Lecture 8 Flashcards
What do cells code for at the beginning of the ventral stream? What happens as you go along the stream?
At the beginning they code for simple stimuli like lines they then progress to more complex stimuli like objects and shapes and then faces which are very complicated
As you travel along the ventral stream what happens to the receptive fields?
They get bigger
Allowing for more complex stimuli to be picked up
Do the ventral and dorsal pathways have a common root?
Yes they both start in the early visual areas, for example V1, V2 and V4
So what is the ventral stream responsible for processing?
Represents motion
Spatial information about the environment
And then most complex where you are in the environment
What are the two important parts of the parietal lobe?
Inferior parietal lobe
Superior parietal lobe
What are the 3 sulci that are important in the parietal lobe? Which areas do they subdivide?
Central sulcus - Separates the parietal from the frontal
Intraparietal sulcus - separates the superior parietal from the inferior parietal *
Parieto-occipital sulcus - separates the occipital from the parietal
What are two key areas within the inferior parietal lobule ?
Angular gyrus
Superior marginal gyrus
Who did an important review paper which plotted all the lesions and tasks on a map of the parietal lobe ?
Culham (2006)
In which area did culham find most of the activation to be?
Mostly in the intraparietal sulcus
What relation does the parietal lobe have to the frontal and occipital lobes?
Thought of as the interface between the two, so between the occipital visual information and the frontal motor control
What is anterior to the central sulcus?
What is posterior to the central sulcus?
Anterior you have the primary motor area of the frontal lobe. Responsible for the specific mapping of muscles
Posterior you have the primary somatosensory area in the parietal lobe which is responsible for the sensations of different body areas
What do we mean when we say the early visual areas are topographic?
Neighbouring points in visual space correspond to points on the cortex
With the left visual field being represented in the right hemisphere
What are the main parietal functions ?
Visuomotor control (eye movements, reaching and grasping) Visuospatial attention
It’s a big structure so it has lots of other jobs too like numeracy and representing numbers as well.
What are some disorders of motor control ?
Optic ataxia
Ideomotor ataxia
What is optic ataxia a disorder of ?
Of coordination and accuracy of visually elicited hand and arm movements
There are no issues with the sensations of the arms and the muscles
Where do you normally find lesions for optic ataxia?
Primarily in the parietal lobe
In the perenin and vighetto (1988) study where did they find lesions in their 10 cases?
All over the parietal lobes
What was the task in the perenin & vighetto task?
What two visuomotor controls does it require?
The posting task
Spatial location, where the disc is
Orientation of the slot
Which errors did optic ataxic patients make?
Spatial - they’d miss the disc altogether
Orientation - be at the wrong orientation for the slot
If DF and the optic ataxic patients are asked to orient their hands in mid air to match the slot who does best and why?
Optic ataxic patients can do this, but DF can’t because she has a visual deficit
When DF and optic ataxic patients are asked to do the posting task who does better? And why?
DF can do this task because it implicit whereas ataxics can’t do it very well at all.
What is ideomotor apraxia?
Disorder in the execution of movement that cannot be accounted for by weakness, ataxia, sensory loss, poor language or in attention to commands
Impairment to control of goal directed motor activities
What is apraxia?
Cognitive motor disorder that involves impaired ability to programme motor systems to perform skilled purposeful tasks
What is the slicing bread task? Who came up with it?
Trackers were placed on the arms and wrist of the individual you then have to act out in mid air, or using a variety of implements or using real bread. Pretend to slice the bread
Sample were MR an ideomotor apraxic and age matched controls
What are the disconnection and motor memory hypothesis?
Disconnection - apraxia is the result of disconnection between language areas and motor areas
Geschwind (1975)
Motor memory hypothesis - representations of learned skilled motor movements are stored in the dominant parietal cortex
Heilman (1979)
According to the motor memory theory why is the task performance impaired ?
Because the whole representation for cutting bread has been lost
How did Clark (1994) try and test between the two theories?
If it is only deficits in how apraxia translate language then impairment should only be on the language / command condition
What were the results of the cutting bread study?
MR struggles to mime cutting bread as well as cutting bread for real
So which hypothesis do the results support?
Hypothesis two
That the whole motor representation has been destroyed
Independent of language
What slightly improved the apraxic patients performance? And why?
Visual and somatosensory cues of the implements and the bread in front of them help the performance of the patients.
This might be because of the interaction between various parts of the cortex but that’s a guess
What is neglect?
In attention to the opposite sides visual field of the lesion
Comes about after lesioning the parietal lobe
If you TMS the parietal lobe How long do you have to, to see neglect for 30 minutes?
44 seconds
What is the visual exploration task? What were the participant conditions ?
Healthy subjects visually explore pictures in 3 conditions
No TMS
TMS to right posterior parietal
TMS to a control region (random unrelated place )
Recorded the amount they looked at the left and right of the scene
What as the prediction of the study?
There would be reduced viewing of the left hand side of the screen in the TMS to the right posterior parietal condition
What were the results of the study?
Without any TMS there was a bias to look at the left of the screen anyway
In the TMS condition there was decreased viewing of the left and more of the right as you would expect
Which is the the where and how stream?
Which is the what stream?
Dorsal
Ventral
