In OS X Lion, Apple changed the default scroll direction from moving the screen in the opposite direction to the cursor to be similar to the iPad and iPhone, where when you scroll the image on the screen moves in the same direction you are scrolling.
This behavior may be expected for touch-screen devices, but for many people the change is a bit confusing, despite the introductory warning that informs you about the change when you first boot Lion.
For people who wish to keep the conventional scrolling behavior, there's an option to do so in the Mouse and Trackpad system preferences. However, some people have been reporting that this setting doesn't appear, especially if they are using third-party mice.
This issue may be because of an incompatibility with mouse firmware as some have suggested in forum postings on the topic, or it may be a problem with Apple's generic mouse drivers. Both of these would require updates to fully address the issue, which likely will not happen soon.
If you want to toggle your mouse-scrolling direction but the settings aren't visible in the Mouse system preferences, there are a couple of approaches you can take:
- Plug in another mouse
This problem seems to be specific to some devices, so one option for getting around it is to temporarily use another mouse, as suggested in the forum link above. Try attaching several mice to your system, and if the setting to reverse scroll direction appears in the Mouse system preferences for one of them, then adjust the setting accordingly. The setting should remain toggled even if you switch back to your original mouse.
- Adjust the settings in the Terminal
The scroll direction settings are stored in the hidden global preferences file for a user account. You can access and change it by running the following command in the Terminal (open the Terminal program that is in the /Applications/Utilities/ folder and then copy and paste this command into it, followed by pressing Return to run the command):
defaults write -g com.apple.swipescrolldirection -bool false
After this command is run, the changes will not take effect right away. The system preferences cause the mouse driver to pick up the new settings, but editing the preferences file does not do this right away, so you will need to log out and log back in to your system for the settings to be loaded into the driver and take effect. To reverse the settings, just repeat the command and change "false" to "true."