simultaneous response

[David McFarlane]

Egbert,

>subjects have to respond to a target by simultaneously pressing two
>buttons.

Before I think much further on this, I need to know whether by 
"button" you mean a button as in the PST Serial Response Box, or a 
key press from the keyboard.  It might make a difference.

I am almost certain that it is completely impossible for E-Prime to 
recognize simultaneous key presses.  Apparently, E-Prime reports 
actual keyboard scan codes rather than the processed key combination, 
e.g., entering the keyboard ^ character shows up as separate presses 
of the {SHIFT} and 6 keys instead of just {^}.  I discovered this 
awhile back, I will separately send you a little test EP1 program I 
made that just shows the raw values of keys and buttons pressed.

Things might work differently with the SRBox or other "button" devices.

Once again, using the normal EP input mask mechanism with an SRBox, 
you may get only the first of two "simultaneous" button 
presses.  However, as I recall, the SRBox really does transmit an 
8-bit code that reveals all buttons pressed at any moment (you can 
demonstrate this to yourself by inspecting the input stream from the 
SRBox using any primitive terminal emulation program, such as 
Terminal Plus!, www.geocities.com/terminalplus).  So, with a bit of 
script that directly reads the serial input you *might* be able to 
get simultaneous SRBox button presses, but I leave it to someone else 
to tell you how to do that.

Finally, with a button box that has each button directly wired to its 
own bit of an I/O port (e.g., an old parallel printer port, or an 
add-in digital I/O card), you can use an E-Prime "Port" device to 
directly read all the buttons in parallel.  That would likely also 
involve some script.  This is the most elegant solution, but it does 
require some extra hardware finesse.

-- David


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