After performing an upgrade or other major system modification, sometimes people experience odd mouse input behavior on their OS X systems. In some cases the system may show a sudden change in speed and acceleration properties of the mouse, and at other times the mouse may appear more or less sensitive to clicks, where single clicks may result in double clicks, or where double clicks may not register.
Unfortunately these behaviors are rare and different enough that there is no single cause and direct solution available for affected users. However, in most situations a configuration error with specific software or hidden system components may be to blame. This can be from problems with third-party mouse drivers to Apple's internal account-based configuration files that store mouse settings.
If you are experiencing this issue, try general troubleshooting steps for isolating the issue to specific areas of the system. These steps will help you determine if your specific problem needs to be tackled in the user account, or if more global settings need to be addressed, such as those for the system or perhaps conflicts with third-party software you may have installed.
If after troubleshooting you find the problem only happens in your user account, try removing the global settings files for your account. These files contain details like the preferred language settings, how windows are managed, custom keyboard hot keys, and recently visited folders on the system, in addition to settings for keyboards and mice. Granted, removing them will require you to set these features up again, but doing so may help recover broken mouse and trackpad functions. To do this, open the Terminal utility (in the /Applications/Utilities/ folder) and run the following commands:
defaults -currentHost delete -g
defaults delete -g
After performing these commands, log out and log back in to the system to see if the changes helped.
If the problems persist in multiple accounts, you can try the following options:
- Reset the PRAM
The PRAM on the system is a small bit of memory that can store hardware-specific settings your Mac uses before the operating system loads, and allows, for instance, the system to provide a mouse speed setting to the boot loader menu if you invoke it by holding the Option key at startup. Resetting the PRAM may help the situation by clearing these settings and having their defaults used instead.
While doing so will revert the default boot volume (if you have a secondary boot device used) and adjust startup sound volumes, the changes should not affect most people's systems with any significance. To clear the PRAM, simply reboot the system and hold the Option, Command, P, and R keys all at once. Allow the system to automatically reset and sound the boot chimes with these keys held, then release them and allow the system to boot normally (the system will continuously reset the PRAM and reboot as long as the keys are held).
- Reinstall third-party drivers
While OS X will handle third-party mice and allow programs and system settings to make use of multiple buttons and controls on them, the system has minimal support for such features; users may wish to install included software for their devices to optimize their use.
Often people install the mouse software from the included CD-ROM, which may be out of date and can cause possible conflicts either immediately or following a system update. Therefore, first try uninstalling the software to see if basic functions work normally by using Apple's internal driver set, and if so, then try reinstalling the latest version of your third-party drivers from the manufacturer's Web site, ensuring first that they will work on your version of OS X.
- Try a new mouse
Another possibility could simply be that the mouse has worn out and needs to be replaced. This may be especially true in situations where single and double clicks do not register properly; the button itself might be experiencing mechanical obstructions. While some mice can be opened and cleaned or otherwise fixed, if this cannot be done, replacing the mouse might be the quickest way to get up and running again. Unfortunately if this is the case, with Apple's built-in trackpads on MacBook systems, then you will need to have the trackpad serviced. In the meantime, you can use an external mouse instead of the trackpad for your various point-and-click functions.