Article An eye-tracking study on the effect of infographic structures on viewer’s comprehension and cognitive load Information Visualization 2018, Vol. 17(3) 257–266 Ó The Author(s) 2017 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/1473871617701971 journals.sagepub.com/home/ivi Azam Majooni1, Mona Masood1 and Amir Akhavan2 Abstract The basic premise of this research is investigating the effect of layout on the comprehension and cognitive load of the viewers in the information graphics. The term ‘Layout’ refers to the arrangement and organization of the visual and textual elements in a graphical design. The experiment conducted in this study is designed based on two stories and each one of these stories is presented with two different layouts. During the experiment, eye-tracking devices are applied to collect the gaze data including the eye movement data and pupil diameter fluctuation. In the research on the modification of the layouts, contents of each story are narrated using identical visual and textual elements. The analysis of eye-tracking data provides quantitative evidence concerning the change of layout in each story and its effect on the comprehension of participants and variation of their cognitive load. In conclusion, it can be claimed that the comprehension from the zigzag form of the layout was higher with a less imposed cognitive load. Keywords Visualization, visual storytelling, infographic, layout, eye tracking Introduction In this study, the main objective is to investigate the effect of the layout of the Infographics in the formation of the mental model and cognitive load. The most important elements of information graphics are the use of visuals (images, graphs, font size and colour).1 Infographics can be easier to read if effective visuals are applied in their structure. The parameters such as balance in the placement of text and graphics are essential in making an infographic aesthetically pleasing to look at.2 The visual elements of an Infographic should be able to narrate the visualized story with a minimal requirement for additional text explanations.3 Several studies support that images and graphs are salient compared to the texts and can capture the immediate attention of the viewers.4 The proper arrangement of visuals and graphs can provide coherence for an infographic design. A coherent layout is very important in guiding the viewers from one section of the infographic to the other related section based on the flow of the story. Besides the visual elements, cultural and language background can be very important in the formation of the layout. English-speaking readers naturally read textual contents from left to right and top to bottom. The results of this study show that the subjects of this study tend to move from left to right and from up to bottom, therefore arrangement of layout plays an important role in the design of the Infographics.5 In order to determine the influence of the layout on the cognitive load, the gaze data of the participants are recorded using the eye-tracking 1 Centre for Instructional Technology & Multimedia, Universiti Sains Malaysia, George Town, Malaysia 2 School of Computer Sciences, Universiti Sains Malaysia, George Town, Malaysia Corresponding author: Azam Majooni, Centre for Instructional Technology & Multimedia, Universiti Sains Malaysia, George Town, 11800 Penang, Malaysia. Email: [email protected] 258 devices. The recorded gaze data for two different Infographic stimuli are analysed and the results are discussed. Without loss of generality, in this experiment, a suggested layout with zigzag form demonstrated better results. Therefore, it could be assumed that this form of layout if applied in the real-world Infographics should be more comprehensible. The predictable orientation of the chunks in this model helps the viewers follow the story of the Infographic more steadily with less distraction. Background The term ‘Infographic’ is the abbreviation for the information graphics. The name has become popular in the past few years. From the novelty perspective, some believe Infographics have been used from a long time ago and even consider the prehistoric paintings in the caves as the early Infographics which tell a story using graphical elements and illustrations.6,7 However, the demand and application of Infographics have been growing rapidly in the past few years. The popularity of the terms searched on Google search engine can be estimated by the aid of Google trends;8 these statistics provide that the term ‘Infographics’ is searched almost seven times more frequent during the year 2014 compared to the same period in 2011. The main purpose of Infographics is to represent information and convey meaning by the aid of graphical elements; this task is sometimes accompanied by small textual contents.9 An Infographic usually contains a story embedded in it; therefore, it can be assumed as a visual storytelling method.10 The modern automated illustration tools have extensively simplified the design process of Infographics, but in the crowded and information overloaded world, attracting and keeping the attention of the audience is an extremely difficult task. Almost 40 years ago, Herbert Simon11 was one of the first researchers to directly point out that attention is a scarce resource in an information-rich world, he also mentioned that: ‘What information consumes is rather obvious: it consumes the attention of its recipients’. Similar to any other storytelling medium, such as novels, scripts and motion pictures, visual storytelling requires a skilled director and an attractive plot to capture the attention of the audience. There exist only a few elaborated guidelines to design a good Infographic and also there is no clear definition for estimating the efficiency