Conventional wisdom would suggest our senses work independently of each other — that the way we feel something moving and the way we see it are completely different. But according to a new essay published in PLOS Biology, this line of reasoning is wrong. The essay suggests that the brain uses the same regions to comprehend the speed and direction an object is moving in, regardless of whether it’s being perceived through sight or touch.

"Sight is obviously different physically from touch, but in both cases the nervous system has to make sense of information that is changing in space and time." said Dr. Christopher Pack, associate professor in the Department of Neurology and Neuroscience at McGill University, in a press release. "There are many ways to do this, but evolution is conservative and so the brain may prefer to reuse strategies that work particularly well."

Both our skin and eyes contain receptors that allow us to feel and see, and as both track movement, the receptors process the movement sequentially. (Imagine a web page loading on a dial-up modem; it typically loads from the top down.) As this occurs, our nervous system takes this information and sends it to the separate parts of the brain where touch and sight are processed. It’s here that neurons respond to only a snippet of the object that we see or feel moving, but that’s really all we need. Part of this quick response is due to the fact that there are neurons designated to respond to only specific directions of movement — if an object moves left, certain neurons will react, while others react when the object moves right.

The researchers say that for us to process an object in motion, our nervous system must send the information processed in the aforementioned regions of the brain to two other regions responsible for processing motion: the middle-temporal area, located at the bottom of the brain, processes movement caught by sight, while Brodmann's area 1, in the top-middle part of the brain, processes touched movement. Both of these areas use the individual signals from their respective sensory neurons to create a complete picture of an object moving.

Pack, along with his colleague Dr. Sliman Bensmaia, associate professor in the Department of Organismal Biology and Anatomy at the University of Chicago, knew about these brain processes from previous experiments involving stimuli arranged in a plaid, crisscrossed pattern. In these experiments, both humans and primates underwent brain scans while they watched the pattern moved across a screen. They also felt the pattern etched onto a plate with their fingers.

Bensmaia and Pack said this process for tracking motion developed because both sight and touch work simultaneously in the real world. For example, when you reach for something falling, you usually see it and (hope to) feel it at the same time, instead of feeling it first and then seeing it after. They said another possible reason the two processes work in concert is because they both evolved from a common receptor type. Nevertheless, further research will help the scientists gain a better understanding of how we perceive the world and interpret information using our senses.

Source: Bensmaia S, Pack C. Seeing and Feeling Motion: Canonical Computations in Vision and Touch. PLOS Biology. 2015.