At certain point this "goshting" you see its normal operation because of the type of screen (E-Ink) but if you get words mixed or its too difficul to read, you can try a reset:
Note: This will not affect your ebooks:
1. Disconnect the reader from the computer
2. Power off you reader
3. Hit the reset at the bottom for 3 seconds
4. Power on you reader
5. The screen will blink and will display "Opening Book", let the reader load your books
See if the problem persist, if so, you can try a hard reset, make sure the reader is fully charged.
Note: This will delete all content from you reader, I recommend you to back uo your data before proceed:
1. Power off the Reader.
2. Press the RESET button.
3. Power ON the Reader.
4. When the screen shows "Opening book..." , press and hold at the same time the "Page Back" button and the Volume + at the bottom until the "Reset All" appears on the screen
If none of the steps above work, then contact Sony to get the screen repaired.