Psych part 7
Terms in this set (97)
physical stimuli that consistently produce errors in perception
Illusions occur when what we see does not correspond to what is physically present in the world
What do illusions tell us about normal vision
Illusions over time
brightness after effect
after staring at a black image and look at a blank screen then you will see the reverse pattern of illumination
experiment: the sensory systems are interested in changing stimulation
-- look at the + in the centre and the purple dots will dissapear
After adapting to a colored patch, a person staring at a white patch will perceive the opposing color (e.g., after adapting to blue, the person will perceive yellow).
negative color after images
Explanation: pigment bleaching / neuronal fatigue and opponent processing of colour
Reconciling Color Theories
- blue, green and red cones
- process green and red in an opponent processing manner
- ganglion cells have opposite inputs from the colored light
- green has a positive synaptic input and red a neg
- ganglion cell responds to green light and is inhibited by red light
opponent processing along with neuronal fatigue cause color after effects
if you stare at a waterfall and then turn away, the scenery you are now looking at will seem to move upward
post adaptation: g is tired so mainly r
An illusion that occurs when you first view a moving pattern, such as stripes moving off to the right (or a waterfall), and then you view a spot of light—the spot of light will appear to move in the opposite direction.
Waterfall illusion, spiral after effect.
Explanation neuronal fatigue and opponent processing of motion direction
Opponent Motion Processing
- you build up movement after effects in different parts of your retina
Illusions Over Time
Brightness after effect
Colour after effect
Motion after effect
Orientation after effect
Adapt (get used) to steady state
Code (overemphasise) change in values across time
Illusions Over Space
Orientation contrast (Zöllner illusion)
Visual qualities are coded relative to the surround
the increase or decrease in an object's apparent brightness by comparison to objects around it
Object brightness coded relative to the surround brightness
the fact that colors can look different depending on the surrounding colors
Object colour coded relative to surround colour
The Zöllner Illusion
Illusions of Size
Object size is inferred from perceived distance and image size
For 2 objects with the same image size, the object appearing further away is seen as larger
The Ponzo Illusion
An illusion of size in which two objects of equal size that are positioned between two converging lines appear to be different in size. Also called the railroad track illusion.
The visual system makes hypotheses about distance to objects based on evidence in the image. Interpretation of size follows.
Objectively equal in separation,
Perceptually equally separated, objectively 30% different
Perspective cues set up false interpretations of distance
Trapezoidal room; creates an optical illusion with one large and one small person
has false distance cues: left & right corners appear equally far but are not.
Objects at different distances appear equally far (retinal size differences are seen as real size differences)
Images that are capable of more than one interpretation
Figure ground reversing figures
2-D images have one or more 3-D interpretation.
Entertain each interpretation, but only one at a time
An outline that is perceptually bi-stable. Unlike the situation with most stimuli, two interpretations continually battle for perceptual dominance.
Conditions for motion perception
Lights flashing with:
close separation and short time interval = motion,
wide separation or long time interval = no motion
Mechanism for detecting motion direction
Local inhibition in one direction
Detects real or apparent motion in direction opposite to inhibition
Relies on apparent motion
Brain interpolates smooth change in shape
Controlling Posture and Action
Posture is less stable with closed eyes
Lee's swinging room
When the room moves, visual motion is attributed to body motion which causes inappropriate posture compensation
the complex motion of points in the visual field caused by relative movement between the observer and environment; provides information about the relative distance of objects from the observer and of the relative direction of movement
focus of expansion = heading direction
Landing a plane on an aircraft carrier
Estimating time to contact /collision (Lee)
Rate of expansion predicts when to react
(e.g. catching a ball, braking, gannet diving)
Detecting Form from Motion
'Kinetic Depth'. Shape from changing silhouette
what way is the ballerina spinning?
Biological motion (Johanasson)
Form of moving body from lights on joints (dots)
Perception of Causality in Collisions (Michotte)
Impression of causality
One object bumps into a 2nd object,
stops, then the 2nd object moves off.
Reduced impression of causality
2nd object moves off before the collision
2nd object moves off after a long delay
Attribution of Purpose(Heider & Simmel)
Cartoon movies in which actors are arbitrary shapes with trajectories appropriate for meaningful actions.
Subjects attribute actions and intentions to the moving shapes (e.g. the big triangle chased the little triangle)
Repeat film until infant observer is bored.
