Second-year Psychology students participating in the University Honours College complete a Research Seminar, during which they write a popular science article about their second-year research internship. Voted as one of the best articles of this year was written by Airi Yamada. Mindwise publishes a modified version of her article.
It is not uncommon to encounter terms such as “right-brained” and “left-brained” in recent media. It has almost become a part of popular science to believe that a “right-brained” person is creative and intuitive while a “left-brained” person is logical and analytical. Although some may consider this brain asymmetry to be a myth, there does seem to be some truth in what these differences present.
There is a marked difference between how the left and right hemispheres process information during visual perception
The popular belief primarily focuses on the contrasting ways in which the two hemispheres “think”. One example is the difference in general perspective – the right hemisphere takes on a holistic view of things (the “bigger picture”), whereas the left hemisphere analyzes matters in more detail. However, does this difference also apply to how the two hemispheres see things? The answer seems to be…yes. There is a marked difference between how the left and right hemispheres process information during visual perception, namely when distinguishing certain aspects of visual stimuli.
These ‘visual stimuli’ can range from scenery to objects, as long as they contain separate features. Researcher David Navon once posed a thought-provoking question: “Do we see the forest before the trees?” (Navon, 1977). In this context, the forest is the holistic view while the trees (that make up the forest) are a much narrower and a more focused component of the whole scene as if looking through a magnifying glass or a filtered lens. In the domain of cognitive psychology, this distinction between the “whole” and the “part” is referred to as the global and local levels of stimuli. It was precisely this global versus local phenomenon that triggered Navon’s interest in which feature was detected first by the human brain. He made use of a self-created stimulus known as a hierarchical letter – a large letter composed of a group of smaller letters – to put his speculations to test. Shortly after this experiment, differences in processing global and local stimuli became apparent between the left and right hemispheres; the left hemisphere was better at processing local aspects while the right hemisphere was more adept at processing global aspects of stimuli. This hemispherical difference in visual processing came to be known as the lateralization effect, and Navon’s hierarchical letters soon became standard tools for testing this concept in the laboratory.
Now that we know that lateralization exists, the question is how can it actually be detected in the brain? For instance, if an object is presented in the left visual field, it will be processed through the left eye and the majority of the perceived stimulus will be transferred to the opposite hemisphere via an area called the optic chiasm. The “opposite hemisphere” in this case is the right hemisphere, receiving signals from the left visual field. Similarly, the information of an object processed in the right visual field through the right eye will be transferred over to the left hemisphere of the brain. This mechanism is now widely embraced by researchers, and has been translated to an experimental paradigm used to test lateralization of visual perception.
Making use of Navon’s hierarchical letters as well as testing an additional stimuli with hierarchical figures, we aimed to reproduce the lateralization effect with a small student sample from the University of Groningen. We hypothesized that the lateralization effect would be present, but wanted to investigate if there were any significant differences between the strength of the effect among hierarchical letters and figures. The participants’ tasks were simple yet strenuous; they were required to pay close attention to hierarchical stimuli presented on either their left or right visual field and give an immediate response to identify the local or the global aspect.
The results were promising – the lateralization effect was indeed present for both hierarchical letters and figures, but the effect was stronger for letters. This can lead to a few implications. First of all, it could have been that the hierarchical figure stimuli were more complex and difficult to perceive than the letter stimuli, leading both hemispheres to “help each other out” during the response tasks. Second, we hypothesize that since the left hemisphere is also associated with a specialization in language processing, this could have altered the strength of lateralization between the stimulus types. In future research, the roles of the two hemispheres have to be further specified – namely whether both hemispheres are capable of assisting each other, or whether each hemisphere only responds to certain stimulus characteristics.
we may conclude that differences in processing exist in the left and right hemispheres both in the way we think and the way we see things
Regardless, given previous research findings and the supporting results from our experiment, we may conclude that differences in processing exist in the left and right hemispheres both in the way we think and the way we see things. Perhaps, it could be that a left-brained, logical person tends to focus more on specific aspects while a right-brained, liberal person would prefer looking at the bigger, broader picture.