Chapter 4 Flashcards
Optic Chiasm
An X-shaped bundle of fibers on the UNDERSIDE of the brain; when visual signals leave the back of the eye through the OPTIC NERVE and meet at the OPTIC CHIASM
At the optic chiasm, some of the fibers cross to the OPPOSITE SIDE OF THE BRAIN from the eye they came from; ALL FIBERS CORRESPONDING TO THE RIGHT VISUAL FIELD (regardless of which eye) END UP ON THE LEFT SIDE/HEMISPHERE, and all fibers corresponding TO THE LEFT VISUAL FIELD END UP ON THE RIGHT HEMISPHERE
Contralateral
Term which describes the fact that EACH HEMISPHERE IN THE BRAIN corresponds to the OPPOSITE SIDE of the visual field
Describe the visual process (step per step)
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How is the “side” of a visual field determined?
The “side” of the visual field is determined based on WHERE THE PERSON IS FIXATING
Anything to the RIGHT of the point of central focus is the RIGHT VISUAL FIELD and is processed by the LEFT HEMISPHERE (same logic for the left visual field) 
Both eyes can see BOTH visual fields
What happens to the fibers of the optic nerve after it passes the optic chiasm?
At the optic chiasm, some of the fibers cross to the OPPOSITE SIDE OF THE BRAIN from the eye they came from:
ALL FIBERS CORRESPONDING TO THE RIGHT VISUAL FIELD (regardless of which eye) END UP ON THE LEFT SIDE/HEMISPHERE
ALL FIBERS CORRESPONDING TO THE LEFT VISUAL FIELD END UP ON THE RIGHT HEMISPHERE
Lateral Geniculate Nucleus (LGN)
A multilayered structure that receives input from both eyes and which is located in the THALAMUS OF EACH HEMISPHERE
Where do approximately 90% of signals from the retina end up in after the “contralateral”?
In the Lateral Geniculate Nucleus (LGN)
In vision, what does the Thalamus serve as?
as a relay station where incoming sensory information makes a stop before reaching the CEREBRAL CORTEX
Superior Colliculus
A structure involved in controlling EYE MOVEMENTS
Where does 10% of signals from the retina go to after the “contralateral”?
To the SUPERIOR COLLICULUS
True/false: Neurons in the LGN have center-surround receptive fields?
True
What do researchers hypothesize the LGN is for and why?
What: Researchers hypothesize that the purpose of the LGN is to REGULATE NEURAL INFORMATION as it flows from the retina to the cortex
Why: Because the signal which the LGN forwards to the cortex is SMALLER than the input the LGN receives from the retina
Feedback
Backward flow of information from the cortex to the LGN that could also be involved in REGULATION OF INFORMATION (the idea that the information the LGN receives BACK from the brain plays a role in determining which information is sent up to the brain)
Visual Receiving Area (Striate Cortex/Area V1)
Area in the OCCIPITAL LOBE that is the place where signals from the retina and the LGN FIRST REACH THE CORTEX
Also called the STRIATE CORTEX because it has a striped appearance when viewed in cross section
Also termed AREA V1to indicate that it is the FIRST VISUAL AREA IN THE CORTEX
Simple Cortical Cells
Cells in the striate cortex that have RECEPTIVE FIELDS that have excitatory and inhibitory areas THAT ARE ARRANGED SIDE BY SIDE (as opposed to the center-surround configuration)
What type of stimulus do Simple Cells respond best to and why?
Which: The layout of the receptive fields in simple cells respond BEST to VERTICAL BARS OF LIGHT, LINE OR EDGE
Why: Because if the stimulus is slightly tilted horizontally, IT STIMULATES THE INHIBITORY FIELDS, SO THE MOST REACTION OCCURS WITH VERTICAL STIMULI
Orientation curve
The relationship between a neuron’s ORIENTATION and FIRING, determined by measuring the responses of simple cortical cells to bars of different orientations
Complex Cells
A neuron in the cerebral cortex that responds to visual stimulation of appropriate contrast, orientation, and direction anywhere in the receptive field; MOST COMPLEX CELLS RESPOND ONLY WHEN A CORRECTLY ORIENTED STIMULUS MOVES ACROSS THE ENTIRE RECEPTIVE FIELD
True/false: Most complex cells also have preferences of direction (they react best to particular directions of movement)
True
End-stopped cells
Another type of cell in the visual cortex that fires in response to MOVING LINES OF A SPECIFIC LENGTH OR TO MOVING CORNERS OR ANGLES
Feature Detectors
Term given to SIMPLE, COMPLEX AND END-STOPPED CELLS collectively, due to their responding to SPECIFIC FEATURES of a stimulus (orientation, movement, etc.)
