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Requires looking over it, choosing which parts of scene are important to notice. We have finite amount of attention and have to choose where to focus
Stimulus salience (relevant) – areas of stimuli that attract attention due to their properties (bieber in a scene)
· Color, contrast, and orientation are relevant properties
· Saliency maps show fixations are related to such properties in initial scanning process (red shirt in crowd of white)
Scene schema - prior knowledge about what is found in typical scenes
•Example: is this something you’d see on a Basketball court? (picture of a soccer game)
• Prior knowledge suggests no!
• Fixations are influenced by this knowledge
• So, it becomes a salient feature to focus on
Experiment by Shinoda et al
· Observers fixations were measured during computer stimulated driving
· They were more likely to detect stop signs when they were at intersections
· People learned this is where stop signs are typically placed
>> Detect printer in kitchen
Task demands override stimulus saliency.
• If we’re deep in thought or focused on getting something done, we tend to ignore things that might otherwise be focused on
• Eye movements and fixations are closely linked to the action the person is about to take. "look before you leap" >>making PBJ, fixation on bread, than plate, than knife, peanut butter… etc.
Experiment by Posner:
> Observers looked at fixation point
>An arrow indicated which side stimulus was likely to appear
>Stimuli appeared that were consistent (valid trials) or inconsistent with the cue (invalid)
>Task was to push button when a target square was seen
showed that observers responded fastest on valid trials.
• Posner believed these results showed that information processing is most efficient where attention is directed.
Experiment by Egly
· Observer view two rectangles
· Cue signals where target may appear
· Task to press button when target appear
Results: Fastest reaction time at targeted position
> "Enhancement" effect for non-target w/in the target
Experiment by Carrasco et al.
Observers saw two grating stimuli with either similar or different contrast between the bars.
Task was to fixate on center point between gratings and indicate orientation of bars with higher contrast.
Small dot was flashed very quickly on one side before gratings appeared.
when there was a large difference in contrast, the dot had no effect.
• when the contrast was the same, observers were more likely to report that the grating preceded by the dot had higher contrast.
• Thus the shift of attention led to an effect on perception
• Participants were shown a picture of a face superimposed over a house
• Attending to the face caused an increase activity in the FFA and attending to the house caused enhanced activity in the parahippocampal place area (PPA)
Inattentional blindness - a stimulus is not perceived even when the person is looking directly at it
Experiment by Simons and Chabris
People shown film of teams passing a basketball.
Task is to count number of passes.
Either a woman/gorilla walks through the teams.
46% of observers fail to report girl/gorilla
Observers were shown a picture with and without a missing element in
an alternating fashion with a blank screen.
• Results showed that the pictures had to alternate a number of times before the change was detected.
• When a cue is added to show where to attend, observers noticed change more quickly.
Also occurs for film shots. (cigarette burns)
• People are “blind” to the fact that they experience change blindness.
• Real objects in the environment change with some type of movement, which is why we normally don’t experience change blindness.
>Ex. w/ person asking for directions (change person and people don't usually notice)
• Experiment by Li et al (2002):
• Observers performed one of three tasks (at same time)
• Central task - determine whether letters flashed in the center of the screen are the same
• Peripheral task - determine whether faces flashed to the side of the screen contained an animal
• Dual task - do the same as the peripheral task and determine the color of a disc
A task-irrelevant stimuli- it doesn’t provide info relevant to task, so paying attention to it weakens your perceptual ability
having participants indicate whether an N or X was present in a group of letters
Easy condition: The target letter was uppercase and the distractors were all lowercase o’s
Hard condition: Target letter was uppercase and so were the distractors; distractors were all
Additional difficulty: Occasionally flashed a cartoon picture during the task
1) Perceptual capacity: we have a certain amount of processing power that can be dedicated to perception at any given tome
2)Perceptual load: indicated how much of that capacity is being taken up
3) Low-load task: Easy, well practiced tasks that don’t require much capacity (driving car easier now)
High load task: Harder, newer task that require more capacity ( talking on phone while learning to drive)
Though the world is made up of many disparate parts, we somehow experience it as a coherent whole
Binding - process by which features are combined to create perception of coherent objects
Binding problem - features of objects are processed separately in different areas of the brain
Breaks down the process of binding into multiple steps
1)Preattentive stage: objects are broken down by the brain into their constituent features, such as color, size, momentum, etc.
