Background

At the Black Box ToolKit we specialize in helping you achieve millisecond accurate presentation, synchronization, and response timing in your computer-based psychology experiments. Here are just a few of the things that can stop you doing just that!


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Input lag on TFT monitors and data projectors in psychology experiments


Input lag is the time it takes an image to appear on screen versus the time when the signal was sent by the computer into the monitor cable from your psychology experiment.

A traditional CRT monitor which if driven at 200Hz can display an image in 5 milliseconds, or one refresh. Typical TFT monitors and data projectors today might take over 10 times as long due to input lag. Input lag is caused by the quality and processing speed of the displays electronics. This can make presentation timing and synchronization with other equipment a real issue.

What's more input lag varies between makes and models of display as the video below clearly illustrates. If you replaced one TFT monitor for the other on the same PC your experiment generator would continue to present visual stimuli as normal and it would record that it had done so at the time you requested. Unfortunately there is no way for your PC or experiment generator to know about the input lag on a given monitor. It only knows when it requested the image be shown and not when it physically appeared in the real world!

In reality as you can see input lag means that you are not presenting visual stimuli at the same time at all. Input lag also means that the image offset is shifted back by the same amount as the lag. If you are synchronising with other equipment such as EEG, MRI, eye-trackers etc. the image will drift still further out of sync. It will also mean that reaction times are likely to be measured as longer and more variable than they are in reality.

Input lag can mean that you are not running the experiment you thought you were and that your results might be questionable.

Read more about input lag on TFT Central

Input lag is the time it takes for a image to actually be displayed on a TFT panel
(this is not the same are panel response time). Here are two different panels
connected to the same graphics card via a splitter to illustrate the effect.

Input lag on data projectors can be even more problematic as the table below illustrates. When image processing is left at the default settings on many projectors, input lag can more than triple as demonstrated with the Acer H9500 (shown in bold).

Image processing off Image processing off CFI/motion smoothing on
Sanyo Z200 16 ms Mitsubishi HC7800 33 ms    Panasonic PT-AE7000U 66 ms
Espon 8350 18.5 ms Acer H9500 41 ms Mitsubishi HC7800 83 ms
Sony HW10 10-20 ms Panasonic PT-AE7000U 41 ms Epson 5010 141 ms
Sony HW20 16-32 ms JVC RS1 50 ms Acer H9500 150 ms
Infocus X10 25 ms BenQ W5000 50 ms BenQ W7000 150 ms
Panasonic AR100U 25 ms BenQ W7000 50 ms
Optoma HD800x 30 ms JVC RS40 70 ms
Panasonic AE300U 30 ms Espon 5010 81.4 ms
Sanyo Z3000 30 ms Espon 3010 100 ms
Panasonic AE4000 33 ms


Input lag measures for commonly available data projectors
(timing data collated from http://www.avsforum.com)

About company


The Black Box Toolkit Ltd was founded in 2003 by a team of psychologists, software experts and electronic engineers.


Dedicated to improving the millisecond timing accuracy and experimental rigor of researchers in the behavioral and brain sciences.

We provide hardware, software and consultancy solutions across a wide range of fields to make this a reality. Print flyer

Get in Touch

  • Phone:
    +44 (0)114 3030056
  • Email:
    info@blackboxtoolkit.com
  • Address:
    The Black Box ToolKit Ltd,
    PO Box 3802, Sheffield,
    S25 9AG, UK