Psychology Class #5
SENSATION AND PERCEPTION - BASIC PRINCIPLES *********
Part 1
To understand sensation and perception, we need to understand the physical structures and functions of the different sense organs, and how the brain converts information from the sense organs into experience.
Sensation - the process of receiving stimulus energies from the external environment.
Transduction - the process of transforming physical energy into electrochemical energy.
Perception - the process of organizing and interpreting sensory information to give it meaning.
Perception is not a direct objective reflection of the world around us…
But rather, an INTERPRETATION.
In our everyday experiences, sensation and perception blend into one continuous process. But in this chapter we’re going to slow down that process to study its parts.
Bottom -up processing - starts with a stimulus input - the sensory receptors register information about the external world and send information up to the brain for analysis and interpretation - detection
Top - down processing - starts with the brain and our experiences and expectations - interpretation
Example : Is this bottom - up or top-down processing?
1. Susie sets up the DVR to record her favorite TV show. ……top-down
2. Jeremy is in his first year of algebra and finds the algebra problems very
Confusing. He finds that he needs to keep going back to the textbook and s
Seeing what steps are next……….bottom-up
What is the purpose of perception?
1 - to make internal representations of the outside world
For example, vision, - helps us to create an internal map of the outside world
2. - to help in survival….p. 162
Evolutionary adaptation in the areas of sensation and perception
For ex. Where the eyes are located on predatory animals - front
Where the eyes are located on animals that are hunted - side
Frogs - feed on flying insects - the receptor cells in their eyes fire only in response to small, dark, moving objects. A frog could starve to death knee-deep in motionless flies.
Another adaptation - our ears are most sensitive to sound frequencies that include human voice consonants and a baby’s cry. Why do you think voice consonants?
SENSORY RECEPTORS AND THE BRAINp.163
Sensory receptors are specialized cells that detect stimulus information and transmit it to sensory nerves and the brain.
3 main types of receptors based upon the type of energy that is transmitted:
1 - photoreception….detects light ( bottom-up), perceived as sight ( top-down)
2. - mechanoreceptor - detects pressure, vibration, and movement - sensation
Perceived as touch, hearing, and equilibrium - perception
3. Chemoreception - detects chemical stimuli - sensation
Perceives smell and taste - perception
In the brain, nearly all sensory signals go through the thalamus - sits at the top of the brain stem - the relay station
From the thalamus, the signals go to the sensory areas of the cerebral cortex
THRESHOLDS
Psychophysics - the study of relationships between the physical characteristics of stimuli, such as their intensity, and our psychological experience of them.
For ex. How far away can you be from the cinnabun counter and still smell the cinnabun?
This leads us to the question of how much of a stimulus is needed for us to detect it?
The term ABSOLUTE THRESHOLD is used to describe the minimum amount of stimulus energy that a person can detect…….50 % of the time.
Absolute thresholds can vary with many factors. One factor is age. Sensitivity to high-pitched sounds declines with aging…..so the absolute threshold would be higher as a person ages…meaning they would need a louder stimulus before it could be detected 50% of the time.
See page 165 SEE ABSOLUTE THRESHOLDS FOR 5 SENSES
Under ideal circumstances, a person’s absolute thresholds are very low….meaning it does not take much of a stimulus for something to be experienced.
The problem is that there is so much NOISE around people that they can’t detect some of the stimuli that are confronting them. NOISE is the term given to irrelevant and competing stimuli.
Ex.: Here’s a riddle for you to solve:
You’re driving a bus with 12 passengers. At your first stop, 6 passengers get off. At the second stop, 3 passengers get off. At the third stop, 2 more passengers get off, but 3 new people get on. What color are the bus driver’s eyes?
This was an example of noise - irrelevant and competing stimuli
SUBLIMINAL PERCEPTION - is when people are affected by information that is presented below their level of awareness….well below their absolute threshold.
Subliminal…..means sub - below - liminal - threshold
p.165 The text indicates that we can be influenced by information that is presented below the conscious threshold…..but it should be noted that recent research indicates that we are not influenced in any lasting way.
Greenwald, over the course of a decade, conducted 16 double-blind experiments evaluating subliminal self-help tapes. His results were all consistent. Not one had any therapeutic effect.
In another experiment, people were asked to rate pictures of faces with a neutral expression in terms of likeability. The subjects were exposed to both pleasant or unpleasant odors, but all were below threshold. Subjects rated more faces as likeable after being exposed to the pleasant smells. This experiment showed an effect of subliminal perception….but not a lasting one
DIFFERENCE THRESHOLD - This term refers to the difference that must exist between two stimuli before the difference is detected - 50 % of the time.
This is also referred to as
The JUST NOTICEABLE DIFFERENCE.
For ex. A musician tuning an instrument must detect small differences between notes
Parents need to detect the sound of their child’s voice amid other children’s
Sheep can detect their lambs from one another
In the 1800’s…a German physiologist, E. H. Weber discovered a principle now known as WEBER’S LAW - two stimuli must differ by a constant proportion, not a constant amount in order to detect a difference
For example…if we add 1 candle to 60 candles we’ll notice a difference
If we add 1 candle to 120 candles we won’t notice a difference
If we add 2 candles to 120 candles we WILL notice a difference
So we know that the proportion is 1 to 60 for noticing a difference
To notice a difference in weight, two objects must differ by at least 2 %
Two lights must differ in intensity by 8 percent
Page 166 in book.
SIGNAL DETECTION THEORY - is a theory about perception that predicts when we will detect weak signals.
for ex. Exhausted parents will notice the faintest whimper from a newborn while failing to notice, louder, unimportant sounds.
Signal detection can have life or death consequences when people are responsible for watching an airport scanner for weapons, detecting radar blips at a air traffic control tower, or monitoring patients in an intensive care unit.
Studies have shown that people’s ability to catch a faint signal drops significantly after 30 minutes.
Further study has shown, however, that this varies depending on the task, the time of day, and even on whether or not the subjects exercise.
To help motivate airport baggage screeners, the U.S. Transportation Security Administration periodically adds image of guns, knives, and other threatening objects into bag x-rays.
When the screeners detect the images, they are congratulated and the images
disappear.
Two important factors in perceiving sensory stimuli are ATTENTION AND PERCEPTUAL SET.
1. Selective Attention - focusing on a specific aspect of experience while ignoring others.
\Attention is not only selective, but it is also shiftable - we can shift our attention fromone thing to another
2. Perceptual set - a readiness or predisposition to perceive something in a particular way.
P. 168 Aces of Spades
GESTALT PSYCHOLOGY - a school of psychology that is interested in how we perceive shapes
The Gestalt school has identified several principles about how we perceive shapes:
1. Figure - ground relationship - the principle by which we organize the perceptual field into stimuli that stand out (figure) and those that recede (ground, as in background).
2. The whole is different from the sum of its parts - for ex. A movie is made up of separate frames, but when put together, it is more than that. We experience or perceivemore than the sum of the parts
ex. #2 - words on the page are actually just marks on the page, but we perceive words and meaning out of them.
3. Closure - p. 180 in text - if we see gaps in a figure, we will fill in the spaces
4. Proximity - objects near each other tend to be seen as a unit…..16 squares end up looking like 4 lines of squares instead of 16 individual squares
5. Similarity - objects that are similar are seen as a unit
End of class.