Measure renewed interest
Violation of expectations - surprise & long looks
12 month olds look the most at incongruent action
Motion Defining Goals
1 year-olds infer unseen goals, i.e. sensitive to likely outcome of an action
Increased attention if agent's action is inconsistent with earlier goal - catching small ball:
does not take shortest path to small ball, continues on non-intercept trajectory
habituation --> incongruent goal --> congruent goal
Motion Processing in the Brain
Neurons in MT/MST are sensitive to motion coherence; MST is notably responsive to optic flow
Visual area V5 (MT)
V5 cells are motion sensitive
V5 damage causes 'motion blindness'
inability to track fast movement
see a series of frozen 'snapshots'
High level object detectors
Mid level pattern detectors
Low level feature detectors
Touch perception can be influenced by psychological factors
high level object detectors
mid level pattern detectors
Bidirectional Processing Models
information flow is bottom up and top down
expectations lower threshold for likely items
information processing guided by higher-level mental processes, as when we construct perceptions drawing on our experience and expectations
More connections descend than ascend.
Only 3% of V1 input layer synapses are from LGN
Vision = 97% reconstruction or hallucination
Recognition of objects is easier in correct context
What letter is? Ħ
TĦE = THE CĦT = CAT
Word context biases interpretation
Word superiority effect
Detecting a letter in is easier when in a word
w/o visual input
Brain Areas Processing Sight of Faces & Places
fusiform face area & parahippocampal place area
Imagining faces & houses activates visual cortex
"walking through home" - parahippocampal area
"playing tennis" - supplementary motor cortex
Detect awareness in the vegetative state
We expect an object moved behind a screen to reappear with the same form when screen removed
<8 months abort search if object hidden
Infants >8 months old search for hidden objects
An object becomes hidden behind a screen
When the screen is moved, >6 month infants surprised if the object is gone (Bower).
Scrub jays cache (hide) food & return:
Sensitivity to detect target presence
% correct = Hits/Targets
Need also to consider False Alarms (False Positives)
Signal Detection Test
Target = Number 8
How many targets?
You win £5 if detect all targets
Reward for hits & no penalty for false alarms
encourages 'target present' bias
How many targets?
Any false alarms - I set a "signal detection question" in exam
No reward for hits and severe penalty for false alarms
encourages 'target absent' bias
this theory predicts how and in what circumstances we can detect a stimulus; assumes there is no single threshold
Target present ("Yes") bias generates false alarms
Target absent ("No") bias generates misses
Bias affected by:
% trials target present
payoff detecting/missing targets
Consider benefits from hits and correct rejections
& costs of misses, and false alarms
e.g. fire alarm
false alarm wastes time
a miss may result in avoidable death
Perceptual priming - conscious & subliminal
Rapid serial presentation 40 ms / image
Brief images (11 ms) are seen but memory is fleeting. They may not achieve full awareness but can affect recognition & bias behaviour.
Brief images and words lower the threshold for activating related objects / concepts.
The word "Alzheimer's" can impair memory performance.
The word "fast" speeds up reading & walking.
Speed associated words quicken walking.
Experimenters can transmit bias to participants
Fixations (pauses) when the eyes still (3 - 4 per second)
Saccades (jumps) between fixations
Slow tracking following a moving object
To direct fovea to features of interest
Vision turned off during eye movement
We cannot see our own saccades in a mirror
Relative coding of motion
Inhibition between similar motion detectors
Compare movement predicted & occurring
ex. The cat's image moves over the retina
Tracking keeps the cat's image on the fovea
Stability of the Visual World
Sources of information for comparison
'Feed-back' from stretch receptors in eye muscles
'Feed-forward' from planed movements
'efference copy' of commands to move eyes cancels incoming image movement
Evidence for feed-forward
Passive eye movement
Press eye to the (gently) scene moves
Paralysis of eye muscles
Try to move paralysed eyes scene jumps
Stability of the Sensory World
Attend to unpredictable events
Ignore predictable consequences of own actions
Sub-vocal speech not recognised as self-generated
Own actions & thoughts controlled by others?
Factors affecting face attractiveness
masculinity in men, femininity in women
Theory Immune competence handicap hypothesis
Composite (Average) Faces
Blending a group of faces shows consistent traits and looks handsome
Attractiveness is Averageness?
Blend of faces is more attractive than originals.
Skin texture gets smoother,
Face becomes more symmetric.
Avoid extreme non-average (mutant) genotypes
Mere exposure: we like what we seen often
Attractive faces are systematically different from average
Eggs (bigger than sperm),
Females choosier than males
Exceptions: sea-horse, stickleback
What do females choose for most offspring?
What do females choose to get most offspring?
Low fluctuating asymmetry, ability to grow to plan.
Honest signals of a costly handicap
Immune competence. Testosterone suppresses immunity; only fit males can afford testosterone cost
Predicts attraction to sexually dimorphic male traits
Fluctuating asymmetry: left = right for population
Low Fluctuating Asymmetry
shows coped with challenges during growth
indicates health & immunity
tail symmetry is preferred in swallows
Is symmetry attractive in humans?
