When I was little I had no depth perception.  Because one of my eyes was farsighted and the other nearsighted, almost nothing I looked at could be in focus in both.  My brain, unable to reconcile the difference, began to ignore the signals from my left eye.  If not for a pair of glasses and months of vision therapy, I would still see the world as though it were a photograph.

That ostensibly doesn’t matter for a large percentage of my time nowadays, which is spent staring at a wafer-thin computer screen with simulated shadows beneath the application windows.  Yet I’m convinced that eye strain isn’t the only consequence of whittling away the hours focusing on a backlit rectangle less than an arm’s length from my face.  Screen time comes at the cost of interaction with the physical world — at the price of sensory experience and associated benefits to learning.

Let’s start with vision.  Your brain uses many cues to determine how objects relate to each other.  But being able to perceive depth through binocular vision — the sense of depth that results from seeing an object from a different angle in each eye — is essential for anything from basketball to gardening.  We often take the ability for granted; something as simple as going down an escalator can be a frightening ordeal if you can’t judge where the steps start to drop.  (Believe me, I know.)

For children in kindergarten and early elementary school, those who performed better on tests for depth perception and visual-motor skills also did better in reading, spelling, writing and mathematics.  This suggests there is a connection between perceiving and interacting with the 3D world and understanding more abstract concepts.  Since depth perception — and related skills such as eye-hand coordination — are to an extent learned, then we may be introducing consequences down the road if we hamper the development of these skills by replacing our children’s Legos with iPads.

Screen time does more than eliminate binocular vision.  It removes taste and also smell, that underappreciated harbinger of memory and invisible mode of interpersonal communication.  Significantly, it eliminates haptic information, what you learn from touching something.  Especially given that the human brain is wired for visual and tactile processing, could we be doing ourselves a disservice by “flattening” formerly 3D activities?

In a recent talk at the Stanford School of Medicine, Dr. Temple Grandin suggested schools reimplement workshop classes with hands-on activities like woodworking or sewing.  For many people, the act of using one’s hands to produce a physical result is a more effective way to learn than traditional lectures.  In fact, researchers are investigating tangible user interfaces that allow users to navigate and analyze digital data through tactile media such as sand, blocks or liquid.  There is even evidence that reading paper books has benefits over reading e-books: The layout and structure of bound books helps readers generate mental maps of their content, while the act of physically turning pages contributes to a reader’s sense that he or she is in control.

Screen time may be even more prevalent outside the classroom.  Americans buy fewer toys and board games for their children as apps and videogames consume more of the young generation’s attention.  Computer chess is familiar to many of us, and recently I learned there is a DVD game version of Candyland.  I won’t even get started on television and movies; despite what advertisers may claim, 3D films are no substitute for reality.

Don’t get me wrong — the digital revolution and the accompanying proliferation of screens has brought more information to more people’s fingertips than at any point in history.  Nonetheless, we shouldn’t forget that even computers have hardware, that we have five senses with which to explore the world beyond our desks.  Requiring less screen time for work and reducing our consumption of on-screen entertainment could supplement efforts to encourage children and adults to exercise or seek in-person social interaction, both key to physical and emotional health.

While we can explore a wealth of material from our computers, we should seriously reconsider how much time we spend on them at home, in the office and on the go for work, for correspondence and for play.  We don’t have to give up our screens entirely, but we should make sure the time we spend on them isn’t just for lack of something better to do.  After all, we each have more than one eye for a reason.  The world was not meant to be flat.

Contact Mindy Perkins at mindylp ‘at’ stanford.edu