Assignment

Read the two posted papers: Cleveland and McGill, Heer and Bostock. Write an essay that builds on the above two articles and explores the questions “What do we know about the role of perception in visualization?” and “Why is it important?” Your essay should include at least 2 additional studies on perception and visualization beyond the assigned reading.

Essay

Human perception plays an important role in visualization. An understanding of perception can significantly improve both the quality and the quantity of information being displayed. Ware defines visualization as a graphical representation of data or concepts, which is either an “internal construct of the mind” or an “external artifact supporting decision making” [1]. visualizations assist humans with data analysis by representing information visually. This assistance may be called cognitive support [2]. A visualization presents the input data effectively if the intended structure of the data and the perceptual structure of the visualization coincide [3]. The understanding of visualized data is directly tied to perception. By understanding the flaws and limits of human perception we can avoid creating visualizations where the user will miss important information. Furthermore, by understanding its functioning, we can tailor the visualization, so the user understands data more accurately, as well as draw the user towards important information [4].

Cleveland and McGill [5] approach is based on graphical perception, the visual decoding of information encoded on graphs and it includes both theory and experimentation to test the theory. The first part is an identification of a set of elementary perceptual tasks that are carried out when people extract quantitative information from graphs. The second part is an ordering of the tasks based on how accurately people perform them. Their theory deals with certain specific perceptual tasks that are believed to be critical factors in giving accurate results and the tasks are in the below order:

  1. Position along a common scale
  2. Positions along nonaligned scales
  3. Length, direction, angle
  4. Area
  5. Volume, curvature
  6. Shading, color saturation

Figure 1 describes the above elementary perceptual tasks that are in an sequential order that people used to extract quantitative information from graphs [5].

Following Cleveland, Jeffrey Heer and Michael Bostock approach used crowdsourcing perception to access the impact of visual encodings enables designers to optimize their visualizations and is vital to design of automatic presentation software [6]. They are also proved that understanding perception is important for an effective visualization design. Their results are very similar to Cleveland and McGill as concerned with perceptual tasks.

Skau and Kosara in their paper thinks data in pie and donut charts is encoded in three ways: Angle, Area of circle wedge and Arc length of the segment on the circle. Their approach is to find out which of these encodings do people read, and how does combination work with each other. they designed a study to separate these 3 encodings and see how people perceive different charts. They designed new charts which enable them to isolate each variable as much as possible. This enables them to test the efficacy of angle, area and arc length independently of their counterpart encodings. Their studies prove angle being least important visual cue for charts and donut chart being as accurate as traditional pie chart [7].

Data visualization is the graphical display of information for data analysis and communication. Data visualization is a powerful means to discover and understand these stories, and to present them to others. The information is abstract in that it describes things that are not physical. Statistical information is abstract. Whether it concerns company stocks, sales performance, or anything else, even it doesn’t pertain to the physical world, we can still display it visually, but to do this we must find a way to give form to that which has none. This translation of the abstract into physical attributes of vision can only succeed if we understand a bit about visual perception [8].

Figure 2 below tells us a story about these numbers that corresponds to sales and they belong to year 2009 and how the sales are effectively divided by each month and region[8].

Figure 3 below tells how color can help audience to identify quickly if the target is absent or present in a visualization. Healey describes how three perceptual properties like color, shape and conjunction in relation to time when used together helps in understanding visualization [9].

References

1.Ware, C. Information Visualization: Perception for Design. Morgan Kaufmann Publishers, Inc., San Francisco, California, 2000. 2.Melanie Tory and Torsten Mo¨ller. Human Factors In Visualization Research, 2004 3.Mehdi Dastani. The Role of Visual Perception in DataVisualization, 2002. 4. https://www.cg.tuwien.ac.at/research/vis/VisPerception.html 5. Cleveland, William S, and Robert McGill. “Graphical Perception: Theory, Experimentation, and Application to the Development of Graphical Methods.” Taylor & Francis, www.tandfonline.com/doi/abs/10.1080/01621459.1984.10478080. 6. Jeffrey Heer and Michael Bostock. “Crowdsourcing Graphical Perception: Using Mechanical Turk to Assess Visualization Design.” Stanford Vis Group | Crowdsourcing Graphical Perception: Using Mechanical Turk to Assess Visualization Design, vis.stanford.edu/papers/crowdsourcing-graphical-perception. 7. Drew Skau and Robert Kosara. Arcs, Angles, or Areas: Individual Data Encodings in Pie and Donut Charts 8. Few Stephen (2014): Data Visualization for Human Perception 9. Christopher G. Healey(2017), Perception in Visualization - - https://www.csc2.ncsu.edu/faculty/healey/PP/