TTL response accuracy

I have about 40 sets of images which are presented as a movie sequence
the sequences are interuptable by a response box using ttl signals as follows
rt:95,(889)>-30
this is the middle response button on port 889 and means goto trial 30 when this response is detected.(trial 30 is an example, after each sequence the rating screen is shown to rate the sequence)

each image is shown for 40ms

the problem we are having is if the button is pushed once
a second or so of images are still presented before the sequence is aborted which gives the participant an unfair advantage in identifying the sequence

if the button is held down the sequence is significantly shorter but still can show a few images past the first image clicked on


In an attempt to fix this the response box was altered as follows
To minimize any problems caused by mechanical bounce I arranged for the switch to provide a 300ms pulse ‘closed’
from the first time a switch closure was detected, so that despite it appears to open and close a few times [which it will]
as far as the program is concerned it will see a closed condition that stays closed for 300ms

it looks as though DirectRT does not detect closure very quickly?


anyway I need the sequence to imediatly cease or go to black screen the instant the response box button is pressed is there any way to do this because the code specifically says to goto the next trial whenever a response is detected im not sure adding the standard response blank screen method will work

thankyou
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If you replace the TTL code with a keypress response (e.g., 57 for the spacebar) does that affect the outcome? I'm just curious to know if it's the logic in DirectRT (in general) or if it's specific to TTL input.

the keypress version works instantly it must be a problem with the ttl code part

That is very odd. Can you send me a sample log data file with say 5-10 trials where you respond consistently--say at around 300ms or so? Maybe once via TTL and once via keyboard? I would like to see what is being saved as the display and RT data for those extra images in the TTL version.