Week 3 - Movement And Action Flashcards
Vision-for-action brain pathways
Area MT (V5)
Area MST
Area MT (V5)
Cells specialised for basic visual motion
Location: (MT: median/ middle temporal) near occipito-temporal border
Example: area MT is active when viewing moving dots compared to static dots
Area MST
Cells specialised for visual guidance of movement
Location: (MST: middle superior temporal) adjacent to and above area MT
Example: patient RR frequently bumped into moving targets in his way
Vision-for-action brain pathways
Akinetopsia
Akinetopsia
Objects in motion cannot be perceived accurately
Vision-for-action brain pathways
First order motion perception
Second order motion perception
First order motion perception
Motion that is caused by luminance or colour changes
Cells in area and MT and MST adapt to this kind of motion
Second order motion perception
Motion that is caused by contrast, texture, or changes in any other feature
Cells in area MT and MST adapt to this kind of motion
NO adaptation when first order displays are followed by second order displays or vice versa
->
Two kinds of stimuli activate different kind sets of neurons and therefore probably involve different processes
Area MT is not the only region sensitive to motion
area MT is not insensitive to any other aspect of visual processing
Action: planning and motor response
vision-for-perception system is involved in motion perception depending on task requirements
Action: planning a motor response
effective grasping
appropriate grasping
Effective grasping
vision for action system
appropriate grasping
vision for action system
vision for perception system
anatomical projections from both visual pathways to premotor cortex
posterior parietal cortex
The human posterior parietal cortex is divided by the intraparietal sulcus (IPS) into the superior parietal lobe (SPL) and the inferior parietal lobe (IPL)
The IPL consists of the angular gyrus (Ang) and the Supramarginal gyrus (Smg) and borders on the superior temporal gyrus at a region often referred to as the temporoparietal junction (TPJ)
Planning -control model
Planning system
Planning system
Used before initiation of movement
Select Appropriate target, decides how it should be grasped, works out timing of the movement
influenced by goals of individual, nature of target object, the visual context, and various cognitive processes
relatively slow as it as it processes lots of information and is influenced by countries processes
Planning depends on visual representations located in the inferior parietal lobe IPL together with motor processes in frontal lobes and basil ganglia
Planning-control model
control system
Control system
Used during carrying out of movement
Ensures movement are accurate, making adjustments if necessary based on visual feedback
influenced Only by target objects spatial characteristics (size, shape,etc) And not by surrounding context
relatively fast as it uses little information and is not influenced by conscious processes
control depends on visual representations located in the superior parietal lobe SPL together with motor processes in the cerebellum
Planning -control model
SPL damage
IPL damage
SPL damage
optic ataxia
A neurological condition where patients have difficulty in making accurate movements despite relatively intact visual perception
IPL damage
Ideomotor apraxia
A neurological condition where patients have difficulty in carrying out learned movements
Direct perception
James Gibson’s Theory
The central function of perception is to facilitate interactions between the individual and his/her environment
Optic array: The structured pattern of light falling on the retina
Optic flow: the changes in the pattern of light reaching an observer when there is movement of the observer and/or aspects of the environment
Focus of expansion: this is the point towards which someone who is in motion is moving; it is the only part of the visual field that does not appear to move
Importance of optic flow
E.G.gives Feedback about direction, attitude and speed
Invariance in the optic array: features that remain constant
E.G.focus of expansion, size constancy
Visually guided action
Retinal flow field: changing patterns of light on the retina produced by movement of the observer relative to the environment as well as by eye and head movements
Extra – retinal information: about had and eye movements (E.G. binocular disparity, convergence, gaze rotation)
Perception of human motion
Biological motion
Social cues
Direction of gaze Head movement Mouth movement Lipreading Hand movement Body movement Implied motion Intentional actions
Perception of human motion
Performance compromised when display is inverted
Locomotor movements recognised easily; also gender
Social and instrumental actions can also be distinguished
A bias to perceive forward motion
Also found in other animals (E.G.monkeys, cats)
Double dissociation: motion blindness/biological motion
Perception of human motion
Neuroimaging studies of biological motion – MT/V5 and STS
STS convergence point for dorsal and ventral visual streams (integration of form and motion)
STS visualisation of action relayed via parietal systems to frontal motor planning regions
STS – connected to OFC and amygdala (social and emotional significance)
STS activated for static images and stimuli that imply biological motion
STS responsive to purposeful hand object actions (E.G.reaching for, picking up, Etc).
Change blindness
Inattentional blindness
Change blindness
Failure to notice large–scale changes to scenes
Inattentional blindness
Failure to notice an unexpected object in a visual display
Common coding
Ideomotor principal
The theory claims that there is a shared representation (a common code) for both perception and action. More important, seeing an event activates the action associated with that event, performing an action activates the associated perceptual event
How mirror neurons code for information
Mirror neurons act as a mapping mechanism between the observation of an action and its execution
Observing someone perform an action activates particular mirror neurons embedded in your motor system
This allows you to simulate performing that movement yourself
Through simulation, you access your own associated intentions, goals, emotions and social values
And you attribute them to the person you are observing
Mapping has to be perfect otherwise wrong attribution of intentions
Movement selectivity is a crucial feature of mirror neurons as successful mapping must be done in a movement selective manner
Basic appeal of the theory: simple neural mechanism for associating external sensory information with their appropriate semantic, social and emotional meanings
But
Electrophysiological studies do not provide evidence for the many theories about Mirror neuron function
Movement disorders
Parkinson’s disease
Features: Akinesia (Loss of movement), rigidity (resisting passive movement) and tram at rest
Aetiology: unknown
Neuro pathology: loss of striatal dopamine (Basal ganglia), Lewy bodies in substantia nigra and locus coeruleus
Movement disorders
Huntington’s disease
Features: involuntary, dance like (choreiform) movement, and dementia
Aetiology: inherited, autosomal dominant – mutation of a gene on chromosome 4
Neuropathology: degeneration of small and medium sized neurons in the striatum (GABA – ergic ), globus pallidus (basal ganglia) &cerebellum
Movement disorders
Sydenham’s Chorea
Features: gradual appearance of chorea (rapid, uncoordinated jerking movements primarily affecting the face, hands and feet) between the age of 7 & 12, subsides 1-4 months after onset.
Aetiology: associated with streptococcal infection or acute rheumatic fever
Neuropathology: cells in the corpus striatum of the basal ganglia are destroyed as a function of the fever
Movement disorders
Dyskinesia
Features: sustained, involuntary contraction of muscles that results in twisting, repetitive movements, and abnormal posture
Types: dystonia – excessive muscle tone leads to distorted limbs/trunks
Neuropathology: lesions to Basal ganglia (dystonia)
Movement disorders
Wilsons disease
Features: tremor, akinesia, dystonia, chorea, walking difficulties
Aetiology: Genetic disorder – disturbed copper metabolism leads to buildup of excessive intercellular copper
Neuropathology: increased copper in the brain, atrophy of straitum (Basal ganglia), increased sponginess of white matter
Movement disorders
Gilles de le Tourette syndrome
Features: motor tics (grimacing, blinking, head jerking, ETC.) And phonic tics (sniffing, snoring, repetition of words – palilalia, echolalia, uttering of obscenities or corprolalia) occur despite otherwise normal behaviour.
Neuropathology: reduced cortical volume and metabolism in basal ganglia
Movement Disorders
Motor Neuron Damage
Features: Muscular paralysis, atrophy such as poliomyelitis, multiple sclerosis, paraplegia, quadriplegia, cerebral palsy
Neuropathology: Dysfunction of motor neurons
