The second reading neatly summarizes several theories and explanations on this phenomenon. I personally liked the Boolean Map Theory the most. It provides a good explanation of how users may conduct a particular visual query. This coupled with the feature hierarchy can give us tools to intelligently design visuals to make the most important information stand out first.

Chapter 2: The content is a little bit overlaped with Christopher Healey. It also deals with the low-level feature analysis first. Triesman’s hypothesis is the main model the author adopted.

One important thing is the nest loop model which appears in both chapters. The two different versions of the maps includes the outer problem solving loop, the middle eye movement loop and the inner pattern testing loop.

I like the perception in visualization very much, a very good review paper that lists the Preattentive processing and then postattentive vision, then the model for change blindness, then the elements in perception. To me, it’s more like that the acctual preattentive processing is a combined process of the first four theorical models.

The readings from chapter 2 and the web-article follows that nice motivation by chapter 1. The main point in these two readings was to understand features that stand-out around certain type of noise. The intelligent controlling of visual channels (color, shape, size, orientation, motion etc) is critical in an effective visual design. Additionally, knowing the relationship between visual channels and whether the search is top-down or bottom up is also important. If we are looking at a visualization with a task in mind very different visual channels will stand-out while suppressing others. But this pop-out and suppression given a top-down search can also be influenced by stereotype in search strategies.

This is a fascinating subject that proves its point very effectively. If we know what we are looking for, we can spot it, but we pay little attention to that we are not looking for. This becomes even more pronounced when we don’t know what we are looking for. Differences in color, shape, boundary, motion can act separately or together to differentiate between objects, as eloquently described by Healey. I’ve noticed my cats can’t see a thing if it doesn’t move. It is really the motion that catches their eyes.

Ware’s numbers on the calculations that go on as our eyes go about seeing, and our brains go about perceiving, were fascinating. Once again, the computing metaphor in how our brain analyzes what we see (the visual bandwidth being the highest) comes through.

[1] http://www.youtube.com/watch?v=Ahg6qcgoay4
[2] http://www.youtube.com/results?search_query=change+blindness
[3] http://www.youtube.com/watch?v=vBPG_OBgTWg

The interesting part for me was just seeing the examination of what is and is not detected without conscious effort. In particular, that simple conjunctions of features don’t jump out the same way that single features can tells us a little bit about what the primary visual centers are doing, but another question is, suppose a feature jumps out – where does it jump out to? I think he did mention that there is no single control center in the brain, which makes sense, so I guess the answer is that anything that jumps out does so by jumping ahead in the where / what pathways via a shortcut.

The attention devoted to eye movements was something I hadn’t expected, but it makes sense in that the center of focus has an enormous impact on what you’re seeing. It’s almost like the world is your hard drive, your eyes are the read head, and the various clues around are like the inodes and lookup tables of the file system – which has no overt organization in the real world, except what we make. I doubt if there are any useful insights from file systems with regard to better organizing visualizations, but the metaphor is kind of interesting to me at least.

My favorite part of chapter 2 was the short section on motion. Animation is something we haven’t covered yet in class, but it seems important. This brief analytic overview was a good introduction to the topic. The rest of the chapter was more or less a repackaging of the information in chapter 27 of the graphics textbook.

Chapter 2 deals with how some visual elements “pop out” from a bunch of others. Explaining what we can see easily, he talks about visual channels that do not differ much or those which stand out. Reading this chapter, I felt the need for organizing visual elements so that crucial patterns are readily discernable while noise does not accidentally pop out. Maybe controlling for excessive numbers of encoding channels could help.

The Healy paper follows logically to chapter 2 of Ware, by explaining why the things that pop out do so. He introduces five theories of pre- and post-attention in low-level perception: feature integration theory, texton theory, similarity theory, guided search theory, and Boolean Map Theory (although he doesn’t tell which is the most dominant one today). I thought that all the theories and his follow-up explanations with color, texture, motion, and nonphotorealism carry a common lesson, which is not to oveload the viewer’s visual information processing capacity by focusing on important channels.

Additionally, Gibson’s theory on affordances, which states that perception is based on directly understanding only possibilities for action, provides an interesting twist on the interpretation of the science of perception. Previously, I’d always taken for granted that perception involves only those objects that we “see,” essentially using the physical definition of vision. I’d never taken the time to consider what in a sense is the purpose underlying perception, let alone consider this as a definition of the concept.

Finally the discussion of the significance of texture brings yet another dimension into the realm of perception that is very easy to overlook. However, given the visual impact of lighting and texture to the perception of shape and object classification, it makes sense that the texture of a visualization can provide another data dimension in order to exploit the perceptual system through visualization techniques.

Healey’s paper really appears to expand on the themes of sensory (preattentive) versus arbitrary (postattentive) processing. What really stood out in his analysis, however, was how many different possible mappings of the two perceptual processing system have been developed. Despite this large number of mappings, the essential themes of preattentive and postattentive processing seem to be common across all models. In general, these themes appear to suggest that more significant features in a visualization should tend to be encoded in manners to play on the preattentive processing system, whereas more complicated features are more likely to be successfully perceived in the postattentive domain.

**Sorry if any of this appears new, the readings were done from Ware’s Information Visualization book roughly corresponding to the assigned chapters of Rethinking Design.

This chapter introduces how people perceive via eyes. We make visual queries every times when we search for visual information. As a result, tracking the visual queries is a crucial point for designers.

The fovea is a new knowledge to me, and eyes make visual queries by pointing them at interesting points. Visual queries are a series of searches for particular patterns. The act of perception is determined by two kinds of procedures, bottom-up and top-down. When doing visual queries, brain can operate to solve the problems by a set of nested loops.

The analogies in this chapter, by viewing eyes as digital lens, brain as computer, help understanding those organs’ function in visualization.

Chapter 2 What can we easily see? :

Visual searching is a common activity for all seeing since we keep reassessing the visual world every time when we look. The patterns that show pop-out effect includes many features that include pre-attentive effects. Colors, shapes, sizes, etc. can be tunable characters. Motions can enhance visibility. Too much motion is one of the worst forms of visual pollution, but carefully using motions is a good technique.

Perception in Visualization

Five theories are introduced in this paper. When talking about Guided Search Theory, the concept of ‘top-down’ and ‘bottom-up’ is mentioned in this paper and they are part of the framework of guided search. In Boolean Map Theory, the process of visual search is divided into two parts, selection and access. The former involves choosing objects to be viewed and the latter determines what information can be withdrawn by viewer.

An interesting point in this paper is that in the experiment by Wolfe, scientists got the conclusion that sustained attention to the objects tested did not make visual search more efficient. It is important when scientists present their data. The conclusion implies that in searching for specific data value, the display may not be as useful as expected. This also changes my original thought about how to make data seen.