1. Sensation and Perception
To represent the world, we must detect physical energy (a stimulus) from the environment and convert it into neural signals. This is a process called sensation.
When we select, organize, and interpret our sensations, the process is called perception.

2. Sensation vs. Perception
Psychophysics: The study of the relationship between physical stimuli and our experience of them.
Sensation
The experience of sensory stimulation
“I see…hear…feel…smell…taste something”
Perception
Creating meaningful patterns from raw sensory information
“I see a cat;” “I hear footsteps” etc.
Bottom-Up Processing
Beginning with stimulation of our senses, we interpret sensory information with our brains
I see a furry, 4-legged creature with a tail and identify this as a dog
Top-Down Processing
Using our schemas and past experiences, we interpret sensory information to construct deeper meaning
The dog is growling and foaming at the mouth and I realize it may have rabies so I will not approach it

3. Sensation:
Definition:
bottom up processing: raw sensory information comes in and then gets interpreted by brain
Perception:
Top down processing: Based upon expectations, motivations, past experiences

4. Say What???
Aoccdrnig to rscheearch at Cmabrigde Uinervtisy, it deosn’t mttaer in waht oredr the ltteers in a wrod are, the olny iprmoetnt tihng is taht the frist and lsat ltteer be at the rghit pclae. The rset can be a total mses and you can sitll raed it wouthit a porbelm. Tihs is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the wrod as a wlohe.
The critical importance of Top-Down processing. Without it, it would take us much longer to process inputs

5. Selective Attention and Change Blindness
Selective attention is purposely focusing your conscious awareness onto a specific stimulus. This means that if you are in a noisy place with lots of people and you purposely pay attention to the person you are speaking with, you are engaging in selective attention.

6. Selective Attention
Perceptions about objects change from moment to moment. We can perceive different forms of the Necker cube; however, we can only pay attention to one aspect of the object at a time.
OBJECTIVE 1| Describe the interplay between attention and perception.
Necker Cube

7. Selective attention Experiment!
Human Earphones
We need four volunteers!
And two textbooks
Dichotic listening

8. Field-dependent or Independent?
Herman Witkin devised the Embedded Figures Test
(EFT) to measure field dependence–independence.
Some people have difficulty locating the simple figures
hidden within the more complex surroundings; in a
sense, they are caught up “in the forest” and “unable to
see the trees.” Witkin referred to such observers as
“field dependent.” Others quickly find the smaller
figures; they see objects independently of their background.
Witkin labeled such observers as “field independent.”
Scores on field dependence–independence are
relatively stable over time.
After more than 30 years of studying this individual
difference variable, Witkin reported that fieldindependent
students tend to favor the natural sciences,
math, and engineering, while the field-dependent prefer
the social sciences and education.

9. How fast can you find the 12 items?
Herman Witkin devised the Embedded Figures Test
(EFT) to measure field dependence–independence and has studied this for more than 30 years)
Field Dependent: Difficulty locating hidden figures within complex surroundings (prefer social sciences and education)
Field Independent: Easily locating
hidden figures (tend to favor natural sciences, math and engineering)
Scores on field dependence–independence are
relatively stable over time.

10. Selective Inattention
Because of selective attention, we are consciously “blind” to most visual stimuli in the environment:
2 famous examples:
Inattentional blindess: Gorillas in our midst basketball experiment.
Change Blindness: Asking for directions and the intruding door experiment.

11. Inattentional Blindness
Inattentional blindness refers to the inability to see an object or a person in our midst. Simmons & Chabris (1999) showed that half of the observers failed to see the gorilla- suited assistant in a ball passing game.
Daniel Simons, University of Illinois

12. Change Blindness
Change blindness is a form of inattentional blindness in which two-thirds of individuals giving directions failed to notice a change in the individual asking for directions.
© 1998 Psychonomic Society Inc. Image provided courtesy of Daniel J. Simmons.

13. Absolute Threshold
One formal definition is that absolute threshold is the smallest intensity of a stimulus that has to be present for the stimulus to be detected 50% of the time.

14. Absolute Threshold Example
Think of an electric burner on a stove. Imagine turning that burner on and then placing your hand directly on it.
At first you won't feel much heat because is takes time for the burner to heat up. But at some point it will get hot enough for you to detect…meaning, there is some temperature that is just hot enough for you to notice it.
This isn't the point at which you get burned, but the point at which it is just hot enough for you to detect the presence of the heat.

