The hand hits a glass, it falls over, and the milk spills over the kitchen table. The observer is immediately sure that it was the clumsy hand that caused this little mishap. Until now, researchers have disagreed whether this causality judgment depends on higher brain functions such as cognitive reasoning, or whether it emerges at an earlier stage during perception, similar to the evaluation of size, color, or motion of an object. An international team of researchers including Martin Rolfs at the Bernstein Center Berlin, Michael Dambacher at the University of Konstanz, and professor Patrick Cavanagh at the University Paris Descartes has now found the answer to this question: Rapid causality judgments are made at the level of visual perception.
In their study, participants watched a repeating video clip in which one disc moved towards another, and the latter disc started to move after being touched by the first. Instead of seeing one disc stopping and the next disc starting to move, both events are seen as one continuous action where the first disc launches the second – similar to colliding billiard balls. Rolfs and his colleagues have now demonstrated that after the repeated observation of these collision scenes, an adaption process occurs: Subsequent interactions involving two discs are less likely to be seen as causal. Similar adaptation aftereffects are known after the repeated perception of basic properties such as color: After looking at an orange light for a short while, you will see a light blue spot when looking at a white wall. These visual aftereffects suggest a habituation of the populations of neurons in those parts of the brain that analyze these specific qualities.
The main result of the study: The adaptation to collision events was specific to the location where the collisions had been seen. Moreover, when the eyes moved, these adapted locations moved with the eyes, just as the color afterimage shifts as you move the eyes around. According to the researchers, these results show that the neuronal structures involved in the judgment of causality must be part of the early visual process as higher level cognitive processes do not show this specificity to eye position. Main investigator Rolfs: “The result moves functions that have previously been thought of as achievements of cognitive deduction into the realm of basic perception, with implications for fields as diverse as philosophy, psychology, and robotics.”
The Bernstein Center Berlin is part of the National Bernstein Network Computational Neuroscience in Germany. With this funding initiative, the German Federal Ministry of Education and Research (BMBF) supports the new discipline of Computational Neuroscience since 2004 with over 170 Mio. €. The network is named after the German physiologist Julius Bernstein (1835-1017).
Dr. Martin Rolfs
Bernstein Zentrum Berlin und
Humboldt-Universität zu Berlin
Philippstr. 13, Haus 6
Tel: +49 (0)30 2093-6775
Rolfs, M., Dambacher, M., Cavanagh, P. (2013): „Visual adaption of the perception of causality“. Current Biology: Jan 10, 2013.