Biological Psychology Unit Two AE Mr. Cline Marshall High School Psychology
Vision How do our brains make 3-D images out of 2-D inputs? We live in a 3-dimensional world, but each of our eyes is only capable of capturing a 2-dimensional image. Get up for a second, move around; see how you know when to avoid a chair or the edge of a table? That's because you can tell how far away objects are from you. This is incredibly important in so many ways. We don't spend our lives bruised from running into furniture. We're able to drive, judging where other cars are in the road and knowing how fast we can go. Think of when you've misjudged the final step on a flight of stairs--you assumed it was higher or lower than it really was.
Vision Imagine if this happened all the time; that's a world without depth perception. Depth perception is so important that it may be hard-wired into our brains. At the very least, it's something we pick up very early. In Gibson and Walk's famous visual cliff experiment, infants as young as six months old perceived a Plexiglas-covered drop-off and approached it nervously. Most refused to cross. Gibson and Walk concluded that these infants could indeed perceive that the drop was there, and knew it could be dangerous for them. But how do we turn flat images into 3-D? There are two main kinds of depth cues: binocular and monocular.
Vision These words really just mean 'two-eye' and 'one-eye'; you can remember it because you look through binoculars with both eyes, but a proper English gentleman holds up a monocle to only one eye. Basically, there are some clues to depth that we can perceive with just one eye and others that we need both eyes for. Let's start with a simple example. Take a look at your desk; let's say you have a stapler on it, as well as a few old mugs. If you can see that the stapler overlaps in front of one of the mugs, you could guess--accurately--that the stapler is closer to you than the mug. This is a monocular depth cue called interposition. Have you ever learned about perspective in an art class?
Vision If you try to draw a road disappearing into the distance, you have the lines converge as they reach the horizon. Next time you're out on a long stretch of road, take a look: the road really does seem to converge to a point as it gets further away. This monocular depth cue is called linear perspective; in a flat, 2- D image, things that are farther away seem to get closer together. They also appear physically higher up; this is the position cue. A car that's further down the road will appear smaller than the same-sized car nearby; this is known as relative size.
Vision If you started driving down this road, you might notice that the things closer to your car seem to move a lot faster than things in the distance. This is called the motion parallax, and even with one eye closed, it would clue you in to how far away things are. Some animals rely more heavily on the motion parallax than humans--have you ever seen a bird bobbing its head around as it looks straight ahead? The bird is trying to achieve its own motion parallax to tell how far away various objects are. A distant barn also probably looks fuzzier and less distinct than a nearby shed. This is another monocular depth cue used by painters to suggest that some objects are farther away than others, and it's called the texture gradient.
Vision You can see this really clearly in images like a field of grass, where the blades nearest to the viewer are distinct but fade to a wash of green in the distance. A related idea is aerial perspective, in which things in the distance appear foggier than things nearby. While monocular depth cues help us learn things about the 3-D world from a flat image, binocular depth cues are involved in helping our brains produce actual 3-D images out of flat sensory input. There's a reason we have two eyes rather than one gigantic Cyclops eye--two eyes a little bit apart from each other generate two slightly different images to send to the brain. This is known as retinal disparity. The brain merges these two slightly different images to create one that looks 3-dimensional.
Vision 3-D movies use this principle to achieve their effect. You know how if you take off your 3-D glasses the movie looks a little fuzzy? That's because there are actually two slightly different images on the screen at once, and the glasses filter the input so that one eye gets one image and one eye gets the other. Then your brain does the rest of the work, putting it together into full 3-D. Over shorter distances, your brain can tell how close things are based on signals it gets from your eyes' muscles. For an object under 50 feet away, your brain can tell how much your eyes have to converge to see it.
Vision Hold up your finger in front of your face and look at it; now bring it closer. As it gets really close, you'll definitely feel your eyes cross more and more; it might even get uncomfortable. This is happening in a less extreme way all the time, and your brain can calculate the convergence angle between the eyes and use it to figure out how far away something is. The brain can also take advantage of your eyes' lenses ability to change their curvature when focusing on particular objects; it knows how much they've changed and can use this to judge depth over small, nearby distances.
