Take a look at that trippy picture above.  You see the different colors and their funky motion.  You probably feel your butt against your seat (unless you are standing and in that case you are probably a little strange).  Ok, now take a whiff around the room- different odors are entering your nose (hopefully something pleasant).  Now listen really closely, what do you hear?  Probably the hum from the computer or some Justin Timberlake in the background (don't be embarrassed, we are all friends here).  Now try to taste what's in your mouth.  Maybe you can dig out a piece of that peanut butter sandwich from between your teeth you ate an hour ago.  Or maybe you have that morning breath flavor funk going on.  Regardless, at this moment, in some distorted way, you are using all of your senses.

Sensation can be defined as the process by which our sensory receptors and nervous system receive and represent stimulus energies from our environment.  What that means is when our body (through our senses) takes in information from everything around us, we are experiencing sensation.  Perception is the process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events.  So basically sensation is taking the stuff from outside of us and bringing it inside our bodies and perception is our body trying to understand what we just took in.  The difference is important.  We are first going to talk about how we sense things and break down each one of our senses in more detail.  We will then try to understand how we perceive the world.  Note that this is under the Biological school of psychology because there is a physiological (bodily) root to these ideas and they are all directly linked to our nervous system.  In fact, I want you to look at sensation as an extension of our nervous system (part of our peripheral nervous system).  Think about it, all of the senses (except smell) go first to our thalamus and then to different parts of our brain (vision to the occipital lobes, hearing to the temporal lobes, touch to the sensory cortex in the parietal lobes etc...).

Let's start off with an important term called transduction.  Transduction is the process by which our body transforms light, sound, touch etc.. into neural impulses that our brain understands.  If you want to play your Ipod on your car radio you need a special wire that will turn the Itunes music into something your car stereo will understand.  The changing of the signals would be transduction.

Now constant stimulation causes a neat phenomenon called sensory adaptation.  Do you feel the underwear you are wearing now?  Probably not, unless it is a beaded thong and in that case you have other issues to worry about.  For the most part, you feel your clothing when you first put it on in the morning, but then lose any sensation of it later in the day.  This is called sensory adaptation and it works for ALL of our senses.  If you play a constant humming sound for long enough, you will lose sense of it.  It even will work for your vision.  If you stare at something for a few minutes it will disappear.  Now if you are trying it now and it does not work, here is the reason why.  Your eyes are constantly moving and never standing motionless, thus it seems as if our eyes are not subject to sensory adaptation.  But if you clamped your eye in one position (please do not try this at home) you would experience sensory adaptation.

Vision

There are essentially four steps to vision.

• First we have to gather light into our eye.

• The light has to be channeled to the back of the eye.

• Transduction occurs.

• The information goes to our brain where we interpret it.

Let's break down the 4 steps in a little more detail.

Step One: Gathering Light

For the AP it is important to understand that we only see a small fraction of the light spectrum.  There are all kinds of light waves out there from long ones (infrared, microwaves or radio waves) to short ones (ultraviolet waves X-rays or even gamma waves (like what made the Hulk)).  The light we can see is in what we call the visible light spectrum, and from shortest to longest goes violet, indigo, blue, green, yellow, orange and red.  The height of the light wave determines it's intensity or brightness.  While the length of the wave determines it's hue (color).  So when we look at am object, these light waves enter our eye.

Step Two: The Light Channeled within the Eye

Once the light hits the eye it goes through a variety of structures.  Take a look at the diagram below.

The white part of our eye is called the sclera and is basically the outside casing of the eyeball..  The cornea is outer covering of the eye. It protects the eye and helps to bend the light.The light goes through a hole in our eye called a pupil.  The pupil is like the shutter on a camera, it opens or closes to let light in.  The colored part of your eye is called the iris.  The iris is a muscle that sole job is to open (dilate) or close (constrict) the pupil.  So when the light goes through the pupil it first hits the lens.  The lens is almost like a magnifying glass that reflects the light toward the back of our eye.  The lens is constantly changing shape depending on whether we are looking at objects close to us or far away.  The bending of the lens is called accommodation.  When adults become old, their lens becomes rigid and they cannot reflect light properly to the back of their eye and need reading glasses.  A really cool thing about the lens is that it reflects the light upside down and inverted toward the back of the eye (retina).  Our brain must switch the image back right side up or we would have serious perception issues.

Step Three: Transduction

Ok, so how does our eye turn the light into neural impulses so that our brain can understand.  Most of the process occurs on the back of the eye called the retina.  The retina is the most important part of our eye (it is often referred to as the brain of the eye).  First, it is important to know that the retina is made up of several layers of cells and the light must pass through all of them to experience transduction (kind of like a water filtration process).

The first layer of cells to be activated by light are called the rods and cones.  Rods see only black and white and are spread throughout the outside of the retina.  Cones see color and are located in the center of the retina known as the fovea.  Rods out number cones by about 20 to 1.  Since the cones are located in the fovea (in the center of the retina) we see color objects better if they are directly in front of us.   Since rods are located on the periphery of the retina- we see black and white better in out peripheral vision.

