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Flashcards in Exam 2 Deck (99):

Spatial Coding Systems

allocentric: object-to-object
egocentic: self-to-object



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)



"where" pathway; spatial relations



"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


Rules of object recognition

How do we go from edge detectors (in V1) to knowing what edges go together?



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

1. preferential to complex stimuli
2. 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


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
- 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

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



Kanwisher experiment

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



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



Evidence for configural processing


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



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)



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



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

1. Preattentive stage: the featural “primitives” in a visual scene are all extracted in parallel across the whole.
2. 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



inability to see entire picture, cannot see clock face (draw 12-6)


Bottom-up processing

feature driven
“reflexive” or automatic


Top-down processing

goal or experience driven


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



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


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 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 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 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



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