Hearing How do our ears transform sound into signals that our brains can process? Did you know where the smallest bones in your body are? They're not in your fingers and toes; they're actually in your ear, and they make up a part of the complicated mechanism that allows our ears to turn vibrations in the air into the sounds that we hear. Sound is made up of molecules vibrating in patterns called waves. When I bang on a drum, the drum's vibrating surface disturbs the air in patterns that, once they reach my ear, can be interpreted as a sound. Unlike light, which can travel in a vacuum through space, sound waves need material to travel--they need some sort of matter to disturb. Sound waves that are shorter hit our ears in more rapid succession; they are said to have a higher frequency.
Hearing Frequency is related to the idea of pitch in music, or the relative highness or lowness of a given sound. When an opera singer hits a high C, she is producing sound waves that are very short and with a high frequency. When a tuba plays a low C, its sound waves are much longer and with a lower frequency. Loudness is related to another feature of the sound wave, called amplitude. Amplitude is basically the size, or height, of the sound wave. The bigger the wave, the louder the sound. You may have heard the term decibel ; that's a scale, rather like degrees for temperature, for saying how loud something is. Unlike degrees, however, the decibel scale is logarithmic.
Hearing This means that if one sound is 10 decibels louder than another, it's actually ten times as loud. A 60 decibel conversation is ten times as loud as 50 decibel rainfall; a 110 decibel rock concert is ten times as loud as a 100 decibel snowmobile. A 90 decibel lawnmower is 100 times louder than a 70 decibel vacuum cleaner--ten times ten. The scale starts at the threshold of human hearing, so zero decibels represents the point at which a sound becomes so quiet that humans can't detect it. Prolonged exposure to noises above 85 decibels can cause hearing loss, either by physically damaging the ear or by damaging the nerves that transmit signals to the brain.
Hearing You know how when you hear a noise, you can usually tell where it's coming from? This is because we have two ears, spaced apart on either sides of our heads. This means that if a sound is coming from the left, it reaches the left ear sooner than it reaches the right. While the difference in time might be really small, your brain automatically interprets this to help you determine where the sound is coming from. Now that we've learned about sound, let's take a look at how the ear processes sound and turns it into signals that can be interpreted by the brain. Sound first enters the ear and reverberates around the pinna, or folds of cartilage in the outermost part of the ear.
Hearing Then it travels down the auditory canal, which amplifies the sound until it hits the eardrum. The eardrum rests up against the ossicles, which are those tiny bones we were talking about at the very beginning. There are three of them, and they help transform the sound from vibrations in the air to vibrations in the fluid inside the nearby cochlea. The cochlea looks kind of like a twisty seashell; it's filled with fluid and with small hair cells that support bundles of cilia, small fibers that can sense vibrations in the fluid. These hair cells send nerve impulses to nearby neurons. These signals then travel down the auditory nerve and into the brain.
Hearing There are a lot of parts of the ear to remember, so I like to use a kind of mean acronym to remember them: if you don't know how hearing works, Please Exit Our Cool Crowd. Pinna, eardrum, ossicles, cochlea, cilia. This is the order in which soundwaves enter the ear and are processed; Please Exit Our Cool Crowd. There are a few theories on how this mechanism transmits a sense of pitch. The frequency theory of hearing says that the neurons attached to the cilia will fire off at the same rate as the frequency of the sound entering the ear; so they fire off more quickly for a higher pitch sound with a short wavelength and more slowly for a lower pitch sound with a longer wavelength.
Hearing This is an elegant theory but one that's problematic when it comes to higher-pitched sounds; neurons actually can't fire fast enough to match the frequencies of some high-pitched sounds humans definitely can detect. Another theory, called the place theory of hearing, takes care of this problem by proposing that different parts of the cochlea react to different frequencies of sound. So more neurons firing from the opening of the cochlea would indicate a higher pitch, and more neurons firing from the end of the cochlea would indicate a lower pitch How do taste, touch and smell work? Also, what is proprioception? Vision and hearing help us to navigate the world; to locate objects, to communicate and to avoid potential danger.