Midterm 4 Flashcards
What is therole of the dorso dorsal branch
role of the dorso-dorsal stream in attention as one of orienting within a salience map (as described above) and involving the LIP and FEF.
Wha is the role of ventro dorsal branch?
ventro-dorsal branch as a “circuit breaker” that interrupts ongoing cognitive activity to direct attention outside of the current focus of processing. This attentional disengagement mechanism is assumed to involve the *temporoparietal region* (and ventral prefrontal cortex) and is considered to be more strongly right lateralized. For instance, activity in this region is found when detecting a target (but not when processing a spatial cue) whereas activity in the LIP region shows a strong response to the cue
3 properties of attention
Attention can be voluntarily controlled (we can decide where or at what to direct our attention).
Attention is selective (we choose among several alternatives where to attend).
Attention has limited capacity (you can’t process all at once).
Definition of attention
Attention is the process by which certain information is selected for further processing and other information is discarded.
Function of attention
Avoid sensory overload. Optimize the use of cognitive resources available.
Contrast between attention & perception:
Perception is concerned with making sense of the external environment, whereas • Attention lies at the interface between the external environment and our internal states (goals, expectations).
Inattentional blindness
Failure to be aware of a visual stimulus because attention is directed away from it.
Often linked to a filter or ‘bottleneck’ in operation
“invisible gorilla test” experiment,– ( observers were told to count the number of passes or to keep track of the number of throws versus bounce passes – 50% did not notice gorilla)
Change blindness
Failure to notice a change, for example, the appearance/disappearance of objects.
— Simons and Levin (1998) carried out studies in which participants started to have a conversation with a stranger. This stranger was then replaced by a different stranger during a brief interruption (e.g., a large object coming between them).
Many participants simply did not realize that their conversational partner had changed!”
Spotlight metaphor
- Attention tends to be directed to locations in space - Spotlight may move from one location to another, highlighting information.
- It may zoom in or out (narrow or wide “beam”)
What controls the spotlight? How does it know where to go?
Endogenous / exogeonous attention.
You - WHO YOU ARE Endogenous Orienting our ability to intentionally attend to something (top-down or goal-directed or voluntary) Exogenous orienting the ability of a sensory event to capture our attention (bottom-up or stimulus-driven or reflexive attention) What ends up being selected depends on the interaction between these two influences.
Endogenous Orienting
our ability to intentionally attend to something (top-down or goal-directed or voluntary) (Imagine you’ve lost your car keys Now you have a goal and you move around your attention to find the keys)
Exogenous orienting
the ability of a sensory event to capture our attention (bottom-up or stimulus-driven or reflexive attention) (Or attention might be captured by salient or important features in the environment Often loud noises, changes in motion, brightness)
Limitations of the spotlight metaphor
-We can split attention between two non-adjacent locations
- Eye gaze ≠ attention (covert vs. overt attention)
Covert attention
Can report letters at attended location even without looking = Covert attention (Hidden from the observer) still cant report (eg. letters) at other locations
there is a natural tendency for attention and eye fixation to go together because visual acuity (discriminating fine detail) is greatest at the point of fixation. Moving the focus of attention is termed orienting and is conventionally divided into covert orienting (moving attention without moving the eyes or head) and overt orienting (moving the eyes or head along with the focus of attention).
Non-spatial attentional selection
(A limitation of the spotlight metaphor)
Object-based attention Different parts of visual ventral stream (representing different stimulus types/properties increase in activity when attended (ie - ‘faces’= stimulus in ‘fusiform face area’ in the visual ventral stream)
Time-based attention: the ‘attentional blink’, (or inability to report a target stimulus if it appears soon after another target stimulus).
Two Cortical Pathways for Visual Perception
Dorsal (“where/how”) stream (Parietal)
ventral (“what”) stream (Temporal)
Lateral Intra-Parietal Area (LIP) - Single cell electrophysiology shows this area encodes…
motor properties (important for saccades)
sensory properties (both sound and vision), enables sounds to be remapped to eye-centred coordinates
Neurons in LIP show remapping of sounds to eye-centred coordinates Example: an LIP neuron responds to a sound coming 20 degrees to the left of the fixation point irrespective of whether the sound source itself comes from the left or center of space (enabling orienting of eyes to sounds.) *relative*
Two Cortical Pathways for Visual Perception [dorsal and ventral] - what do they do
Dorsal (“where/how”) stream (Parietal)
- Locating objects in space
- Guiding actions directed at those objects
- Attention (spatial or not) - in conjunction with frontal areas
ventral (“what”) stream (Temporal)
- identifying of objects
- attaching meaning/ significance to them
saccade
(/sɨˈkɑːd/ sə-KAHD, French for jerk) is a quick, simultaneous movement of both eyes between two phases of fixation in the same direction.