>The rolling ball is red, moving to the right, etc.
We don’t perceive things as separate pieces. We don’t see them because this step happens before we focus
Illusory Conjunctions - features that should be associated with an object become incorrectly associated with another.
Flash variety of shapes, colors, number for half second
o Free floating features
o Focus on number more than shapes
attention is brought to bear on the scene
>the objects formely analyzed into pieces are bound toughte into a coherent scene
Balint’s syndrome: patients with parietal lobe damage show lack of focus attention results in incorrect combination of features
Conjunction search- finding target with two or more features
· Requires putting together multiple pieces of data
· Patients with parietal lobe damage cant perform conjunction searches well compared to those without damage
** Parietal lobe is destination for the "where" stream
A major symptom of autism is withdrawal from contact with people.
• People with autism can solve reasoning problems about social situations, but cannot function when placed in these situations.
Non-autistic observers: Looked at eyes of actors to determine emotional state
• Looked in the direction a person pointed
Autistic observers look at socially irrelevant stimuli
• Thus, where autistic individuals pay attention in a social situation may lead to perceiving the world differently.
All participants performed at 99% accuracy.
• But, activation of the STS for nonautistic people was higher in the incongruent condition.
• Autistic people showed equal activation in both conditions.
• Results suggest that autistic people cannot read intentions of others.
felt that traditional lab research on perception was:
1)Too human focused – not enough about how animals perceive
2)Too artificial- observers were not allowed to move their heads
3)unable to provide an explanation for how pilots used environmental info to land airplanes
Conceived of the environment as rich with info and regularities
1)Vision guided by optic array= structure created by surfaces, textures, and contours in the environment
2)Optic flow- appearance of objects as the observers move past them
3) Gradient of flow- difference in flow as a function of distance from the observer
4) Focus of expansion- point in distance where there is no flow
Self-produced information - flow is created by the movement of the observer
- As you move through the world, information moves around you
- Creates an unchanging point of reference – you! (you know how tall you are/ how fast you're moving)--Invariant information - properties that remain constant while the observer is
moving (chairs don't move as I walk around room)
As we move, the information around us is constantly updated, as we get a new perspective on things
• Example - Somersaulting
• Could be performed by learning a predetermined sequence of moves; thus
performance would be the same with and without vision
That expert gymnasts performed worse with their eyes closed.
• They use vision to correct their trajectory.
•Novice gymnasts do not show this effect.
13-16 month old children placed in “shifting room” floor was stationary but walls and ceiling swung backward and forward
The movement created optic flow patterns
--- Fall forward when room goes forward
-- Children swayed back and forth in response the flow patterns created in the room
**Showed that vision has powerful effect on balance
Neurons in medial superior temporal area of monkeys respond to flow patterns
>Monkeys trained to respond to the flow of dots on a computer screen
· Indicated whether the dots flowed left, right, forward, back
As monkeys did task, microstimlation was used to stimulate MST neurons that respond to specific directions of flow patterns
· Judgments were shifted in the direction of the stimulated neuron
Measure speed of vehicle and direction of gaze of driver
>When driving straight, driver looks straight ahead but not at focus of expansion
>When driving around a curve, driver looks at a tangent point at side of the road
= suggest drivers use other info in addition to optic flow to determine their heading (might be noting the position of car in relation to the center line or side of road)
Visual direction strategy - observers keep their body pointed toward a target
• Walkers correct when target drifts to left or right
• Blind walking experiments show that people can navigate without any visual stimulation from the environment.
Type of navigation task where a participant needs to use environmental cues to understand where to go
Example: “Turn left onto spring street.” In order to know when to turn left, you need a landmark
• A variety of studies have been done that show that perception is key to this type of action
> Hippocampus, parahippocampus gyrus, retrosplenial cortex
Observers studied a film moved through a virtual museum
· told they should be able to act as a guide within a museum
· exhibits appeared both at decision points where turns are necessary and non decision points
Presented with objects they had seen as exhibits and ones they had not seen
proposed that perception of the world is made of affordances: a potential for action (what is an object used for? ) –not about waves/light
>Found the relationship between an organism and objects in its environment are different
Ex: the chairs in room are stand onable for me, but not for my infant daughter
-People with certain types of brain damage cant name an object, but can describe what object is used for
Neurons in the parietal lobe that are silent when a monkey was not behaving, fire when the monkey reached to press a button to receive food.
