Exam 2 Flashcards
Spatial Coding Systems
allocentric: object-to-object
egocentic: self-to-object
Pohl
functional organization of visual pathway
monkeys – lesioned posterior parietal cortex (PPC) and inferior temporal cortex (IT)
landmark discrimination –> spatial discrimination (food hidden in adjacent well to landmark; correct=retrieve food, incorrect=empty well shown to convey no reward)
object discrimination –> choose food well
PPC: important in landmark task, not important in object (spatial, visual relationships, dorsal)
IT: important in object task, not important in landmark (object and pattern recognition, ventral)
Dorsal
occipital–>parietal
“where” pathway; spatial relations
Ventral
occipital–>temporal
“what” pathway; object recognition
Object recogniton
process of matching representations of organized sensory input to stored representations in memory
The binding problem
If ventral-stream neurons encode stimulus identity but not location, and if dorsal-stream neurons encode stimulus location, but not identity, how is this information brought together to create the unitary, “bound” percept that we experience of an object occupying a location in space?
Binding criteria
Nearness of lines
Nearness of color
Coherent motion
Experience!
Rules of object recognition
How do we go from edge detectors (in V1) to knowing what edges go together?
proximity connectedness color closure continuation
Colinearity v. relatability
Colinearity - orientations are similar
Relatability - easy to connect one line to the next
Gross experiment (hand)
waved hand in front of display screen –> high response
neuron’s preferred stimulus: hand
other stimuli could drive response based on hand similarity
responded regardless of location (large receptive field)
visually receptive IT neurons responded to complex stimuli
- preferential to complex stimuli
- large receptive fields
an IT neuron with responses selective to a hand
Type and Token
type: category (ex: faces)
token: example within this category (ex: specific face of someone)
Gross face cells selective for type, not token
Gross Experiment (face)
Single neuron recorded in temporal cortex
Neuron likes faces (category or type) - but not any particular face (token)
responds comparably to human and monkey faces
gradually less responsive as features are removed
did not respond to stimuli that wasn’t face
Gnostic cell
hypothetical neuron that represents a complex but specific concept or object
Issues with grandmother cell theory
Problems: 1.Need a lot of neurons!
2.Response ambiguity
vulnerability of system that relies on highly specialized neurons on the apex of the processing system–damage?
how would the system a priori know how many gnostic cells are required to represent every distinct object it would acquire throughout its life
Hierarchy of stimulus representation
bridging gap between V1 and IT/STP (superior temporal gyrus)
complete object recognition
component shapes
conjunction of features
low level features
progressively higher levels of stimulus representation are constructed at progressively higher levels of the system by selective integration of more elemental information from lower levels
Lines and colors represented by V1 neurons are assembled by higher visual areas into recognizable objects
Filling in contours
Visual illusions provide evidence for top-down influences
Zurich
find selective neuron
present illusory contour
lower, but still selective response
inference from v4 fed back to v2
aperture problem
each neuron with a small receptive field is, in effect, viewing the visual scene through a very small aperture
view invariance
recognizing objects irrespective to viewpoint
particular shape invariant - location - size - cue (color, motion, lines, texture)
Visual agnosia
not knowing through visual information
–> cannot experience perception of an object
limited to vision
ex: tactile modality intact (holding keys)
object knowledge is okay
Visual prosopagnosia
inability to recognize faces
Template matching theory
image generated by a stimulus is matched to internal representation (template)
works well when object is well specified and unique
Challenges for template matching
imperfect matches
not powerful enough for general pattern recognition
ex: many fonts of m
cannot account for flexibility of pattern recognition system
Feature matching theory
detect objects by the presence of features
each object broken down into features
ex: broken down A
These 3 features are in most As Line features activated by visual cortex
Stored representations
Stored representations ≈ features that are relatively common to all instances of object, and relatively rare in non-instances
Problem to feature matching
many objects contain similar features
doesn’t work for faces – same features
Recognition by components
Biedelman
geon model
Complex objects are made up of arrangements of basic, component parts; 24 of them
Tanaka experiment
how specific do neurons get?