Lateral Intra-Parietal Area (LIP) is important for attention because:
Important for attention because…
- Doesn’t respond to all* sensory stimuli (sparseness) *or the same stimuli all the time. NOT linked to presence (necessarily) - linked to attention
- Responds more to stimuli that are unexpected such as sudden flash (i.e. important for exogenous attention)
- Responds more to stimuli that are task relevant (i.e. important for endogenous attention) and to current position of the eyes (both needed to plan a saccade).
- Codes a spatial ‘salience map*’ in which only the locations of the most behaviorally relevant stimuli are encoded. *which is selecting attention at any given time
Frontal-Parietal Attention Mechanisms
Corbetta & Schulman (2002) suggested that the dorsal stream should be subdivided into two:
- Dorso-dorsal route (including LIP and “frontal eye field” region) involved in orienting in a salience map (important for endogenous orienting).
- Ventro-dorsal route (involving the “temporoparietal junction (TPJ)” and “ventral prefrontal cortex” (VFC)) acts as a ‘circuit breaker’ (e.g. attentional disengagement from ongoing activity caused by exogenous stimuli)
Spatial attention (LIP)
LIP codes a spatial ‘salience map’ in which only the locations of the most behaviorally relevant stimuli are encoded.
At any given time LIP is ‘selecting’ attention
Salient
Any aspect of a stimulus that, for whatever reason, stands out from the rest.
•Dorso-dorsal route
(including LIP and “frontal eye field” region) involved in orienting in a salience map (important for endogenous orienting).
LIP (lateral intraparietal area) and FEF (frontal eye field)
•Ventro-dorsal route
(involving the “temporoparietal junction” and “ventral prefrontal cortex”) acts as a ‘circuit breaker’ (e.g. attentional disengagement from ongoing activity caused by exogenous stimuli)
TPJ and VFC
* involved in interrupting the current of attention (exogenous)
Hemispheric Differences
(aka lateralization)
Spatial
- Parietal lobes represent full visual field but in a graded fashion (salience map)
- BUT: brain damage in humans to right parietal lobe has more profound effects than damage to left (‘neglect’)
- Possibly right LIP contributes more to salience map (right hemisphere spatial dominance makes left visual field more salient).
•Attention is selective, can be voluntary, and has limited capacity
▫Example:
Inattentional blindness
Inattentional blindness
Attention is a bit like ….
But…
a spotlight
▫But: it can be covert as well as overt
•Directing the spotlight:
▫Voluntary/top-down processes/endogenous/goal-directed
▫Reflexive/bottom-up/exogenous/stimulus-driven
▫Frontoparietal attentional networks
(dorso-dorsal and ventro-dorsal routes).
Dorso-dorsal route
Components?
Function?
(Where/How Stream) * Parietal *
LIP (“Lateral intra-parieta larea”) and FEP (“frontal eye field”) – involved in orienting on a salience map ** important for endogenous orienting **
Superior longitudinal fasciculus
posterior parietal cortex
(– according to Corbeta & Schulman)
**** This hypothesis has been challenged ****
Ventro-dorsal route
Components
function
(Ventral “What” Stream) * Temporal *
TPJ (“temporal junction”) and VFC (“Ventral prefrontal cortex”)
Inferior longitudinal fasciculus
Inferior Temporal Cortex
Acts as a “circuit breaker” (e.g. attentional disengagement from ongoing activity caused by exogenous stimuli)
(– according to Corbeta & Schulman)
**** This hypothesis has been challenged ****
Hemispheric Differences
(aka lateralization)
- Parietal lobes represent full visual field but in a graded fashion (salience map)
- BUT: brain damage in humans to right parietal lobe has more profound effects than damage to left (‘neglect’)
- Possibly right LIP contributes more to salience map (right hemisphere spatial dominance makes left visual field more salient).
endogenous orienting
Endogenous Orienting our ability to intentionally attend to something
(top-down or goal-directed or voluntary attention)
?? ‘spatial’ attention
Visual spatial attention is a form of visual attention that involves directing attention to a location in space. Spatial attention allows humans to selectively process visual information through prioritization of an area within the visual field.
