Chapter 5: Sensation and Perception
Chapter 5:
Sensation and Perception
All Senses have 3 Characteristics• Sense organs: Eyes, Nose, Ears, Skin, Tongue…gather information about your environment
• 1. Transduction
• 2. Adaptation
• 3. Sensation/Perception
Transduction
• When a sense organ changes or transforms physical energy into electrical signals…example:
A skunk’s spray/molecules enters your nose, molecules get transformed into electrical signals/impulses. These signals get interpreted by your brain as unpleasant odor
Adaptation
Adaptation• Example: Your skin will not feel your clothing once it adapts to them being on…
Some sense organs adapt quickly…some more slowly…depends on the intensity of the stimulation…
Will your senses eventually adapt to any stimulation despite intensity level?
Yes or No and why???
Adaptation
Your sense organs WILL NOT adapt to intense forms of stimulation if the stimulation will cause physical damage…extreme heat or cold on your skin for example…or…
…certain intensely harsh visuals…
• Sensation: Process in which the sense organs’ receptor cells are stimulated and relay information to brain centers for processing…Example: Hearing a sound or seeing a light
• Perception: Process by which an organism selects and interprets sensory input so that it has meaning…Example: Identifying the sound as a phone ringing or the light as a star
Sensation and Perception are linked to form the entire process through which we gain sensory input, convert it to electrochemical energy, and interpret the info so it makes sense…organization, form, and meaning
Sensation vs. Perception
Gathering info about the world takes 2 steps1. Electrical signals reach the brain where they are turned into Sensations
Sensation vs. Perception
Gathering info about the world takes 2 steps• 2. The brain quickly changes sensations into perceptions
Perception Expectancy• Do expectations affect our perception of the world around us?
seel
whack
dack
Perception Expectancy
The expectations of what was upcoming affected how you perceived nonsense words and respond to questions.
Structures of the Eye
Explaining the Eye’s Blind Spot
The front of the eye acts like a camera lens, differently directing light rays from each point in space so as to create on the back of the eye a picture of the world. The picture falls on a sheet of photoreceptors (red in the diagram), specialized brain cells (neurons) which are excited by light.
Explaining the Eye’s Blind Spot
• The sheet of photoreceptors is much like a sheet of film at the back of a camera. But it has a hole in it. At one location, called the optic nerve head, processes of neurons collect together and pass as a bundle through the photoreceptor sheet to form the optic nerve (the thick black line extending up and to the left in the diagram)
Explaining the Eye’s Blind Spot• The Optic Nerve carries information from the eye to the rest of the brain. At this location, there are no photoreceptors, and hence the brain gets no information from the eye about this particular part of the picture of the world. Because of this, you should have a "blind spot" (actually two, one for each eye), a place pretty much in the middle of what you can see where you can't see.
Image Reversal
Image ReversalImages need to be reversed so we can see objects much larger than the size of our pupil and so that we may have peripheral vision. Example: The Washington Monument
Psychophysics• Study of the relationship between physical stimuli and a person’s conscious experiences of them…between Mind and Body
• This study usually begins with the study of Sensory Thresholds…think of a threshold as a dividing line, a point where things become different…such as a threshold for pain…
•No Pain Medication Needed
•Pain Threshold Reached
•Drug Me Now or Else
Absolute Threshold: Smallest strength of a stimulus that can be detected…minimum level of stimulation necessary to excite a perceptual system such as vision
…Example: What is the minimum amount of light needed for a person to say that they see it?
Inattentional Blindness• A person’s inability to detect unexpected objects when intently focusing on other objects
Inattentional BlindnessResearch shows that when a person pays very close attention to an object/event other events/objects (that are unexpected) go unnoticed…Example: Many airline pilots who have to pay attention to hundreds of dials and switches on the dash have struck other planes on the runway…other PLANES…these are not small objects. So what does this tell us?
Inattentional BlindnessThere is no such thing as Multi‐tasking
Our brains can only do so much at one time…we can only focus full attention on one thing
Experiment on Multitasking
The Stroup Effect (Automatic Filtering)
• Your brain has a filter that causes you to miss large features in your environment‐ automatic filtering of distractions (like the Penguin and the Jabberwokies).
It’s probably a good thing we do have it as it makes life a heck of a lot simpler. But can you think of a case where it would be better to have more conscious control over your attention’s focus?
The Stroup Effect (Automatic Filtering)
You will be shown a list of colored words; as they appear say the FONT color aloud as quickly as you can.
