LANCASTER UNIVERSITY

1996 EXAMINATIONS

Part II (Final Year)
COMPUTER SCIENCE (2 hours)
363 Cognitive Modelling of HCI

Answer THREE Questions

1. (a) Briefly discuss what is meant by the term mode error.

Give examples of situations arising in real systems where one might expect mode errors to occur.

Give examples from real systems of facilities that reduce the possibility of mode errors. [12 marks]

(b) With respect to Macintosh systems:

(i) dragging a file icon onto the Wastebasket icon deletes the file. Dragging a disc icon onto the Wastebasket ejects the disc. Dragging an icon for a shared folder onto the Wastebasket disconnects the user from the shared folder

(ii) dragging a file icon between folders on the screen moves the file between the folders, unless one of the folders is on a floppy disc, in which case the file is copied between the folders.

For both cases, briefly discuss any inconsistencies between the commands, and discuss reasons why the designers may have allowed such inconsistencies to exist. [8 marks]

2 . Some studies in HCI have examined user interaction with devices or computer simulations of devices. Discuss what such studies can tell us about more conventional modes of interacting with computers, such as programming, for example. [20 marks]

3. Discuss the following statement:
?Despite recent developments in multimedia computing and
virtual reality, human-computer interaction continues to rely
predominantly on the user's visual channel of communication?
Then speculate on how future applications may make more use of users' non visual channels of communication. [20 marks]

Please turn over ...

4. The following is a screen from a spreadsheet program:

The designer of the program has observed users using a method to locate a cell on, or to the right of, the current screen that involves clicking in the scroll bar to the right of the position indicator box (see diagram) at the bottom of the screen 0 or more times to get to the target screen, then clicking the mouse after moving the pointer to the required cell.
The designer wishes to introduce a "Goto cell" command, which is invoked by selecting "Goto cell" from the "Go" menu (using the mouse) at which point a dialogue box appears. The user then types the cell reference <letter><number> (e.g. "G7") into a field (which is already selected and ready to receive text) then clicks an "OK" button. The display then changes (if necessary) to the screen containing the target cell, which is automatically selected, resulting in the system being in the same state as that following the first method.
The designer wishes you to determine at which point the "Goto cell " method will become more efficient for a user than the first method. Use a parametric keystroke analysis to help you to perform this analysis. Consider only rightwards movement (i.e. the row of the target cell is within the rows currently displayed).
Briefly discuss whether or not your analysis indicates that the "Goto cell" method would be a useful addition to the system. [20 marks]

Please turn over ...

Notes:
(a) the cell columns are labelled A..Z, then AA..AZ, then BA..BZ, up to ZA..ZZ

(b) the mouse used is of the single button variety

(c) the menus in the system are ?pull down?; to select an item, you press the mouse button on the menu title, hold the button down until the pointer is over the desired option, then release the mouse button (see also the comments for the D operator in the table below).

A table of operations and associated times that should help you with your analysis follows:

End of paper