Major Concepts (pp.109-125)

Here are the notes from class last week.  Please note that I have altered some of the writing and added additional information (in italics) for clarity.


Why do psychologists study cases of sensory loss?  Psychologists are interested in cases of sensory loss because they emphasize senses and how they work.  On a more personal level, it shows human resilience and the ability to adapt.  -Roberto, Edgar, Danny, and Oscar


What is the difference between sensation and perception?  Sensation is the changing stimulation in a way the brain can understand, whereas perception creates a way to explain that sensation.  Sensation is when you intake a sensory stimulus and the stimulus turns into a neural message, transferred to your brain. Perception is the explanation of why you feel what you are feeling.  Perception relies on past experiences or interactions (especially schema).  -Cesar, Jose, Gaby, and Isaiah
Our minds interpret what our senses detect.


How are sensation and perception related?  Sensation and perception are related because they are dependent on each other.  Without the ability to intake sensory information, one wouldn't be able to perceive the outside world.  -Miriam, Sonia, Sandy, and Maya
Remember that in the case of sensory loss, the inability to intake a specific sensation, humans and other animals tend to compensate by relying on other sensations.  For example, a person who is blind may have refined auditory abilities.


How does visual stimulation become perception?  It undergoes three stages.  First, physical stimulation; second, neural messages; third, the process of perception.  -Lizsandra, Joshawn, Carlos, and Carolina
Ensure that you understand our brain doesn't automatically know what it sees, hears, smells, etc.  We don't automatically process sensations.  Our ability to intake sensory information always begins with some sort of stimulus.  The stimulus means nothing without our body's ability to process it.  Our body intakes the stimulus and then processes the stimulus (physical energy) into a neural message.  This is called transduction. After the stimulus is processed into neural messages through the transduction, the signal travels from receptor cells along sensory pathways to specific processing areas in the brain.  Sensation occurs when the brain extracts information from the neural message.  The brain then adds any additional information (schema, etc.) to create the perception of the stimulus.  Note that these are four specific steps that must occur in this order.  This is sometimes challenging to wrap our minds around because the process happens so quickly it seems as thought it's simultaneous.


What is sensory adaptation, and why do we need it?  Sensory adaptation is the diminishing responsiveness with sensory systems to prolonged stimulation.  For example, when you adapt to the feel of cool water.  We need it because it announces changes in our external world.  -Alyssa, Leah, Brian, and Leticia
In other words, we don't notice big changes once we get used to them (after we've been exposed to them for a period of time and the stimulus doesn't change).  With the pool example, the water feels cold at the beginning, but your body adapts to it relatively quickly.  After constant exposure to a stimulus, our nerve cells fire less frequently.  This has an evolutionary basis because our body needs to remain alert to intake new sensory information and react to it.  Our sensory receptors are alert to novelty (new information.)
Fun fact:  If all this is true, then why don't objects disappear if we stare at them?  Actually, our eyes are constantly moving, of fluttering, even when we are "staring" at something.  
Did you know that people with schizophrenia experience more eye fluttering than those without schizophrenia?


What is the difference between absolute threshold and difference threshold?  The absolute threshold is the minimum amount of stimulation needed to be detected by the sensory cortex.  The difference threshold, also known as the just noticeable difference, is the smallest physical difference between two stimuli that can be detected.  For example, if you have the music blasting really loud, in order to hear a difference, you must turn it down to a really low volume.  If the volume is low, you will likely easily tell the difference if you turn it up slightly.  -Ebony, Yolanda, Taayler, Felicia, Luis
Absolute threshold is the minimum stimulation we need to detect a particular light, sound, pressure, taste, or odor 50% of the time.  For example, a hearing specialist could test your absolute threshold for sound by exposing each of your ears to varying sound levels.  For each tone, the test would define where half the time you correctly detect the sound and half of the time you do not.  For each of your senses, that 50-50 recognition point defines your absolute threshold.  Remember that absolute threshold may vary with age.  
Extra credit:  Respond to this post commenting on the information in this link.  How is absolute threshold related to this brief article?
The difference threshold is the minimum difference a person can detect between any two stimuli half the time.  The detectable difference increases with the size of the stimulus.  For example, if you add one ounce to a 10-ounce weight, you will probably detect the difference; add one ounce to a 100-ounce weight and you probably will not.  See the information below about Weber's law.  


Does a person's absolute threshold remain constant?  No.  It varies in every person, and it depends on a person's physical condition and situational context.  For example, a person walking down an unfamiliar neighborhood may have a lower absolute threshold (better ability to detect stimulation), for they try to be more aware of their surroundings much more than in their own neighborhood.  -Taylor, Bianca, Jennyfer, and Nancy
This example includes the idea of signal detection theory, see the posting below.


What is Weber's law?  Weber's law says that the just noticeable difference, or difference threshold, is determined by the intensity of the stimulus.  -Lizsandra, Joshawn, Carlos, and Carolina
Weber's law deals with constant proportions, not amounts.  For the average person to perceive their differences, two lights must differ in intensity by 8 percent.  Two objects must differ in weight by 2 percent.  And two tones must differ in frequency by only 0.3 percent (Teghtsoonian, 1971).  It's easier to notice the difference if the original stimulation is low, but more difficult to notice the same increase in stimulation if the original stimulation is high.  This is why it's hard to tell that someone has turned down the volume three notches if the volume was originally very high, but if the volume was originally low, turning it down three notches is much more noticeable.  Likewise, a person can tell the difference when a person puts on one vs. three squirts of perfume.  It is much more difficult, however, to tell the difference when a person puts on eight or ten squirts.  This isn't always true, but it may help you in your thinking.
Weber's law is very mathematical, so the most important takeaway is that you understand that we are dealing with proportions (percentages), not actual amounts.  For example, lifting a 15 pound box and then adding a 5 pound weight to the top of it is not the same as lifting a 50 pound box and adding a 5 pound weight to it.  You must always consider the original stimulation.


What is signal detection theory, and how does it relate to absolute threshold?  Signal detection theory is the idea that a person's psychological state impacts our ability to detect weak signals.  This is exactly what is demonstrated in Taylor, Jennyfer, Bianca, and Nancy's example above.  People can respond differently to the same stimuli depending on the context, including the person's experience, expectations, motivations, and alertness.  A person walking in an unfamiliar neighborhood may be able to detect a weak stimulus, like a slight sound, because the person doesn't know the area and doesn't know what to expect (or could be afraid).  A person who is accustomed to the neighborhood may not notice the same stimulus.
Another example is an exhausted parent of a newborn who will likely notice a faint whimpering from the baby's cradle, but may fail to notice the phone ring while they are sleeping, although the phone ring is a stronger stimulus.

What is subliminal persuasion or subliminal stimulation?  How does it relate to absolute threshold?  Stimulation could be below or near a person's absolute threshold.  Subliminal persuasion is when you're influenced to do something without being aware.  It relates to threshold because persuasion happens so close to absolute threshold that it is hard to notice, as a person is not consciously aware of it.   -Oscar, Danny, Edgar, and Roberto
The important thing to note here is that much of our information processing occurs automatically, out of sight, off the radar screen of our conscious mind.  However, the consensus is that advertisers and other subliminal persuasion attempts are not able to manipulate us with "hidden persuasion".