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Chapter 5

PSYA01H3 Chapter Notes - Chapter 5: Color Vision, Conjunctiva, Christofer Johnsson

Course Code
Steve Joordens

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Chapter 5 ± Sensation
Sensory Processing:
Sensation ±The detection of elementary properties of a stimulus
(e.g. seeing a movement)
Perception ±The detection of the more complex properties of a stimulus, including its location and
nature; involves learning.
(e.g. seeing a baseball coming towards us and realizing we have to move left to catch it)
-No line of distinction between the two
-Perception is more complex
Example: Fireworks
Î Seeing the colors would be a sensation
Î Seeing it as beautiful is a perception
Another Example: Speaking another exotic language
Î For most of us hearing the person would be a sensation. This because we can hear the sound
Î We cannot make a perception of this because we have no knowledge of the language. We have
never heard that sound to make meaning. It just stops at sounds for us.
Transduction ±The conversion of physical stimuli into changes in the activity of receptor cells of
sensory organs.
-How the brain interprets to physical stimuli
Sense organs pick up different senses of energy.
We are not sensitive to everything out in the world. We have feelings sometimes as we see the world.
Example: infra red goggles ± if we wear these we can see heat patterns. When we turn that into a higher
frequency... we can see it in a different way. THIS MEANING THAT THERE ARE OTHER
Î Example: Light is an energy that has certain frequencies FIGURE 5.6
Î Types of Transduction accomplished by sense organs FIGURE 5.1
Receptor Cell ±A neuron that directly responds to a physical stimulus such as light, vibrations, or
aromatic molecules.
-Release chemical transmitter substances that trigger other neurons
Sensory Coding:
-Action potential strength is constant
- Potentials are coded to convey stimuli intensity.

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-Two Types: Anatomical Coding, Temporal Coding
Anatomical Coding: A means by which the nervous system represents information; different features
are coded by the activity of different neurons.
-Different neurons of the body code for different senses (i.e. the eye neurons will only send sight
information to the brain, and no other sensory information. The brain knows if eye neurons are
stimulated, the information being sent is sight information.)
Temporal Coding: A means by which the nervous system represents information; different features are
coded by the pattern of activity of neurons.
-Firing faster or slower indicates the strength of a stimulus
-Faster firing = Stronger
-Slower Firing = Weaker
(e.g. Touch) Firing of a particular set of neurons tells what part of the body is being touched. Firing rate
indicates strength of the touch.
Psychophysics ± A branch of psychology that measures the quantitative relation between physical
stimuli and perceptual experience.
The Principle of Just Noticeable Difference:
Just Noticeable Difference (JND) ±The smallest difference between to similar stimuli that can be
distinguished. Also called threshold.
Î Example: going to the optometrist and they flip the lenses and ask you which lens is better they
keep going until the point where you cannot notice a difference anymore. Another example is
looking at an object while it gets brighter and brighter.
Weber Fraction ±The ratio between a just-noticeable difference and the magnitude of a stimulus;
reasonably constant over the middle range of most stimulus intensities.
Weber Æ Measured the JND of people
-People could only distinguish weights different in weight by a factor of 1/40. (e.g. 40 from 41, 80 from
-Brightness of white light by a factor of 1/60.
-Known as Weber fractions.
-Each time a difference in intensity of a stimulus was detected = 1 JND.
(1)-The ability to detect differences (JND) decreases as the intensity of the stimulus increases.
-B/c more energy is required to distinguish between stimuli of higher intensity.

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(2)-Some stimuli however, such as pain and electric shock are opposite (i.e. require less E for higher
intensity stimuli.)
K= constant
I= Intensity
B= If b is between 0 and 1, scenario 1 is used
If b is greater than 1, scenario 2 (for pain and electric shock) are used
Signal Detection Theory:
Threshold ±The point at which a stimulus, or a change in the value of a stimulus can be detected.
Difference Threshold ±Another name for just noticeable difference, of two stimuli (JND)
Absolute Threshold ±The minimum value of 1 stimulus that can be detected.
Green & Swets Æ Signal Detection Theory experiment
-Flashed a light, warning the subject of a possible sound that may follow.
-The more faint the sound, the more bias the subject as to whether or not they heard it.
Signal Detection Theory -A mathematical theory of the detection of stimuli, which involves
discriminating a signal from the noise in which it is embedded and which takes into account the
**By convention, threshold occurs when the subject can detect the stimuli 50% of the time**
Response Bias ±7KHWHQGHQF\WRVD\³\HRU³QZKHQXQVXUHWKDWDQHYHQWoccurred.
Hits ±Saying YES when stimulus IS presented.
Correct Negatives ±Saying NO when stimulus IS NOT presented.
False Alarms ±Saying YES when stimulus IS NOT presented.
Misses ±Saying NO when stimulus IS presented
Hit - saying a stimulus is present when it is. CORRECT
Miss - saying a stimulus is not present when it is. WRONG
False Alarm - Saying a stimulus is present when it is not. WRONG
Correct Rejection - Saying a stimulus is not present when it is not. CORRECT
-Monetary incentives are used to eliminate response bias and achieve optimal results (i.e. 1$ is given for
every hit/correct n. And 0.50$ is fined for every miss/false alarm.
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