What are your settings in Preferences > Performance? Do you have Cache levels set to a value higher than 1? (a value of one can lead to problems)
Try unchecking GPU acceleration in the same place. You will need to restart Photoshop for that to take effect. If this step helps, then make sure your video card driver is up to date. (I don't how you go about that with a Mac)
thanks for your reply. I checked the settings you suggested, all were as they should be. However, I did select advanced settings in Graphics Processor Settings and chagned it from basic to normal and it seems to have fixed the problem.
And thanks for sending the youtube links.
Thanks for the prompt. It didn't occur to me to check the GP settings. Your help is much appreciated
Hey, you are way ahead of me. I was going to wait to see how you got on before suggesting changing the Advanced settings, but you worked it. You might have to stick around and help answer other people's questions.