True/false: Feature Detectors are less selective about what stimulus they fire to than photoreceptors
False
The farther one moves from the retina, the more neurons tend to fire to more COMPLEX stimulus (whereas photoreceptors will fire to a dot, feature detectors are more selective)
Selective Adaptation
Situation in which neurons that are tuned to a certain property eventually become fatigued when firing to that specific stimulus, AND ADAPT by:
(1) DECREASING ITS FIRING RATE
(2) WHEN THE NEURON DOES FIRE, IT FIRES LESS WHEN THE STIMULUS IS PRESENTED AGAIN
True/false: Neurons ONLY ADAPT in response to their specific stimulus
True
How do researchers measure selective adaptation to orientation?
1) Measure a person’s CONTRAST THRESHOLD to lines of various different orientations
2) Adapt that person to ONE orientation by having them view a HIGH-CONTRAST ADAPTING STIMULUS
3) Remeasure the contrast threshold of all the other differently-oriented lines
Selective Rearing
Situation in which if an animal is reared in an environment that contains ONLY CERTAIN TYPES OF STIMULI, then neurons that respond to these stimuli will become more prevalent
Neural Plasticity (Experience-dependent Plasticity)
Phenomenon in which the PROPERTIES OF NEURONS can be shaped by PERCEPTUAL EXPERIENCE
Neural plasticity ALLOWS for selective rearing, because it is a foundational process for LEARNING
What is the difference between SELECTIVE ADAPTATION and SELECTIVE REARING?
While SELECTIVE ADAPTATION is a SHORT-TERM EFFECT, SELECTIVE REARING is a LONG-TERM EFFECT
“Use it or Lose it” Effect
Phenomenon in SELECTIVE REARING in which neurons which are CONSTANTLY exposed to a CERTAIN STIMULUS remain active, while neurons that DO NOT respond to that stimulus (and are thus not active) GRADUALLY LOSE their ability to respond to their respective stimulus
Retinotopic Map
The electronic map of the retina on the cortex, in which locations on the cortex correspond to locations on the retina
The map is a DIRECT REFLECTION from the retina to the striate cortex, meaning that two “points” that are close together ON THE RETINA will activate neurons that are CLOSE TOGETHER ON THE BRAIN
Cortical Magnification
The apportioning of a large area of the cortex to the significantly smaller fovea, whose signals account for 8-10% of the retinotopic map
(SPATIAL REPRESENTATION of the visual scene on the cortex is DISTORTED and more space is allotted to the fovea)
Cortical Magnification Factor
The SIZE of the magnification of the fovea’s signals in the cortex
The extra cortical space allotted to objects a person looks directly at provides the extra neural processing needed to accomplish tasks that require HIGH VISUAL ACUITY
True/false: Cortical magnification affects our perception if size
False, it only allows us to have more DETAILED vision
Location Columns
Organized regions of neurons in the STRIATE CORTEX that are PERPENDICULAR to the surface of the cortex, so that all neurons within a location column have their receptive fields at the same location on the retina
Each LOCATION COLUMN also has ORIENTATION COLUMNS for all possible orientations
Orientation Columns
Organized regions of neurons containing cells that RESPOND BEST to a PARTICULAR ORIENTATION
ADJACENT orientation columns have cells with slightly different preferred orientations, and these preferred orientations CHANGE IN AN ORDERLY FASHION (A column that responds best to 90 degrees will be right beside a column that responds best to 85 degrees)
Hypercolumn
A location column with ALL of its orientation columns, which receives information from ALL POSSIBLE ORIENTATIONS that fall within a small area of the retina
Is well-suited for processing information from a small area in the visual field
Tiling
Effect that describes how the information of ADJACENT LOCATION COLUMNS work together to cover the ENTIRE visual field
Ex: When you look at a tree trunk, the VERTICAL ORIENTATION of it activates neurons in the 90-degree orientation columns in EACH location column as necessary
Extrastriate Cortex
Collective name for areas V2, V3, V4 and V5 in the OCCIPITAL LOBE, where the visual signal proceeds to after being processed in the striate cortex (areas are termed this way because they are OUTSIDE the striate cortex)
How does the visual system “build up” the visual representation?
