Mountain Lion's Accessibility Features
Accessibility in OS X Mountain Lion is mostly designed for users with disabilities or who have difficulty handling the keyboard, mouse, or trackpad. The Accessibility System Preferences pane has three sections — Seeing, Hearing, and Interacting — each of which has one or more subsections.
The Accessibility Seeing section
Seeing has three subsections. The Display subsection lets you display the screen with inverted colors. Check the Use Grayscale box to desaturate your screen into a grayscale display (so it looks kind of like a black-and-white TV).
Select the Show Accessibility Status in Menu Bar check box to see the status of all of the Accessibility Preferences in your menu bar.
The Zoom subsection is where you can turn on a terrific feature called hardware zoom, which lets you make things on your screen bigger by zooming in on them. To control it by keyboard, select the Use Keyboard Shortcuts to Zoom check box.
Then you can toggle it on and off with the shortcut Command+Option+8 and zoom in and out using the shortcuts Command+Option+= (the equals key) and Command+Option+– (the minus key), respectively. Try this feature even if you’re not disabled or challenged in any way; it’s actually a great feature for everyone.
Finally, the More Options button lets you specify minimum and maximum zoom levels, display a preview rectangle when zoomed out, and toggle image smoothing on or off.
The Accessibility Hearing section
The Hearing section has a single subsection called Audio, which lets you choose to flash the screen whenever an alert sound occurs.
This feature, created for those with impaired hearing, is quite useful if you have a MacBook Pro or MacBook and want to use it where ambient noise levels are high or if you don’t want your Mac to disturb those around you.
There’s also a Play Stereo Audio as Mono check box. Not sure why you’d need it, but it might be helpful for those who listen to audio using a monaural (that is, one ear only) Bluetooth headset or those with hearing impairment in only one ear.
The Accessibility Interacting section
The Keyboard subsection offers two types of assistance:
The Sticky Keys application treats a sequence of modifier keys as a key combination. In other words, you don’t have to simultaneously hold down Command while pressing another key.
For example, with Sticky Keys enabled, you can do a standard keyboard shortcut by pressing Command, releasing it, and then pressing the other key. You can select check boxes to tell you (with a beep and/or an on-screen display) what modifier keys have been pressed.
As useful as Sticky Keys can be, they’re really awkward in applications like Adobe Photoshop, Adobe Illustrator, and other applications that toggle a tool’s state when you press a modifier key. So if you’re a big Photoshop user, you probably don’t want Sticky Keys enabled.
Slow Keys lets you adjust the delay between when a key is pressed and when that key press is accepted.
The Mouse & Trackpad subsection offers options for those who have difficulties using a mouse or trackpad by using keys on the keyboard to navigate rather than a mouse or trackpad.
You can also increase the cursor size from the normal setting (16 x 16) to about 64 x 64.