PSYC 204 UIUC Exam 2

"What" pathway

• from the occipital lobe to the temporal lobe -> ventral

• recognizing the identity of objects

• inferior temporal lobe: larger receptive fields compared to V1; complexity of information increases from posterior to anterior temporal lobe

"Where" pathway

• From the occipital lobe to the parietal love -> dorsal

• Recognizing the location of objects (for actions involving them)

Evidence supporting "what-where" distinction

• Neurons in the inferior temporal lobe respond to the same object regardless of its size, location, or orientation, but do not respond to other objects

• The two streams work together & communicate extensively

Patient D.F.

• Carbon Monoxide poisoning

• Damage to ventral stream (object recognition)

• Sees flashlight and thinks it might be a flashlight

• She can't just look at something and tell you what it is; she's fine spatially

How to achieve object constancy

Ability to recognize objects presented in very different conditions (viewpoints, luminescence, surroundings) despite variation in the physical stimulus

Grandmother cell theory

• Recognition arises from the activation of neurons that are finely tuned to specific stimuli.

• Assumes that the final perception of an object is coded by a single cell

• Limitations: cannot account for the acquisition of new representations, the fact that we lose neurons constantly, and the change of representations over time

Ensemble Encoding Theory

• recognition results from the collective activation of many neurons rather than one gnostic cell

• explains why objects with shared features often get confused

• (object recognition persists if the cell dies, novel objects are recognized by similarity to existing feature representations)

Global vs. local processing

• Global processing: objects

• Local processing: faces

Global processing

localized to the right ventral stream, important for analyzing whole objects (ex: faces)

Local processing

lateralized (largely under the control) to the left ventral stream, important for analyzing the parts of an object (ex: letters)

Navon letters

patients with right hemisphere damage (rely on right hemisphere) are better at global processing

Face inversion illusion

inverted stimuli can disrupt holisitc processing. Inversion especially impairs recognition of faces, suggesting that holisitc information is critical for processing faces

Face-specific hypothesis

faces are distinct objects due to their evolutionary relevance

Distinct face procession regions

Fusiform Face are (FFA)

superior temporal sulcus (STS)- both face and bodies; facial motion perception

the expertise hypothesis

it's possible that faces are only 'special' because we have so much experience with them

supportive evidence for expertise and face-specific hypothesis

FFA activation increases as expertise develops

object recognition

parts & wholes

Other specialized systems for object recognition

face recognition: fusiform face area, occipital face area and superior temporal sulcus

other body parts: extrastriate body area, and fusiform body area

Agnosia

• Inability to recognize visually presented objects, but recognition can occur through other modalities (e.g. touch, audition).

• Impairment can be at the level of perceptual integration or at the level of the link between visual perception and memory.

apperceptive agnosia

• Ventral-stream disorder

• The patient's ability to achieve object constancy is disrupted

• Recognition is impaired for objects presented from non-standard views or with a limited amount of information

integrative agnosia

inability to integrate features from parts, or parts of an object into a coherent whole

associative agnosia

• Impaired with bilateral posterior (occipital-temporal) lesions

• Failure of visual object recognition that cannot be attributed to perceptual abilities

semantic categorization

• Impaired ability to understand the meaning of an object => matching function test

• Copy drawings, cannot draw from memory

Prosopagnosia

• Deficit in face recognition that cannot attributed to dementia or visual perceptual problems.

• In extreme cases may not even recognize their spouses, children, or their own face. Can correctly identify visually other objects.

• Acquired and congenital

"What" pathway

• From the occipital lobe to the temporal lobe -> ventral

• Recognizing the identity of objects

• Inferior temporal lobe: larger receptive fields

Attention

the process by which certain information is selected for further processing & other information is discarded

bottom-up processing

attention is involuntarily captured by external stimuli (reflexive/exogenous attention)

selective attention

the process of picking out & maintaining focus on a particular quality, object, or event and ignoring other stimuli or characteristics of the stimuli due to limited capacity to process all the information

inattentional blindness

when your attention is guided by specific goals, you tend not to notice other details irrelevant to your goal

change blindness

when your attention is guided by specific goals, you tend not to notice changes in the scene

orienting

moving the focus of attention

overt attention

when the focus of attention corresponds with eye fixation & with what is suggested by posted & head movements

