Timing issues - Serial Response Box

[Paul Groot]

Hi Valerio,

You best option with eprime is to use the serial button box on a *NATIVE*
RS232 port. I.e., keep away from USB to RS232 converters if timing accuracy
is critical. RS232 ports use a baud rate to specify throughput (in this
case configurable to 9600 or 19k2, if I remember correctly). Specific to
the serial response box is the so called CPS-setting, which defines the
number of bytes are send to the computer per second. This defines the
resolution data flow (i.e. refreshes per second) and is 800 by default.
Native RS232 ports are interrupt driven, so latencies should be minimal.
Although PST doesn't give any details about this, I think that EPrime has
some built-in intelligence to increase the accuracy of the reported RT's.
(The data stream has a fixed CPS-rate, so it is possible to fix for small
'hiccups' in the interrupt handling.) Such a mechanism could also minimize
RT-variance when using a USB converter.

If USB is your only option, you should have a look at the following page:
http://www.pstnet.com/support/kb.asp?TopicID=1835

Also, I personally think that the 1ms requirements are overrated for almost
all experiments...

cheers
Paul


On 30 July 2013 13:42, Vaaal <valerio.biscione at gmail.com> wrote:

> Hello to everyone,
>
> I am struggling to get accurate reaction time without starting put my hand
> in engineering stuff, since I don't have the required knowledge to do like
> that.
> I would like to buy a Serial Response Box, but the technical details in
> the page are really not enough. I am particularly worried about the serial
> port connection.
> I know that the pooling rate of the usb port is normally 125 hz, that is 8
> milliseconds. I am able to overclock that value in order to have a pooling
> rate of 1000Hz, which is 1 milliseconds, which is quite fine. But, I am
> still not sure of the accuracy of my measurement, just because using a
> normal keyboard can add some latency in the process of transmitting
> information.  This is why I am willing to buy a professional device.
>
> The problem is that I don't know the technical specification of a serial
> port. There is anything similar to a pooling rate of a serial port? If it
> is so, how much it is, and there is any way to overclock it? Basically how
> much accurate is the response box?
>
> The other option is to use DirectIN High Speed Button-Box here
> http://www.empirisoft.com/directin.aspx, which actually uses a USB port
> that I can overclock. BUT since I use E-Prime I would like to buy a piece
> of hardware that is designed to be used with E-Prime, just to avoid
> unnecessary headache in the future.
>
> So generally my question is: what are the limit and the advantages of
> having a serial port? Do you think that the Serial Response Box is really 1
> ms accurate? Do you use any other equipment?
>
> Thank you for your reply,
> Valerio
>
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