Perception can be measured

A team from the CITEC Cluster of Excellence has jointly developed a process with which visual perception can be recorded very precisely. Monitors have always been a problem: Computer screens with high resolution are very expensive. Conventional monitors, on the other hand, cannot be timed precisely enough for many measurements. With a twist, the team has now succeeded in using gaming monitors that are significantly cheaper - and that work very precisely by reprogramming the software.

A letter lights up on the screen. When does a person actually perceive it? How long does the symbol have to appear for this? This is sometimes not so clear - because it is difficult to measure the stimulus threshold over time depending on the representation. "Many conventional monitors only send images at a certain frequency," says Dr. Christian Poth from the Neurocognitive Psychology Research Group, which is involved in CITEC.

Letters then always appear on the screen for certain times - for a 100 Hz screen, for example, for 10 or 20 milliseconds. “In this way, we can only measure very imprecisely how quickly someone perceives something,” says Poth. Certain mathematical functions can be used to calculate approximate values ​​for such cases, but these require a number of theoretical assumptions that cannot be directly checked.

There are high-speed projectors that allow a much finer representation in terms of time - but these have so far been extremely expensive. An interdisciplinary team of psychologists and computer scientists at CITEC has now succeeded in using conventional gaming monitors in such a way that image stimuli can be displayed with high temporal resolution.

For this purpose, the scientists used an LCD monitor that receives images from the graphics card at a flexible time. “We are now able to display images at a variable frequency,” says Poth. The screen used has a maximum frequency of 144 Hz, so that an image can be displayed for a minimum of seven milliseconds. "Everything that is displayed for longer than seven milliseconds can now be fine-tuned."

For example, it is possible to display an image for exactly 7.3 or 7.9 milliseconds. "Completely new gaming monitors even allow an even smaller process," says Poth. "There even a minimum presentation time of 4 milliseconds is possible".
The idea for the project arose in a joint working group headed by Professor Dr. Mario Botsch (computer graphics and geometry processing) and Professor Dr. Werner Schneider (Neuro-Cognitive Psychology) is headed. "We have already implemented a number of cooperation projects together," says psychologist Poth. "At one of our meetings we talked about our problem with the monitors - and that's how the idea came about."

It took the group around a year to come up with a solution, said Poth. “It's actually very simple,” he says: It only required a small change in the software. The code reduces the frequency in which the graphics card transmits information to the monitor by a certain value. As a result, a new image appears exactly every 7.4 milliseconds instead of every seven milliseconds. "In this way we can now measure the perception and the threshold of consciousness very precisely," says Poth.
But why is it really important to know these values ​​of perception so precisely? "Our working group is first of all about basic research," says Poth: "For example, we are concerned with the question of how people open up the outside world for their actions through their perception."

Exact measurements of visual perception play a role for many disciplines, says the scientist: “It is about very elementary parameters such as perception speed, which are also important in neuropsychology.” Specifically, for example, when measuring failed brain functions: “This is for Relevant to people who have had a stroke or who suffer from dementia. "

In the long term, the new measurement method may also have implications for better adapting cognitive interaction technology. “The more precisely you can measure a person's basic perceptual abilities, the better you can adapt technical systems to them,” says Rebecca Förster from the research team. This means that technical devices can also be used by people with impaired visual perception.

A research article about the project has been published in the journal “Behavior Research Methods”. For the project, the researchers from the Cluster of Excellence CITEC worked with the computer science professor Dr. Ulrich Schwanecke from the Rhein-Main University of Applied Sciences.

Original publication:
Christian H. Poth, Rebecca M. Foerster, Christian Behler, Ulrich Schwanecke, Werner X. Schneider, Mario Botsch (2018). Ultra-high temporal resolution of visual presentation using gaming monitors and G-Sync. Behavior Research Methods.

Dr. Christian H. Poth, Bielefeld University
Cluster of Excellence Cognitive Interaction Technology (CITEC)
Phone: 0521 106-4505
Email: [email protected]

Author of the article: Maria Berentzen