critical features
- -> isolate single neuron
- -> present monkey with dozens of 3D objects to find driving cell
- -> reduction process until neurons no longer fire
not responding to specific objects, instead tuned to a simpler, reduced set of generic features
tiger’s head is recognized by the simultaneous activation of many neurons that each represent
What’s special about faces
Recognition of con-specifics critical for survival
Faces seem to be recognized by configuration
Inversion has more detrimental effects on faces than on other classes of objects
Faces recognized as individuals
Thatcher effect
more difficult to detect local feature changes in an upside-down face, despite the same changes being obvious in an upright face
when face is rotated away from upright, adults see it as decreasingly bizarre
tuned especially to upright faces
differentiation depends heavily on configuration (the structural relationship between individual features on the face)
Configural processing
Determine extent to which quantitative spatial relations deviate from prototype (average)
Recognition based on “distance” between perceived item and prototype
Faces differ in relative sizes of parts and distances between them
Evidence for configural processing
Famous faces: better at recognizing caricatures than veridical drawings
caricatures make deviations from prototype more evident
Inferotemporal cortex
IT
Kanwisher experiment
FFA
area in fusiform gyrus much more active response to face stimuli
Face inversion
face-specific processing system that can be accessed only by upright faces
parts of the face are not processed independently
prosopagnosia
Configural processing
perceiving relations among the features of a stimulus such as a face
contrasted with ‘featural processing’
Composite face effect
Evidence for configural processing
Subjects are slower and less accurate in recognizing the top half of one face presented in a composite with the bottom half of another face when the composite is upright and fused
can detect the difference when the composite is inverted or the two halves are offset laterally
–> disrupts holistic processing
This phenomenon demonstrates that when upright faces are processed, the internal features are so strongly integrated that it becomes difficult to parse the face into isolated features
Caricatures
Evidence for configural processing
Caricatures
Participants’ recognition of facial expressions was enhanced when differences between locations of features in an expression face and a reference-norm face (e.g., neutral face) were accentuated
The exaggeration of these deviations in a caricature may enhance recognition because it emphasizes the features of the face that are encoded.
Face superiority effect
2 noses vs. 2 faces differing only in nose
Better discriminations when whole face present! (and better memory for the noses presented with faces)
face superiority effect disappears when inversion occurs
parts of the face are not processed independently
recognizing nose less accurate than recognizing larry’s face
Evidence for configural processing
Recognize faces based on spatial relations between features
Composite face effect (can’t tell difference when fused, can tell difference when holistic processing is broken)
Caricatures (easier to recognize bc encoded features are exaggerated)
Inversion (face-specific processing system that can be accessed only by upright faces)
Thatcher (more difficult to detect local feature changes in an upside-down face)
Evidence for featural processing
Scrambled faces and Isolated features
recognition can still be found in features alone
Modular organization v. distributed representation
brain is organized into subcomponents or modules, each dedicated to processing and representing a particular type of visual information
brain processing and representation are distributed, that is, any information is processed by many different parts of the brain and any brain region is likely to represent many classes of information (Haxby)
Box thought experiment
How do we move from feature recogniton in v1 and v2 to higher perception of box?
before recognition: fire at same rate, not at coincidence, offset in time
after recognition: lines that make up square fire synchronistically, temporal coincidence, this may be what’s needed for object recognition
Ventral Temporal Cortex
Object Recognition in Ventral Temporal Cortex
Organization for object recognition [ventral object vision pathway]
Hemispatial neglect
right parietal lobe
fail to pay attention to stimuli on one side of space, usually the left
being made aware does not alter effects
also show a reduced tendency to explore neglected side of space with either eye or limb movements
looking at plaza
memory unaffected, attention affected
attention disorder, not intention
William James
attention is “taking possession by the mind”
Overt v. covert attention
overt attention - eye movements
- most direct way to shift attention
- primarily aware of foveal objects (due to poor peripheral resolution)
covert attention - attending without looking
- mental focus
Hemholtz
first discovered covert attention
Helmholtz would attend to a particular region of his visual field (without moving his eyes in that direction). When a spark was lit to briefly illuminate the box, he found he got an impression of only the objects in the region he had been attending to, thus showing that attention could be deployed independently of eye position and accommodation.
Eye specialization
fovea: resolution
periphery: motion (hence shooting stars out of the corner of your eye)
Siccades
quick, continuous eye movements around fixation points
successive eye movements to understand
one of the best ways to attend
Cherry experiment
dichotic listening test
each ear receives conflicting info, asked to record what is heard in left ear
–> don’t remember right
- echoic memory (~2 sec), name, taboo words
–> brain really able to filter out
some part of brain is taking in info, not being processed by higher levels
–> adaptively important areas break through that level of consciousness (name)
“cocktail party problem” Can filter out irrelevant info and focus on one stream at a time
make downstream processing easier
Importance of attention
Makes downstream processing easier
brain = limited energy metabolism
- ignore irrelevant neuronal signals
- boost reliability of the relevant signals
Posner effect
covert spatial cueing
reaction time benefit when correct cue, reaction time cost with incorrect
when cues were VALID, response time was faster
–> when attending to one thing, at cost with another thing
Preattentive v. attentive
preattentive: register basic features without attention, parallel search, fast and equivalent RT, regardless of set size, bottom-up
ex: popout search
attentive: control of viewer, adding features lowers RT, serial search, linear RT with set size, top-down
ex: conjunction task
Treisman
Feature Integration Theory
features are recognized early, automatically, and in parallel across visual field
object perception occurs separately and later through focused attention that “glues” features together
2 STAGES OF PROCESSING
- Preattentive stage: the featural “primitives” in a visual scene are all extracted in parallel across the whole.