• This response only happened when the animal was reaching to achieve a goal.
• Suggests that perception might be a goal-oriented process, or based on actions
Neurons that only activate in the context of imitation
In the cortex of monkeys:
• Respond when a monkey grasps an object and when an experimenter grasps an object
• Response to the observed action “mirrors” the response of actually grasping
• There is a diminished response if an object is grasped by a tool (such as pliers).
respond to action and accompanying sound (easier)
Mirror neurons may help link sensory perception and motor actions
1. No need for abstract representations; instead, ground everything in action
2. Affordances mean we don’t need to process everything, just what is relevant for action.
· The act of processing the world is removed from the brain and placed in the environment/organism link
· thus if prey remains motionless, less likely to be noticed
· Akinetopsia- blindness to motion
·Assists in organization of stimuli
-Cue for determining what world around us looks like
1)Apparent and real motion - activation of visual cortex from both sets of
stimuli was similar
2)Thus the perception of motion in both cases is related to the same brain mechanism.
Ecological approach (Gibson)
• Information is directly available in the environment for perception.
• Optic array - structure created by surfaces, textures, and contours, which change as the observer moves through the environment.
Local disturbance in the optic array
-A part of the optic flow changes, while the rest remains the same
-Indicates the object that changed is moving, not the observer
• Global optic flow
-Overall movement of optic array
-Indicates that observer is moving and not the environment.
Corollary discharge theory - movement perception depends on three signals
Image displacement signal (IDS) - movement of image stimulating receptors across the retina
Motor signal (MS) - signal sent to eyes to move eye muscles
Corollary discharge signal (CDS) - split from the motor signal, sent to a different part of the brain
Movement is perceived when comparator receives input from:
• corollary discharge signal, OR
• image displacement signal.
Movement is not perceived when comparator receives input from:
• both corollary discharge and image displacement signals at the same time.
area in humans leads to perception of movement of stationary environment with movement of eyes
· Real-movement neurons in moneys that response only when a stimuli’s moves and don’t respond when eyes move
· This may occur in medial temporal cortex, which is located in the where/ action stream
Monkey trained to indicate direction of fields of moving dots.
Neurons in MT cortex that respond to specific direction were activated.
Experimenter used microstimulation to activate different direction sensitive neurons.
Monkey shifted judgment to the artificially stimulated direction.
observation of small portion of larger stimulus leads to misleading information about direction of movement
--- Neurological studies show biological motion is processed by STS and FFA
Participants viewed point light stimulus for activities. Task was to determine whether motion was biological or scrambled
• Implied motion
• No-implied motion • At rest
Results showed areas of brain responsible for motion fire in response to pictures of implied motion.
Three different receptor mechanisms are responsible for color vision
Behavioral evidence: Observers adjusted amounts of 3 wavelengths in a comparison field to match a test field of one wavelength
- Observers with normal color vision need at least 2 wavelengths to make the matches (red, blue, yellow)
-Observers with color deficiencies can match colors by using only 2 wavelengths
Found pigments that respond maximally to:
o Short wavelength (419 nm) blue
o Medium wavelengths (531 nm) green/yellow
o Long wavelengths (558 nm) red
· Later researchers found genetic differences for coding protein for the three pigments (1980s)
affects 1% of males and 0.02% females
· Individuals see short wavelengths as blue
· Neutral point occurs at 492nm
· Above neutral point, they see yellow
• They are missing the long-wavelength pigment
• So, don’t easily see the green/red part of the spectrum
affects 1% of males and .01% of females •
Individuals see short-wavelengths as blue
• Neutral point occurs at 498nm
• Above neutral point, they see yellow
• They are missing the medium wavelength pigment
• Individuals see short wavelengths as greenish, and dimmed
• Neutral point occurs at 570nm
• Above neutral point, they see red
• They are most probably missing the short wavelength pigment
Color vision is caused by opposing responses generated by blue and yellow and by green and red
· color afterimages and stimulus color contrast show the opposing pairing
· types of color blindness are red/green and blue/ yellow
> American flag experiment
Three mechanisms red/green,blue/yellow,andwhite/black
The pairs respond in an opposing fashion, such as positively to red and negatively to green
These responses were believed to be the result of chemical reactions in the retina.
