Types of Apraxia (1)
Limb kinetic apraxia- problems with basic motor coordination, difficulties in hand and finger dexterity e.g. cannot pick up a paper clip. Cannot be explained by more elemental motor problems. Damage to motor cortex.
Conceptual Apraxia- loss of knowledge of how to use an object but no loss of motor function. Inappropriate use of tools. Damage to parietal cortex.
Ideational Apraxia- difficulty in executing correct sequence of steps of complex action but have knowledge of how to do it correctly e.g. miss out step or incorrect order. Damage to patietal cortex.
Verbal-motor dissociation apraxia- fail to respond to verbal commands to make movement. Possibility that this is a disorder of speech processing, not motor performance.
Visual Agnosia (5)
Stage 5: Semantic knowledge- Associative
- Patient FRA unable to access objects visually, but can access semantic knowledge if asked in an auditory way- accessed by different modalities
- If semantic knowledge was damaged, we couldn't access it any way (Humphreys and Riddoch)
- Patient HO had a lesion of the temporal lobe- was good at object decision tasks- stored structural descriptions were in tact. However, couldn't access semantic knowledge via any modality- semantic access agnosia
Visual agnosia (4)
Stage 3: Mapping to stored structural descriptions- Apperceptive
- Patients with an issue here cannot mentally rotate objects so are unable to recongise something from an unusual view
- Unusual views test: patient shown unsual and usual view of an item- can they tell that they are the same item or different
- Patients with lesion to right posterior area unable to recongise object from unsual views
- Highlights a problem in perceptual system which derives a representation of an object from sensory input and then matches to our knowledge about objects
- Biederman says in usual views 'geons' that make up objects are distorted. Our perceptual system usually sorts this out but in patients with RP lesions, they are impaired.
Stage 4: Stored structural knowledge- Associative
- Patient FRA: left hemisphere stroke- no apperceptive- had percept of the object, but could not name it. Performed badly on matching tasks, when asked which image matched the word, and when asked to rank images in order of real life size (need some stored knowledge to do this)
- HOWEVER, when the objects were presented as auditory stimuli he could do this- so can access semantic knowledge, just not visually
- Object decision task- patient HJA- asked to say if an object was real or not (both plausible looking items)- need to access knowledge about function- couldn't do this
Inability to carry out skilled actions. Likely to do with motor planning.
Caused by left hemisphere damage. 33% of patients who have LH damage after stroke develop symptoms but not always permanent.
Steinthal (1871) defined apraxia as a defecit in voluntary actions but also included rifficult recognising objects (agnosia) in his definition.
Liepmann- patient MT- unable to imintate simple hand positions or pantomimes with right hand (controlled by LH), but no issue with left hand so not an issue of comprehension.
Pick- an aphasic patient who could understand simple orders. Made errors when asked to use an object, particlarly when it required a string of actions like lighting a candle. 1st attempt- held match with both hands, nothing else. 2nd attempt- ground match into the candle. 3rd attempt- had match lit for him, lit the candle and put it into his mouth.
Osiurak et al.- patient MJC- left parietal skull fracture- difficulty in pantomiming actions and imitating. E.g. when asked to use a screwdriver. More problems if no scew was present- as if cues aided performance
Visual Agnosia (1)
Difficulty recongising an object using vision alone.
It is not a visual problem because their sensory input is fine.
Can be caused by brain damage, strokes, dementia and neurological disorders. Damage to the left hemispere.
Dr. P: Shown a pair of gloves. Could desribe in greate detail, a clear percept with intelligent guesses. Some semantic infomation missing.
HJA: Described a carrot as a brush, an onion as a necklace etc.
Matching to functions test: patients shown 3 items- 2 with same function but look different, one which looks similar but has a different function.
The patient has to choose which have the same function. To be able to do this, you must have some stored knowledge of the items.
Visual agnosia (6)
Unusual views test:
- 20 objects- 50% of trials where A and B were the same object.
- Participants with right posterior damage performed worse.
- This didn't arise because they did not know what the objects were, because they could correctly identify objects in the usual view
Marr's theory of vision- divides it into 4 basic stages:
1. Primal sketch- edges, bars, lengths and constrast.
2. 2 1/2 D sketch- view-centred, depth cues and surface textures added
3. 3D sketch- object centred-representation
4. Semantic interpretation- meaning is attributed to stimulus.
When compared to patient H and R- e.g. stage 2 and line differentitation.
Warrington- perceptual and semantic agnosia- HJA- he could copy out a drawing (so many thought he had associative agnosia) but it took 6 hours to do this, suggesting a problem with percept (apperceptive) but also failed to identify 3 drawings so...
