When using the brushes, I utilize the bracket keys to change the size
The main issue is that the diameter of my brush stops partially and therefore I can not really see the size of my brush. Can anyone help me with this. This issue started after I updated to Mac OS X Yosimite
What version of Photoshop are you running?
I have Photoshop CS6 Extended.
You can Reset the Brush Tool, select the Brush tool and ctrl-click on its' icon in the Options bar.
Next try a Preferences reset: Hold down cmd-opt-shift while starting Photoshop and agree to the Reset.
if that does not work I suggest a reinstall. The upgrade has been know to damage CS5 installs.