Free Psychology for Dummies by Adam Cash

Some people are good at eyeballing distances. Personally, I need a tape measure, ruler, land-surveyor, and a global positioning satellite to figure distances. Depth and distance are calculated by our visual systems using two inputs:
monocular cues
and
binocular cues.
    Monocular cues are simple; we know that some things are bigger than other things. Dogs are bigger than mice. Cars are bigger than dogs. Houses are bigger than cars. Because we know these things from experience, whenever we see a mouse’s image on our retina that is bigger than the image of the dog in the same scene, we know that the mouse is closer to us than the dog. If we see a dog that’s bigger than a car, the dog is closer. The rule is that things that cast bigger images on our retinas are assumed to be closer. Artists use this rule all the time when they want to depict a three-dimensional scene on a two-dimensional canvas.
    Binocular cues are interesting and also a little weird. Remember the Cyclopes from the Sinbad movies? He only had one eye, and according to binocular vision rules, he would have had a hard time figuring out distances. Binocular distance cues depend on having two eyes to provide information to the brain.
    •
Convergence
is one such binocular cue and refers to information provided by the muscles of the eyes to the brain to help calculate distances. When your eyes are pointing inward, toward the nose, the brain knows that you’re looking at something close to you. When your eyes are pointing outward, the brain knows that you’re looking at an object that is farther away.
     

     
    •
Stereoscopic
vision is the second type of binocular cue. Try this real quickly. Make a viewing frame with your hands by joining your thumbs at the tips and extending your index fingers up, while keeping the rest of your fingers folded. Then, close one eye and focus on an object around you. Frame the object in the middle of the box. Now, close that eye and open the other. What happened? The object should have moved. This happens because of stereoscopic vision. Each of our eyes gives us a slightly different angle on the same image because they are set apart. Our brains judge distance using these different angles by calculating the difference between the two images.

Hearing
    Sound travels in waves and is measured by its
amplitude
or
wave size
and
frequency
or
number of waves per unit time
. Each of these translates into a psychological experience: Amplitude determines loudness (my neighbor’s rock band), and frequency provides pitch or tone (the screeching lead singer of my neighbor’s rock band). The structures of the ear are specifically designed to transduce, or convert, sound-wave energy into neural energy.
    A sound first enters the ear as it is funneled in by the
pinna.
Our crumpled-up outer ear is designed as a “sound scoop.” As the wave passes through the ear canal, it eventually reaches the eardrum, or the
tympanic membrane.
The vibrating eardrum shakes three little bones
(malleus, incus,
and
stapes,
Latin words for
hammer, anvil, and stirrup),
which amplifies the vibration.
    After the sound wave reaches the inner ear, the
cochlea,
auditory transduction occurs. The cochlea contains the hardware for the transduction process. The cochlea is filled with fluid, and its floor is lined with the
basilar membrane.
Hair cells
(they actually look like hairs) are attached to the basilar membrane. The sound waves coming into the inner ear change the pressure of the fluid inside the cochlea and create fluid waves that move the basilar membrane. Movement of the basilar membrane causes the hair cells to bend, which starts the transduction ball rolling. When the hair cells bend, their chemical properties are altered, thus changing their electrical polarity. As I discuss in Chapter 3, when a cell’s polarity is altered, it is in a position to fire and send a neural signal. The sound waves, now turned into neural electrochemical energy, travel to the
auditory