[Eeglablist] Correct for EGI latency error functions

Tue Oct 13 09:43:19 PDT 2015

Dear Kay,

Thank you for sharing information. This is very important!

Makoto

On Mon, Oct 12, 2015 at 6:09 AM, Kay Sung <ksung3 at jhmi.edu> wrote:

> Regarding the latency issue, there were actually two announcements about
> the latency issue from EGI (they are attached below).
>
> The original notice says that there was a significant timing delay in most
> of Net Amp models but later they changed it.
>
> I don’t know Isaiah’s codes reflect the most recent announcement from EGI.
>
> In their second announcement, EGI said that they found latency delay only
> in NetAmp 300 model with some specific versions of Netstation.
>
>
>
> See below.
>
>
>
>
>
> *** Original announcement ****
>
>
>
>
> *Electrical Geodesics, Inc. Advisory Notice: Anti-Alias Filter Effects on
> EEG Timing*
>
> This advisory notice is to alert users of EGI’s GES 300 and 400 series
> amplifiers to the delay of EEG data inherent in the anti-aliasing filters
> of these amplifiers. These delay values have not been effectively
> communicated to EGI customers and need to be considered when aligning
> events (such as events generated from E-Prime or from digital inputs) to
> the EEG.
>
> The digital Finite Impulse Response filters used prior to A/D conversion
> delay the EEG by a fixed interval. This interval is known for each sampling
> rate and amplifier model:
>
>
> *Sampling Rate*
>
> *NA 300*
>
> *NA 400*
>
> *NA 405*
>
> *NA 410*
>
> 1000 s/s
>
> 8 ms
>
> 36 ms
>
> 36 ms
>
> 13 ms
>
> 500 s/s
>
> 18 ms
>
> 66 ms
>
> 66 ms
>
> 34 ms
>
> 250 s/s
>
> 36 ms
>
> 112 ms
>
> 112 ms
>
> 76 ms
>
> 125 s/s
>
> 72 ms
>
>
>
>
>
>
>
>
> Without adjustment, the EEG is delayed with respect to real time and to
> event markers that are aligned with real time. This delay does not affect
> timing of events manually entered by the user with respect to the EEG
> during acquisition.
>
> Particularly for the Net Amps 400, 405, and 410 models at lower sampling
> rates, the delays may be significant in considering EEG and ERP timing. To
> adjust for this delay, users must add a positive value in the “Offset
> Segment” field in the segmentation tool, in addition to E-Prime Event or
> digital input event (DIN) offsets.
>
> This adjustment is only required for real time events that are recorded
> during acquisition. Events entered during review or from the operations of
> tools after data acquisition are already aligned correctly with the EEG.
>
> To make the delays clear to each user, both the EGI technical manuals and
> EGI Support training will be modified to underscore the importance of
> including these delays in the event alignment and segmentation process. In
> addition, the Net Station software (version 5.1.1) will provide an option
> for automatic adjustment.
>
>
> <http://cts.vresp.com/c/?ElectricalGeodesicsI/25e92832cf/6774d3b846/1bb8b10916/utm_content=gfrishkoff%40gsu.edu&utm_source=VerticalResponse&utm_medium=Email&utm_term=&utm_campaign=Advisory%20Notice%20-%20Anti-Alias%20Filter%20Effects%20on%20EEG%20Timing>Please
> contact EGI support <supportteam at egi.com> for any questions.
>
>
>
>
>
> *** Second announcement ****
>
>
>
>
> *Electrical Geodesics, Inc. Update to Anti-Alias Filter Effects on EEG
> Timing Advisory Notice*
>
> This is an update to an advisory notice issued to users of EGI’s GES 300
> and 400 series amplifiers on the delay of EEG data inherent in the
> anti-alias filters of these amplifiers.
>
> In the original advisory notice, it was noted that the digital Finite
> Impulse Response filters used after analog-to-digital conversion delay the
> EEG by a fixed interval by the following values:
>
>
> *Sampling Rate*
>
> *NA 300*
>
> *NA 400*
>
> *NA 405*
>
> *NA 410*
>
> 1000 s/s
>
>  8 ms (0.52)
>
>  36 ms (0.63)
>
>  36 ms (0.52)
>
>  13 ms (0.52)
>
> 500 s/s
>
>  18 ms (0.63)
>
>  66 ms (1.03)
>
>  66 ms (1.03)
>
>  34 ms (1.10)
>
> 250 s/s
>
>  36 ms (2.07)
>
>  112 ms (0)
>
>  112 ms (0)
>
>  76 ms (2.07)
>
> 125 s/s
>
>  72 ms (2.53)
>
>
>
>
>
>
>
>
> Without adjustment, the EEG is delayed with respect to real time and to
> event markers that are aligned with real time. This delay does not affect
> timing of events manually entered by the user with respect to the EEG