Higher-level extrastriate areas have receptive fields of GRADUALLY INCREASING SIZES which means the representation of the visual scene BUILDS UP, adding more aspects of the visual scene like corners, colors, motion, shapes, etc. as the signal “moves up”
Ablation
Refers to a DESTRUCTION or REMOVAL of tissue in the nervous system, which Leslie Ungerleider and Mortimer Mishkin used to better understand the functional organization of the visual system
Object Discrimination Problem
One of the experimental tasks used by Unger and Miskin, in which an object is shown to a participant, and then they are presented with a task that INCLUDES the originally presented object PLUS ANOTHER STIMULUS
The purpose of the experiment is see if the participant is capable of DISCRIMINATING the original object and pick it out
Landmark Discrimination Problem
Another experimental task used by Unger and Mishkin where the participant is asked to perform some task at a established “landmark” (like close the lid of the bottle on top of X counter)
Ventral Pathway (“What” Pathway)
Pathway leading from the STRIATE CORTEX to the TEMPORAL LOBE, responsible for determining an OBJECT’S IDENTITY
Located in the lower part of the brain
Dorsal Pathway (“Where” Pathway)
Pathway leading from the STRIATE CORTEX to the PARIETAL LOBE, responsible for determining an OBJECT’S LOCATION
Located in the upper part of the brain
True/false: Information can flow back and forth between the Parietal and Temporal Lobes
True
Double Dissociations Method
Method used to study the “where” and “what” pathways
Process:
Takes two participants, one that has damage to the Parietal Lobe, while the other has damage to the Temporal Lobe
Studying these patients can allow experimenters to see how each region operates separately and together
Patient D.F. (Who, what was her condition and what researchers learned with her)
A 34-year old woman who suffered damage to her VENTRAL PATHWAY; as a result, D.F. was not able to match the orientation of a card given to her, to the orientations of a slot; Nevertheless, when asked to PUT the card IN the slot, she was capable of rotating it and performing the action
Even though D.F. couldn’t perform STATIC ORIENTATION-MATCHING, she was still capable of carrying out the action
Milner and Goodale used the method of DOUBLE DISSOCIATIONS to study D.F., and along with other test subjects, were able to show the ventral and dorsal pathways also serve for judging orientation and for coordinating vision and action (respectively)
“How Pathway”
Dorsal Pathway (helps us perceive the orientation of a stimulus)
“Action Pathway”
Ventral Pathway (helps us determine how to behave towards a stimulus based on its orientation”
Inferotemporal Cortex (IT Cortex)
A region of the brain on the inferior (lower) portion of the outer layer (cortex) of the temporal lobe that has the LARGEST RECEPTIVE FIELDS IN THE VISUAL SYSTEM, and are thus capable of responding to more complex stimuli in the environment
Neurons in the IT cortex respond to HIGHLY COMPLEX AND SPECIFIC STIMULI (only responding to specific shapes and forms)
IT Neuron Specificity
The idea that the IT cortex has a group of neurons which are selectively reactive to FACES
(Some neurons are also selectively reactive to hands)
How do visual signals affect memory?
Some of the signals leaving the IT cortex reach structures in the MEDIAL TEMPORAL LOBE (MTL), including the PARAHIPPOCAMPAL CORTEX, the ENTORHINAL CORTEX and the HIPPOCAMPUS
Hippocampal and MTL neurons respond not only to the visual perception of specific objects or concepts, BUT ALSO TO MEMORIES OF THOSE CONCEPTS
HAGAN GELBARD-SAGIV and Co. EXPERIMENT (how perception affects memory)
Hagan showed epilepsy patients 5 to 10 second video clips
As the participants viewed the video, some neurons responded better to certain clips than others based on the subject of the video
When Hagan asked the participants to think back on any of the videos they saw, they remembered best (most detailed) the clips which had elicited HIGHER NEURON FIRING
Supported the idea that neurons in the MTL that respond to PERCEIVING specific objects may also be involved in REMEMBERING these objects
Mitesh Kapadia Experiment
Experiment in which they recorded the response of neurons in the visual cortex to a vertical bar located in the neuron’s receptive field, with two vertical bars located alongside it, but outside of the receptive field; the results showed that the firings INCREASED
Illustrated CONTEXTUAL MODULATION
Contextual Modulation
The effect of stimulating OUTSIDE of the receptive field
True/false: The amount of attention given to an object can shift the location of a neuron’s visual field
True
