The only time you see the actual image pixels is when your viewing zoomed to 100%. At any other zoom level your looking as a scale image not the actual image. Print size image when view at 100% will not fit on your display for it can only display 2560x1600 a 4.1Mp 8:5 aspect ratio. Most digital cameras even cell Phone capture images with more pixels and usually have a 4:3 or 3:2 aspect ratio images some will also capture smaller image sized to HDTV a 16:9 aspect ratio 1920x1080 pixels 2.1 MP these will fit on your display and be a closer match to your display's 16:10 aspect ratio.
If your working on a large or small image you can have Photoshop zoom it to fit on your display there will be border for image Aspect Ration and Your Displays area aspect ratio will differ . If you zoom it to fill the screen the zoom level will be above or below 100% the image will be softer if above 100% then the actual image. Adobe Photoshop uses a quick scaling so the scaled image is not the best it could be scaled. If you want to see a better display size image you could re-size the image up or down in size resampling the image you have with a interpolation method like bicubic or bicubic smoother. The image will be better then Photoshop zooming the image. But remember every time you resample an image you loose some image quality. Not a single original pixel remains you have a completely new image interpolated from an other. I do not recommend resampling your image to fit on your low 100 ppi resolution display.
When you print the image at a higher resolution then your display's 100PPI the printed image will be sharper and smaller then the image displayed on your display.
There are settings in Bridge that govern the quality of the preview. Change those, clear the cache, and see whether that helps you with the quality.