1. When evaluating how information presented via a computer interface to a human is transformed by the human into a response, it is often useful to consider three distinct stages: Perception, Cognition, and Action. In class, we discussed some limitations that humans have in these stages.

Consider a complex computer system to be used in a safety-critical situation, such as controlling a fuel burning power plant, an electrical power distribution network, an industrial chemical reactor, or a high speed train. Designers of user interfaces for these systems must be aware of various human limitations.

For each of the two stages Perception and Cognition, do the following:

a) Give an example of a particular limitation that should be considered when designing a human user interface.
b) Explain how a naive programmer might design a poor interface by not taking this limitation into account.
c) What might be the consequences of a poor design?
d) Explain how an interface could be designed to avoid these negative consequences.

• If you are right handed, use the keyboard and the mouse with your left hand only (and comparably if you are left handed).
• Type with just 2 fingers (it can be difficult to stop yourself from using more than 2).
• If you are right handed, put your right arm in a sling or bandage that prevents you from bending your elbow and from flexing your shoulder joint (and comparably if you are left handed).
• If you wear glasses, use the computer without your glasses.
• Switch your video display to black-and-white or greyscale mode (if possible).
• Reduce the resolution of your screen to be very low (if possible).
• Significantly reduce the contrast of your screen.
• If you have an application program requiring sound output, turn the volume down so low that you can barely hear it. If possible, adjust the tone controls so that only a narrow band of frequencies is output.
• ... and other changes that you might think of.

a) What did you do to simulate a deficit or disability?
b) Which application(s) or program(s) did you use and for how long?
c) What aspects of the human computer interfaces made it particularly difficult or problematic for you to use your computer?
d) In what ways and how severely did your simulated deficit or disability affect your use of the computer? Describe your experience with reference to different dimensions, such as efficiency, productivity, error rate, ease of use, subjective satisfaction, frustration, your feelings, emotions, etc., compared to your normal experience.
e) Assuming you had to live with your deficit or disability forever, what changes to the interfaces would you like to have? How would those changes help?

a) the camouflaged bird which could be recognized only when moving
b) the fact that the different types of cones in the human retina are present in significantly different numbers
c) the observation that some shapes are relatively difficult to distinguish from one another (e.g. P and R, Ù and Ú), while others are easy to distinguish from one another (e.g. O and V, \ and /)
d) the observation that a three dimensional effect can be achieved by appropriate shading, shadowing, texture, etc.
e) the fact that the maximum resolution of human eyesight is about 60 cycles/degree.