Psychology Lecture 19.docx

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17 Mar 2012

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Psychology Lecture 19
Sensation and perception
Ernst Weber- interested in our subjective states and perceptions of the world. Different weights,
and you have to see which weights are heavier, which lights are brighter
How do we perceive the external world?
Finishing the ends of sentences, its an instinctive ability for humans to be able to finish
Our brain is a little ahead of our ears, the world is being analyzed, interpreted and assumptions
and predictions are being made as well
Bottom up , and top down influences (memory, previous experiences) analyzing that input and
guiding how we perceive it
Sensation and perception
Sensation- senses, (input devices) : sight, sound, smell,
Focus on sensory systems. How do we go from patterns of light, into perceiving human beings
We need to understand the eye ball, to understand how we perceive our senses
Viewing optical illusions
Perception is the end product of sensation to give you an output
Sensation is the detection of simple stimulus properties, such as brightness, colour, sound
frequencies, sweetness,
Perception is the detection of objects, their location, their movements, their background,
Fireworks, we perceive it to be fireworks in the city. When its really different kinds of light
Sensation is the raw sensory input
Perception is what you ultimately, see or hear it as
Transduction is the first step of sensation
The process that changes the physical stimulus from the external world into a neural impulse
The process that changes it from a physical energy into a neural impulse is called transduction
Different sense organs are sensitive to different kinds of energies
Specific receptor/nerve cells react to the energy and stimulate a neural impulse
Table 5.1 different sensory systems and what they are sensitive to
Skin can sense touch, temperature and vibration
Muscles can sense pain,
Light we are sensitive to the tiny black bar on the colour scale
The world that we perceive , theres a lot more in the world and around us that we just don’t
see, and our sensory systems are our only connections to the external world
Morse code- could use to communicate to one another
We can communicate a very rich message
Temporal coding , the rate of neural firing can help the brain distinguish between different kinds
of inputs
Anatomical coding: the way a message is perceived depends on where it originated.
If you tap on your eye, you will perceive flashes of light
The action of tapping stimulates the receptor cells at the back of the eye, and they tell the brian
theres light existing
Psychophysics physics of the mid
Two grey circles , and eventually one of the circles will seem different Ernst weber
Webers procedure, and he starts with two variables that are equal and trying to see when we
humans notice a substantial difference.
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The difference that the two stimuli in order for humans to be able to see the difference
20 percent more (weber fraction) constant along the intensity of the stimulus
How bright of a light can we pick up? How loud of a sound can we detect?
Subliminal messages in advertisements
Lecture 20
Subliminal perception-
Jastrow’s Subliminal Perception Experiment
The notion (and evidence) for perceptual defense
The experiment: subject and experimenter, the cards had letters or digits on them,
experimenter starts walking backwards and the participant has to say when they can’t see
what’s on the card anymore
People would be 60% accurate
They concluded that the existence of some entity other than the primary waking self that is
sensitive to information that the primary waking self is not sensitive to
Jastrow claimed they found that point where we go from being aware, to not aware
Perceptual defense , we cant see negative words (shit)
Perceptual defense system is preventing certain words from getting into our conscience
We have a natural tendency to leave from left to right
How much of a sound does there have to be before you can recognize it?
Signal detection theory: involves presenting a stimulus on some trials and not on others, then
asking subjects on each trial to state (guess) whether or not a stimulus was presented
Hit: when a stimulus is present when it is
Miss: saying a stimulus is not present when it is
False Alarm: Saying a stimulus is present when it is not
Correct Rejection: Saying a stimulus is not present when it’s not
How do we get rid of bias?
Hit should equal false alarm rate
- The line of null sensitivity shows equal false alarms, and it reflects equal false alarms
- Is there a word? Perfect perception when you always say yes when a stimulus is present, and
there is no false alarm rate
- Red points on graph , upper triangle is where hits are greater than false alarms, which is what is
expected where people can see the stimulus
- The trick is to use some manipulation that will vary the response bias, and test a given subject
under a number of levels of manipulation (payoffs)
- When a point is off this null sensitivity the bigger the difference between hits and false alarms ,
the further you are off the line the better you are at seeing the stimulus
Lecture 21
Some of our senses are primarily concerned with providing information about stimuli and events in
our immediate environment (e.g touch, smell ) . Others provide information about stimuli and
events that are further away (e.g. vision, audition)
Clearly, knowledge about things in our immediate environment can be critical as actions can than be
taken that either bring the stimulus close if its desirable, or make sure it stays far away if it is
Of our “early warning” senses, vision is primary. So how does it work?
Reptiles sense vibrations, have poor vision
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