- Focussed attention stage: Attention is directed to a location, the primitives there are combined to form a whole.
Balint’s Syndrome
extreme form of visual neglect, damage to both parietal lobes
Optic Ataxia: inability to move the hand to an object by using vision
Ocular Apraxia: cannot control eye gaze
Simultanagnosia: inability to recognize more than one object shown at the same time
Selective attention
Tune in to important information, tune out of irrelevant stimuli
Attention is a limited resource, so selective attention allows us to tune out unimportant details and focus on what really matters
Dichotic listening
listening to different acoustic events presented to each ear simultaneously
Optic ataxia
cannot accurately reach for things
Ocular apraxia
cannot control eye gaze
Simultagnosia
inability to see entire picture, cannot see clock face (draw 12-6)
Bottom-up processing
feature driven
“reflexive” or automatic
exogenous
fast
Top-down processing
goal or experience driven
voluntary
endogenous
slow
Spatial attention
a form of visual attention that involves directing attention to a location in space
Neural correlates of attention
PPC: posterior parietal cortex
LIP: lateral intraparietal cortex, eye movement
PRR: parietal reach region, reaching movement
Lateral intraparietal cortex (LIP)
Parietal reach region (PRR)
both critical for spatial attention
LIP: eye movement, PRR: reaching
Goldberg & Wurtz monkey experimentation
more driven by hand movements than by eye movements
Fronto-parietal network
x
Moore & Fallah paper
Premotor theory of attention testing
Moore and Fallah (2004)
- Controlling spotlight of attention with microstimulation of FEF in monkeys
- Microstimulation: electric current that produces APs in neurons
- When microstim. applied to FEF, saccade to a particular location would be produced
- Level of stimulation was enugh to produce covert shift of attention
- The closer the stimulation was to the target dimming, the stronger its effect on accuracy was
- Activation of FEF improved attention
- Stimulation directly shifted spatial attention
- Moore’s experiment shows that FEF increases response in visual neurons and that target detection improves as resuls
- FEF is critical brain area for controlling where attention is directed
- Part of netwrk of brain areas that act together to control attention
- Moving your eyes and docusing our attention onto object A versus B might feel like different behaviours, but appears that it’s the same neural mechanisms and processes
- > premoror theory of attention
Broadbent’s model of selective attention
Registration –> perceptual analysis –> semantic encoding
selective processing occurs after complete perception
Goldberg & Wurtz
(a) passive fixation: light flashing but goal-irrelevant, visual response of 4 APs
(b) Saccade to stimulus: LIP, attend to stimuli because flashing is now goal-relevant
(c) Reach for object: monkey attends to goal-relevant stimulus by reaching, largest increase in response
upregulation of neuron firing is attentional correlate
more driven by hand movements than by eye movements
moving past visual response, now have attentional response
Spatial attention: relationship between visual stimuli and subsequent brain activation
Attentional effects are seen in visual cortex in the hemisphere contralateral to the attended target
You can modulate V1 with attention–not pure!
Goldberg & Wurtz
(a) passive fixation: light flashing but goal-irrelevant, visual response of 4 APs
(b) Saccade to stimulus: LIP, attend to stimuli because flashing is now goal-relevant
(c) Reach for object: monkey attends to goal-relevant stimulus by reaching, largest increase in response
upregulation of neuron firing is attentional correlate
more driven by hand movements than by eye movements
moving past visual response, now have attentional response
Attention v. Intention
Goldberg: attention
Snyder: intention
Snyder & Anderson
PPC mediates between sensory attention and motor intention
delayed response task
LIP saccade immediate jump
PRR smooth movement
trained monkeys to saccade to a distractor item before responding; at the offset of the distractor, they were to respond. In this case, the cells were modulated more by the response than by the location of the distractor item, indicating they represented movement intentions independent of spatial allocation of attention
intention: LIP
action: PRR
Armstrong & Moore Paper
Frontal eye field (FEF) V4
Motor field
Super- and sub-threshold stimulation
microstimulation
Working memory
Working memory is a cognitive system with a limited capacity that is responsible for temporarily holding information available for processing
Prefrontal cortex
Concluded that the monkey’s ability to use “immediate memory” was impaired. “It was as if ‘out of sight, out of mind’ were literally applicable.”
