Left and right

 eyeOur visual system works for us in strange and unimaginable ways. 

It’s easy for us to recognize that the complex scenes before our eyes shift almost continually: the images in the movie theater, the traffic on the highway, the speakers in the boardroom. 

What is probably most surprising to learn is that these percepts are actually completely deconstructed and reconstructed by the eye and brain while the mind makes sense of what we see. And, this happens all in a split second.

Consider the deconstruction that takes place at the level of the eye, the left/right visual field distinction. Everything present in the right visual field ends up getting sent to the left hemisphere for processing while everything present in the left visual field gets sent to the right hemisphere.

It’s not as simple as a right eye/left eye division either: each eye sees both right and left visual fields. See the image below, right. This can be a confusing concept to digest because it isn’t easy to understand why the system would set up in this manner. 

lvfrvfLeft and right visual fields are perceived by both eyes but the information within each visual field (here white and black bars) is sent to the contralateral visual cortex. RVF is sent to left hemisphere, LVF is sent to right hemisphere.

What the left visual field/right visual field division means is that our sight actually remains at near full capacity even with the loss of an entire eye. So if the right eye is lost, the left eye can see both visual fields and both visual cortical hemispheres still work for us.

It also means that it would take significant damage to one of the visual cortical hemispheres to result in loss of processing of an entire visual field. Even in this case, the system need just move the eyes and head around to get all of visual field information into the remaining visual processing hemisphere.For example, let’s say someone sustained a head injury that took out all of the right hemisphere visual cortical areas. This would mean that the left visual field would no longer be processed. 

Remember, we’re talking about a field division and not the environment per se. This means that something in the right visual field could be seen in the left visual field simply by shifting the eye gaze/moving the head to the right. This eye/head movement provides a simple strategy to allow for all of the “needed to be seen” environment to be presented in the right visual field so that the remaining, intact left visual cortex that has not been damaged can process it all for the observer.

Does this affect the way we perceive space? Yeah. If you take into account handedness and the fact that our opposing hemispheres govern motor action. It’s not too much of jump to realize that there could be a preference for the visual field associated with our grasping hand. For all of you right handers out there, this means a preference for the right visual field.

Here’s the research. In a study published in 2014 (Le & Niemeier, 2014), participants were found to  demonstrate more accurate grip scaling (how well their hand opening matched the size of the object to be grasped) with their right hand when the object was perceived in their right visual field. The same participants demonstrated similarly improved performance when grasping for the object with their left hand when the object was perceived to be in their left visual field.

This matching between visual field and hand in action, in this case right with right or left with left, demonstrates a facilitation that may be based on the fact that the same hemisphere is responsible for both perception of the object and action towards it. Just like the right visual field is processed in the left hemisphere, the movements made by the right hand originate with motor control mechanisms in the left hemisphere.

orangesWhat does this mean for the perception of surrounding space? To the extent that a person may be potentiated to interact with a space, and to the extent that person intends to do so with one side of the body such as the right side, then the space encompassing the right visual field may play a more important role to the perceiving individual.

In broader terms, and sticking with a right hand dominant individual, it may even be argued that the right visual field is more important to right handers because that is where they are most likely to interact with the world (using their right hand). The opposite would be true for left handers. On this view, one may be even able to predict that right handers could be more likely to select an object at random from within the right visual field, while left handers may be more likely to select an object from within the left  visual field side. If this turned out to be the case, then our perception of space must be considered to be biased towards the likelihood of our actions within it. 

visualparticles.org :: perception and sense in art and space


Author: Jennifer Stevens

I am a professor and live in Williamsburg, VA (USA).

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: