I.R.I.S. Readiris 14 for Windows User Guide - Manual (Page 32)

Section 2: Getting Started
36
Select feeder> when you are using a duplex scanner, which scans
both the front and backside of a page.
Once you've selected a scanner model, you must configure you
scanner driver.

Click Configure to select your scanner driver.
If you do not see your scanner listed in the Select Source
window, then your scanner driver has not been installed
properly. Re-install your scanner driver before trying to
configure it in Readiris. The scanner driver can usually be found
on the website of your scanner manufacturer.
Once the scanner has been configured you can start scanning, using
the default scanner settings.
For more information about the different scanner settings and how
to change them, see the topic Selecting the Scanner Settings.