Chapter 5: Perception and Encoding 2/18/2013 1:01:00 PM
Primary Visual Cortex
Located in the occipital lobe, they are preserving a map of visual
space. The map of visual space is inverted (upside down, and
Fovea- central part of vision, comes from the retina. Sending
information to the most posterior part of the occipital lobe.
o Central part of division gets many more neurons compared to
information from the periphery (like primary motor cortex), or
There are 6 layers of neurons
o All LGN ends up in layer four, where all the synapses are.
Separate for each eye and each system.
o P-Pathway- details and colors. Blobs- neurons in V1 that get
input and are related to color vision.
o Other cortical structures called pinwheels- related to
orientation of edges
Area V1 or Striate Cortex
Eye Dominance Columns
o Pinwheels are responding to bars of light with sensitivity to
different angles. It resembles a pinwheel.
Area V2 or Area 18
Extra-Striate Cortex- regions that are surrounding the primary
o They also have a preserved spatial layout, neurons that are
creating a map of visual space.
o No longer have columns that differentiate the eye. Respond
to edges moving in a particular direction, more complex than
Map of Cortical Areas
Multiple visual areas, V1, V2, V3, and V4
What kind of stimulus is best to getting a response in a certain
region? “optimal stimulus”
V4 and V5 Areas
V4: Color pathways
Optimal stimuli: only sensitive to moving object, receptive fields are
very big, M-pathway February 20, 2013
Neurophysiological Evidence of Concurrent Processing
Different cortical areas are activated by different stimulus
Why do we see something that is not actually there? What’s been
found is that when someone is perceiving motion, Area MT/V5 is
active even though nothing in the visual environment is moving.
The same goes for color in Area V4. (Optical Illusions) It is
artificial activation in Area MT that are coding for motion.
Even though there is no red light present, a spike of activity leads
to the perception of red because of staring at the green.
Having to put together two separate features, get information from
both cortical processes. If you have distractions, it takes longer
because you are doing the search differently (you have to actively
look and direct your attention to each location and space to confirm
the conjunction between the two features). In order to do this
search (putting together two different kinds of features) requires
direct attention to a location in space. It allows you to bind
together these features, and that’s because they are co-localized.
Direct your attention one by one in order to find the target. We
perceive things as being unified even though different areas of the
brain process them as differently.
Feature Analysis- effortless processing
Feature Integration- slower, more effortful processing in order to
glue together the outputs of what is being processed.
Effects of Lesions
o Deficit in opsin (cones), usually red- green colorblindness.
o Acquired as a result of stroke (cortical damage or loss of all
cones to area V4) Loss of ability to distinguish all color
You can have deficits that are selective to specific parts
of the visual field, this is due to the retina topic map in
o Cannot see movement, like when something is moving and
how fast it is moving. (Cars would appear out of nowhere).
No ability to see if object moves from Point A to Point B.
Described like a strobe light, or seeing the world in separate
o Lesions of Area 17, cortical blindness, nothing is wrong with
your eyes but you have lost the ability to see because you
have cut out Area V1
o You can also lose one half of visual space if there is a lesion in
only one half of the hemisphere (Remember video where he
can’t see the finger wiggle)
Cortical vs. Subcortical Pathways
Orienting your attention to a particular location in space- retino-
Blind sight- you still have visual information coming in even though
you technically cannot see it. People can make a motor response
based on something in the visual environment even though they
cannot visually see it.
Slower to respond to something in their preserved visual field if it is
simultaneously presented in their blind field, rather than just being
presented in their preserved visual field.
Blind sight- Preserved Subcortical Pathway
Sensory apparatus hooked up to a motor apparatus. Visual
awareness is separate and is doing something else other than
guiding movement of our eyes in space.
Eyes will move to periphery area before you are even aware.
People are slower compared to when there was just one target in
their good visual field. People are somehow aware that there is a
stimulus in the blind field of vision.
Animal Lesion Study Localization vs. Discrimination Task
o Animals have trouble orienting space in the localization task
o You get a double dissociation. Animals do fine with visual
discrimination because they have an intact visual cortex.
Superior colliculus is used.
Visual System Summary
“Divide and Conquer” strategy Ear and Hearing 2/18/2013 1:01:00 PM
Auditory System Overview
Cochlea leads to the auditory cortex in the temporal lobe
Cochlea contains the basilar membrane surrounded by fluid
o Has hair cells that interact with the tectoral membrane. It is
sensitive to different frequencies, thinner end is for higher
o Vibration of hair cells trigger action potentials, determine
frequency on where the membrane is vibrating
o Frequency and amplitude is encoded
Range of Sound
20 and 20,000 hz
1,000 and 4,000 hz is where speech falls
recognizing auditory patterns that is related to speech
o Speech signals happen very quickly
o Latency potentials= latency of 1- 5 ms
o Much slower in the visual system to receive a potential
Audition= sense of hearing
Sound waves are characterized by:
o Frequency (pitch)
o Timbre (pattern or quality)
o Amplitude (volume)
Sounds vary over time (speech)
Hearing Problems with Aging
o Very common, decline in the ability to hear high pitched
o Degeneration in the cochlea
o 11% of older adults
o Constant high pitched ringing or whistling sound in the ears
Cues for Sound Localization
Interaural Time o Difference in arrival of sound to 2 ears
o Difference in volume of sound reaching 2 ears Chapter 6: Higher Perceptual Functions 2/18/2013 1:01:00 PM
Combining lower-level features into objects, interface between
perception and memory
Agnosia- inability to recognize visual objects (they can still see,
there is nothing wrong with their sensory processing. Lower levels
of processing are intact, higher level is not there, they cannot put
elements into coherent whole).
