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SE4D03 – Computer User Interfaces• The Science of Visualization – continued

– Visual Attention• Attention comes in two types of considerations:

1. Low-level as considered below, and2. High-level as considered later, where problem solving is most

important• Consider the eyeball a searchlight, sweeping the visual world

under the guidance of human cognitive centres, where a snapshot is taken upon every fixation of the eye.

• Each snapshot will take a parse of between 4 and 12 items per fixation and is held in a visual buffer, called the iconic buffer which holds the snapshot for 0.1 or 0.2 seconds as it is read into short term memory.

• The eye can take on two types of attention spaces:1. Detailed narrow focus of information, which concerns the image

concentration about the fovea where vision detail is most acute, and

2. Generalized pattern sensing where a larger space can be absorbed but with much less detail than in (1).

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The Science of Visualization -- I• Visual Attention – cont'd

• Eye Movements – moving the eyes causes different parts of the visual environment to be imaged on the high-resolution of the fovea; for instance as you read a line of text in a book, your eye makes between two and five jerky movements which are called saccades, per second.– In visual searching, the eye moves from fixation to fixation, taking

about 200-600ms to extract the information and from 20 to 100 ms for the saccade.

– Measured maximum saccade rates have been clocked at 900 degrees/second

– If the visual field contains moving objects, the eye can lock-on and track the motion; this is called smooth pursuit eye movement.

– If the visual field contains movement towards or away from the eye, the eye will accommodate this by either converging as the motion comes closer or diverge if it moves further away. This is called vergence movement, which can be either smooth or saccadic. This accommodation to refocus can take about 200 ms.

– Note that the refocus and eye movement are neurologically coupled so that virtual reality displays may be fraught with illusion possibilities.

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The Science of Visualization -- II• Low-Level Visual Attention

– A concept has been defined as the Useful Field of View (UFOV)– UFOV defines the size of a region from which humans can extract

information that is displayed. For instance, if the material displayed is highly dense than the UFOV may be 1- 4 degrees of visual angle; however, if it is sparsely populated then the UFOV may be as large as 15 degrees.

– The UFOV varies roughly with the target density to maintain a constant number of targets in the region of interest.

– This concept can also aid in understanding the effect of tunnel vision when the operator is under stress. When this happens the UFOV is narrowed so that only the most important information at the centre of the region is processed. In fact, tunnel vision has a more general meaning that when the cognitive load goes up in an individual, the UFOV narrows.

– Therefore these concepts are important when an interface must attract the user’s attention away from normal operations where an immediate response to an emergency situation is required.

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The Science of Visualization -- III• Low-Level Visual Attention – cont‘d– Preattentive Processing

• When viewing visual objects, some objects appear to “pop-out” from their surroundings when viewed. That is, prior to conscious attention, something of an early visual processing occurs which selects those items for examination; this is called preattentive processing.

• In interfaces that purport to offer information “at-a-glance”, then arrangement of items must be such as to identify for preattentive processing those objects that are critically important beforehand.

• Features of objects that can be preattentively processed include:– FORM: line orientation, line length, line width, line collinearity, size,

curvature, spatial grouping, blur, added marks (graphical annotations), numerosity,.

– COLOUR: hue and intensity– MOTION: flicker and detection of motion.– SPATIAL POSITION: 2D position, stereoscopic depth and

convex/concave shape from shading– Some examples follow on the next slides.

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The Science of Visualization --

IV

• Low-Level Visual Attention – cont‘d

• Preattentive Processing– All samples

at right are preattentive except “Juncture & “Parallelism”

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The Science of Visualization -- V• Low-Level Visual Attention – cont‘d

• Preattentive Processing– Therefore are there item dimensions that emphasize pre-

attentiveness property? Generally no, since this depends on the strength of the particular feature and the context. More contrast is good, but more complexity is not, as shown in the bottom two right in the previous slide.

– Thus it is better to highlight a word than to underline all but the attentive word. In fact, simple numerosity is preattentive but complex numerosity is not. – At the lower left is an

example where we need to locate a grey square, from amongst black and grey squares and circles. This is NOT preattentivebecause we must serially search for both squares and grey colour. This is called a conjunctive search.

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The Science of Visualization -- VI

• Low-Level VisualAttention – cont‘d

• PreattentiveProcessing

– ConjunctiveSearching

• There is a caveat when conjunctive searching is involved and that is using spatial grouping. Above, the upper right cluster is not preattentive when looking for the grey circle but in the lower right, the grey ellipse is preattentively processed.

– Highlighting• Given the use of computer graphics, there is

other methods of highlighting. One example is the blur (and also the grey-over or disable) common in graphical operating systems. The example at the lower left is the blur (a generalization of the fish-eye lens effect). However, here in visualization land, this is termed semantic depth of field variation.

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GUI du Jour -- I• Navigation Considerations

• Selecting “change” brings up “Computer Name Changes” which also does workgroup name changes!

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GUI du Jour -- II• Navigation Considerations – cont’d

• Insert Function brings up Paste Function window

NOTE: “insert” means input, “paste” implies a previous “cut”

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GUI du Jour -- III• Navigation Considerations – cont’d

• Adobe main window (left) allows users to select <New Group>, but the window brought up (right) is titled “Edit Group”

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GUI du Jour -- IV• Navigation Considerations –cont’d

– Selecting “Mail Folders” in upper windows brings up the “Manage Folders” window

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GUI du Jour -- V • Navigation Headers• Upper is “Subscribers”• Lower is “Newsletters”

– Highlighting