Other theories- continued:
Joknston and Heinz: Flexible theory- selection can occur at several stages of processing. Selection at the buffer if the message is difficult to attend. Selection at the filter if moderate to attend. Selection at LCP if easy to attend.
Lavie: Perceptual load theory- selection depends on perceptual load (task difficulty).
- Experimented by manipulating set size (the number of items on a screen). PPS asked to identify a letter in the centre with interferring distractor which was either congruent (the same letter) or incongruent. PPS response was quicker with congruent target when perceptual load is low. However, when perceptual load is higher, there is little difference in RT.
Low load task- easy- more attention free to pick up distractor- RT slower for incongruent task. High load task- harder- less attention free to pick up distractor- RT not as different
- If the task is easy, late selection. If the task is hard, early selection.
Late selection theory:
Deutsch and Deutsch- all stimuli processed fully with message selection determined at the end of processing, just before response. Competing stumuli weighed for importance and most important stimuli selected for response after both messages are fully processed.
X- effortful, ridgid, and doesn't explain a lack of awareness of unattnded message.
Treisman: Suggests that filter isn't all or nothing. Infomation in the unattended channel is either attenuated or reduced.
- DHT- two messages played, some point, messages switches to other ear, ended up merging these messages. Only way this is possible is if they were aware of the unattnded message to a degree. Also, content in unattended ear affected shadowing performance- the more dissimilar the messages, the easier shadowing is.
- The theory states that unattended stimuli are attended in a hierachical fashion, with physical cues etc. processed first, with grammar and meaning later. If processing capacity is insufficient, then we do not process the message to the top of the hierachy.
Visual agnosia (2)
Two types- Lissauer:
Apperceptive Agnosia: problem with the percept of an object. Unable to form stable representation so cannot recognise it. Farah found patients are unable to copy pictures of match basic shapes.
Associative Agnosia:Normal percept- able to copy and describe what they see. Cannot identify the object. Unable to map percept to stored knowledge.
Humphreys and Riddoch split Lissauer's types into further subtypes using case studies to deomstrate how agnosia can cover many different issues with the percept.
Shape/Feature coding---> Figure ground segmentation --> Mapping to stored structural descriptions --> Stored structural descrpitions --> Semantic knowledge (Green= Apperceptive, Orange= Associative)
Problems with each of these featuers produces different symptoms of Agnosia. The model shows the cognitive systems involved in recognising an object. The inability to do any element of this leads to different types of Agnosia.
Visual Agnosia (3)
Stage 1: Shape/Feature coding- Apperceptive
- Unable to copy pictures or match basic shapes
- Fail Efron shapt matching times (telling if two items are the same or different)
- Some argue coding issues could be pseudoagnosia which is a sesnory problem
- Patient CF gives evidence that shape/feature coding is not a a sensory problem: she failed the Efron test and couldn't desribe the position of a slot or rotate her hand to match suggesting she could't encode the shape. BUT she was able to to place a card accurately into the slot, suggesting she could SEE the item.
- Patient DF was impaired at shape perception but good at making actions towards the shape so clearly has knowledge of size. This occurs because there are two pathways involved in visual processing- Ventral (identifying), Dorsal (making movements towards). DF has a lesion in the ventral area.
Stage 2: Figure ground segmentation- Apperceptive
- Patient Mrs. FGR suffered cortical degeneration. Could discriminate between shapes but couln'y make figure ground distinction: in overlapping figure tasks she attributed wrong feature to wrong shape.
- People who are unable to make figure ground segmentation cannot attribute that each different line belongs to a different shape.
Alien Hand Syndrome (3)
Supplementary motor area (SMA) plans compex movements. Both left and right SMA are active when one hand is carrying out a task. Any planned movement must be supressed in the ipsilateral hemisphere to the active hand.
But, in AHS, no supression occurs and so the AH tries to become invlved in any task. When the task is simple and is already being done by the normal hand, it may try to do the 'next best action' which could be the opposite!
Alien Hand Syndrome (2)
AHS could be an umbrella term as it is a very varied syndrome.
Some patients depersonalise the hand, e.g. calling the hand 'it', some shout when it goes out of control. However, patients know the hand belongs to them.
Marchetti and Della Salla propose Anarchic hand syndrome when patients know the limb is theirs.
Patient JC- stroke damaged frontal areas and corpus callosum so developed AHS. Symptoms included unresponsiveness (hand won't carry out actions), uncontrolled actions (preseveration of simple actions. Complex actions continued- movement imitated intentionally but they won't stop. Intermanual conflict), subjective reactions to hand (attributed actions to right hand, calling it 'it').
