visual dot probe experiment: position of words & pictures

[Nate Vack]

On Wed, Jun 1, 2011 at 4:42 PM, Paul Groot <pfc.groot at gmail.com> wrote:
> Hi Nate,
>
> I really don't think that is true. Flat screens have the same kind of
> serial refresh mechanism for updating pixels. It's easy to check with
> a photo-sensor and oscilloscope. Or if you don't have access to that:
> just switch of the onset synchronization in a rapid alternating
> black-white sequence:
> trial sequence with 3 empty text objects (A,B,C):
>
> A=duration=100ms, prerelease=100, background=black, onset synced
> B=duration=[S]ms, prerelease=[S], background=white, onset NOT synced
> C=duration=0ms, prerelease=0,background=black,onset synced
>
> Just run those trials in a trial list (N=20) and try values for [S]
> which are smaller than the refresh interval.  You can also put the
> trial list in a block list with sequential range for the S attribute.
>
> You will see the same kind of horizontal distortions as with CRT
> monitors, caused by fragmented screen updates. That would not be
> possible with a fast bit-blitting pipeline.

Huh! Neat. Didn't expect that. Thanks!

On this same topic, however: it's been my experience that different
"identical" monitors are oftentimes not particularly identical, even
when they come in the same lot -- I used to run computer labs, and the
images produced on a shipment of Dells varied quite a lot.

So if you really care about the timings of visual stimuli, you'll want
to develop some kind of validation for your actual hardware.

Cheers,
-Nate

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