Studied by 1 person
Akinetopsia
unable to perceive motion
cannot tell if movement is occurring
cannot see the “in between” when objects are in motion
Rods
sensitive in low light
lower acuity
color-blind
periphery of the retina
Cones
Need more light
higher acuity
color-sensitive
in the fovea
Visual system
light to perception
In the eye:
photoreceptors
bipolar cells
ganglion cells and the optic nerve
int he thalamus:
Lateral geniculate nucleus (LGN)
In the cortex:
V1: the primary visual projection area, or primary visual cortex, located in the occipital lobe
if damaged = “blind”, no sight
Lateral inhibition
a neuron’s response to a stimulus is inhibited by the excitation of a neighboring neuron
occurs in cells in the retina
each active cell inhibits its neighbors
Emphasizes the “edge” of the stimulus → “creates a contrast in stimulation that allows increased sensory perception”
Receptive field
the size and shape of the area in the visual world to which that cell responds
on-center/off surround cell
stimulus in center leads to fast firing rates
stimulus in surrounding are leads to slower firing rates (relative to baseline)
Edge detectors
each cell will respond to a vertical, or horizontal light respectively
the receptive fields of some visual neurons are lines of particular orientations
binding problem
parallel processing splits up processing of our world → but we do not see the worlds as disjointed
spatial position
helps solve the binding problem
reassembling of pieces references position
neural synchrony
helps solve the binding problem
the rhythms of neurons that are firing in response to the same item (some for color, some for motion, etc.) tend to be in sync
Attention binding
critical for the binding of visual features
when ________ is overloaded, people will make conjunction errors
ex: seeing a blue “H” and a red “T” but reporting a red “H”
sensation
absorbing raw energy (e.g., light waves, sound waves) through our sensory organs
for the most part, everyone has the same ___ to the same stimulus
Transduction
conversion of this energy to neural signals
Attention
concentration of mental energy to process incoming information
perception
selecting, organizing, and interpreting these signals
the process of recognizing, organizing, and interpreting information from senses
Not an exact copy of “the world”
based on our past experience and expectations
Bottom-up processing
when the environment (stimuli) influences our thinking
perception may start with the senses
incoming raw data
energy registering on receptors
Top-down processing
when our thinking influences how we see (understand/perceive) the environment
making inferences based on context, guessing from experience, and basing one perception on another
perception may start with the brain
person’s knowledge, experience, and expectations shape perception
occurs quickly, automatically
Recognition-by-components (RBC)
bottom-up processing
we perceive objects by perceiving elementary features
Geons: three-dimensional volumes
objects are recognized when enough information is available to identify object’s geons
geons
discriminability: ____ can be distinguished from other geons from almost all viewpoints
Resistance to visual noise: ______ can be perceived in “noisy” conditions
distinctiveness: 36 different _______ have been identified
Helmholtz’s Theory
theory of unconscious inference
we infer much of what we know about the world
likelihood principle: we perceive the world in the way that is “most likely” based on our past experiences
Perceiving size
bottom-up processing
the size of the image on the retina
Top-down processing
the perceived distance of the object
the size of the object relative to other objects in the environment
Depth perception
the ability to see things in three dimensions (including length, width and depth), and to judge how far away an object is
occurs even when looking at 2D images
is present, at least in part, at birth in humans and other animals
Binocular cues
depth cues that require the use of two eyes
Retinal disparity
used to perceive depth between two near objects by comparing the different images from both retinas
is a bottom-up cue of depth → it is not based on knowledge about the world
Monocular cues
depth cues available to either eye alone
are top-down cues of depth → they are based on the knowledge you have about the world
Includes
relative size
interposition
relative motion
light and shadow
linear perspective
Constancy
things look different depending in the angle, distances, and lighting but our perception is constant
Perceptual _____
Size
Shape
Brightness
Color
Size constancy
we perceive the size of an object as constant from different distances
however, context matters (ex: moon illusion)
Shape constancy
even though the shape of the door on our retinal image differs, we see the true shape of the door as unchanging
Gestalt Laws of Perceptual Organization
reflect experience, are used unconsciously, but may be occasionally misleading
similarity
proximity
good continuation
closure
simplicity
Form perception
the process through which the basic shape and size of an object are seen
figure-ground: organization of visual field into objects that stand out from their surroundings
grouping: the perceptual tendency to organize stimuli into meaningful groups (gestalt principle)
utilizes both bottom-up and top-down perception processes
good continuation
law of continuity
we tend to see shapes/lines as being continuous even when occluded
simplicity
law of good figure
every stimulus pattern is seen so the resulting structure is as simple as possible
similarity
similar things appear grouped together
proximity
things near each other appear grouped together
closure
we tend to perceive closed figures rather than incomplete ones
object recognition
process through which the object is identified
utilizes both bottom-up and top-down perception processes
recognition through features: small elements that result from the organized perception of form
ie: visual search task
Serial search
search every stimulus one by one for target
RT depends on display size
Parallel search
target stimulus “pops out” from the rest
RT does not depend on display size (or is dependent to a much lesser degree)
feature-based recognition
damage to the parietal cortex results in difficulty in judging how more than one feature is bound together in objects
integrative agnosia
disruption of parietal cortex via TMS
subject can do a feature search but not a conjunctive search
Word frequency effect
high frequency words recognized better
Repetition priming effect
recently viewed words recognized better
Word superiority effect
letters recognized better in the context of a word
response when asked whether “DARK” has an “E” or a “K” is more accurate than when “E” or “K” is presented alone
effect does not occur if a letter string such as “JPERW” is used instead of a real word
Feature nets
propose that recognition depends on a network of “detectors”, organized in layers of increasing granularity
"Neural networks”
have receptive fields
fire above threshold
detectors do not represent actual individual neurons
recent firing = higher starting activation level
explains word frequency effect and repetition priming
bigrams
a pair of consecutive written units such as letters, syllables, or words
can be part of the neural network
helps explain the word-superiority effect
Ventral stream
the what pathway
refers to the visual paths in the temporal cortex
specialized for identifying and recognizing objects
Dorsal stream
the where pathway
refers to the visual path in the parietal cortex
helps the motor system to find objects and move towards them
Single dissociation
one function is lost, another remains
ie: one stream is damaged but not the other
shows that the what and where rely on different mechanisms, although they may not operate totally independent of one another
Double dissociation
requires two individuals with different damage and opposite deficits
indicates that the what and where streams must have different mechanisms and operate independently of one another
Visual agnosia
the inability to recognize objects despite satisfactory vision
there are many types of visual agnosia, caused by damage to various visual areas (occipital, temporal, or parietal)
can identify people and faces
their knowledge is accessible to other pathways (ie: touch), but not their visual pathway
Prosopagnosia
is a type of agnosia also know as face blindness
occurs after damage to the fusiform gyrus of the inferior temporal cortex
can see the textures and features of a face but cannot put them together to recognize or identity the face
Holistic processing
we process faces as a whole
harder to process just the top or just the bottom when the faces are aligned
Note
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