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Sensation and Perception Exam 3

Terms in this set (50)

What is monochromatism? What causes it, and what problems are associated with it?
-Complete color blindness (shades of gray)
-Only have rod system
-Usually hereditary
-Not able to see fine detail very well (poor acuity)
-Bright illumination conditions: would have to wear really dark sunglasses to be able to see (hypersensitivity)
What is dichromatism? What causes the three types of dichromatism?
missing one cone or one cone doesn't work as well
Restricted range of color vision
Can match any color using 2 wavelengths
Cause: abnormal gene on X chromosome
--Causes lack of one photopigment type
What is the cause of achromatopsia?
-Results from localized damage
-Damage to area V4 in ventral pathway
-These cells are very vulnerable when brain is deprived of oxygen
-Usually due to stroke
How does aging affect color vision, and why?
Lens absorbs more short-wavelength light
Blues look darker; confused with greens
Lens becomes more yellow; reduces blue light from reaching retina
What is the fundamental problem of depth perception, that results from the nature of
the retina?
we have to construct 3D but we only get 2D image from eyes
What are the limitations of accommodation and vergence as depth cues?
-The cue is the muscle tension
-Change in shape of lens so we can keep something in focus as it moves away or towards you
-Weak cue: Slow, Limited range (20 cm to 3 m)
What do all of the pictorial depth cues have in common?
they're all available in a 2D image
What assumption does the visual system make about lighting that leads to the
perception of depth?
Light coming from above (because the sun) makes things look like they're popping out. Light on bottom makes it look like it's caved in
What is the constructivist approach, as it applies to depth perception?
use of multiple types of sources and cues to infer depth
How does motion parallax serve as a cue to an object's distance from the observer?
things between you and fixation: move faster and in opposite direction
things beyond point of fixation: move slower and in same direction
What is binocular disparity?
Eyes are separated: each has a different view of the world
Difference between two views = binocular disparity
What is the horopter? What determines the location of the horopter, and what does
the horopter have to do with binocular disparity?
Horopter: imaginary curve passing through fixated point
All points on horopter fall on corresponding points of retina
No binocular disparity for points on the horopter
Why are images outside of Panum's Fusion Area experienced as double images
(diplopia)?
Get double image because each eye is seeing the object as being in two different locations...triangle (left eye sees it as on the right...right eye sees it as on the left)
- Images not fused = Images fall on non-corresponding points on retina
What is the effect of depth on the amount and type of binocular disparity?
Increase distance from horopter (depth) → increase amount of disparity
Object beyond horopter: uncrossed (images move inward)
Object closer than horopter: crossed (images move outward on retina)
What is the correspondence problem? What do random-dot stereograms suggest
about the correspondence problem?
-Need to match images in one eye to images in other eye
-People are able to see depth in these images
Explain how attention is related to one's conscious experience of visual stimuli.
we have the ability to exclude different things in order to focus on certain things instead of everything at the same time
Describe evidence that talking on a cell phone impairs attention and driving
performance.
-studies show that break onset is delayed when using cell phone
-also people on cell phone don't recall seeing billboard when talking on cell phone (inattentional blindness)
Why does talking on a cell phone impair driving performance?
When talking on cell phone, you have reduced attention to the things you should be paying attention to; slows reaction time
What is the role of attention, according to feature integration theory?
binding primitive features of objects together (color and orientation)
Describe properties of the preattentive and focused attention stages of perception
Preattentive: doesn't involve attention, automatic/unconscious, happens across entire scene at once, extraction of perceptual primitives
Focused: Direct attention to different places in scene and you bind together primitive features, Attention binds together primitive features, Effortful, conscious direction of attention to different parts of the scene
Describe the visual search task. Contrast feature search and conjunction search
You have distractors and target.
Feature search condition: target has some feature that makes it different from others in the scene. O has curvature unlike the V
Conjunction search: Looking for target which doesn't have a unique feature; just has a unique combination of features. R among Q and P
Why are search slopes higher in conjunction search than in feature search?
Conjunction search, you have to do a serial self terminating search for the target
-more distractors = more things to look through
How does preattentive processing affect texture segregation?
texture is a primitive feature??
What are saccades? Why do psychologists find them so interesting?
-Rapid changes of fixation that are used to bring object's image onto fovea
-They are affected by cognitive factors such as memory, goals, and attention (a way to understand the way people understand the world)
Describe the properties of saccades during reading
Regressions: backwards movement; eye movement back to look at something they've already looked at
Skipping: shorter words and more common words are skipped over
--people tend to skip over/not fixate on shorter/more common words
What is the purpose of smooth pursuit and saccade movements?
-saccades: bring the object's image onto the fovea; You're focused on one thing but then there's something else you want to look at
-smooth pursuit: you have object fixated on fovea and object moves so you follow it to keep the object's image on the fovea
What is a possible purpose of miniature eye movements?
benefit=constantly refreshing things on the retina...photoreceptors respond best to changing input because they adapt to stable images
What do both the kinetic depth effect and biological motion illustrate about motion
perception? (put differently, what do they both have in common?)