Theories of IMA:
Disconnection hypothesis- Gerschwind: damage to motor tract connecting parietal areas (higher level areas formulate movements and lower level areas which execute the task).
Left pariteal cortex stores motor representations of an action (engrams)- if these are damaged, motor performance affected. The engram is still intact if patients can do the task automatically but the pathway is damaged so can't be accessed for voluntary action.
When do we select stumuli for further processing?
The split span technique- Broadbent: pps played three pairs of numbers, one of each pair in each ear. Found pps reported numbers back by ear, suggesting we process stimili by ear.
Broadbent's filter theory: Input (left or right ear) --> Sensory Buffer --> Filter --> Limited capacity processor (LCP). - Suggests that all stimuli enter sensory buffer but oly one input passes through the buffer at a time, the other remains for later. Infomation reaching the LCP becomes concsious.
- Early selection model- prevents the cognitive system from becoming overloaded
- Moray- repeated sets of words in unattended ear 35 times and found pps did not recongise or remember the words. they were stuck in the sensory buffer and decayed, never reaching the LPC.
- However: Moray- people recongise their own name in unattended message suggesting it has undergone some processing, not just remaining in sensory buffer. Corteen and Wood- conditioned city name with electric shock. When the city name was later played in unattnded ear, pps have 36% galvanic skin response, though claim not to have heard it- clearly processed the word but no memory. Von Wright et al.- replicated but only found GSR on some trials. Gray and Wedderburn- played parts of two messages in either ear but reported messages grouped by meaning, rather than ear. Underwood- pps better at picking up infomation from unattnded ear with practice (8% to 67%)- sensory buffer doesn't account.
We need attention to see things- if we don't pay attentuon then we can't process them further.
The Cocktail Party and dochotic listening tasks- early studies of attention (Cherry):
Noticed that we can pin point and follow one conversation among many. We can't shut off noise like we can with vision (shut eyes) so all the infomation enters the brain and wants to be processed. We must be able to pick out certain things- but how?
- Dichotic listening tasks- play one message in each ear and asked pps to attend one of them. They were able to report the attended message better. The unattended message was still there, just not attended to.
- Dichotic listening task with shadowing- asked to repeat word for word what is being said in attended message. There was poor infomation processing in unattended message which is odd because we are still experencing it perceptually.
Broadbent reported that pps detected pitch of voice and bleeds/tones (phsyical aspects) of unattended message but not semantic meaning, language etc. Physical aspects are helpful at separating the two messages.
Bottleneck- both messages go in but only one is processed
Types of Apraxia (2)
Tactile Apraxia- unable to use hands as a 'sense organ'. Hand skills are not related to object exploration.
Ideomotor apraxia- inability to pantomime, imitate, use tools. Movements are usually spatially incorrect and slow. Patients can sometimes do these actions automatically. Caused by damage to the link between parietal and pre motor cortex.
Possible other Apraxias- Dressing apraxia (usually leave one side undressed). Facial apraxia (e.g. unable to protrude a tongue on command). Oral apraxia (e.g. cannot pretend to blow out a match).
Idemotor apraxia (IMA):
Diagnosis criterion: motor problems not due to any other motor or cognitive disorder. Understand what they're told to do (not aphasic). Just have problems doing the correct action.
Defectis: orientation errors (e.g. holding comb upside down), spatial and temporal erors (e.g. making wrong carving movements- up and down rather than back and forth), extra or unnecessary movements, may use a body part instead of tool (e.g. hand to cut bread).
Diagnosis test: TOLA- test of oral and limb apraxia.
- Patients asked to perform 20 gestures classified along two dimensions- tool use and limb movements.
- Trasitive task (gestures using tools), intransitive task (gestures not using tool), proximal task (involve upper limb), distal task (involves only the hand).
- TOLA is incomplete as it doesn't assess how patients use tools.
Alien Hand Syndrome (1)
Where the hand acts of its own free will. The left hand usually interferes with the right hand.
Can occur after lesions to the medial frontal lobe and corpus callosum.
The corpus callosum connects the brain hemispheres, telling each side what the other side is doing. Sometimes it can be divided in patients with epilepsy.
Parkin and Barry- patient MP- damaged corpus callosum- tug of war with own hands e.g. one hand opens the draw, the other closes it. AH disrupted everyday activites e.g. throwing in uncracked eggs when making an omelette.
Bogen- patient with AHS- one hand did up buttons, the other undid. Diagnostic Apraxia- one hand acting in opposition to the other.
Baks et al.- patient woke up to find hand choking them
Kumral- patient unable to stop AH from grabbing nearby objects
Biran et al.- patient found eating hard as AH opposed normal one