changing picture in a frame by onclick button in another frame

i have a framset with 3 frame src. i have a button in my upper frame and i need to onclick have it change an image in the lower frame. i keep getting an error object expected.
this is my code. please help.
var pics=new Array("art.jpg","babybirds.jpg","emily2.jpg")
var thisPic=0
function loadPicture() {
parent.lower.location.href ="lower.htm"; {
if(parent.lower.document.images){
if (parent.lower.document.tmuna.complete){
thisPic++
if (thisPic==3){
thisPic=0
}
parent.lower.document.src=pics[thisPic]
}
setTimeout("cycle()", 3*1000)
}
}
}