(Posner's Cuing task) Voluntary orienting of attention

manipulated by a cue, which may be valid (correctly indication the location of a target) or invalid (incorrect cue) cueing is endogenous because attention orientation is driven by subject's goal

involuntary orienting of attention

when an external cue (e.g., bright flash) draws attention to one of the two target locations

covert attention

the focus of attention is not accompanied by eye or head movements

Helmholtz's covert attention experiment

• We can enhance perception if we focus our attention on a location in the visual field

• However, enhancing perception in one part of the visual field takes place at the expense of other areas

Frontal lobe

ventral & superior prefrontal cortex (frontal eye fields) maintaining vigilance

Parietal lobe

representation of spatial information, involved in top-down attention control of spatial orientation

frontoparietal network

reorienting attention

superior colliculus

involved in directing eye movement

pop out vs. conjunction search

-target defined by a single feature (pop out) vs. by a conjunction of features (conjunction) that are also shared by distractors

- pop out search us fast & pre-attentive while conjunction search requires attention in sequential manner/must attend to each individual object to detect targets

feature integration model (treisman & Gelade, 1980)

features of an object are integrated in sequential manner; attention must be paid to one feature at a time. Thus conjunction search is low

Balint's syndrome

only one or a small subset of available object is perceived at the same time, although patients can see each object when presented individually

hemispatial neglect

• Reduced attention to one (usually left) side of the scenes & objects, as though they do not exist.

• Affects the side contralateral to the side of damage.

divided attention

the ability to split attention between different sources of information or different tasks

Cherry's Cocktail Party Effect

ability to follow one conversation in the presences of many other simultaneous conversations

Broadbent's Early-Selection Model

• Selection occurs before the stimulus is fully processed - ignored inputs are minimally perceptually processed.

• Physical characteristics of inputs are used to select one input for further processing, and all other inputs are lost.

Cherry's Dichotic Listening Paradigm

• Participants repeat inputs presented to one ear while ignoring those presented to the other ear.

• Participants can still pick up some auditory info in the ignored ear (e.g., whether it is a voice and gender of voice) although most of the content is lost

Treisman's attention model

Physical characteristics are used to select one input for full processing, and other inputs undergo partial processing

Late-Selection Models

Attentional filtering occurs after the completion of perceptual processing of the sensory inputs, at stages where info had been recorded as semantic or categorical representation (e.g., "chair") (Deutsch & Deutsch, 1963)

Dorsal (fronto-parietal) Attention Network

• Frontal and parietal areas

• Concerned primarily with the control of spatial attention

• Involved in voluntary attention to goal-directed location and targets

Ventral attention network

• Temporoparietal junction and ventral frontal cortex

• Involved in stimulus-driven control (e.g., attending to unexpected stimuli) that is needed for disengaging and re-orienting attention to attend to novel stimuli

Spinal cord

lower level effectors

Motor neurons

project from the ventral horn to muscle fibers

Alpha motor neurons

causing muscle contraction

Gamma motor neurons

adjust the tension in the muscle for precision

Spinal cord interneurons

coordinating simple reflexes (e.g., knee jerk reflex)

Cortical/Direct control:pyramidal/corticospinal (CST) tract:

• Direct connection between the cortex and spinal cord

• Originates mostly in the primary motor cortex, 80-90% crosses over in the medulla to regulate the contralateral side of the body.

• Regulates fine movement of parts.

• Damage leads to permanent loss of the fine control of the extremities.

Subcortical/indirect control

• Extra-pyramidal tracts: indirect control over spinal cord activity. Originate in the brainstem. Receive inputs from cortical and subcortical structures.

• Regulate large and coordinated movements, such as posture, balance, muscle tone, startle and escape reflexes, etc.

Subcortical motor structures

cerebellum & basal ganglia

Cerebellum

• Does not initiate motor commands.

• Coordinates movements by correcting unanticipated errors in ongoing motor processing in the motor and premotor cortices.

Motor functions

• Motor planning and execution.

• Posture and balance.

• Combines sensory and motor info to predict where and when an object will be.

• Damage leads to balance disorders

Basal Ganglia

components include striatum (caudate & putamen) globus pallidus, functionally connected to thalamus substantia nigra, and subthalamic nuclei

Basal Ganglia function

• Action control, selection and initiation of action

• Every area of the cortex interacts with the basal ganglia via recursive loop circuits

Direct pathway

excitatory

Indirect pathway

inhibitory

Diseases of Basal Ganglia

Huntington's and Parkinson's

Hungtington's disease

• Genetically based, usually expressed later in life; caused by neuronal death in the indirect pathway in the striatum

• Symptoms: too much motion, often inappropriate chorea (uncontrollable, jerky movements)

