1. Questions for lesson 3
Perception
11/27/2018
lesson 3

2. Reality
Is photographic reality necessary for effective web sites? No because perceptions depend on whether visual analyzers fire not the physical signals. Anything that fires the analyzer will be effective, whether it is “real” or not
11/27/2018
lesson 3

3. Ambiguity
How can a figure to be ambiguous at a sensory level? Surely base sense data is defined?
How should web sites treat ambiguity? Sense data is not defined. Perception involves the formation of the best hypothesis to fit incoming sense data. Some sense input can fit two hypotheses equally, and thus are ambiguous. Usually it should be avoided, but could be used for interest or humor
11/27/2018
lesson 3

4. Kanizsa’s triangle
Why do we sometimes see edges and shapes with very little in the way of boundary changes (eg Kanizsa’s triangle) Because the visual system deduces the cause of sudden line termination is an edge and then enhances the deduced boundary so a brightness difference is perceived
11/27/2018
lesson 3

5. Color How is color represented in a computer?
How is it represented in the brain?
How does color relate to light frequency?
As three numbers for red, green, blue The brain processes red, green, blue, and also saturation and luminance. This gives five channels not three
Not in a simple way e.g. see notes on white, yellow, brown, black
11/27/2018
lesson 3

6. Text colors What are the best colors for fine text? Why?
What if you cant use those colors? Black on white or white on black. Because this gives the greatest boundary changes in red, green and blue (hue) channels, and saturation and brightness
Use larger or clearer font
11/27/2018
lesson 3

7. Blue/Green contrasts
Why is it bad to present figures with blue/green contrasts? Because a significant proportion of men cannot distinguish blue-green
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8. Saturation What is saturation? Why is it important in web site design?
The amount of white, ie the amount of equal frequencies of RGB
Children seem to prefer pure bright colors, while adults prefer more subtle saturated color contrasts
11/27/2018
lesson 3

9. Boundary What is the basis of shape perceptions?
What is a common reason for shapes (such as letters) being unclear?
Why are button icons often unclear?
Where is this perception generated in the visual system?
Boundary contrasts
insufficient boundary contrast
As above, for the key features of the icon (see next lesson)
Probably begins at the retinal level but is enhanced by higher levels
11/27/2018
lesson 3

10. Processing
There seem to be two main categories of visual processing. What are they?
Shape and color, and position and movement
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lesson 3

11. Constancy
Why do signal changes caused by orientation, color, illumination and distance of an object not confuse us?
We conclude an object’s size from the size of the image on the retina. T/F
What does this mean for web site design?
Do our senses trick us? because the visual system is designed to compensate for such changes
It also depends on judged distance
Considerable variation in colors and shapes will still give an effect
Yes but for good reason
11/27/2018
lesson 3

12. Perception What is perception affected by?
Why is the total effect important in perception?
What is a minimalist approach?
Because all analyzers and channels interact, and something that is not effective alone may be effective in combination with something else, and things that are effective alone may not work when combined (the Frankenstein effect).
To use very few signals, but ensure they are consistent and no signal contradicts the desired effect
11/27/2018
lesson 3