Regarding DynamicForm select items with multiple:true

I have created a DynamicForm having an item with type select and attribute multiple true.
Its listing all the values in checkbox format, Can we programmatically select the checkbox items?

Below is the code snippet:
this.filterForm = isc.DynamicForm.create({
ID: this.ID + "_filterForm",
numCols: 8,
autoFocus: false,
parentInstance:this,
items:[
{ type: "select",
name: "filter_serviceType",
multiple:true,
defaultValue:"Select one",
valueMap:{source1:'source1',source2:'source2',source3:'source3',source4:'source4'},
title:"Throughput",
width:150,
},
],
itemChange : function(item, newValue, oldValue){


}
});

I want all the items to be selected when its rendered, could you please let us know how to do that?