of the design. However, some general conceptual requirements based on the standards stated by the Roman architect Vitruvius are presented by Moere and Purchase.2 The Vitruvius triangle states the basic requirements for an architectural design: soundness, utility and Information Visualization 17(3) attractiveness.2 These requirements have been addressed and labelled as Appeal for attractiveness and Comprehension and Retention for utility by Lankow et al.3 There has been an ongoing debate about the appeal or beauty (usually referred as aesthetics) of visualizations between the psychologists, artists, architects, computer scientists and philosophers.12 According to Fechner,13 the most central principle of aesthetics is ‘the right combination of diversity in unity’. Moreover, basic adjustable features of aesthetics such as colour, contrast and clarity;14 simplicity and complexity;15 and balance and scale16 along with novelty17 and surprise18 have been analysed intensively by the researchers to find the effectiveness (aesthetic impression) of each of the features in the design of visual artefacts.19 The appeal of an Infographic presentation is necessary for attracting the attention of the viewer; nonetheless, the main goal of any visualization is to deliver abstract information to the viewer. Therefore, comprehension and the retention of the visualization are the key factors in the design of any Infographic.20 In order to successfully maintain these factors, storytelling based on instructional design strategies can be applied. Storytelling is a very successful way for transferring knowledge,7,21 although an Infographic aims to take advantage of this technique, but it is the receiver that perceives the presented visualization. Eventually, the viewer starts developing a mental model after seeing the external visual and textual elements inside the Infographic.22 In the process of developing the mental model, the viewer automatically creates connections between the mental model and the external visualization.22 According to the scaffolding theory, a temporal framework can improve the understanding of the viewer; additionally, according to the chunking principle, the cognitive load can be reduced by presenting the visualizations in small chunks.23,24 In this study, both the scaffolding theory and chunking principle are applied to design the experiment. The main goal of cognitive load theory is to introduce methods to enhance the intellectual performance of the learners;25 therefore, monitoring cognitive load can show the effectiveness of visualizations.26 Motivation The goal of designing Infographic is to transfer knowledge (mostly conceptual knowledge) to the viewers in a very short time, premised on the assumption that there are three main elements in the scenario of Infographics design: message (story), the sender (story teller) and receiver (viewer). The designer should go Majooni et al. 259 Figure 1. Schematic form of the layouts for stories A and B. through a sequence of steps, which includes ‘gathering, processing, pictorial rendering, analysing and interpreting data’.27 Because of the nature of the Infographics, the designer attempts to map the story to be attractive and clear so that the viewer can develop the intended mental model of the story with the least effort.7 Card et al.28 have presented a visual mapping model that includes four sequential steps. At the first and second stages, the designer possesses original data and prepares data tables. In the third stage, the data tables are transformed/mapped into visualizations. Finally, in the last stage, the designed visual structure is transformed to view. The process of mapping the data tables into visualization can be carried out by several visualization techniques.29 In this study, the main concern is to overview the layout issue of the infographic. Several studies have discussed issues about the layout, and automated design of layouts,30 but to the best of our knowledge, there has not been any study investigating the layout of visualization using eye-tracking techniques and analysing the cognitive load yet. There are two main research questions in this study: (1) What is the effect of layout in the formation of the mental model? (2) Which type of suggested layouts is effective in decreasing the cognitive load? The answer to these statements is investigated using the comprehension questions and analysing the gaze data including the fixations, saccades, the number of the blinks and the pupil dilation of the subjects. Experiment The experiment includes two stories (A and B) which compare two types of layouts (1 and 2) for each story. The designs are based on chunking principle, scaffolding theory and Cards method28 manipulating two different layouts. The schematic shape of the layouts for A-1, A-2, B-1 and B-2 are presented in Figure 1. As it can be seen from Figure 1, in the story A, the layouts 1 and 2 compare the Stairs (Steps) with the Zigzag organization, also in the story B the layouts 1 and 2 compare Vertical columns with Horizontal rows organization of the chunks. In order to reduce the possible bias caused by external variable, the effort has been to identify effective variables and remove the sources of bias. The variables related to the subjects such as age, gender, educational and cultural background are addressed by inviting participants from almost the same age, cultural and educational background and an equal number of male and 260 female participants from the same ethnics. The participants are put into two groups with different tasks each one containing both types of stimuli. Similarly, in the design of the tasks, the duration of the task, the applied colours and symbols, font size and other graphical elements are kept constant. Information Visualization 