Notice that these are also complements on the color wheel
Researchers performing single-cell recordings found opponent neurons (1950s)
o Are located in the retina and LGN
o Respond in an excitatory manner to one end of the spectrum and an inhibitory manner to the other
Perception of colors as relatively constant in spite of changing light sources
·-Sunlight has approximately equal amounts of energy at all visible wavelengths
Tungsten lighting has more energy in the long wavelengths
o Objects reflect different wavelengths from these 2 sources
o But we still see the object as the same
Observers shown sheet of colored paper in 3 conditions
· Baseline- paper and observer in white light
· Observer not adapted - paper illuminated by red light; observer by white
· Observer adapted - paper and observer in red light
1) Baseline - green paper is seen as green
2) Observer not adapted - perception of green paper is shifted toward red
3) Observer adapted - perception of green paper is slightly shifted toward red
o Partial color constancy was shown in this condition
o understanding of paper doesn’t change much
Achromatic colors are perceived as remaining relatively constancy
Perception of lightness:
-Is not related to the AMOUNT of light reflected by an object
-Is related to the PERCENTAGE of light reflects
· Light bulb and sun seen same brightness (10:1) ratio
Illumination edges- edges where lighting of two surfaces changes (a/b) color the same, same object
1) Information in shadows- system must determine that edge of a shadow is an illumination edge
2)System takes into account the meaningfulness of objects-------Shadow is distinct and not an object
3) Penumbra of shadows signals an illumination edge
· Boarder between shadows and objects (so you can tell it’s a shadow and not black paint circle)
The moon appears larger on the horizon than when it is higher in the sky.
• One possible explanation:
• Apparent-distance theory - horizon moon is surrounded by depth cues while moon higher in the sky has none.
• Horizon is perceived as further away than the sky - called “flattened heavens”.
-Since moon in both cases has same visual angle, appear larger at horizon
Fluid-filled snail-like structure (35 mm long) set into vibration by the stapes
Divided into the scala vestibuli and scala tympani by the cochlear partition
Cochlear partition extends from the base (stapes end) to the apex (far end)
Organ of Corti contained by the cochlear partition
Basilar membrane vibrates in response to sound and supports the organ of Corti
Tectorial membrane extends over the hair cells
Cilia bend in response to movement of organ of Corti and the tectorial membrane
Movement in one direction opens ion channels
Movement in the other direction closes the channels
• This causes bursts of electrical signals.
• Which fibers are responding
>Specific groups of hair cells on basilar membrane activate a specific set of nerve fibers;
• How fibers are firing
>Rate or pattern of firing of nerve impulses
Frequency of sound is indicated by the place on the organ of Corti that has the highest firing rate.
Békésy determined this in two ways:
Direct observation of the basilar membrane in cadavers.
Building a model of the cochlea using the physical properties of the basilar membrane.
• Base of the membrane (by stapes) is:
>Three to four times narrower than at the apex.
>100 times stiffer than at the apex.
• Both the model and direct observation showed that the vibrating motion of the membrane is a traveling wave .
Indicates the point of maximum displacement of the basilar membrane
Hair cells at this point are stimulated the most strongly leading to the nerve fibers firing the most strongly at this location.
Position of the peak is a function of frequency.
Electrodes are inserted into the cochlea to electrically stimulate auditory nerve fibers.
• The device is made up of:
a microphone worn behind the ear,
a sound processor,
a transmitter mounted on the mastoid bone,
and a receiver surgically mounted on the mastoid bone.
Békésy used basilar membranes isolated from cadavers and his results showed no difference in response for close frequencies that people can distinguish.
New research with live membranes shows that the entire outer hair cells respond to sound by slight tilting and a change in length.
• Basilar membrane can be described as an acoustic prism.
There are peaks in the membrane’s vibration that correspond to each harmonic in a complex tone.
Each peak is associated with the frequency of a harmonic.
Place coding is effective for the entire range of hearing.
Temporal coding with phase locking is effective up to 5,000 Hz.
-most of hearing is done toward back of brain
-parts next to each other in cochlea are also next to each other in brain
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