Can also result from impairment of link between visual perception
and memory (specific to vision)
When a person touches it, he can immediately tell you what it is.
When he perceives it, he cannot tell you what exactly it is, even
though he knows what a teabag is.
Had a stroke, and was left with agnosia.
He can name objects, but he had a deficit in recognition.
Could recognize what his fingers did.
Where and What Pathways
Two major outputs from occipital lobe
o Ventral Pathway (Inferior longitudinal fasiculus)
Deficits restricted to vision, anterior- visual memory,
posterior- visual discrimination
Bilateral lesions required- if you only lesion one side,
the remaining hemisphere can take over one function
Information can cross over
Info crosses via corpus callosum,
combination lesions demonstrate this, less
cross-over in dorsal stream (where pathway
is more segregated)
o Dorsal Pathway
What is Temporal, where is parietal?
Lesions in lobes and compare to controls
o Landmark task vs. object discrimination task
Physiological Support for the What-Where Distinction
Parietal Lobe Neurons
o Large receptive fields
o Many neurons have peripheral receptive fields Ideal for detecting peripheral objects as soon as they
enter the field of view
Less in the center or in the fovea, they detect the
onset of a stimulus as it moves into our vision
(when you get the most firing)
Tuned to stimulus onset
Inferior and Middle Temporal Lobe Neurons
o Always encompasses the fovea, ideal for detecting objects
o Has very complex characteristics
Human Neuroimaging Data
PET study (1995)
Changing the demands of the task
o Is the spatial arrangement the same here as it is there?
o Activation that is more dorsal in the parietal lobe
o Are those the same three objects?
o Activation that is more ventral in the temporal lobe
Human Brain Lesion Studies
Case of Patient D.F.
o Names of objects if given a description
o Low level perceptional abilities
o Severe visual agnosia
Uses more object centered information
Parietal Lobe Lesions (Where/How)
o Relatively rare to get restricted lesions so there are a lot of
other problems as well
o Optic ataxia- difficulty using movements to help vision
Temporal/Occipital Lobe Lesions (What)
o Cannot figure out what an object is- visual agnosia
o Anomia- lost the storage area for what specific objects are
o Prospagnosia- restricted to faces, cannot recognize facial
Computational Problems in Object Recognition
Variability in Sensory Information o Object Constancy- able to recognize an object even with vast
View-Dependent or View-Invariant Recognition
o Perception proceeds from analyzing a viewpoint’s information
We store information in semantic memory- experience
of seeing “a bike at a certain angle”
Pros: Acts fast to recognize object because you
have stored information
Cons: Relatively expensive in the amount of
storage space you need
o Sensory input defines basic properties, such as major and
Create a representation of what the object would look
like if it was rotated
Pros: Efficient in terms of storage
Cons: Slower in terms of how fast you can
recognize an object
Do we have a neuron that responds to specific stimuli?
Hierarchy of lower level features to the point where specific stimuli
cause neurons to fire
The “ensemble coding” theory
o A number of features are present together
o Different cells respond to different features
Lesion Studies of Object Recognition
o Recognition can occur through other modalities such as touch
o Differentiate from memory loss or other problems (agnosia)
o Differentiate from sensory loss
Subtypes of Agnosia
o Apperceptive Agnosia
A failure to integrate features into a coherent whole,
disconnect between perception and memory
Case Study (could not recognize these things)
Letters (except those composed of straight
segments) Could not copy drawings
Rectangles of equal areas oriented differently
Faces (including own)
o Associative Agnosia
Normal visual representation that cannot be used to
Tests of Agnosia
Tests that would challenge the system that would make it more
difficult to recognize the object (challenging)
Fragmented, deleted information
Patients are having trouble with object constancy (car in the
parking lot when it’s dark)
Tests of object constancy abilities: patients impaired
o Changed lighting conditions on the stimulus
Overlapping drawings. The task is to give them crayons and have
them color in the various objects.
Case Study- F.R. A. has a deficit in putting objects together
Requires categorization by semantic properties
Knows what the objects look like, but cannot connect the functions.
He tends to match up things that “look” more similar, but they
cannot match up the meaning of the object.
Warrington’s model: Left hemisphere is important for semantic processes.
Leads to associative agnosia, whereas the right hemisphere leads to