More symmetric face shape preferred
Manipulating Masculinity of Face Shape
Male masculinity shows strength & immunity. It should be attractive?
Surprising aversion to masculinity
feminine= warm honest "dad"
masculine= cold dishonest "cad"
Sexual selection for parental care?
Selection may favor preference for facial features indicating paternal investment.
High testosterone linked to marital problems
Hormone Levels Across the Menstrual Cycle
Between day 0 and 14 of menstrual cycle
Increased attraction to masculinity when fertile
Menstrual cycle and preferences
Fertility highest in late follicular phase
Preference for masculinity follows fertility for short - but not long-term relationships
Parallel effects for
Masculine voice quality
Masculine dominant behaviour
Male pheromone odor
Women's attraction to odors
Fertile phase - prefer male pheromone
Mate selection occurs for both sexes
In several primate species
Feminized faces in women are more attractive
If long tails are attractive to males and females nd tail length varies, how will individuals pair up?
If humans compete for attractive partners how will humans pair up?
For long term relationships, less actractive women prefer lower level of masulinity anf focus less on symmetry
Attractive women may extract greater commitment from symmetric / masculine men
We learn attraction to individuals we can get/keep
Own Status and Competition
Women report own attractiveness and judge faces for
(a) long-term relation (e.g. marriage)
(b) short-term relation (e.g. 'fling')
Choose faces manipulated in masculinity or symmetry
Attractive women prefer more masculine men
Attractive women prefer more symmetric men
Imprinting on parent characteristics
Imprinting. Early exposure to parent traits affects later mate preferences in birds and mammals
Male lambs fostered by female goats prefer goats to sheep as sexual partners
Imprinting in humans
Does a husband resemble a woman's father or mother?
Faces of families: daughter (adopted at 2-8 years), husband, father & mother at marriage.
Task: match husband face to 4 alternatives
Results: (chance =25%)
Opposite sex parent and partner are similar.
Imprinting on opposite sex parent
Pheromones: Airborne chemicals influencing physiology or behaviour.
Awareness not needed for effects
In humans not a wonder aphrodisiac!
Gibson's Theory of Direct Perception
A theory of perception that argues that all information necessary for perception is available to the sensory system and no cognitive processing is necessary to complete the perceptual process
Visual information controls actions directly.
Visual properties of objects 'afford' actions
e.g. sitting on, picking up, poking
We recognize which action can be achieved
Perception & Action
Perception guides action; action changes perception
parietal lobe: direct controls of actions
temporal lobe: recognition & memory
Ventral Pathway Damage cannot recognize objects, orientation, size.
Patient DF poor at matching a handle to target orientation
- Patient DF can guide actions visually (e.g. posting an elongated object into oriented aperture)
Action. Dorsal Pathway, V1--> Parietal lobe
Damage --> ataxia: cannot guide actions
but can recognize objects.
Perception. Ventral pathway, V1--> Temporal lobe
Damage --> agnosia: cannot recognize objects
but can guide actions.
circles equal in size
Visual control of action does not suffer illusions.
Grip size during reaching under 'online' visual guidance is accurate.
Action - perception coupling
Are the motor and the perceptual systems integrated?
Can action production influence perception
Motion perception primed by actions
Rotation with ambiguous direction.
Turn hand (clockwise,
Think 'turn clockwise'.
Display moves with your action or plan!
Common code for perception & action control.
See intended or associated effects of action.
Mirror Neurone Systems
Cells fire during performance of hand actions
Cells fire when others seen or heard doing the same action
Seeing and doing use same brain systems
Action recognition depends on production ability
(Understanding Actions &) Mirror Neurons
Pre-motor cortex 'mirror neurons':
discharge during the observation and execution of an action,
discharge when the action goal hidden but can be deduced,
discharge when an action can only be heard,
Could enable understanding actions of others by translating them into our own actions
Support imitation or empathy?
Seeing or Doing
Does our mirror system respond to the sight of actions because they look familiar or because we know how to do the action?
Compare brain response to sight of actions
visually familiar (but not performed)
motorically familiar (often performed)
Active more to seeing own-sex than other-sex dance moves.
Same & opposite sex dance moves were equally visually familiar.
Mirror system active when see actions within our motor repertoire.
Analyse others' actions in terms of how we would perform them.
A Touching Sight
Does observing someone else being touched activate our own somatosensory cortex?
Movies of actors being touched on their legs
Touch of the subject's legs
Some brain areas activated by both sight and touch
touch: subject has eyes closed --> brush leg-->SI: primary somatosensory cortex-->
SII: secondary somatosensory cortex,
group results: Overlap: both seeing & feeling touch --> touch to your leg is represented in my brain
Simulation model of (understanding others)
(touch, disgust, actions) matched to our own social stimulus
Social perception requires understanding the actions, sensations and emotions of others.
