Visualization of Eye Gaze Data using Heat Maps Shijia Liu

Overview Background Existing Techniques Modifying Heat Maps Using pupil’s horizontal and vertical coordinates Fixation maps Heat maps Modifying Heat Maps Visualization Options Conclusion

Background Eye movements ↔ Internal brain processes Window into human mind

Why the eyes’ movements is important? From the collected eye-movement data, researchers can determine whether users were looking at the appropriate objects, whether the users are reading some particular words or phrases, learn the relative intensity of the user’s attention to various parts of a web page, and find out whether the user was searching for a specific item .

Techniques for Eye Gaze Visualization Most straightforward technique: Providing a simple plot of the pupil’s horizontal and vertical coordinates against time. Then stimulus image as the background.

Techniques for Eye Gaze Visualization More advanced visualization techniques -Fixation Maps Convert the raw data into a set of fixations.

Techniques for Eye Gaze Visualization Fixation Maps Traditionally, fixations are represented by circles And saccades are represented by lines connecting the circles.

Techniques for Eye Gaze Visualization A modern visualization technique – Heat Map Was derived from the fixations maps. Heat Maps Fixation Maps

Techniques for Eye Gaze Visualization Heat Maps Heat maps better separate different levels of observation intensity than fixation maps. Color mapping is usually selected so that the longer the observation, the warmer color used to represent it.

Techniques for Eye Gaze Visualization An existing modification of the technique uses opaque heat maps with no shadow over the unobserved areas . However, this kind of visualization hides details of the stimulus image. This tends to hinder the analysis.

Modifying Heat Maps How to modify, the color ? Transparency?

Modifying Heat Maps In this current implementation, the background can be partly or totally hidden by a shadow or fog. Shadowing means covering the background picture in black, whereas fogging is covering it in white.

Modifying Heat Maps Transparency Longer fixations add more transparency than shorter ones. A fixation longer than some threshold makes the display totally transparent at the location.

Modifying Heat Maps Fixations & Pixels In fact, the measured gaze position(1 fixation) contains a group of pixels. Radius

Modifying Heat Maps Every pixel in the heat map related to a particular gaze location( fixation) extends the transparency to the neighboring area. How could we distribute the transparency in one fixation?

Modifying Heat Maps Functions of Transparency Distribution: Linear Linear+Sine Wave Gaussian

Modifying Heat Maps Functions of Transparency Distribution: In this figure, the x axis denotes distance from a fixation, and the y axis denotes influence on the transparency.

Visualization Options There is a dialogue window contains the controls for setting the type of transparency and its distribution.

Visualization Option Sensitivity (S) denotes the radius of influence. Brightness level (BL) is used as the gain for the distribution functions. It shows the minimum fixation duration (FDi) that makes the view totally transparent at the place of its occurrence. Hiding level (HL) denotes the initial level of the shadow’s or fog’s opaqueness. Totally hidden background of the view corresponds to HL of 100%.

Visualization Options Slicing It means how do we want to slice or change the transparency None Steps Mask Relief

Visualization Options Slicing Options 1.By default –None Which means that transparency just changes by one of the distribution rules and no slicing is applied.

Visualization Options Slicing Options 2.Steps Transparency is shaped like terrain steps. The width of each step equals the value of Step level in pixels.

Visualization Options Slicing Options 3.Mask Similar to the 1st one(none). With the option Mask checked, transparency lower than the value of Mask level is not applied to the visualization.

Visualization Options Slicing Options 4.Relief Similar to the 2nd one(Steps) With the option Relief checked. This makes visualization similar to the topographic map.

Visualization Options How do we get the value of Transparency for a pixel in one fixation? Transparency Ti of a single pixel at distance D from the ith fixation in the Linear distribution is calculated using the following expression:

Visualization Options For the Gaussian distribution, we keeps T = 100% when FD = BL for any value of S and BL: Any Ti can not less than 0 or greater than 1.

Visualization Option Color Scheme We can also add color scheme to modify the area with semi- transparent colors. Blue – Green – Red – White; Blue – Green – Red; Blue –Red; Green – Yellow – Red – White; Green – Yellow – Red.

Conclusion This technique is an extension of heat-map based visualization method. In this case, eye gaze is allowed to add transparency to the shaded background. This way the details of less relevance are hidden whereas more intensively observed areas become more conspicuous through increased transparency.

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