17(3) divided into a sequence of small chunks of data. In the second step, the chunks are translated into graphical elements accompanied with small textual data (story elements). In the last step, each chunk is organized by composing the layout nodes. The steps used for the design of the stimuli are similar to those suggested by Card et al.28 Participants In this experiment, 23 local undergraduate (second year) students from the same field of study (School of Housing, Building and Planning, Universiti Sains Malaysia) and nationality participated. Three of the participants had poor eye-tracking calibration in the final results; therefore, their results were eliminated from the final experiment results and gaze data of the remaining 20 participants (10 females, 10 males) were used for the analysis. The age range of the participants was between 22 and 23 years with standard deviation of less than 1 year. All the participants were randomly put into two groups of experiment with similar content but different designs (each group containing n = 10 participants). Apparatus In order to record the gaze data, in this experiment, remote eye-tracking device (SMI, ‘iView X RED’, 50 Hz) is used. In order to achieve the best results, the device was calibrated and the calibration is validated before each task and the level of the eye-tracking cameras were adjusted based on the height of the subjects. At the final stage, the results of the subjects with lower calibration score were ignored. The recorded gaze data are then transferred for the further analysis. Material Two stories are visualized to design the Infographics and are used as stimuli in this experiment. Each story is presented with two different layouts (2 stories 3 2 layouts = 4 stimulus). The graphical elements and colours used for each story are identical and only their layout differ. The Infographics contain general information from two different general areas. In the first set, layout A-1 is based on a single Stairs (Steps) path from left to right and top to bottom, whereas layout A-2 is based on a single Zigzag path from top to bottom with the same story. In the second set, layout B-1 has divided the page into three major vertical columns, whereas layout B-2 has divided the page into three horizontal rows. The schematic form of the layouts is presented in Figure 1. In order to apply the layout, initially, the arbitrarily selected pieces of textual information are outlined and Procedure Subjects were randomly assigned to one of the two groups I and II. These groups each contained two separate tasks (A and B) recorded by eye-tracking device. There was a 1-min break between the first and the second task. The instruction and the steps of the experiment were briefly described to the subject to achieve better calibration on the eye-tracking device. After each task in the experiment, each participant was asked to answer questions related to the comprehension of the Infographic. The participants are assured that the results of the questions are anonymous and will not be distributed. The process of the experiment was straightforward and no other interaction was made with the subject. The assigned exposure duration for each stimulus was 1 min, the amount was equal for all the participants. According to the initial pilot study, 1 min was sufficient for the tasks. Results In order to explore the comprehension of the subjects, scores of the answers to the questions are calculated. The comprehension scores for each group are presented in Table 1. The analysis of the gaze data and score of the questions for each task can be used to study the effect of layouts on the comprehension and cognitive load of the subjects. To analyse gaze data and compare the variations of the cognitive load, a threshold method is applied to study the sequence of saccades. In the second analysis, the overall increase in the cognitive load for each stimulus is calculated using the CLS (Cognitive Load Score) calculation methods.31 Comprehension In order to calculate the comprehension score for the tasks, immediately after each task, the subjects are asked to answer a set of conceptual questions about the viewed Infographics. Because of the short period of the tasks and existence of no time span between the tasks and the questions, the long-term memory is not involved and only the comprehension is estimated. The final results presented in Table 1 demonstrate the scores of the subjects in respect to every stimulus. Majooni et al. 261 Table 1. Average gaze data for each stimuli. Stimuli Blinks (per minute) Pupil dilation (%) Average saccades (mm) Average overall fixation (ms) Average fixation count Efficiency Score (%) A-1 A-2 B-1 B-2 0.3 0.2 0.238 0.3 33.33 31.3 32.5 34.9 36.70 44.33 42.80 38.35 236 209 212 255 187 210 189 173 0.57 0.95 0.54 0.34 76 95 60 51 Figure 2. Sample of a saccade symbolic representation. Saccade patterns When the visual attention is directed to another location, the eyes move fast to position the fovea to the point of attention to achieve higher resolution image from the attention point. This fast movement of the eye (relocation of gaze) is called as saccade.32 Monitoring saccades can be very helpful in providing the scan path of the stimuli. As mentioned in the earlier sections, the information used to design the infographic were initially outlined and each item has been translated into one graphical element and accompanied abstract textual contents (chunks). The chunks are placed such that subject sees one chunk at a time. Accordingly, the fast eye movements (saccades) between each fixation show the path in which the subject goes through the chunks in the infographic. However, the subject starts this path from the most salient position of the infographic. In addition, the subjects tend to explore the whole infographic in the first 2–5 s to create an overall understanding of the whole story. In this analysis, we categorize the saccades for each stimulus into three groups (short, medium and long saccades) according to their length. This grouping is related to the distance between the chunks inside every infographic layout. The medium size saccades are the ones which are in the range of the distance between two neighbour chunks in the stimuli. The saccades longer than and shorter than the medium-sized saccades for each stimulus are set as long and short saccades, respectively. The symbols (S, M and L) are assigned to ‘short, medium and long’ saccades, respectively. This method is similar to threshold filtering in the symbolic dynamics. Figure 2 demonstrates a sample of a saccade symbolic representation. 