Parkinson's Disease

• Loss of dopaminergic fibers in substantia nigra

• Symptoms: resting-tremors, rigidity in movements, shuffling gait, stooped posture

• Treatments: stimulating dopamine receptors, or deep brain stimulation

Cortical motor structures

Primary motor cortex (M1)

Primary Motor cortex (M1)

• Voluntary movement

• Somatotopic representation of the body

• Origin of the corticospinal pathway

• Directly produce motor movements, or modulate spinal circuits to excite or inhibit more complex movements

Secondary motor cortex

premotor cortex, prefrontal, and supplementary motor cortex

Premotor cortex (PMC)

• Involved in externally guided action

• Important for the preparation of actions

supplementary motor area (SMA)

involved in internally guided action

prefrontal cortex

• Involved in planning and higher aspects of the control of action, such as selection of action, and maintenance of goals and responses

• Setting and maintaining long-term goals

• Damage to the PFC (prefrontal cortex) does not impair execution but actions become inappropriate or disorganized

Short-term memory (STM)

short-term retention of information measured in seconds to minutes; limited capacity (about 7 chunks of information) the brain's 'post it note'

Working memory

• Short-term retention in which information can be maintained (contents remain accessible) or manipulated (can perform mental operations over contents)

• Ex: you'll need to retain in memory some numbers and perform logical/arithmetic operations on them

Posterior cortices

main storage of information

Baddeley and Hitch's model for working memory

• Emphasize the maintenance and manipulation of information retained for a short time

• Two separate STM stores: phonological loop and visuospatial sketch pad, for auditory and visuospatial information respectively

central executive mechanism

controls and coordinates the interaction between the two subordinate systems and long-term memory (LTM): function of prefrontal cortex

Long-term forms of memory (LTM)

information retained for a long time measured in days to years

(Declarative) Explicit memory

knowledge to which we have conscious access and we can report verbally

Episodic memory

• Memory of past events in our lives (what, where, when, with who) associated with context (source memory)

• Personal and subjective (MTL lesions)

Semantic memory

memory of world knowledge (i.e., facts, physical laws), that does not relate to our lives, not associated with the specific context in which such knowledge was acquired; objective

(Nondeclarative) Implicit memory

our behavior is influenced by previous experiences without conscious recollection of those experiences -> we cannot verbally report such memories

Procedural memory

mediated by the striatum (ex: knowing how to ride a bike, inflexible)

Priming

• Prior exposure to a stimulus facilitates our response to it

• Can be perceptual, conceptual, and semantic

• Neocortex

Medial temporal lobe (MTL) structures

• Hippocampus( horse-shaped, blue color) & interconnected structures: entorhinal cortex, perirhinal cortex, parahippocampal cortex

• Amygdala (red): encodes affective qualities of experience

Retrograde amnesia

problems with remembering past memories (retro: past)

Anterograde amnesia

problems forming new memories (antero- forward), but consolidated past memories are not affected

Amnesic patients suffer

From both Anterograde, and Retrograde

Amnesia is caused by damage to the

MTL (medial temporal lobe)

Case study: H.M

• Had most of the hippocampus and connective MTL cortices surgically removed in order to treat epilepsy

• Severe, global anterograde amnesia and temporarily limited retrograde amnesia (intact remote memories) with intact short-term memory. Can't form new declarative memories, but show signs of procedural learning.

• Preserved perceptual, motor, and cognitive functions

Insights from H.M.

• MTL is essential for the ability to form new declarative memories, but not for STM or the ability to form new non-declarative memories.

• MTL is not likely the site for LTM storage, as his retrograde amnesia only affected more recent LTMs

Spatial memory

• The hippocampus is also important in binding information together to form a holistic memory representation i.e., encoding the contextual information of an episodic memory.

• Ex: there are place cells along the hippocampus that maintain a map of spatial information, enabling the encoding of the spatial environment along with memory.

McGuire et. al (2000)

London taxi drivers tend to have larger hippocampus, particularly the posterior segment

Encoding

• The process of organizing and transforming incoming information that creates memory traces to be stored.

• Each aspect of an event activates the cortical areas involved in perceiving the different aspects of the event.

• The hippocampus stores a summary representation of the whole event, with pointers to the location of the traces distributed over the cortex.

Storage

the process of retaining information in memory

Consolidation

the process that stabilizes a memory over time. Imparied episodic memory in amnesia may be a deficit in consolidation

Standard model of consolidation

initial rapid consolidation (hippocampus) followed by a slower permanent consolidation (memory finally stored in neocortex)