Gestalt Principles:
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Gestalt psychologists believed “the whole is different (Greater) than the sum of its parts”
(Perceive whole stimulus rather than individual part) (Watching movie of slightly different static
pictures every second)
Motion: Emergent property of the sequence of pictures.
Gestalt Principles: We are either born with these laws of organization or we acquire them rapidly. Law
that describes how we organize visual input.
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1: Figure-ground: Ability to distinguish an object from its background in a visual scene.
(Figures have distinct borders to give it form over background)
2: Proximity: Tendency to group elements close together in space (Regions of high
density = one group)
3: Closure: tendency to fill in gaps in contour to perceive whole object (Automatically fill
in parts we can’t see to perceive a single object)
4: Similarity: tendency to group together physically similar elements (Group together
objects of same type)
5: Continuity: Ability to perceive simple, continuous form (Rather than combination of
awkward forms) (Perceive each stem of flower as single continuous line)
6: Common Fate: tendency to group together elements that change the same way.
(Objects moving together in the same direction = grouped)
Pattern/Object recognition
Expectation shapes what we see
object recognition:
1. Establish figure from background
2. Bottom-up processing: Object recognition guided by features present in stimulus. (Analyze
individual features and comparing them to similar features from memory)
3. Top-down processing: Object recognition guided by own beliefs/expectations. (
a. Can be primed: Processing more efficient if
participant primed to expect a word from
category.
b. Needs input from stimulus before
expectatons of stimulus can influence
recognition.
Top-down and bottom-up processing guide object recognition. It can rely
on varying degrees of processing.
Bidirectional Activation: Both bottom-up and top-down processing.
)
Geon theory: have 36 representative geons (simple geometric forms) stored in memory. (Con: 1: Certain
stimuli difficult to determine which geons. 2: Brain injury can affect recognition for only certain types of
objects)
Template theory: we compare objects to templates in memory. If match found = familiar object and
people can name by activating connections to other language areas in brain. If no match = unfamiliar
object makes new template stored in memory. (Con: 1: Would have to store large number of different
templates to recognize all different objects encountered.)
Prototype theory: we compare objects to our ideal prototype (Most typical/ideal example of object).
Multiple brain systems process different components of vision
in parallel
Perceptual Constancies:(Exist from prior knowledge and cues from our scene)
We retain perceptual constancy despite variation in visual stimuli
Perceptual Constancy: Ability to perceive object as unchanging even though visual image produced by
object is constantly changing.
1. Shape Constancy: Object perceived as constant shape despite shape of its retinal image
changing with shifts in point of view or change in object position.
2. Location Constancy: Object perceived as stationary despite changing location on our retina
due to body movements (While driving we don’t perceive objects outside to be moving)
3. Size Constancy: Object perceived to be the same size of its retinal image varying with
distance. (Don’t shrink in size as walking away from object)
4. Brightness Constancy: Object perceived
to be same brightness despite reflecting
more/less light onto retina.
(Objects=same brightness whether in
high/low illumination)
5. Color Constancy: Object percieved to
have constant color despite illumination conditions.
Cues in scene indicate perceptual constancies (Depth cues indicate size of object relative to its distance).
Brain integrates motion of all elements in a scene (You driving towards bus, not bus backing into you)
Visual illusions: arise from ambiguities in perception. Occur because
perceptual strategies used in situations where they don’t belong. Can be
overcome by removing relevant contextual info. They are an active
process.
Cultures without exposure to right angles less susceptible to Muller-Lyer illusion. (Size constancy)
Ames room: manipulates distance to trick size constancy.
Ponzo illusion: manipulates depth cues to trick size constancy.
Feature Detectors
Brain processes stimuli in one region before passing it on to the next
Magno (From periphery of retina. Used for detecting changes
in brightness, motion + depth) and Parvo (found throughout
retina. Used for detecting color, pattern + form) cells in
retina transduce light into neural impulse.
Ganglion cells (with their small receptive fields) = first step to object recognition. From retina, axons of
these cells exit eye via optic nerve, to LGN, to primary visual cortex in occipital lobe.
Each neuron is very specific about what will make it fire the most. They fire maximally to stimuli of a
certain shape, size, position and movement. Defines receptive field for that cell.
Simple cell: Responds maximally to a bar of
certain orientation in a particular region of
the retina.
Complex cell: responds maximally to a bar of certain
orientation and direction of movement, regardless
of where the bar is located within receptive field.
Hypercomplex cell: responds maximally to bar of
particular orientation and direction of movement,
ending at specific points within receptive field.
Ventral stream:
Visual info must be combined to make sense of a visual scene. Visual integration begins in extrastriate
cortex (Visual association cortex). Has many subregions that each receive different type of info from
primary visual cortex about visual scene.
Dorsal stream: take info from visual cortex to parietal cortex, processes spatial info.
Ventral stream: “what” stream. Processes info on what object is, form and color. Takes info from visual
cortex and sends to temporal cortex, where all parts of feature info come together. Cells in temporal
cortex respond to very specific and complex stimuli (Objects represented by activity patterns rather than
specific neurons)
Development of pattern/object/face recognition
Infants do not perceive patterns, objects and faces the
way we do. They prefer lots of high contrast with sharp
boundaries between light and dark regions.
Infant’s poor visual
acuity may limit their
ability to perceive
whole forms.
Young infants have trouble perceiving overlapping objects
(because it requires ability to use cues like pattern and
colors. To tell what parts of object belong together. Don’t
have this skill until 5 months old). At 3 months old, can tell
there’s two separate objects only if object moves
independently. At 4 months old, beginning to understand
brightness, color, shape constancy. By 4-5 months,
demonstrate size constancy.
Infants under 2 months focus their gaze on the outer contours of the face (hairline and chin).
Early experience with faces that develops our preference for them, and at birth we have a preference to
look at complex, high-contrast stimuli (Faces or not).
Normal/Abnormal Visual Development
Innate readiness and external stimulation (environmental) interact in a normal development.
Early visual deprivation doesn’t allow proper feature detection.
Sensitive development periods in kittens: 1 month old kept in dark for 3-4 days experience visual
degeneration. For an entire week -> severe and permanent visual degeneration damage.
Cataracts = disrupt light from passing through lens of the eye (thick cloud in lens). Complete loss of
ability to perceive objects, patterns and details.
Visual Agnosia and Prosopagnosia
Damage to primary visual cortex does not disrupt object recognition. Able to perceive objexts in those
intact boundary areas of visual field.
Damage to extrastriate (visual association) cortex disrupts object recognition, not sight. Able to see
objects but difficulty recognizing them (Visual agnosia)
Object Agnosia: inability to perceive objects. Unable to identify different objects by sight but can see
objects perfectly, have normal visual acuity and able to recognize and name objects by touch.
Prosopagnosia: inability to recognize faces (But not facial features). Can still recognize regular objects.
Rely on other cues, such as voice, smell, way they walk.
Form perception: allows us to recognize objects we use and to distinguish friends from enemies.
Organizes our depiction of the world.
Primary visual cortex (V1) Responds to lines of specific orientation and motion
Temporal lobe: Responds to more complex stimuli like hands, faces, fruits.