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IntroductionChemical education researchers interested in evaluating and improving students’ abilities to visualize chemical phenomena at the particulate level have demonstrated that the use of computer animations depicting chemical processes at the particulate level can improve chemistry students’ visualization skills (Williamson and Abraham, 1995; Russell et al., 1997; Sanger and Greenbowe, 2000; Sanger et al., 2000, 2001, 2007; Sanger and Badger, 2001; Ardac and Akaygun, 2004; Kelly et al., 2004; Vela´zquez-Marcano et al., 2004; Tasker and Dalton, 2006; Kelly and Jones, 2007, 2008; Gregorius et al., 2010a, 2010b; Rosenthal and Sanger, 2012, 2013a, 2013b;Williamson et al., 2012).Most of this research used these particulate-level computeranimations as part of instructional interventions designed to improve students’ conceptual understanding of chemical phenomena. This study is one of a growing number that have started to use these animations as part of the assessment process (Sanger et al., 2007; Naah and Sanger, 2012, 2013; Rosenthal and Sanger, 2012, 2013a, 2013b). Rosenthal and Sanger (2013a) compared the particulate explanations of an oxidation–reduction reaction involving copper metal and an aqueous silver nitrate solution from two groups of students who had viewed a chemical demonstration of this reaction and one of two different particulate-level computer animations of this reaction. The two animations depicted the same chemical reaction, but differed in the levels of complexity of the visual images used in these animations. The animation created by Michael J. Sanger (referred to as the‘more simplified animation’) used a static camera angle, did not depict water molecules in solution, and depicted objects moving and colliding in a single plane. The animation created as part of the VisChem project (Tasker and Dalton, 2006), and referred to as the ‘more complex animation’, used a changing camera angle, solution, and allowed objects to move in front of or behind each other. This study showed that students viewing the more simplified animation provided better explanations for eight different concepts related to the oxidation–reduction reaction compared to the students viewing the more complex animation.Students viewing the more simplified animation also provided more accurate balanced chemical equations for this reaction compared to the students viewing the more complex animation. Quotes from students in both groups suggested that those viewing the more complex animation underperformed compared to those viewing the more simplified animation because themore complex animation depicted extraneous information and either did not depict relevant information or depicted relevant information that was difficult for students to see due to the detrimental effects of the extraneous information. In a follow-up study, Rosenthal and Sanger (2013b) compared how the order of viewing the two different animations of the copper–silver nitrate oxidation–reduction reaction affected the students’ particulate-level explanations of this reaction. They found that students who viewed the more complexanimation followed by the more simplified animation provided better explanations for seven concepts and provided more correct balanced chemical equations than those students who viewed the animations in the reverse order. Students who favoured showing the more complex animation followed by the more simplified animation believed that the more complex animation will get students’ attention (by entertaining or confusing them), and then the more simplified animation will more clearly explain what is happening in the reaction, leading to improved learning. However, interpretation of the results from this study are complicated by the fact that many of the students’ explanations were directly tied to the version of the animation they were viewing, and so the differences in their explanations may be an artefact of the last animation viewed and not necessarily the order in which the two animations were viewed.One of the conclusions from this last study (Rosenthal and Sanger, 2013b) was that viewing the more simplified animation served as an instructional cue (Mayer and Gallini, 1990; Patrick et al., 2005; Mayer and Wittrock, 2009; Cook et al., 2011; Linand Atkinson, 2011) that assisted students in interpreting the more complex animation. However, this assertion was not specifically tested in that study. The goal of the present study is to determine how viewing one of the animations affects theparticipants’ subsequent explanations of the other animation. Theoretical frameworkWhen describing chemical phenomena, chemists often use three related but distinct representational levels—the macroscopic, particulate, and symbolic levels (Johnstone, 1993; Gilbert and Treagust, 2009; Johnstone, 2010; Talanquer,2011). The macroscopic representation involves qualitative observations of chemical phenomena made using the five senses (colour changes, odours, heat changes, etc.), the particulate representation involves the behaviour of atoms, molecules, andions involved in the chemical phenomena, and the symbolic representation involves the use symbols (numbers, mathematical formulas, chemical symbols and formulas, balanced equations, etc.) to represent more abstract concepts.The effectiveness of using computer animations of chemical processes at the particulate level is based on Mayer’s cognitive theory of multimedia learning (Mayer, 2001), which was adapted from Paivio’s dual-coding theory (Paivio, 1986) and Baddeley’s model of working memory (Baddeley, 1986). Mayer’s theory assumes that learners possess separate cognitive channels for processing visual (pictorial) and auditory (verbal) information, that learners have limited processing capabilities in each channel, and that learners engage in active learning by attending to relevant information, organizing this information into mental schema, and integrating this new knowledge with pre-existing knowledge.Mayer’s theory of multimedia learning incorporates cognitive load theory (Baddeley, 1986; Sweller, 1994; Sweller and Chandler, 1994), which assumes that learners have limited working memory and an unlimited long-term memory. If the cognitive load of the instructional lesson exceeds the limits of the learner’s working memory, then learning will be hampered or diminished. There are two types of cognitive load that affect learning (Sweller, 1994; Sweller and Chandler, 1994). Intrinsic cognitive load is a property of the content to be learned; concepts that can be processed sequentially and independently of one another represent low intrinsic load, while concepts that must be processed simultaneously represent a higher intrinsic load. Extraneous cognitive load, on the other hand, is a function of how the instructional material is presented. Since the way a lesson is presented does not change the content to be learned, any extraneous cognitive load imposed by the way in which the lesson is presented uses up cognitive resources without improving learning (Lee et al., 2006).Therefore, the goal of instructional design is to reduce extraneous cognitive load by manipulating verbal (text and narration) and pictorial information. For example, Mayer (2001) provides seven principles of multimedia design to minimize extraneous cognitive load based on the results of several educational research studies. Other researchers (Lee et al., 2006; Homer and Plass, 2010) have shown that adding iconic information to the symbolic visuals used in computer animations can improve student learning by minimizing extraneous cognitive load. Symbolic visuals use arbitrary representations to depict an object or concept, while iconic visuals use representations that are tied to the object or concept by surface-level relationships (e.g., when depicting an object being heated, using a slide bar with the word ‘Temperature’ above it represents symbolic visuals; showing the addition or removal of Bunsen burners below the object being heated or cooled represents iconic visuals). These researchers have shown that the positive effects of providing iconic information are largest when the students have low prior knowledge and when the concepts are highly complex (Lee et al., 2006; Kalyuga, 2007; Homer and Plass, 2010). MethodologySubjectsThe sample consisted of 55 volunteer students (19 males and 36 females) enrolled in the same section of a second-semester introductory chemistry course intended for chemistry, biology, and health science majors and taught by the same chemistry instructor. Each participant was interviewed for 40–70 min after receiving classroom instruction on oxidation–reduction reactions and electrochemistry. The participants were randomly assigned via coin toss to one of two groups—one group (N = 26) viewed the more simplified animation before viewing the more complex animation while the other group (N = 29) viewed the more complex animation before the more simplified animation.Computer animationsThe more simplified animation of the silver–copper reaction was created by the second author (Fig. 1a). This program was animated as two-dimensional such that when two objects approached each other, they were animated as colliding andbouncing off one another. The total viewing time for this animation is about 30 s; this animation was shown to the participants without narration. The animation shows coppercoloured circles in an organized pattern (copper metal) placed against a blue background (water). In the blue background, several silver-coloured circles with a ‘+’ symbol (silver ions) and an equal number of blue/red atom clusters with a ‘’ symbol on it (nitrate ions) move freely. As the reaction occurs, two silver circles approach a copper circle, and a red ‘e’ (electron) is transferred from the copper circle to each of the two silver circles. When the ‘e’ are transferred, the copper ci
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