Pass business object as parameter into a value converter

I have a custom column in a xamgrid (data grid) and want to pass a row's data object as a parameter into a value converter. Is this possible?

<TextBlock  Text="{Binding RelativeSource={RelativeSource Self}, Converter={StaticResource captionConverter}}"  />

with this code, all that gets passed into the value converter is the text box itself.

Thank you for any help you can offer.