Spatial attention is the ability to focus on specific stimuli in a visual environment. When people look at scenes, although they may feel like they are looking at a complex mixture of stimuli, their attention is actually drawn to a handful of critical pieces of data. The brain identifies the most important information in the scene for further examination and the coordinated planning of movements. In people with neurological disorders, errors of this type of attention can develop.
Object - based attention
non-spatial attentional selection(?)
Diff. parts of visual ventral stream (representing different stimulus types/properties) increase in activity when attended (e.g. fusiform face area when face is attended)
Time-based attention
*Non-spatial attentional selection
The ‘attentional blink’ (or inability to report a target stimulus if it appears soon after another target stimulus)
salience
is the state or condition of being prominent. The Oxford English Dictionary defines salient as “most noticeable or important.”
- LIP (abbreviation for..)
- Part of ___ stream
- ^along with _____
- Important for ______
- Lateral intra-parietal area
- Dorso dorsal stream
- FEF (frontal eye field)
- involved in orienting in a salience map (important for endogenous orienting).
Hemi-spatial neglect
A failure to attend to stimuli on the oppisute side of space to a brain lesion
Hemineglect, also known as unilateral neglect, hemispatial neglect or spatial neglect, is a common and disabling condition following brain damage in which patients fail to be aware of items to one side of space. Neglect is most prominent and long-lasting after damage to the right hemisphere of the human brain, particularly following a stroke. Such individuals with right-sided brain damage often fail to be aware of objects to their left, demonstrating neglect of leftward items.
The deficit may be so profound that patients are unaware of large objects, even people, towards their neglected orcontralesional side - the side of space opposite brain damage. They may eat from only one side of a plate, write on one side of a page, shave or make-up only the non-neglected or ipsilesional side of their face (same side as brain damage). Their drawings may fail to include items towards the neglected side, for example when placing the numbers in a drawing of a clock (Fig.1). Many patients are often also unaware they have a deficit (anosognosia).
Classically, the neglect syndrome has been associated with damage to the right posterior parietal cortex. More recent studies have begun to challenge this view, suggesting instead that a more widespread network of areas may be involved, including those that have been implicated in studies of neuroimaging of attention (discussed further in theNeuroanatomy of neglect below; see also Corbetta & Shulman, 2002 and Husain and Rorden, 2003). Differences in the location and extent of lesions (brain damage) across patients may contribute to the heterogeneity of the condition.
Tests of Hemi-spatial Neglect
copying
line bisection
drawing from memory
cancellation
VISUAL EXTINCTION
•If cued on the left part of the visual field, patients are often able to detect objects there, especially if the object is presented alone
▫Phenomenon of “visual extinction” suggests different perceptual representations are competing for attention (and visual awareness)
stimuli compete for attention in neglect condition
*Balints Syndrome Simultanagnosic patients can / cannot
can recognize single objects but CANNOT compute spatial relationships between objects
But when is an object an object? E.g. is a face an object, or several objects (e.g. eyes, nose etc.)?
Evidence suggests that these patients can group several parts into wholes if they share color, shape, or are connected
Top-down factors important too (e.g. “are ovals at top or bottom?” versus “is face the correct way up?”)
Perceptual vs. representational neglect
(seeing and imagining)
A double dissociation has been found between perceptual and representational neglect, suggesting the brain uses different spatial reference frames for representational (mental imagery) and perceptual space.
