Teaching:TUW - UE InfoVis WS 2009/10 - Gruppe G12 - Aufgabe 1 - Preattentive Processing

Preattentive processing

Visualization is so effective and useful because it utilizes one of the channels to our brain that have the highest bandwidths: our eyes. But even this channel can be used more or less efficiently. One special property of our visual system is preattentive processing.

[Kosara, 2002]

One very interesting result of vision research over the past 20 years has been the discovery of a limited set of visual properties that are processed preattentively (i.e. without the need for focused attention). Typically, tasks that can be performed on large multi-element displays in 200 milliseconds or less are considered preattentive.This is because eye movements take at least 200 milliseconds to initiate. Any perception that is possible within this time frame involves only the information available in a single glimpse. Random placement of the elements in the displays ensures that attention cannot be prefocused on any particular location. Observers report that these tasks can be completed with very little effort.

[Healey et al., 1996]

Preattentive features

Feature	Picture	Feature	Picture
orientation A different orientation of a certain object can be used to distinguish it from the other objects preattentively.		length, width, size Differences in size can be used for the preattentive distinction of various objects.
closure A closed object in a pool of unclosed objects can be detected preattentively.		curvature The curvature of an object can be considered to detect it preattentively.
density, contrast The difference of the density of certain objects to the density of the surrounding objects can be detected preattentively.		number, estimation A group of objects with a certain feature can be detected preattentively dependent on the number of objects.
colour (hue) The hue of the objects is used to divide the elements into two groups (i.e. a red group and a blue group) though the form varies randomly from object to object. Tests did show that it is easy for subjects to identify the hue boundary as either vertical or horizontal.		intensity, binocular lustre The intensity of an attribute (in this case brightness) can be used for the preattentive detection of an object.
intersection		terminators
3-D depth cues, stereoscopic depth Describe attributes of objects that are used to distinguish between objects in 3D space. In this example the distance of the shadow which implies that the further the shadow is away from the oject the greater is the distance between the object and the plane it casts its shadow on.		flicker Describes the abrubt change between two different states of the same attribute. In this example visiblity.
direction of motion Differences in the direction of motion can be detected preattentively especially if the motion is directed against the flow of general motion.		velocity of motion Another motion related cue for preattentive processing is the difference of the continuity of a certain motion speed between an object and its environment.
lighting direction The lightning is normally constant for all objects in a certain scene so variations in the lightning of a single object can be used a preattentiv cue.		3D orientation The orientation in a 3D space can also be used as a cue for preattentive processing.
artistic properties

Compiled list from [Healey, 2005], [Chipman, 1996]

It is important to note that some of these features are asymmetric. For example, a sloped line in a sea of vertical lines can be detected preattentively. However, a vertical line in a sea of sloped lines cannot be detected preattentively. Another important consideration is the effect of different types of background distractors on the target feature. These factors must often be addressed when trying to design display techniques that rely on preattentive processing.

[Healey, 2005]

Examples for preattentive processing

Detecting the Red Object preattentively.[Healey et al., 1996] One visual variable and very easy to find it.

Detecting the Circle preattentively.[Chipman, 1996] It is more difficult but still preantentiv.

Examples of two target detection tasks: (a) target can be detected preattentively because it possess the feature “filled”; (b) target cannot be detected preattentively because it has no visual feature that is unique from its distractors.[Healey et al., 1996]

Region segregation by form and hue: (a) hue boundary is identified preattentively, even though form varies randomly in the two regions; (b) random hue variations interfere with the identification of a region boundary based on form.[Healey et al., 1996]

Conclusion

Any visual processing of that item prior to the act of selection can be called “preattentive”.[Wolfe, Treisma, 2003]

Preattentive processing can help to rapidly draw the focus of attention to a target with a unique visual feature (i.e., little or no searching is required in the preattentive case). [Healey, 2005]

References

• [Kosara et al., 2002] Robert Kosara, Silvia Miksch, Helwig Hauser. Focus+Context Taken Literally IEEE Computer Graphics & Applications (CG&A), Special Issue on Information Visualization, 22(1), pages 22-29. Created at: January/February, 2002. http://www.kosara.net/papers/Kosara_CGA_2002.pdf .

• [Healey et al., 1996] Healey, C. G., Booth, K. S., and Enns, J. T.. High-Speed Visual Estimation Using Preattentive Processing. ACM Transactions on Human Computer Interaction 3(2), pages 107-135, Created at: 1996. http://www.csc.ncsu.edu/faculty/healey/download/tochi.96.pdf .

• [Wolfe, Treisma, 2003] Jeremy M Wolfe, Anne Treisma. What shall we do with the preattentive processing stage: Use it or lose it?, Todd S Horowitz poster presented at the Third Annual Meeting of the Vision Sciences Society. Sarasota. Created at: May, 2003. http://search.bwh.harvard.edu/links/talks/VSS03-JMW.pdf .

• [Healey, 2005] Christopher G. Healey. Perception in Visualization. Department of Computer Science, North Carolina State University. Created at: May, 2005. http://www.csc.ncsu.edu/faculty/healey/PP/index.html#Tri_Cog_Psych:80 .

• [Chipman, 1996] Gene Chipman. Review of High Speed Visual Estimation Using Preattantive Processing (Healy, Booth and Enns). Created at: 1996, Retrieved at: October 24, 2005. http://www.cs.umd.edu/class/spring2002/cmsc838f/preattentive.ppt#267 .