How to remove this delay?

[Barry Levine]

I've got a line of code in a script that executes when a specific event 
  occurs:

   show image "largeLetter" with visual effect iris open slowly with 
sound the filename of player "currentLetter"

It works fine and causes no errors. However, while this particular line 
of code is executing, I have a number of image objects moving around on 
screen. Each object contains the following code:

on moveMe
   if not the uAllowMove of me then exit moveMe
-- uAllowMove is a custom property (true or false)
   ------
   # THIS SETS THE MOVEMENT SPEED
   put 3 into tRate
   ------
   # THIS ADDS AN OFFSET VALUE
   put 1 into tOffset
   ------
   # THIS SETS THE BOUNDARIES
   if right of me > (width of graphic "fieldOfPlay" + 100) then set the 
xDir of me to "-"
   if left of me < (left of graphic "fieldOfPlay" - 100) then set the 
xDir of me to "+"
   if bottom of me > bottom of graphic "fieldOfPlay" + 6 then set the 
yDir of me to "-"
   if top of me < top of graphic "fieldOfPlay" - 100 then set the yDir 
of me to "+"
   ------
   # SET NEW LOCATION OF DOT
   put item 1 of loc of me into xLoc
   put item 2 of loc of me into yLoc
   set loc of me to (value(xLoc & the xDir of me & tRate & the xDir of 
me & tOffset) & "," & value(yLoc & the yDir of me & tRate))
   send "moveMe" && x & "," & y to me in 20 milliseconds
end moveMe

Obviously, the uAllowMove property of each of the moving images is 
True. Again, no errors. However, while the "show image..." line of code 
is executing, the image objects (six of them at any given time) stop 
moving until the visual effect is complete. I'd like to keep everything 
moving smoothly. Any ideas? Would a "send" command do this  - something 
like SEND "SHOW IMAGE... blah, blah"(so that it can occur without 
stopping the rest of the handler from executing)? Or does the action 
("show image...etc") cause everything else to stop until the code is 
complete? If this is the case, would there be any other code that could 
be used. My purpose in the visual effect is simply to draw the user's 
attention to the appearance of the image (as it has changed from what 
it had been prior to the execution of code earlier in the script).

If the "send" command is the answer, would someone show me the proper 
syntax using the line of code above?

(BTW - I do not recall the lista who provided the custom property code 
but I have his name buried in the Rev eMail folder. You know who you 
are - Thank you!)

Any response on-list or off-list would be appreciated.

Regards,
Barry