Space & Action

Question 1

Which 3 pathways from the lateral geniculate nucleus (LGN) are differentially involved in perception of action?

Answer 1

To superior colliculus; magnocellular (dorsal - fast, efficient processing); parvocellular (ventral – slow, effortful processing)

Question 2

What kind of movements does the superior colliculus control?

Answer 2

Ballistic movements

Question 3

Describe how visual information travels along the geniculostriate pathways

Answer 3

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

Question 4

The retinotectal pathway travels between which two main regions?

Answer 4

Superior colliculus and LGN

Question 5

Information from the LGN branches into 2 pathways, ventral and dorsal, and the functional properties of the neurons of each pathway deal with what?

Answer 5

Different types of visual input

Question 6

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?

Answer 6

Magnocellular – dorsal stream to parietal; parvocellular – ventral stream to inferior temporal

Question 7

Early divergence of magnocellular and parvocellular functional subsystems are set up at what stage of development?

Answer 7

Embryonic primate visual systems; infrastructure is set up from the start

Question 8

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?

Answer 8

Parasol cells (which are bigger) fall in the 2 magno layers; midget cells (with small dentrites) fall in the 4 parvo layers

Question 9

Describe the properties of the parvocellular pathway

Answer 9

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)

Question 10

Describe the properties of the magnocellular pathway

Answer 10

Transient response; monochrome; high contrast gain; lower spatial resolution; faster response; larger receptive fields; deals with motion

Question 11

Which streams deal with the where and what of visual perception?

Answer 11

Where – dorsal; What – ventral

Question 12

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)

Answer 12

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)

Question 13

Damage to which parietal regions in the dorsal stream resulted in poorly directed reaches in macaques (Rushworth et al., 1997)?

Answer 13

Areas 5, 7 and MIP

Question 14

Selectivity in visually guided action is fine-tuned in early development. At what stage are “reach” profiles almost as refined as an adult?

Answer 14

By 64 weeks

Question 15

What does Ataxia result from?

Answer 15

Results from lesions in the dorsal stream of cortex

Question 16

Describe the symptoms of Ataxia and what is preserved

Answer 16

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

Question 17

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?

Answer 17

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

Question 18

As well as reach, ongoing research has found dorsal stream/parietal lobe activation to determine what?

Answer 18

Grasp (pre) shaping

Question 19

In V1, firing is organized retinotopically. In which region does this not occur?

Answer 19

Inferotemporal (IT) cortex; same population of neurons firing; higher level of information processing

Question 20

Describe the properties of the Inferotemporal cortex, and what lesions in this region has led to in monkeys

Answer 20

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

Question 21

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?

Answer 21

Inferotemporal cortex, suggesting higher processing

Question 22

Agnosia refers to impaired recognition of familiar objects through vision. What factors is it not due to?

Answer 22

Loss of low-level visual processes (acuity, luminance discrimination, colour sensitivity, etc); generalised intellectual loss (e.g. dementia); loss of semantic information about objects

Question 23

What techniques can patients with agnosia use to recognise objects, and what kind of objects do they tend to recognise easier?

Answer 23

They can use other sensory modalities (e.g. audition/touch); real objects best as opposed to photographs worse or line drawings (worst)

Question 24

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?

Answer 24

Widespread damage to occipital cortex bilaterally, plus some subcortical damage involving the globus pallidus, and inferotemporal pathway

Question 25

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?

Answer 25

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

Question 26

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

Answer 26

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

Question 27

The dorsal stream contains magnocellular cells in the posterior parietal cortex and guides action (how). What does the ventral stream contain?

Answer 27

Parvocellular cells in the inferior temporal cortex and guides gnosis/knowledge (what)

Question 28

What kinds of tasks have developmental dyslexia been shown to be affected by?

Answer 28

Tasks requiring fast, low contrast processing (magnocellular)

Question 29

Compare magno and parvo neurones in regards to luminance (light/dark) and chromatic (red/green) sensitivity

Answer 29

Magno show high luminance but low chromatic sensitivity; parvo show high chromatic but low luminance sensitivity

Question 30

Abnormal visual processing in which pathway might be a risk factor for autism in infants?

