refresh rate USB

[Michiel Spape]

Hi,
Whilst that is true, he might just have meant the EEG (and so on) sampling rate. Obviously, indeed, "windows" can handle sub-millisecond accuracy just fine (provided, provided, provided), but the type of port (USB/PS2/Parallel/etc) and device make much more of a difference. If I remember correctly, PST had something to say on the matter, long ago, and advised always to use USB keyboards at least (rather than PS/2 keyboards). Have a look here:
http://www.pstnet.com/eprimedevice.cfm
... I did, just now, and it turns out you might well be right in a way. Have a look at timing characteristics and read through the article.

Personally, I have a pragmatic attitude towards these things. It may well be, for instance, that the PST SRBOX has superb timing characteristics, but have you ever tried pressing their buttons? I know, for a psychologist - mind and timing is everything - it is hard to remember, but those buttons take quite a bit of force to press. Imagine, for one, that it *must* take longer to press these buttons (they seem like soviet pieces of tech to me - i tend to like the look, but...), as opposed to say, a touchpad (which hardly needs any press), and that motor noise may well influence your experiments. For instance, if I do a finger-tapping test (press the space bar as often as you can within 10 seconds), I get average values of about 55 - pretty much exactly the norm from clinical literature. Now, I do the same with a mac keyboard (those white ones with buttons of about 3 mm above the rest of the keyboard, really light press required) - and suddenly i get values ranging from 65 to a massive 80. I say this difference (181 ms/press vs ~138 ms/press) is pretty massive (more than my average effect). So, my attitude is then: get good equipment, but don't stare yourself blind on the numbers.

Best,
Mich


________________________________________
From: e-prime at googlegroups.com [e-prime at googlegroups.com] On Behalf Of Peter Quain [pquain at une.edu.au]
Sent: 07 July 2011 22:35
To: e-prime at googlegroups.com
Subject: Re: refresh rate USB

I think USB polling rate and USB data transfer rate are 2 different things

At 03:20 AM 8/07/2011, you wrote:
>Hi together,
>
>I plan an experiment in which Reaction Times for two conditions will
>be compared and not too much of a difference is expected. Let's say 15
>ms. I am wondering if an USB keyboard is the appropriate choice for
>such an experiment. I've heard that USB usually has a refresh rate of
>120 Hz, meaning that responses are checked every 8 ms. That's a lot of
>noise added to the real reaction times.
>
>On the other hand, EEG data and other stuff CAN be transferred much
>faster than 120 Hz via USB cable. THe question is, whether Windows (or
>E-Prime) can handle this.
>
>What is your experience here?
>
>Thanks a lot and so long,
>Tobias
>
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