TTL pulses - timing - never sent triggers

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Aliez
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Joined: Wed Dec 15, 2010 8:02 pm
Location: Boston

TTL pulses - timing - never sent triggers

Post by Aliez » Fri Jun 17, 2011 9:48 pm

Hi,

When I check the triggers I've sent to the erp system, I see "event names" which I've never sent to the ERP system, what could be the problem? for example I'm completely sure I've never used event name "31", but I have 18 events with that name in on block of my study.

I believe that I'm not aware of one of the rules of sending TTL pulses for events in ERP system & the system is adding up my event triggers(numbers). I'm thinking of 2 possible reasons for that:

1)How fast can we send signal to ERP system? I've been looking at the events for a while. I have some missing trials & some ghost events (never sent triggers), I figured out that these ghost event could be sum of real events (i.e 11+20=31 in which 11&20 are real events and 31 is the ghost). I've been sending signal to parallel port pretty fast, so in this example I send 11 and 20 immediately after each other. Because of this I'm getting "11 signals" less than expected & many unwanted "31 signals".

2) Another example of ghost events in my case is event named "6", I managed to find a few of these 6s. They appear only when I send signal 2 first & then 4 (this time there is a short delay between these events). I'm thinking it might be due to the fact that parallel ports use "logarithmic method" to send data, so it adds up numbers to each other (i.e 00000001 + 00000010 = 00000011 or so). Is there a particular rule for sending events to the ERP system? lets say when I send "1" as the first event, what should(could) be the following event sequence sent after this? is there any limitation for that? is there any way to stop/clear an event or all previous events (i.e. even "1") and then send a new event?

FYI: I use windows vista & MATLAB 2008.

Thank you,
Ali

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