Space & Action Flashcards
Which 3 pathways from the lateral geniculate nucleus (LGN) are differentially involved in perception of action?
To superior colliculus; magnocellular (dorsal - fast, efficient processing); parvocellular (ventral – slow, effortful processing)
What kind of movements does the superior colliculus control?
Ballistic movements
Describe how visual information travels along the geniculostriate pathways
Info on temporal sides of each eye travel inpsilaterally to the LGN via the optic chiasm; info on nasal sides crosses over at the optic chiasm and travels contralaterally to the LGN; then radiates through the tectum, superior colliculli, along optic radiation to V1
The retinotectal pathway travels between which two main regions?
Superior colliculus and LGN
Information from the LGN branches into 2 pathways, ventral and dorsal, and the functional properties of the neurons of each pathway deal with what?
Different types of visual input
The retinal cell properties of magnocellular and parvocellular pathways have implications for the function of the distinct areas of the cortex that they project to. What areas are these?
Magnocellular – dorsal stream to parietal; parvocellular – ventral stream to inferior temporal
Early divergence of magnocellular and parvocellular functional subsystems are set up at what stage of development?
Embryonic primate visual systems; infrastructure is set up from the start
Magno and parvo cells and their characteristics are different even before they’ve left the retina. Which retinal cells are preordained to fall in which layers of the LGN?
Parasol cells (which are bigger) fall in the 2 magno layers; midget cells (with small dentrites) fall in the 4 parvo layers
Describe the properties of the parvocellular pathway
Has sustained response; sees colour; ; low contrast gain; higher spatial resolution; slower firing of neurons; small receptive fields (can deal with small details in the environment)
Describe the properties of the magnocellular pathway
Transient response; monochrome; high contrast gain; lower spatial resolution; faster response; larger receptive fields; deals with motion
Which streams deal with the where and what of visual perception?
Where – dorsal; What – ventral
Starting from a central location, neurons within the dorsal stream have differential firing profiles depending on their tuning function. Describe how neurons in macaque monkeys displayed selectivity for orientation/direction of reach (Taira et al., 1990)
They had to move a joystick in different directions, then a needle was inserted and neuronal firing rates recorded; they fired maximally when the monkeys moved 45 degrees to the right; the further away from the direction, the less the firing rate (direction specific)
Damage to which parietal regions in the dorsal stream resulted in poorly directed reaches in macaques (Rushworth et al., 1997)?
Areas 5, 7 and MIP
Selectivity in visually guided action is fine-tuned in early development. At what stage are “reach” profiles almost as refined as an adult?
By 64 weeks
What does Ataxia result from?
Results from lesions in the dorsal stream of cortex
Describe the symptoms of Ataxia and what is preserved
Inability to use visual information to guide movement of hands, leading to incorrect/awkward movements and errors in accuracy (over/undershoots); deficits more severe in periphery of visual field (further from fixation); Ability to fixate (foveate) is preserved
In Milner et al.’s (2003) study, controls and stroke patient AT, who had haemorrhagic softening in the parietal-occipital territory, had to fixate on the centre and reach for targets with increasing distance from fixation. What was found?
Controls showed a little distortion reaching for peripheral targets, but AT could not reach past the region of foveation; significant undershoots (even where fixating) and shift inwards towards the central point
As well as reach, ongoing research has found dorsal stream/parietal lobe activation to determine what?
Grasp (pre) shaping
In V1, firing is organized retinotopically. In which region does this not occur?
Inferotemporal (IT) cortex; same population of neurons firing; higher level of information processing
Describe the properties of the Inferotemporal cortex, and what lesions in this region has led to in monkeys
Finely tuned for response selectivity for complex shapes; invariance across retinal image size, spatial location (large receptive fields) and orientation in the picture plane; Lesions result in visual discrimination deficits
Farah and Aguirre (1999) presented Ps with objects, faces and words and were asked to view them passively or actively (by responding to the info); Which region showed the greatest activation in this object recognition?
Inferotemporal cortex, suggesting higher processing
Agnosia refers to impaired recognition of familiar objects through vision. What factors is it not due to?
Loss of low-level visual processes (acuity, luminance discrimination, colour sensitivity, etc); generalised intellectual loss (e.g. dementia); loss of semantic information about objects
What techniques can patients with agnosia use to recognise objects, and what kind of objects do they tend to recognise easier?
They can use other sensory modalities (e.g. audition/touch); real objects best as opposed to photographs worse or line drawings (worst)
Patient DF suffered carbon monoxide poisoning from a malfunctioning heater, and after her recovery, was left with severe visual agnosia. What did MRI scans conducted 13 months after the injury indicate?
Widespread damage to occipital cortex bilaterally, plus some subcortical damage involving the globus pallidus, and inferotemporal pathway
In Goodale and Humphrey’s (1998) study, patient DF was given a perceptual matching task (ventral stream - matching orientation of the aperture), and a visuo-motor “posting” task (dorsal stream – posting the object through a slot). What was found?
DF was impaired in orientation matching (symbol recognition), but not as much for visuo-motor posting; impaired “what” but intact “where/how”; so problem is in visual perception rather than visually guided action
In Milner et al.’s study, they had DF with optic agnosia, and RV with optic ataxia, perform a task involving grasping of unrecognized objects. Compare the results
RV knew what it was but couldn’t pick it up; DF didn’t know what it was but could pick it up; RV showed poor visually guided action, but DF could overcome her deficit by using her fingers in a way to successfully make a lifting action
The dorsal stream contains magnocellular cells in the posterior parietal cortex and guides action (how). What does the ventral stream contain?
Parvocellular cells in the inferior temporal cortex and guides gnosis/knowledge (what)
What kinds of tasks have developmental dyslexia been shown to be affected by?
Tasks requiring fast, low contrast processing (magnocellular)
Compare magno and parvo neurones in regards to luminance (light/dark) and chromatic (red/green) sensitivity
Magno show high luminance but low chromatic sensitivity; parvo show high chromatic but low luminance sensitivity
Abnormal visual processing in which pathway might be a risk factor for autism in infants?
Magnocellular
Though in the past processing in the ventral and dorsal streams were thought to work separately, what do we now know?
They both inform each other; what can influence how; these interactions are referred to as embodied cognition – bidirectional action-perception influence
Embodied cognition is a two-way process, whereby aspects of cognition are constrained by the physical body. What are some ways in which these interact?
Through high-level constructs; interactions with the environment; motor system/bodily constraints can influence thoughts; thoughts influence the motor system
Provide 3 examples of how we’ve come to associate movements with meaning and how one influences the other
Pencil in lips – results in positive affect, thus positive assessment of presented stimuli; heaven and hell – directs attention up/down; political parties – directs attention left/right
Describe how Glover et al. found direction-specific effects of articulation on reaching
When Ps had to read a word on a screen and then reach for a wooden block, the word’s meaning changed/interfered with the visually guided action; e.g. if the word said bottom and they had to reach for the top, their movement would be lower
The parietal cortex contains the sensory cortex. What are sub-regions within this region associated with, and what can damage here lead to?
Body representation (body in connection to the environment); Damage can lead to distortions to different aspects of body representation; changes to the afferent information being received by parietal cortex
What are the motor, premotor and supplementary motor cortices involved with?
The planning, control and execution of voluntary movement
The somatosensory cortex is the main receptive area to which sense, and what is it proportional to?
Touch; It’s proportional to the relative density of tactile receptors on that body part
The primary motor cortex is located in the precentral gyrus and somatosensory cortex in the postcentral gyrus. From where does each hemisphere receive its information from?
From the opposite side of the body
The association area between motor and somatosensory cortices provides a hub for what kinds of sensory information?