262 Information Visualization 17(3) Figure 3. Density map of the gaze data for story A and story B layouts. As it can be seen from Figure 2, there exist more than five repetition of type ‘S’ saccade between every couple of type ‘M’ saccade. By investigating the area of interest (AOIs), it can be presumed that the subjects relocate their gaze from one chunk to another chunk with type ‘M’ saccade whereas they tend to explore the whole infographic in the beginning and at the end of the experiment using type ‘L’ saccades. Density map A density map (also called as heatmap) diagram provides information about the number and duration of eye fixations of a subject on stimuli acquired from an eye-tracking device. In the density map diagram, the longer fixations are represented by red and yellow colours, whereas green and blue colours represent less attention and shorter fixation time.33 Figure 3 demonstrates density map diagram for story A and story B layouts of all subjects. As it can be seen from this figure, the fixations are overlapped on the layout of the Infographics. According to the density map diagrams, it can be concluded that majority of the fixations are in the upper half of the page, which confirms the claim that the upper portion of the Infographics is more salient. Cognitive load analysis There exist two other features besides the fixations and saccades that can be recorded easily using the eyetracking devices. The number of the blinks and pupils dilation during the experiment are two measures that can help estimation of variation of the cognitive load.34–37 Pupil dilation. Klingner et al.36 have investigated the effect of an increase in cognitive workload on the pupillary dilation. They have concluded that subtle changes in the pupil diameter can be used to measure the cognitive workload. In this study, in order to compare the overall cognitive load between two different types of layouts for each story, the numerical integral dilation of the pupil diameter for each eye is calculated. Figure 4 shows a sample of papillary dilation on infographic type A-1. Majooni et al. 263 Figure 4. Sample of papillary dilation on infographic type A-1. Blinks. Blinks rate can also be a good measure of the cognitive load and fatigue.36,38–40 Based on the study conducted by Recarte et al.,41 the number of blinks can even be more effective in estimating the increase in the cognitive load caused by the visual searching in comparison to the pupil dilation. They claim that the cognitive load estimation based on pupil dilation method cannot differentiate between the mentally and visually challenging tasks. However, in this study, similar to the method suggested by Majooni et al.,31 the blinks rates and the pupil dilations are recorded and stored in a database (along with the saccades, fixations and the gaze location) for all the subjects. Efficiency. The efficiency measure is calculated using the classification of the number correct answers to the questionnaire, the blinks rate, the saccades length, the number of fixation and the average of fixation duration. The normalized value of the Efficiency is a measure between zero and one, when it is closer to one it means the design has been more efficient from both cognitive load and comprehension point of view. In the CLS method, five distinct and independent parameters (saccades length, fixations length, blinks rate, pupil dilation and the score of the questions) are effective in classification of the value of the efficiency score. Each one of these parameters separately affects the efficiency score. The maximum and minimum for each parameter is first identified and then the classification is applied to avoid the presence of any bias. The method can easily be applied to any type of infographic or visualization. The value is equally dependent on the score of the questions, pupil dilation, blinks rate and number of long saccades and fixations. The classification is operated using the Weka software, which is a collection of neural network algorithms for data mining tasks.42 In this study, the Zigzag layout A-2 had the lowest amount of blinks rate and pupillary dilation and highest amount of correct answers and accordingly achieves highest efficiency rate. In contrast, the Horizontal rows layout B-2 with the lowest comprehension and highest pupillary dilation has the lowest efficiency score. Analysis of AOIs. The designed Infographics are based on chunks order and their relations in a sequential format; therefore, in this experiment, the sequences of the fixations on AOIs are investigated. In order to complete this task, an indexed AOI is assigned to each one of the chunks with the order intended by the designer. The average visit sequence of the AOIs for each stimulus is then calculated based on the number and latency of the visit. For each AOI, the average visit order and average visit latency are assigned and then again a second sequence is generated based on these latencies and visit order. In