Can derive structure from motion: depth and shape information
What is the effect of background on real movement perception?
Adding background elements (maybe like lines) helps to perceive motion even if the stimulus is moving at a slower pace
What is apparent movement?
Perception of motion in absence of actual motion
Describe the effects of manipulating interstimulus interval (ISI) on the perception of
apparent movement.
Really short/long ISI=people don't see motion
Seeing motion=60-200 ms
Longer distance suggests it may need longer ISI
30-60 ms = seeing partial movement
What are movement aftereffects, and how would you explain them (simply)?
View constantly moving stimulus --> view stationary stimulus
Perception: movement in opposite direction
Explanation: fatiguing motion detectors
What information can be derived from biological motion?
Gender
Emotional state
Identity of familiar people (or self)
Give an example of one way in which motion perception is "smart."
-"movement continues in the same direction" heuristic
-occlusion heuristic
-Normally: "shortest-path constraint": perceive shortest motion path possible
--except when long ISI and it doesn't make sense (human stimuli)
What evidence suggests that cells in MT play an important role in the conscious
perception of motion?
moving dot experiment with monkeys
-cells more active when more dots are moving in same direction
Firing rate increases
Direction judgment more accurate
Explain Corollary Discharge Theory. How does it account for:
o the perception of motion during smooth pursuit movement?
o the absence of motion perception following a saccade?
o the perception of motion with a passively moving eyeball?
Movement perception depends on three types of signals
Efferent signals: motor commands that are sent to an eye muscle
Corollary discharge signal: copy of efferent signal
Afferent signal: image movement on retina
Smooth pursuit
-CDS reaches comparator
-Afferent signal does not because the object isn't moving on retina
Saccade
-CDS reaches comparator
-Afferent signal reaches comparator
--When eye moves it causes the image to sweep across the retina
Passive
-Eye moves but not because brain sent a signal to move eye
--Pushing the eye with your finger
-Don't get efferent or CDS, but you get afferent because the retina is moving
Protanopia
lack L cone pigment
Insensitive to red
Incidence: 1.3% males, 0.02% females
Short wavelengths appear blue
Long wavelengths appear yellow
Deuteranopia
lack M cone pigment
Insensitive to green
Incidence: 1.2% male, 0.01% female
Short wavelengths appear blue
Long wavelengths appear yellow
Tritanopia
(probably) lack of S cone pigment
Insensitive to blue and yellow
Incidence: 0.001% males, 0.003% females
Short wavelengths appear greenish
Long wavelengths appear reddish
Ocular disorders
Caused by glaucoma, diabetes
Diabetes: has to do with growth of blood vessels across retina
Primarily affect S cones
What are the types of monocular cues?
-Oculomotor; cues we get from muslces in the eye
-Pictorial; cues we get from a 2D image; image that's available from a 2D image
-Movement-based; cues based on things moving around in the environment and our movement
Name and describe pictorial cues
Occlusion: Interposition: one object partly blocks (occludes) another
Height in the field: Objects below horizon: higher objects appear farther
Objects above horizon: lower objects appear farther
Relative size: If 2 objects are same size, closer one casts larger retinal image
Familiar size: Knowledge of object's size influences perception of distance
Cast shadows: Distance of object from its shadow indicates height
Texture gradient: Texture elements appear smaller and denser with distance
Aerial perspective: Distant objects appear less clear
Linear perspective: Parallel lines appear to converge as they recede in depth
Name and describe motion-based cues
Motion parallax
Deletion/accretion: Overlapping objects(occlusion); Observer moves: objects move relative to each other
Stereopsis
-deriving depth from binocular views; process of using binocular disparity to find out where things are located in depth
-2 stages
First: determine amount of binocular disparity
Take image and figure out how different the view that each eye has
Second: use this to determine depth
-We have cells that are tuned to different amounts of disparity and to crossed or uncrossed images... in v1 we are already picking up the amount of disparity in an image
Panum's fusion area
region of fused images around horopter
Vestibulo-ocular movement
-If body/head moves, your eyes move in the opposite direction to keep fixated on object
-Mechanism
Input from inner ear
Sense head movement
Akinetopsia
seeing the world as a series of still images (lack of motion perception)
Induced movement
Stimulus against background → background starts to move
Perception: stimulus is moving
Example: moon behind clouds
Autokinetic movement
Fixate on point of light in completely dark room
Light appears to move
Explanation: involuntary eye movements
Move eyes and the stimulus moves, and they misinterpret stimulus movement but it's only the eye moving
Paralyzed eye
There is an efferent signal and CDS, but not afferent because eye didn't move
-therefore perceive motion, even though eye isn't moving and world isnt moving
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