15. Sensory Thresholds Absolute threshold (Demonstration #1)
The minimum amount of energy that can be detected 50% of the time
E.g. At what point can you hear the presence of a sound?
More examples for humans:
Taste: 1 gram (.0356 ounce) of table salt in 500 liters (529 quarts) of water
Smell: 1 drop of perfume diffused throughout a three-room apartment
Touch: the wing of a bee falling on your cheek from a height of 1cm (.39 inch)
Hearing: the tick of a watch from 6 meters (20 feet) in very quiet conditions
Vision: a candle flame seen from 50km (30 miles) on a clear, dark night

16. A Challenge to Sensory Thresholds?
Signal Detection Theory challenges the notion of the absolute threshold.
SDT is a mathematical model that predicts how and when we will detect the presence of a faint stimulus or signal
There is NO single absolute threshold
Detection of a stimulus depends on a person’s experience, expectations, motivations, and fatigue. 16

17. Difference Threshold
The difference threshold, a.k.a. the just noticeable difference (jnd), is the minimum difference in stimulation needed so that a person can detect the difference between two stimuli.

18. Difference Threshold Example
For example, let's say I asked you to put your hand out and in it I placed a pile of sand. Then, I add tiny amounts of sand to your hand and ask you to tell me when you notice any change in the overall weight.
As soon as you can detect any change in the weight, that difference between the weight of the sand before I added that last bit of sand and the amount of sand after I added it, is the difference threshold.

19. Sensory Thresholds Difference threshold (Demonstration #2)
The smallest change in stimulation that can be detected 50% of the time
Also called the just noticeable difference or JND
e.g. At what point can you tell that the TV volume has been raised?
Weber’s Law
States that the difference threshold is detected by a constant minimum percentage of the stimulus, not a constant amount
e.g. to detect a difference in weight, the change must be 2% of the original stimulus’ weight

20. Weber’s Law Psychophysics
Weber-Fechner law  Originated by the German physiologist Ernst Heinrich Weber (1795–1878) in 1834 and elaborated by his student Gustav Theodor Fechner.
The law states that the change in a stimulus that will be just noticeable is a constant ratio of the original stimulus. It was later shown not to hold for extremes of stimulation.

21. Weber’s Law- Example
Weber’s Law – If we can distinguish a Just-Noticeable Difference in sound intensity between 100 hand bells and 110 hand bells, we may argue that we may be able to distinguish the difference between 10 and 11 hand bells, or between 300 and 330 hand bells: a 10% difference in each case. So argued the German physiologist E H Weber.
Our thresholds for detecting differences are a roughly constant proportion to the size of the original stimulus. (approx. 10%)

22. Sensory Adaptation
We get used to things. This goes for lots of things in life including smells, sounds, sights, games, people, situations…seems like after a while we get used to everything.
One reason we get used to everything is because of sensory adaptation, which is reduced sensitivity to stimulation that results from repeated or prolonged presentations of that stimulation.

23. Sensory Adaptation Example
For example, my car was in for service recently and the dealer gave me a rental to use while the car was being serviced. As soon as I got into the car I was overwhelmed by the smell of smoke (even though I asked for a non-smoking car). It stunk!
But after driving the car for 30 minutes or so, I didn't really notice the smell. I got used to it because I was immersed in it. I experienced sensory adaptation.

24. Subliminal
Subliminal: As humans, we have great abilities to perceive things (e.g., to see things happening far away, to hear sounds at a distance, etc.). However, we also have limitations. For example, eagles can see much, much better than humans. When we are presented with some information that is just below our conscious awareness but still reaches our brains, it is a subliminal message - meaning, the information is getting into our systems and to our brains without us truly being aware of it.
You may be familiar with the idea of subliminal messages is advertising in which a message is flashed so quickly that we don't "think" we saw it (containing the message the advertiser wants us to get) but our brains actually processed it. The idea being that we will still respond to that message even though we didn't realize we saw it.

25. Camel Cigarettes

27. Subliminal Perception?
We know that below threshold (subliminal) stimuli bombard us regularly…
BUT…do we respond to these stimuli that are below our level of awareness?
Research shows that the effect only occurs in controlled laboratory studies
Research outside the laboratory shows no significant, lasting effect of subliminal information
Priming
The often unconscious activation of certain associations for the purpose of altering perception, memory or response
Individuals flashed a pleasant or unpleasant image before viewing a photo of a person were influenced to judge the person positively is they saw a pleasant picture and negatively if unpleasant
Subliminal Research at Duke University
Subliminal Advertising Experiment (Demo #3)
Subliminal McDonald's Advertisement