the last step, the similarity of the sequence of visited AOIs versus the intended order of chunk’s sequence is estimated using classification of similar clusters method. Table 2 provides the average similarity of the AOIs index order versus chunks order. According to the similarity results, the AOI sequence of the layouts A-2 is slightly more similar to the intended chunk order compared to the AOI sequence of layout A-1. In the case of sequence 264 Information Visualization 17(3) Table 2. Average similarity of the AOI’s sequences versus chunks order. Stimuli Story A (%) Story B (%) Layout 1 Layout 2 69 72 64 41 besides using the fixation data for identification of attention, we classified the saccade data into three categories and compared the eye movement behaviours of the subjects using the saccades classification (Figure 2) and the pupil dilation (Figure 4). Layout and cognitive load similarity, story B-1 has better similarity score compared to B-2. The analysis of order of AOIs is based on the calculation of Bayesian similarity of clusters method and does not necessarily prove the efficiency of any of the layouts and it can only be addressed as an insight. Discussion Comprehension The answer to the first research question of this study can be investigated by comprehension score of the subjects, meaning that the layouts can be significantly effective in conveying information. With the study of the scan path of each of the subjects, we noticed that the subjects tend to move from one chunk to the other chunk usually following the path provided by the layout. The observation demonstrates that, during the experiment, the subjects tend to go back a few (two or three) chunks and start over (revisit the chunks). This revisit of AOIs can either be interpreted as the difficulty of understanding43 or steps of making the connection between the previous and current chunk (inductive reasoning). The analytic study of pupil dilation shows that this eye movement behaviour was almost the same for all the subjects. Therefore, it can be claimed that it is related to the visual memory and the process of mental model formation rather than the difficulty of the information. Saccades According to Treisman and Gormican,44 human eye can process simple visual objects in a time period as short as 40–50 ms. In this study, the number of revisits and dwell time for each AOI has been calculated. The average dwell time for each AOI has been in the range of 80–250 ms. However, the dwell time was not proportional to the number of words and elements in each chunk. In some cases, two similar chunks with almost exactly the same amount of content had an extremely different average dwell time. In this case, it can be claimed that the subject was no more looking at the AOI and actually was busy processing the information and building the mental model. In this study, In order to study the variation in the cognitive load and also calculate the average workload for each stimulus, the average number of the blinks and the sum of dilation of the pupils for each stimulus is calculated for all the subjects. In order to calculate the workload, the results are linearly normalized between zero and one and workload score is calculated based on the number of blinks and integral of pupil dilation for each subject and stimuli. In addition, results provide that the average saccade length for the subjects viewing stimuli A-2 in the first 30 s has been slightly longer than Stimuli A-1. This difference could be caused by the distances difference between chunks in each stimulus. The analysis of the recorded parameters for each participant on each stimuli can be used to calculate overall efficiency index for each subject. The average of overall efficiency index of each layout for all subjects is calculated and presented in Table 1. According to the results, it can be concluded that the layout A-2 which is based on a Zigzag path has significantly higher efficiency index compared to layout A-1. In addition, the layout B-2 (three vertical columns) has been more efficient compared to top-down layout B-1 (three horizontal rows). Conclusion Instructional design strategies, such as scaffolding theory, if applied in the design of Infographics can be effective in decreasing the cognitive load and reducing the initial confusion. In this study, two contexts are presented in the form of Infographics. The two contexts are initially split into small chunks (following the chunking principle) and then the chunks are presented on four different layouts (two for each context). All of the layouts are organized according to the scaffolding theory. The main goal of this study is to investigate the effect of the layout on the comprehension and cognitive load of the subjects. In order to investigate the effect of each layout on comprehension of the participants, a set of brief conceptual questions are asked about the Infographics from the subjects. In addition, to identify the effect of each layout on the cognitive load of subjects, their gaze data (fixations, saccades, blink rate and pupil dilation) were recorded. The gaze data for the participants were analysed using simple Majooni et al. linear classification method. Finally, the results suggest which layouts perform better in decreasing workload and increasing comprehension. In addition, from the results of the experiments, in can be concluded that using natural left-right (up-down) eye movement of the viewers could be useful in the layout design and improvement of the comprehension of the viewers from the Infographics and visualizations. Funding This research was supported by University Sains Malaysia, Centre of Instructional Technology and Multimedia (Grant No. 1001/PMEDIA/817072). References 1. 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