BLUE
YELLOW
PURPLE
GREEN
RED
Easy right?
Now remember you’re calling out the FONT color as fast as you can…
BLUE
YELLOW
PURPLE
GREEN
RED
ORANGE
GRAY
PINK
The Stroup Effect (Automatic Filtering)
This can take some people up to 50% longer to correctly identify and say the right color. This is a case where your brain’s automatic functions interfere with your ability to perform.
The Stroup Effect (Automatic Filtering)
The Stroup Effect relies on interfering signals in your brain that compete for your attention…color is processed in a section of the brain called the Ventral Stream, while active reading takes place in the Temporal and Occipital Lobes. Your attention filter is unable to damper your brain’s instinct to read the word itself and naming the font color becomes difficult.
Visual Perception• Is Visual Perception always truthful?
• Does an object’s size and shape change when it is moved farther away???
• Is the Earth round or actually FLAT???
Visual Perception: Visual Spectrum
Notice that your eyes only pick up a small amount of the light from the total electromagnetic spectrum
Size Constancy
The size of an image on your retina gets LARGERor SMALLER as you move CLOSER to or FARTHER AWAY from an object
Size ConstancyDue to our ability of our visual perception system, we recognize that objects remain constant in size regardless of the distance from the observer or the size of the image on our retina. 3 things make this happen:1. Previous experience with the true sizes of
objects2. The distance between the object and the
person3. The presence of surrounding objects
Size ConstancyAs an object moves AWAY from the viewer, its perceived size does not change in relation to the that of the objects around it…this is why knowing the size of surrounding objects helps us determine a perceived object’s distance from us, as well as its actual size…we judge an object’s size by comparing it with surrounding objects.
Size Constancy
Size ConstancyThe center circles are actually both the same size, yet they appear to different because of their relationship to the surrounding circles. Our brain perceives the circle surrounded by larger circles as smaller, because it is smaller in relation to the surrounding circles. The opposite is true for the circle surrounded by smaller circles.
Size Constancy
Size Constancy
Try this interactive site that shows/explains size constancy:
http://science.howstuffworks.com/question491.htm
Shape Constancy
The ability of our Visual Perceptual System to recognize a shape despite changes in its orientation or the angle from which it is viewed.
Shape Constancy
A very different view of the same checkerboard; in both images the checkers are perceived as round and the board as square
Depth PerceptionAllows you to estimate your distance from an object and the distance between that object and another one.
We also see in 3 dimensions: height, width, depth.
Both monocular (using one eye) cues and binocular cues (using two eyes) are used in depth perception.
Depth PerceptionAre people with only one functioning eye able to: ‐ Land an airplane?
‐ Drive a car?
‐ Hit and catch a baseball?
How can we prove or disprove this?
Depth Perception
Stand up and cover one eye…now walk around the room and avoid bumping into other objects…
Depth PerceptionLinear Perspective is a monocular cue that arise from the stimulus itself; often seen in photos and paintings…distant object appear to be closer together than nearer objects.
A painter will show distance by making parallel lines converge as they recede…
Depth Perception
Depth Perception
Interposition is another monocular cue for depth; when one object blocks out a part of another, the first appears to be closer.
Optical IllusionsWhen normal visual process and depth cues seem to break down, you experience an optical illusion, which is a perception of a physical stimulus that differs from measureable reality or from what is commonly expected. The Moon Illusion is a natural one; notice the actual size of the moon and the size of its image on the retina do not change, the moon seems about 30‐50% larger when on the horizon vs. overhead
Optical IllusionsThis image cannot currently be displayed.
Optical IllusionsHow can optical illusions be explained?
They have not been explained to date but there are theories…some researchers say that some visual illusions have to do the with the object’s background; that we have had prior experiences with specific stimuli and therefore our perceptions are well developed and constant…when the moon is overhead, it is against a featureless background, but against the horizon, objects are closer to the moon. Objects in the landscape provide cues about distance that change our perception of the size of the moon.
Optical Illusions• Muller‐Lyer Illusion (Read for explanation)
Optical Illusions
Optical IllusionPonzo Illusion
Optical IllusionsPonzo Illusion (Read for explanation)
Optical IllusionsOuchi Illusion
Optical IllusionsOuchi Illusion
Optical IllusionsAmes Room
Optical IllusionsAmes Room
Optical IllusionsAmes Room
Optical Illusions