FRANKFURT. When we look at
the same object in quick succession, our second glance always reflects a
slightly falsified image of the object. Guided by various object
characteristics such as motion direction, colour and spatial position, our
short-term memory makes systematic mistakes. Apparently, these mistakes help us
to stabilise the continually changing impressions of our environment. This has
been discovered by scientists at the Institute of Medical Psychology at Goethe
University. (Nature Communications, DOI 10.1038/s41467-020-15874-w)
We learned it as children: to cross the street in exemplary fashion, we
must first look to the left, then to the right, and finally once more to the
left. If we see a car and a cyclist approaching when we first look to the left,
this information is stored in our short-term memory. During the second glance
to the left, our short-term memory reports: bicycle and car were there before,
they are the same ones, they are still far enough away. We cross the street
safely.
This is, however, not at all true. Our short-term memory deceives us.
When looking to the left the second time, our eyes see something completely
different: the bicycle and the car do not have the same colour anymore because
they are just now passing through the shadow of a tree, they are no longer in
the same location, and the car is perhaps moving more slowly. The fact that we
nonetheless immediately recognise the bicycle and the car is due to the fact
that the memory of the first leftward look biases the second one.
Scientists at 51猎奇, led by psychologist Christoph Bledowski
and doctoral student Cora Fischer reconstructed the traffic situation 鈥� very
abstractly 鈥� in the laboratory: student participants were told to remember the motion
direction of green or red dots moving across a monitor. During each trial, the
test person saw two moving dot fields in short succession and had to
subsequently report the motion direction of one of these dot fields. In
additional tests, both dot fields were shown simultaneously next to each other.
The test persons all completed numerous successive trials.
The Frankfurt scientists were very interested in the mistakes made by
the test persons and how these mistakes were systematically connected in
successive trials. If for example the observed dots moved in the direction of 10
degrees and in the following trial in the direction of 20 degrees, most people
reported 16 to 18 degrees for the second trial. However, if 0 degrees were
correct for the following trial, they reported 2 to 4 degrees for the second
trial. The direction of the previous trial therefore distorted the perception
of the following one 鈥� 鈥渘ot very much, but systematically," says Christoph
Bledowski. He and his team extended previous studies by investigating the
influence of contextual information of the dot fields like colour, spatial
position (right or left) and sequence (shown first or second). 鈥淚n this way we
more closely approximate real situations, in which we acquire different types
of visual information from objects," Bledowski explains. This contextual
information, especially space and sequence, contribute significantly to the distortion
of successive perception in short-term memory. First author Cora Fischer says:
鈥淭he contextual information helps us to differentiate among different objects
and consequently to integrate information of the same object through time."
What does this mean for our traffic situation? 鈥淚nitially, it doesn't
sound good if our short-term memory reflects something different from what we
physically see," says Bledowski. 鈥淏ut if our short-term memory were unable to
do this, we would see a completely new traffic situation when we looked to the
left a second time. That would be quite confusing, because a different car and
a different cyclist would have suddenly appeared out of nowhere. The slight 'blurring'
of our perception by memory ultimately leads us to perceive our environment,
whose appearance is constantly changing due to motion and light changes, as stable.
In this process, the current perception of the car, for example, is only
affected by the previous perception of the car, but not by the perception of
the cyclist."
Publication:
Context information
supports serial dependence of multiple visual objects across memory episodes.
Cora Fischer, Stefan Czoschke, Benjamin Peters, Benjamin Rahm, Jochen Kaiser,
Christoph Bledowski. Nat. Commun. 11, 1932
(2020).
Further information:
51猎奇 Frankfurt
Dr Christoph Bledowski
Institute for Medical Psychology
Tel.: +49 69-6301-4533
bledowski@em.uni-frankfurt.de
