The phrase “Attention à la marche en descendant du train” echoed through the platform as I grabbed my bag and stepped from the train. Ready to explore the beautiful, world-renowned city of Paris, I proudly raised my head and firmly stepped forward with intent. However, I couldn’t help but ask two very important questions. Where am I, and where can I find the delicious food?
Thoughts of savory crepes, warm baguettes, and chocolate-filled croissants distracted me during my voyage, somehow causing me to step off at the wrong station. I stopped and unfolded my pocket metro map, promptly realizing my disorientation landed me somewhere in the center of the complex Parisian underground maze. I wondered how I lost track of time so fast by simply staring through the window of the train. I was practically blinded by my quest for French desserts, but just about ready to go back home to Cité Universitaire.
In the two subsequent weeks that zoomed by, I paid much closer attention to my surroundings. Though I indulged in wonderful Parisian delicacies, and adapted to the city life, I also started perceiving my environment with more respect for sensory information. Doing so kept me from getting lost and allowed me to focus more. This habit greatly coincided with our neurosciences classes that started focusing on the brains interaction with bodily functions like motion, vision, and hearing.
With my senses primed, I took note of Paris’ every little detail, and learned how to travel as an expert tourist and passenger, exploring what Paris has to offer both above and below ground.
Above ground, I saw beautiful gardens and remarkable architecture. I experienced the jostling waves of the Seine while on a boat tour, and got dizzy staring up at the Eifel tower. I also heard countless sirens, and noticed pedestrians don’t care about traffic lights.
Below ground, I listed to musicians perform inside metro hallways and I watched entertainers dance in moving trains, all accompanied by the hum of bustling crowds and the sound of screeching metal pressing together to slow down trains. In this wild sub-terrain, I also noticed that closing automatic doors don’t care about rushing passengers, and warnings of “attention à la marche” exist for a reason.
Some things however literally caught my eye. As I stared outside of a train window one day, I caught a short glimpse of a nearby pole while we zoomed by. This was strange considering how slow and peaceful the buildings and scenery in the background passed by. I looked more closely, noticing the tracks below the train and the platform steps to the side of the train, moved incredibly fast while the landscape a few hundred meters out barely seemed to move at all. At this speed, the steps were actually dangerous!
I realized my mind must be playing tricks on me since the train was moving at the same speed compared to the ground, shared by both the tracks and the landscape. A few days later, I noticed this effect again at the roundabout circling the Colonne de Juillet at the Place de la Bastille (a great monument, see link 1)where cars near me seemed to move faster than those furthest away. I wanted to know more so, like any student investigator, I decided to search and see if neuroscience could provide and answer to this puzzling question.
The above process, called motion parallax. is a visual cue that signals depth where objects that are closer appear as if they move further across the visual field, while those that are farther away move less (Kim et al., 2015)
A recent study by Kim et al. (2015) looks at the neuroscience behind this cue and explores a specific area of the brain called the middle temporal (MT) area that could be responsible for the perception of depth from motion parallax. Although another study by Nadler et al. (2008) found that this part of the brain carries information about depth, it was not necessarily clear what kind of information was transmitted. The data from Kim et al. (2015) fill this gap by hypothesizing that the MT specifically carries information about the perception of depth.
The experimenters take two male monkeys, trained to respond to dots they see on a screen, and set them up with recording devices for their eyes. Researchers then fix the monkeys with electrodes in their MT areas, located by the use of MRI imaging. Finally, testing involves placing monkeys on a motion platform where the monkeys’ eye movements and brain signals provide computer-collected data.
The results from Kim et al. (2015) show that the MT will actually predict a monkey’s decision regarding its perception about depth. This paper gives a lot of support to the field of neuroscience because it reveals more information about the MT with sound methods.
The study finds that the MT further contributes to the perception of depth but it does not show that the area is entirely responsible perception. Although very recent, this article comprises one train-cart in a long train of studies on the MT. It lacks particular novelty and demonstrates that there is still much to learn about vision and the brain. Research in animals should definitely continue, but it would find it very interesting blend more than one study to find bigger applications. For example, Nawrot and Stroyan (2012) show that humans require about 30ms to detect depth from motion parallax. What if scientists could use deep brain stimulation (DBS) in the MT to provide brain enhancement for car accident prevention? I am incredibly excited for this research to continue.
Through my city travels, I hope to walk down the beautiful streets of Paris and remember that neuroscience allows me to navigate safely and effectively. My time in Paris is showing me that even though life has twists and turns, senses are needed to make “sense” of them (pun intended). I hope one day, a breakthrough in research and technology will allow us to better watch our steps!
Kim HR, Angelaki DE, DeAngelis GC (2015) A functional link between MT neurons and depth perception based on motion parallax. J Neurosci 35:2766–2777 Available at: http://www.ncbi.nlm.nih.gov/pubmed/25673864 [Accessed June 8, 2015].
Nadler JW, Angelaki DE, DeAngelis GC (2008) A neural representation of depth from motion parallax in macaque visual cortex. Nature 452:642–645 Available at: http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=2422877&tool=pmcentrez&rendertype=abstract [Accessed June 8, 2015].
Nawrot M, Stroyan K (2012) Integration time for the perception of depth from motion parallax. Vision Res 59:64–71 Available at: http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=3349336&tool=pmcentrez&rendertype=abstract [Accessed June 8, 2015].