** THE SPATIAL MAP YOU FORM FROM MEMORIES IS DIFFERENT FROM ACTUALLY BEING THERE
Different Spatial Reference Frames for object-based and space-based neglect
Some neglect patients attend to objects on the left side of space but omit to attend to one half of the object itself (object-based neglect)
Forms a double dissociation with space-based neglect
Some neglect patients attend to objects on the left side of space but omit to attend to one half of the object itself (object-based neglect)
Forms a double dissociation with space-based neglect
FIT and object perception
“illusory conjunctions”
What if you cant pay attention? (eg because objects are presented too quickly)
▫ Report a conjunction of features that you never actually saw
Illusory conjunctions provide evidence that attention is needed to combine an object’s features correctly
FIT and visual search (Feature search)
FIT and visual search:
Case 1
Recall: FIT says attention is needed to bind together multiple features
But only one feature is needed to find the target (So this kind of feature search doesn’t need attention) - Reaction time is independent of number of distractors
Case 2:
• Try to find the blue “T” in the array ((Two features needed to find the target – Color and shape))
Now two features are needed to find the target So this kind of conjunction search DOES need attention — More distractors, longer reaction time
FIT
• Conjunction search:
- Feature search: a single feature is enough to identify the target, attention not needed, RT does not increase with increasing distractors
- Conjunction search: must find a combination of two features to identify the target, attention is needed, RT increases with increasing distractors
Evidence for Semantic Processing of Unattended Stimuli: Negative Priming
Biased Competition Theory
Evidence
Within ventral stream: neurons reduce their specificity of responding when multiple stimuli in their receptive field (whole is less than sum of parts)
• Within parietal lobes: brain damage affects attention when multiple stimuli compete (i.e. extinction)
Premotor Theory of Attention
Evidence (1/2)
Rizzolatti et al. (1987): A centrally presented digit (e.g. 2) indicates where target a likely to appear, but it may sometimes appear elsewhere.
• An unexpected shift of attention is harder when crossing midline (location 3 requires new saccade in the opposite direction) than not (location 1 only requires modifying existing saccade in the same direction).
Notice locations 1 and 3 are equidistant from location 2.
Premotor Theory of Attention
Evidence (2/2)
Moore & Fallah (2001). Monkeys had to press a lever when detecting a change in luminance in a specific region of the visual field.
Detection was faster when Frontal Eye Fields (a prefrontal area involved in planning saccades) were weakly stimulated electrically:
- weakly enough not to produce a saccade.
- importantly, it only facilitated detection if the change in luminance happened in the appropriate receptive field.
LTM - DECLARATIVE VS. NON DECLARATIVE
• Declarative (explicit) vs. non-declarative (implicit) memory • Declarative memory: consciously accessible ▫ Includes episodic + semantic; impaired in HM ▫ This suggests MTL is critical for declarative memory • Non-declarative: not consciously accessible ▫ Skills, priming, habits ▫ Are these impaired in HM?
MEDIAL TEMPORAL LOBE
STRUCTURES?
MTL CONSISTS OF :
HIPPOCAMPUS
PARAHIPPOCAMPAL CORTEX
PERIRHINAL CORTEX
ENTORHINAL CORTEX
retrograde vs. anterograde amnesia
•Anterograde amnesia
▫Difficulty with memory for events AFTER brain damage
Forming new memories
•Retrograde amnesia:
▫difficulty with memories from BEFORE brain damage
Retrieval of old memories
REMOVAL OF MTL including hippocampus (PATIENT HM)
Whats spared // impaired?
•Dissociation #1:
•Short-term memory: Spared
•Long-term memory: Impaired
- Forgot the events of daily life as quickly as they occurred
- Inference: LTM but not STM depends on the MTL
- But: Childhood memories relatively intact…
HM: Dissociation #2
•Severe anterograde amnesia
•Gradient of retrograde amnesia
•Inference: MTL is critical for forming new memories and retrieving recently formed old memories
▫Less critical for retrieving distant memories
HM: Dissociation #3???????
•Episodic vs. semantic memory
•Episodic memory:
▫Memory for events of own life
▫Anterograde: strongly impaired
▫Retrograde: gradient of impairment
- ▫*
- So HM has a problem with long term memory, especially with forming new memories*
- Is that true for all kinds of long term memory?*
•Semantic memory
▫Memory for facts about the world
▫Anterograde: strongly impaired
▫Retrograde: seemingly not impaired?
▫But: most semantic knowledge acquired early in life, and is frequently re-encountered (rehearsed)
▫When this is taken into account, there is also a gradient of retrograde impairment for semantic
•Take-home: episodic and semantic memory are different, but both depend on the MTL
▫
•Together, episodic and semantic memory are called declarative memory
Third dissociation: episodic vs. semantic (notice question mark here)
Where are long-term memories stored?
▫Can the MTL be the place where memories are stored?
•HM’s oldest episodic and semantic memories were intact
▫Can the MTL be the place where memories are stored?
▫No. Otherwise those older memories would have been also eliminated.
•Memories appear to be stored where the information was initially processed…
