In this lesson, we will explore what binocular cues are, how we utilize them to discern how distant an object is from us, and how they work to create our unique sense of depth perception.
What Are Binocular Cues?
Very simply put, binocular cues are information (or cues) taken in by two eyes (binocular), versus one eye (monocular). Now this may not seem very exciting, but what your brain does with this information really is. By collecting information from your right and left eyes and then integrating it, your brain is able to construct a three-dimensional interpretation of the world. That’s right, binocular cues are what allow us to see 3D!3D is another way of saying that we interpret objects in our environment based on our sense of depth perception, also known as stereopsis. Binocular cues give us our natural ability to determine where in space an object sits relative to our own body – our sense of depth perception enables us to discern where to place our feet, if the ground is sloping up or down, or to determine how far an object is away from us.
In other words, depth perception allows us to discriminate between things near versus things far.Ok, so now that we know that the body uses binocular cues to determine depth perception, let’s take a look at what these cues really are. This first one that we will explore is called retinal disparity, while the second is referred to as binocular convergence.
Retinal disparity, also known as binocular parallax, refers to the fact that our eyes are about 6.3 centimeters apart on our face on average and, as a result, each sees the world from a slightly different angle.
You can test this by extending your pointer finger at arm’s length and alternating opening and closing your eyes. You’ll notice that, as you do this, your finger seems to shift depending on which eye you’re looking through.Retinal disparity may seem like a cool parlor trick, but how does it actually work to give you a sense of depth perception? Well, the different angles that your right and left eyes see an object from actually enable you to see more of the object itself.
You’re literally seeing the same object but from a slightly different perspective; thus, you’re taking in slightly different information about the size, shape, positioning, and contours of an object. Your brain takes these slightly different views and integrates them into a three-dimensional image of the object.Have you ever viewed a ‘Magic Eye’ image? They appear like a random series of dots or shapes until your eyes adjust and then, bam, a 3D image appears. These types of images are known as autostereograms because they are a 3D (‘stereo’, for stereopsis) image (‘gram’) that your eyes find automatically (‘auto’) without the need of any special viewing tool.
They actually rely on your retinal disparity to reconstruct the sense that a three-dimensional object is hidden in the image. They’re created by superimposing two images, one of the object as would be seen by your left eye and one of the same object as would be seen by your right eye. Once you find the right focal distance, the hidden image seems to magically pop out of nowhere because each eye is provided with the appropriate angle of the object as if it were a real 3D object sitting before you.
Binocular convergence is the other binocular cue that enables your sense of depth perception. It refers to the physiological angles that each of your eyes needs to rotate to focus on any given object. It’s what’s known as a proprioceptive sense (meaning a sense of one’s own self) in that it uses feedback information from the muscles of your eyes to understand your eyes’ rotation in their sockets and, as a result, the distance the object is from you.
Ok, so what does that even mean? Well, let’s repeat the test from above, except this time extend your pointer finger at arm’s length and, while keeping both eyes open, draw your finger towards your face. You’ll notice that at a certain point, the muscles in your eyes strain due to the degree of your eye-cross, and the single image of your finger diverges into two. If you do this test in reverse (starting at your nose, draw your finger out), at a certain point the two images of your finger will converge into one. In other words, binocular convergence is the phenomenon where your eyes rotate inwards to focus on an object, and the degree to which they rotate indicates to your brain how near or far an object is – nearer objects require a greater degree of inward rotation than objects farther from your face.
Binocular cues are visual information taken in by two eyes that enable us a sense of depth perception, or stereopsis.
Retinal disparity, also known as binocular parallax, refers to the fact that each of our eyes sees the world from a slightly different angle. Binocular convergence, on the other hand, is a proprioceptive sense using feedback information from the muscles of your eyes to understand your eyes’ rotation in their sockets and, as a result, the distance the object is from you.
As you come to the end of the lesson, you should make a goal to:
- Define what binocular clues are
- Explain depth perception
- Discuss retinal disparity and how it enables depth perception
- Understand how autostereograms work
- Consider what binocular convergence is and its role in depth perception