Lower and higher level; all sensory information, dealing with our own body as well as objects in the environment; vision, audition, touch, kinaesthesis and proprioception
What are Reference Frames, and how are they coded?
Coordinates/sets of axes describing the location of an object relative to body parts; Initial coding is centred on the relevant sensory organ, but subsequent coding is based on the effector that’s going to be used; the brain has to account for the difference/disparity between the current and desired location
Depending on whether we’re using a body-centred, head-centred, or eye-centred model for our reference frame, what must the brain do, and in what region does this occur?
Translate coordinates to suit the body part; Specific areas in the posterior parietal lobes
What role does the Lateral Intraparietal Area (LIP) play in translating coordinates/reference frames?
Controls saccadic eye movements; activates to immediate (saccade to a target) as well as delayed responses (saccade after a delay)
What does the Parietal Reach Region (PRR) activate to in regards to reference frames?
Reaching; to immediate and delayed responses
What role does the Anterior Intraparietal Area (AIP) play in translating reference frames, and what happens when this area is depressed with GABA?
Grasp planning; grasp shaping to different shapes and sizes; When depressed with GABA, reaching but not grasping occurs (grasp shaping is distorted)
To do reference frame translations, what information must the LIP and PRR take from body-related signals?
Where the object is; where the body/arm/hand/fingers are (i.e. reference coordinate systems); what body part to respond with
If we plot the firing rate of neurons from an eye centred or limb centred reference frame on a graph, what do we see?
The curves shift from the head-centred location to match the fixation of the eye or limbs (+/- 10 degrees)
If we use a head-centred reference frame on a head-centred location of a sensory target, how do neurons respond?
They will fire at the same rate, no matter where the fixation is
If we use an intermediate reference frame on a head-centred location of a target, what changes do we see in the firing of neurons?
The curve shifts from the head-centred location between 10 degrees on right and left (shifts 5 degrees each way)
Batista et al. recorded a monkey PRR encoding reaches to visual targets in an eye-centred reference frame. The task was to fixate on a red LED, and reach to a green LED. What was found?
When the hand location remained constant and eye movement shifted there was a change in the neuronal response profile; but when the hand location varied, the neuronal response profile remained the same
Combined sensory representation of the body gives rise to ownership and agency over the body’s movements. What is a body representation schema essential for?
Selecting relevant visual information and to guide the planning and execution of actions
Provide 4 examples of distortions in body respresentation
Left-sided neglect in body parts as well as the environment; loss of representation of limbs; out of body experiences; rubber hand illusion
What occurs in patients with left hemispatial neglect following right parietal lobe lesions?
They fail (or are slow) to process information coming from the left side of the environment; excessive engagement of attention on items in right side of space, and reduced disengagement of attention away from the right side items
Left hemispatial neglect is a disorder of internal representations. As well as failing to process info from the left, what other alterations do these patients show?
Alterations in interacting with the left side of the environment; fewer eye movements; reduced reaching; bumping left side of body into obstacles; can also show neglect of the right side of their body
What is intrinsic spatial coding, and when is it essential?
It’s knowing what our own body parts are doing; Essential when a body part is going to be obscured from vision at some stage in the movement planning and execution; helps maintain internal representations
PJ suffered a head injury, losing consciousness for 30mins. A few years later she experienced jerking of the right arm and seizures, and upon assessment they discovered a cyst encroaching on which brain regions?
Cortex and subcortical white matter of left superior parietal lobe
Although patient PJ suffered no visual neglect, extinction or other visual deficits, what problems did she complain of?
Perceiving her right arm and leg to drift and fade unless she’s able to see them; loss of knowledge in limb positions in bed; tripping passengers over on public transport with her drifting leg
Based on PJ’s drifting limb symptoms, what did Wolpert et al. conclude?
Superior parietal lobe is critical for sensorimotor integration by maintaining an internal representation of the body’s state