Ok- so the lens reflects the light back to the retina and it hits the rods and cones.  If the rods and cones fire- they send the information to a second layer of cells called bipolar cells (you have to no nothing about these bipolar cells except they pass on the light to the next set of cells).  So the bipolar cells give the information to a layer of cells called the ganglion cells.  The axons of the ganglion cells make up our optic nerve which sends the information to the thalamus in our brain (where the optic nerve hits the retina is sometimes called our blind spot- I will show you how to find it in class).  In case they ask (which I doubt they will- but if you are going for that 5 on the AP- the specific part on the thalamus that attaches to the optic nerve is called the lateral geniculate nucleus (LGN) and the area that the optic nerves crosses/intersects in our head (remember our cerebral cortex is contralateralized) is called the optic chiasm.  This is a very simplified version of transduction in the eye- but I think it suites our purposes (suites our purposes- what an adult and nerdy thing to say).

Step Four: Vision in the Brain

We should already know from the brain chapter that the thalamus sends the visual information to the occipital lobe in the cerebral cortex.  We interpret the image in the visual cortex in the occipital lobe.  When you watch TV- you see all kinds of things at the same time. Let's say you are watching 24 and Jack Bauer is about to torture some random terrorist to save 145,000 people.  You see Jack's shape, his motion, his colors and all kinds of other cool stuff about Jack at the same time.  Scientists say that in our visual cortex we have specific cells that all have specific jobs.  Some of these cells may just see shape.  While other cells have the sole job to see motion.  We call these types of cells feature detectors.

 

OK- there is ONE last aspect left to cover about vision.  That is how do we see color.

There are two theories of color vision.

• Trichromatic theory: this theory is actually quite simple (so I like it more).  It says that we have three types of cones in our retina.  We have cones that detect red, blue and green and from a combination of those three colors we can see almost everything.  Now you artists out there are now saying, dude- those are not primary colors!! The problem is that you are thinking in terms of paint, not light.  Go check out a Projector TV and tell me what color the three bulbs are.  The problem with this simple theory is that is does not do a good job explaining color blindness or afterimages.  Ok - what is an afterimage.   Stare at the red dot in the green square and count to forty.  Then stare at the white square and tell me what you see (actually you really can't tell me, so tell yourself- or your mom).

• 

• Opponent-Process Theory:  this theory states we have three types of receptor cones and they each handle a pair of colors (red/green, yellow/blue, and black/white).  If one sensor/color is firing, it slows the other from firing.  The theory does a good job at explaining afterimages.  Your cones, after firing red for awhile, will rest and fire the opposite green, when not being stimulated.  It also explains color blindness well.  Most people that have trouble seeing colors usually cannot see either tints of red/green or blue/yellow.

Hearing

Hearing  aka audition starts with auditory stimulation , which travels through the air like waves.  It is caused by changes in air pressure that result from vibrations.

Pitch and loudness are two psychological dimensions of sound.

Pitch: measured in hertz (Hz).  One cycle per second on a hertz.  The greater the number of cycles per second the higher the pitch.

Loudness: measured in decibles.  The loudness is determined by the height, or amplitude, of sound waves.

Structure of the ear:
Outer ear: shaped to funnel sound waves to the eardrum, a thin membrane that vibrates in response to sound waves .
Middle ear: contains eardrum and three small bones (hammer, anvil, and stirrup), which also transmit sound by vibrating.  The middle ear act as an amplifier.  It increases the pressure of the air entering the ear.  The stirrup is attached to another vibrating membrane, the oval window.  It balances the pressure in the inner ear. 
Inner ear: Oval window transmits vibration into the inner ear which contains the body tube called the cochlea (snail).The cochlea contains two longitudinal membranes that divide it into three fluid-filled chambers.  One is the basilar membrane.  The organ of corti, sometimes referred to the “command post” of hearing, is attached to the basilar membrane.  Thousands of hair cells “dance” in response to the vibrations of the basilar membrane.  This up and down movement generates neural impulses, which are transmitted to the brain via the 31,000 neurons that form the auditory nerve.

Smell  and Taste are the chemical senses.  This is were we are underprivileged.

                Smell: an odor is a sample of the substance being sensed.  Odors are detected by sites on receptor neurons in the olfactory membrane high in each nostril.  Their firing transits impulses through the olfractory nerve.  It is unclear how many basic kinds of odors there are.

                Taste: There are four primary taste qualities: sweet, sour, bitter, and salt.  Of course flavor is more complex than that.  Taste is sensed through taste cells, receptor neurons located on taste buds.  You have about 10,00 taste buds, most located on sides and back of tongue.

Kinesthesis

The sense that informs you about the position and motion of parts of the body.

Vestibular Sense

Tells you whether you are upright.  Sensory organs located in the semicircular canals.  Tell body if it is falling and changing speed .