Answer 30

Magnocellular

Question 31

Though in the past processing in the ventral and dorsal streams were thought to work separately, what do we now know?

Answer 31

They both inform each other; what can influence how; these interactions are referred to as embodied cognition – bidirectional action-perception influence

Question 32

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?

Answer 32

Through high-level constructs; interactions with the environment; motor system/bodily constraints can influence thoughts; thoughts influence the motor system

Question 33

Provide 3 examples of how we’ve come to associate movements with meaning and how one influences the other

Answer 33

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

Question 34

Describe how Glover et al. found direction-specific effects of articulation on reaching

Answer 34

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

Question 35

The parietal cortex contains the sensory cortex. What are sub-regions within this region associated with, and what can damage here lead to?

Answer 35

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

Question 36

What are the motor, premotor and supplementary motor cortices involved with?

Answer 36

The planning, control and execution of voluntary movement

Question 37

The somatosensory cortex is the main receptive area to which sense, and what is it proportional to?

Answer 37

Touch; It’s proportional to the relative density of tactile receptors on that body part

Question 38

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?

Answer 38

From the opposite side of the body

Question 39

The association area between motor and somatosensory cortices provides a hub for what kinds of sensory information?

Answer 39

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

Question 40

What are Reference Frames, and how are they coded?

Answer 40

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

Question 41

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?

Answer 41

Translate coordinates to suit the body part; Specific areas in the posterior parietal lobes

Question 42

What role does the Lateral Intraparietal Area (LIP) play in translating coordinates/reference frames?

Answer 42

Controls saccadic eye movements; activates to immediate (saccade to a target) as well as delayed responses (saccade after a delay)

Question 43

What does the Parietal Reach Region (PRR) activate to in regards to reference frames?

Answer 43

Reaching; to immediate and delayed responses

Question 44

What role does the Anterior Intraparietal Area (AIP) play in translating reference frames, and what happens when this area is depressed with GABA?

Answer 44

Grasp planning; grasp shaping to different shapes and sizes; When depressed with GABA, reaching but not grasping occurs (grasp shaping is distorted)

Question 45

To do reference frame translations, what information must the LIP and PRR take from body-related signals?

Answer 45

Where the object is; where the body/arm/hand/fingers are (i.e. reference coordinate systems); what body part to respond with

Question 46

If we plot the firing rate of neurons from an eye centred or limb centred reference frame on a graph, what do we see?

Answer 46

The curves shift from the head-centred location to match the fixation of the eye or limbs (+/- 10 degrees)

Question 47

If we use a head-centred reference frame on a head-centred location of a sensory target, how do neurons respond?

Answer 47

They will fire at the same rate, no matter where the fixation is

Question 48

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?

Answer 48

The curve shifts from the head-centred location between 10 degrees on right and left (shifts 5 degrees each way)

Question 49

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?

Answer 49

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

Question 50

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?

Answer 50

Selecting relevant visual information and to guide the planning and execution of actions

Question 51

Provide 4 examples of distortions in body respresentation

Answer 51

Left-sided neglect in body parts as well as the environment; loss of representation of limbs; out of body experiences; rubber hand illusion

Question 52

What occurs in patients with left hemispatial neglect following right parietal lobe lesions?

Answer 52

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

Question 53

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?

Answer 53

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

Question 54

What is intrinsic spatial coding, and when is it essential?

Answer 54

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

Question 55

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?

Answer 55

Cortex and subcortical white matter of left superior parietal lobe

Question 56

Although patient PJ suffered no visual neglect, extinction or other visual deficits, what problems did she complain of?

Answer 56

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

Question 57

Based on PJ’s drifting limb symptoms, what did Wolpert et al. conclude?

Answer 57

Superior parietal lobe is critical for sensorimotor integration by maintaining an internal representation of the body’s state