Apply multiple filter values to one field with OTA (VB)

Hi, is there a way to apply more filter values to one field, so I can get all defects for instance which are assigned to person X or to person y. I tried to do it like this

[...]
testInstanceFilter.Filter(AssignedTo) = personX
testInstanceFilter.Filter(AssignedTo) = personY
[...]

But is is not working, it delivers an empty list. In case I just take one person as a filter it works perfectly. I assume it makes an and-search and I do not know how to achieve it treates both as an or-search. Is there a way to do so?