3/27 Lecture

An Example to kick off class:

In the lecture, we looked at a device that can be used to make songs. It creates music. There are two sliders on the screen. The user can change the metrics. He or she can change the jazz factor and the happy factor. The design choice reflected the complexity of the underlying model. This example shows that the gulf of evaluation and the gulf of execution must be met. → This system did a good job of managing gulf of execution.

Human Motor Performance on Basic Input Tasks:

Next, in class, we completed an experiment using our laptops. Macs and PCs have different screen sizes. We viewed a model for a Mac screen and a model for a PC screen. We had to move the mouse across the screen. We had to move it horizontally. The results for the class were that the people in the PC condition took longer than the people in the Mac condition. The people in the PC condition took 865 milliseconds while the people in the Mac condition took 777 milliseconds. → Takes longer on PC because of the tendency to overshoot.

Index of Difficulty:

Fitts’ law connects the index of difficulty and the movement time. It is a function of both distance to travel and target size.  log₂(D/W) represents the index of difficulty, in bits. D represents the width of the screen. W represents the width of a menu. There is a linear relationship between the index of difficulty and time. The movement time, in seconds, is equal to a+b*log₂(D/W).

The mouse was introduced 50 years ago and we are still using it. Interestingly, the mouse adds no extra noise to pointing, nor does it decrease efficiency, compared to the bare hand. This helps make the mouse the optimal input device for pointing. The ability of humans to transmit information through the neural motor system is 10.53 bits/second. Uniformly scaling everything does not make it more efficient.

Morphing Menus:

One way to adjust menus is to change the size of various items depending on the frequency with which they are clicked. Items clicked more frequently will appear larger than items clicked less frequently. This makes it different from a static menu.

Another type of menu is a frequency-based menu. This menu has ordering based on frequency. More frequently clicked items will appear higher in the menu than other items.

Size of the cursor:

There may always be exactly one target in the bounds of a cursor. If you grow all of the buttons in the visual space, everything stays the same but in the clickable space everything is much larger → changes clickable space, not visual space.

Motor Performance versus Age:

Fine motor control peaks in the late teens, then slowly decreases. Strength peaks in the 30s, then decreases. Errors decrease as age increases. As we age, we end up choosing strategies that favor accuracy over speed.

Contributed by Dhruv Suri, Mason Hale, and Nicki Adler 

About the author: Dhruv Suri

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