Chunking
Chunking is a term referring to the process of taking individual pieces of information (chunks) and grouping them into larger units. By grouping each piece into a large whole, you can improve the amount of information you can remember.
limit: number of objects an average human can hold in working memory is 7 ± 2
Maintenance
Maintenance rehearsal: information repeated to keep from fading from working memory
Representation and Operations
Representations are symbolic codes for information stored either transiently or permanently in neuronal networks. Operations are processes or computations performed on representations.
Verbal WM
Verbal WM - verbal rehearsal
Representations are symbolic codes for information stored either transiently or permanently in neuronal networks.Operations are processes or computations performed on representations.
Visuospatial WM
visuospatial WM -maintenance of spatial location shapes
Phonological loop
verbal info
Visuospatial sketchpad
visual info
Dorsal stream, ventral stream attention
- When attention shifted from one visual field to another, ventral set of brain regions withing fronto-parietal network was engaged (TPJ, VFC) -> bottom up, exogenous control
- After this shift, attention sustained at location or towards a feature, dorsal set of brain regions were engaged (FEF, IPS) -> trop down, endogenous control
Principle sulcus of the dorsolateral Prefrontal Cortex (DLPFC)
These monkey data predict that lesions to human dlPFC will impair spatial WM performance, including the accuracy of MGSs. However, human neuroimaging studies typically find persistent activity or multivoxel decoding of information restricted to the PCS, posterior to the likely homolog of the monkey principal sulcus in the dlPFC
specialized in a certain type of working memory, namely computational mechanisms for monitoring and manipulating items, or if it has a certain content, namely visuospatial information, which makes it possible to mentally represent coordinates within the spatial domain
Oculomotor delay response task
were trained to remember the location of a target in order to make a rapid eye movement to i
Mnemonic Scotomas
memory deficits for particular hemifields or visual field locations, unaccompanied by simple sensory or motor deficits
Delay-dependent error
impairment is delayed dependent: longer delay, more demands on memory and impairment is worse
Frontal eye field (FEF) in Superior Prefrontal Sulcus
FEF = motor neuron, primary function: eye movement
Control
Control elaboration - assigning meaning to information
relating new concepts to old concepts that are already in the long-term memory so that these new concepts ‘stick
mneomnics ex
Tripartate model of WM
central executive: directs attention and coordinates activity
phonological loop: verbal info
visuospatial sketchpad: visuospatial info
episodic buffer: brings in info from LTM
Den Heyer & Barrett
“what where task”
A grid flashed on screen with letters in a certain position.
Condition 1 had to match visual patterns before recalling the shape of the grid, where they were and what letters they were.
Condition 2 had to count backwards. They were then asked to reconstruct the grid. C,1 recalled the letters but could not remember where they were positioned on the grid, however C,2 recalled where the letters were but not what they were.
Results: relative to unfilled controlMemory for “what” (i.e., the letters) 68% worse following verbal vs. 56% worse following spatial distractionMemory for “where” (i.e., the locations)45% worse following verbal vs. 90% worse following spatial distraction
Neuropsychological Double Dissociation
ELD: visuospatial deficit (corsi), intact verbal
PV: extremely poor at serial recall of verbal material (digits, letters, words) but shows no visual memory impairment
NOT a perceptual deficits: intact phonological & visual discrimination
Corsi block test
Corsi block-tapping test is a psychological test that assesses visuo-spatial short term working memory. It involves mimicking a researcher as he/she taps a sequence of up to nine identical spatially separated blocks. The sequence starts out simple, usually using two blocks, but becomes more complex until the subject’s performance suffers
WM, STM
Short-term memory (STM) refers to the span of information (e.g., a telephone number, an array of objects) that one can hold in mind without assistance from the MTL. Although it is quickly lost when attention is directed elsewhere, it can, in principle, be maintained indefinitely.
Working memory refers to the mental manipulation of information in STM, such as performing mental arithmetic, or reordering items into numerical or alphabetical order.
Delay response test
monkey, perfectly performed, with PFC lesion: 50% correct
delayed response task
It is during the transition from cue to delay that apparently the greatest number of prefrontal units discharge at firing levels higher than
Why so much importance on PFC
Experimental Lesions of Monkey Prefrontal Cortex- damage leads to WM impairments
Electrophysiology of Monkey Sulcus Principalis- persistent neural activation during delays–> suggests cognition
Brain driving attentional spotlight
back, parietal= sensory, where
frontal=action–>eye movements
