Using SuperLab with PowerBooks
Last Revision: April 21, 1999

The information in this article applies to:

• Users of SuperLab for Macintosh who want to run experiments on Apple PowerBook laptop computer

Summary

When users move their experiment from a desktop Macintosh to a PowerBook, they are sometimes surprised to find that their experiment does not run the same way it did on the desktop Mac. Some of the symptoms are:

• The ADB Keyboard input module does not work on some models

• The presentation of pictures becomes slow or irregular

• Pictures seem to stay longer on the screen

The Power Manager

The cause of the first two symptoms is usually the Power Manager. This is a clever piece of system software developed by Apple specifically for PowerBooks. Its purpose is to reduce power consumption and make the batteries last longer between charges.

Unfortunately, a consequence of the Power Manager is that the ADB Keyboard input module works only on some PowerBook models. On others, SuperLab will crash. On yet other models, SuperLab will appear to work fine but will in fact ignore some responses -- a subject would need to press a key two or more times. This happens because the Power Manager seems to slow down considerably the rate at which the ADB Manager works. The only remedy is to use the Generic Keyboard input module. If reaction time accuracy is important, you will need to use a response pad.

What is ADB?  The Apple Desktop Bus was introduced in 1987 with the Mac SE and Mac II. It is a wiring method for connecting up to 16 desktop devices together such as mice and keyboards. It has been replaced by the Universal Serial Bus on the iMac and newer models. The ADB Manager is the part of Apple's system software that is responsible for handling ADB devices.

Another consequence of the Power Manager is that the presentation of visual stimuli slows down and/or becomes irregular. Sometimes the same stimulus will be presented faster than others. The reason for this is that the Power Manager slows down the processor in your computer when there is no user activity. This literally means an action by the user such as typing on the keyboard or moving the mouse. Presenting a visual stimulus does not count as user activity. As our user in France Marie-Anne Henaff discovered, "if I move the mouse during the presentation the speed of presentation is correct".

The solution for this problem is to disable the Power Manager. You can do so from one of the control panels. Also, if at all possible use your A/C adapter instead of running the PowerBook on batteries, although this has proven to be far less effective than disabling the Power Manager.

LCDs and Persistence

Some users have noticed that their visual stimuli are staying on the screen longer. This is called persistence and is a normal side effect of Liquid Crystal Displays (LCDs) used on nearly all laptops. LCDs cannot erase on item as quickly as your desktop computer can.

This problem affects only certain experiments, e.g. those were a cue or a stimulus is presented on the screen for a brief duration of, say, 250 milliseconds or less. This problem does not affect experiments where the stimulus stays on the screen until the subject responds.

The only solution that we can recommend is to use a laptop computer with an active matrix display, often also called a TFT display, instead of a passive matrix display or STN.

The issue of persistence is becoming less and less relevant as technology advances. The quality of LCDs is improving all the time. Hopefully this will no longer be an issue in a few years' time.