> during acquisition.
>
> The delay values in the original Advisory Notice were verified with the
> most recent versions of Net Station 4.5 and 5.0, representing the software
> versions that are most widely used by our customer base. The original
> Advisory Notice was issued immediately after this verification effort.
>
> Since releasing the original Advisory Notice on 28 August 2014, we have
> continued our verification testing to confirm these delay values in all
> other versions of Net Station associated with the NA 300 amplifier, in
> order to provide our customers not using Net Station 4.5 or 5.0 with more
> specific guidance.
>
> With the NA 300 amplifier, we found that the filter delay is only present
> in Net Station version 4.4 and later; events are correctly aligned with the
> EEG data when acquired with earlier versions of Net Station (4.3.1 and
> earlier). Furthermore, we found that for data recorded with Net Station
> versions 4.4 through 4.5.7, the correction values for the default 250 s/s
> sampling rate (which is likely used by the majority of customers) is 8 ms.
>
> For data acquired with the NA 400, NA 405 and NA 410 amplifiers, there is
> no modification to the delay values presented in the original Advisory
> Notice.
>
> Starting with Net Station 4.4, all data files contain an amplifier serial
> number. This information can be used to determine whether adjustments are
> required for a given data file acquired with an NA 300 amplifier. Contact
> EGI support for information on how to locate the amplifier serial number
> (if present) in the data file.
>
> EGI will release a tool to adjust the latency delay in affected files in
> the coming weeks. In addition, the Net Station software (version 5.1.2)
> will provide an option for automatic alignment during acquisition.
>
>
> <http://cts.vresp.com/c/?ElectricalGeodesicsI/becac2c8a8/2eeb100ff4/ec13d0112a/utm_content=ascherme%40uvm.edu&utm_source=VerticalResponse&utm_medium=Email&utm_term=&utm_campaign=Update%20to%20Advisory%20Notice%20-%20Anti-Alias%20Filter%20Effects%20on%20EEG%20Timing>Please
> contact EGI support <supportteam at egi.com> for any questions.
>
>
>
>
>
> *From:* eeglablist-bounces at sccn.ucsd.edu [mailto:
> eeglablist-bounces at sccn.ucsd.edu] *On Behalf Of *Makoto Miyakoshi
> *Sent:* Saturday, October 10, 2015 5:53 PM
> *To:* Isaiah Innis <isainnis at indiana.edu>
> *Cc:* EEGLAB List <eeglablist at sccn.ucsd.edu>
> *Subject:* Re: [Eeglablist] Correct for EGI latency error functions
>
>
>
> Dear Isaiah,
>
>
>
> Thank you for sharing this info. I heard of it from Elise, one of visitors
> here. EGI users, please pay attention!
>
>
>
> Makoto
>
>
>
> On Fri, Oct 9, 2015 at 9:48 AM, Isaiah Innis <isainnis at umail.iu.edu>
> wrote:
>
> Hello eeglab list:
>
>
>
> Those of us who use EGI hydro-cel systems received "Advisory Notice:
> Anti-Alias Filter Effects on EEG Timing" warning that there is a fixed
> latency delay present for any event codes sent to the EEG during recording.
> The EEG is delayed with respect to the events, and needs to be corrected by
> either shifting the EEG forward or the events back. While it is possible
> to correct this within NetStation, since our lab analyzes data exclusively
> using eeglab I wrote a series of functions to correct the delay within
> eeglab. It is my hope that others may find this beneficial. However, I am a
> matlab novice and would like to see if anyone on the list has any comments
> or suggestions.
>
>
>
> You can download a .zip archive with the functions here: <
> https://www.dropbox.com/sh/2udz5qrdb79b2b8/AAAS6Bws_O65gJnpnATS1azza?dl=0
> >.
>
>
>
> If you have any questions or criticisms upon reviewing the functions,
> please contact me at: isainnis at indiana.edu
>
> If there is interest, I will make this a plugin for ease of use.
>
>
>
> Thank you,
>
> --
>
> Isaiah Innis
> Indiana University '13
> EEG Technician, IUB IRF
>
>
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>
>
>
>
> --
>
> Makoto Miyakoshi
> Swartz Center for Computational Neuroscience
> Institute for Neural Computation, University of California San Diego
>
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-- 
Makoto Miyakoshi
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego
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