I was just dealing with this problem with my hubbie's phone (Samsung Galaxy Nexus - he's a Droid 😉) and after no luck in this forum or others, I finally figured out HOW to download my photos/videos withOUT having to install separate software, etc.
Here's how.....
1) Plug your phone into your computer (make sure the debugging is enabled, as talked about above)
2 ) Settings > Storage
3) In the uper righthand corner is a line with 3 vertical dots - click on this --- when clicked on, "USB computer connection" should appear - click on this
4) If you're just wanting to sync your photos, etc to your iPhoto click on "Camera (PTP)"; if you're wanting to sync other stuff, I think you need to click on the other "Media device (MTP)" option
--- Note: I was just needing to download photos/videos, so the PTP option was fine for me and worked great; however, if you're wanting to sync other things, you may want to select the MTP option and go to andriod.com/filetransfer to download the software for Mac.
Hope this helps! 😀