Seeing or hearing others' actions activates our premotor action plans 'as if' we do the actions.
Witnessing touch activates our secondary somatosensory cortex 'as if' we are touched.
Witnessing other's disgust activates our insular cortex 'as if' we experience disgust.
Witnessing others in pain activates similar brain regions to experiencing pain ourselves
Action Perception & Production
TMS (trans-cranial magnetic stimulation) of motor cortex produces electrical potentials in muscles.
Seeing actions using the same muscles reduces the threshold for TMS produced muscle potentials.
Hearing speech and seeing lip movements increases tongue and vocal muscle excitability.
Motor theory of speech perception: we simulate production of speech we hear.
Attending to one object type
Boosts activity in relevant brain system
Attend faces ... fusiform face area
Attend houses ,... parahipocampal place area
85% miss gorilla in image when cancer screening
(Why does the world appear) static (when our eyes move?)
Vision turned off during eye movement
We cannot see our own saccades in a mirror or mobile selfie
We do not notice change in the world that occurs during a saccadic eye movement
Subjects attending to one object or position can be blind to other objects and unexpected events
Subjects must attend to objects to notice them
but attention may not be enough.
Changes (saccades and events) can distract us.
Change Blindness examples
While a door is carried between people, one person changes identity 50% of observers don't notice the change
Flash disrupts spotting image change
ex. Look for signal relevant to driving
-- Flashes within the image decrease chance of seeing other changes
Slow Changes Go Unnoticed
Change is noticed by the motion between the original and new form of an item
We miss change
(a) if it happens slowly,
(b) if an irrelevant transient (e.g. flash, saccade) occurs between the original & new forms,
(c) if the changes occur in moving arrays
Movement itself can prevent us noticing changes in colour, size, shape (motion silencing illusion)
Seeing Depends on Attention
Inattention blindness events not seen
Attention control problems (neglect) can mean that part of the world is selectively ignored
Neurological disorder in which a patient does not attend to anything on one side (usually the left side)
left side is underestimated
mild form present in normal people
seen in object drawing
Damage to Right temporal/parietal cortex
Inattention to left side of space & objects
Cross items only on right of an array
Bisect right of lines
Draw only right side of objects
For cells responsive to faces, most code head view responding to mainly to one view (e.g., face, profile)
Evidence for coding of attention direction
2/3 cells code gaze & face view
2/3 cells code face & body view
Importance: gaze > face > body
e.g. wrong gaze direction inhibits correct face view
Problems processing gaze
Spontaneous attention following deficit
but good at gaze geometry
Using Attention Direction
get food out of dominant's sight (chimps),
re-hide food if seen (jays),
define what others know or believe (kids).
knowledge used competing / cooperation
objects of fear (monkeys)
words for objects looked at (kids)
Nature vs. Nurture
Nativist (e.g. Descartes)
Perceptual abilities inborn
Empiricist (e.g. Berkeley)
Perception depends on experience
Test only when mobile,
goats fearful on deep side, day 1,
Size constancy (Bower)
Trained head turn response with peekaboo reward
generalises to trained size at changed distance
Looking preference 2 min old
Imitation of facial gestures (tongue protrusion)
Recovery from Blindness
Figure - ground segregation
Cross modal matching: touch to vision
Problems in interpretation
Unknown experience before blindness
Adult knowledge used in interpreting vision
Degeneration of the visual system
Experience & the Nervous System
A few hours experience biases V1 cell orientation tuning (Blakemore)
Visual Cortex (Blakemore)
Orientation sensitive cells present at birth.
Visual environment influences the distribution of orientation sensitive cells.
Critical period of influence (3-7 weeks in cats).
Cells responsive to simple aspects faces may be inborn,
but show effects of experience
Experience and Perception
Effects of Culture
Recognition of letters and words
Inuit perception & discrimination of snow
Colour words blue & green (Whorf)
short term & long-term
Drawings and art use conventions & knowledge.
Adaptation to Prisms
How far can the brain adapt to changed vision?
Prisms shift the visual world in one direction
Adaptation in chicks?
--> prism goggles for chicks
--> Motor system matures; consistency in aim increases
But ability to hit target does not !
Adaptation in humans:
Visual - motor coordination compensates.
Adaptation leaves an aftereffect:
behaviour biased in compensatory direction
Why should the system adapt?
Eye changes shape
Need to re-calibrate visuo-motor coordination
Adaptation to Inverted Vision
Initially world looks upside down (and is sickening)
After weeks of adaptation world looks 'normal'
Motor skills return: cycling, skiing possible