. Pour le cinquième traitement, un nouveau texte, de difficulté équivalente, est utilisé.

Mesure. Le test comprend 100 questions à choix multiple (20 questions par thème). D'après les exemples fournis en annexe, les questions à choix multiple portent sur les informations illustrées du texte.

Sujets. Vingt-cinq adolescents de 9e année (classe de géographie), âgés en moyenne de 14:9 ans, participent à l'expérience.

Traitement. Le même matériel que dans l'expérience 4 est utilisé, chaque thème étant cependant préparé en cinq versions. Les sujets lisent tous les thèmes, mais chaque thème dans une autre version, selon la procédure du carré latin, avec contrebalancement de l'ordre de présentation. Comparativement aux expériences 3 et 4, cette procédure augmente la validité interne de l'expérience.

Discussion générale. " There are three findings of particular interest reported in these studies. First, Experiment 1 showed that comprehension of a text is not improved by the presence of a technical illustration with content related to but not overlapping the content of text. Second, Experiments 2, 4, and 5 demonstrated that presentation of the same conceptual and spatial content in both an illustration and text results in better comprehension than simple repetition in either text or illustration. Third, as shown in Experiments 2, 3, 4, and 5, when it was possible to present essentially the same content either in an illustration or as text, comprehension was superior for the illustration.

In the first study, there was very little overlap between the content of the illustration and the content of the text, although they were related. Under these conditions, the presence of the illustration had no effect on the comprehension of text. The failure to find an improvement in the comprehension of text when accompanied by an illustration is consistent with findings from some early studies. [...]

In the last four studies presented here, comprehension of spatial content presented as an illustration was found to be superior to comprehension of the same content presented as text. [...]

The results of this series of studies have implications for the presentation of technical material such as geographical content. First, technical illustrations present information in their own right, and are not simply adjuncts to the content presented in text. Second, when spatial content lends itself to presentation either as an illustration or as text, presentation as an illlustration is likely to lead to greater comprehension. Third, important information presented in text should also be presented in an illustration if possible, to improve comprehension. Overall, the results suggest strongly that those responsible for preparing texts and materials with technical content should take at least as much care in the drawing of illustrations as they take with the writing of the text " (p. 293-295).