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Object Recognition

eloisefeeney27 Biological Englisch 45 Karten

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  1. 1What is output from the occipital lobe?Two major fibre bundles, The inferior longitudinal fasciculus follows a ventral route into the temporal lobe. The superior longitudinal fasciculus takes a more dorsal route to the parietal lobe
  2. 2Ungerleider & Mishkin(1982) proposed that processing along these pathways was designed to elicit fundamentally different types of information. The occipitotemporal pathway is specialised for object perception and recognition. The occipitoparietal pathway is specialised for spatial perception, for determining where an object is
  3. 3Pohl (1973)Studies on monkeys showed lesions in the temporal lobe caused deficiencies in object recognition and lesions in the parietal lobe cause deficiencies in analysing spatial perception of objects
  4. 4How did Pohl carry out experiments for parietal lesions?(1973) Landmark task- two wells, one near a cylinder contains food and the other is empty. The cylinder position is varied. If the monkey (with bilateral parietal lesion) got 28/30, the position was reversed. Monkeys learned the initial task but failed on reversal
  5. 5Describe physiological properties of the neurons in the parietal and temporal lobeNeurones in the parietal lobe respond to stimuli in a non selective way and respond to stimuli presented in the periphery and exclude the fovea. Neurons in the temporal lobe always encompass the fovea
  6. 6What did Desimone (1991) do?Studied 151 cells in the temporal lobe and their response to various stimuli such as simple bars of varying colour and orientation and complex stimuli such as photographs and 3D models.
  7. 7What did Desimone (1991) find?110 cells responded to at least one of the stimuli. 41% acted like parietal cells and were activated by any cells and firing rates were similar across all. The remaining 59% exhibited selectivity and responded more vigorously for certain complex stimuli
  8. 8What did Kohler et al (1995) do?Used PET to scans while looking at two displays containing three images. In the position task, pps had to determine f the object was in the same location. In the object task, they had to determine if it was the same.
  9. 9What did Kohler et al find?(1995) During the position task, regional cerebral blood flow was higher in the right parietal lobe. In the object task it was higher bilaterally at the junction between the occipital and temporal lobes.
  10. 10Goodale & Milner (person)(1992) Patient D.F. had a severe deficit in object recognition and could not name common objects and could only give crude descriptions. However, if an object was placed in her hand she could recognise it.
  11. 11Goodale & Milner (task)(1992) Patient was given a cylindrical block to look at with a slot cut out. The orientation of the block varied. In the explicit matching task, she was given a piece of card to show the orientation of the slot, but failed to do so. When asked to place the card in the slot she did so easily. She orientated her hand before reaching the block so not based on tactile feedback
  12. 12What is optic ataxia?Patients is not able to coordinate visual inputs and muscle movements to be able to reach out for objects. Associated with lesions in the parietal lobe
  13. 13What is object constancy?Our ability to recognise objects in various situations despite variations
  14. 14How can sensory input from objects vary?Viewpoint, illumination and its context (rarely seen in isolation)
  15. 15Grandmother cells(Lettvin, (1967) refer to the concept that we have special gnostic units in the brain which are specialised to process different attributed of objects.
  16. 16What is wrong with the theory of grandmother cells?1. Suggests final percept of an object is coded by a single cell. Cells are constantly firing and refractoring so would be highly susceptible to error.
    2. If the cell died, would there be a sudden loss of recognition for an object?
    3. Doesn't account for how we are able to perceive novel objects
    4. How do we recognise things which change over time?
  17. 17Ensemble theoryObject recognition results from activation across compelx feature detectors. Objects are perceived when higher order neurons are activated, specialising in a certain aspect of the object. So recognition is due to a collective activation (deCharms et al, 2000)
  18. 18What does the ensemble theory account for that grandmother theory doesn't?Accounts for why we regularly confuse objects as they activate many of the same neurons. Losing some neurons doesn't degrade our ability to recognise objects as the remaining neurons are enough to suffice. Accounts for how we recognise novel objects, as they bare similarity to familiar objects , so we activate units which represent their features
  19. 19Lissaeur(1890) Distinguished between recognition deficits which are sensory based and those that reflect the inability to access memory visually. Apperceptive agnosia (ventral stream disorder) describes failures in object recognition linked to problems in perceptual processing. Associative agnosia is when patients derive normal representations but cannot use this information to recognise thigns
  20. 20What is apperceptive agnosia?Inability to see form, they are able to see objects and avoid obstacles but recognising what they are is difficult.
  21. 21Warrington (1985)80 patients with right and left lesions who were asked to recognise incomplete pictures and letters. RH showed a poorer performance than controls and LH lesions. LH lesions had little effect on performance. This lateralisation is observed in a variety of tasks, indicating a perceptual categorisation in patients which is impaired.
  22. 22Unusual View Object TestWarrington (1982) subjects shown 20 pictures of objects, each shown from a usualy view and an atypical view. Patients with right posterior lesions had difficulty identifying objects from the unusual view. People with LH and right anterior lesions did significantly better. R posterior hemisphere is a principle player in perceptual catagorisation
  23. 23Associative agnosiaFailure of visual recognition that annot be attributed to perceptual abilities. They have a memory for objects if said aloud but are unable to name objects from sight. Caused by a left hemisphere lesion in the occipitotemporal region
  24. 24Matching by Fuction TestWarrington- subjects have to match two objects which are functionally similar from three pictures. Patients with left or right posterior lesions were impaired
  25. 25What is the first stag of Warrington's model?The perceptual categorisation stage in which perceptual inputs are matched with stored representations of visual images. This stage is essential for dealing with the variability of sensory information. Associated with processing the in right hemisphere, and characterised as presemantic as names are not yet processed
  26. 26What is the second stage of Warrington's model?Semantic categorisation, depends on the left hemisphere. Visual input is linked with knowledge in long term memory concerning the name and function
  27. 27Problems with the Warrington model of agnosiaNeuropathological studies ave not always found a correspondence between associative agnosia and left hemisphere lesions and unilateral RH lesions can produce associative agnosia
  28. 28Category specific agnosiaPatients exhibit a disproportionately worse perception for either living or non living objects, such as patient J.R. (worse for living). He had a 90% success rate for recognising inanimate objects and only 6% for living objects.
  29. 29How does Warrington's model explain category specific agnosia?Results from a selective loss from the knowledge system.
  30. 30Perception of facesMost important thing we recognise. Prosopagnosia is a deficit in the ability to recognise faces which cannot be attributed to a deterioration in intellectual function.
  31. 31Farrah(1990) identified 81 patients with prosopagnosia, 46 had bilateral lesions and 25 had unilateral. The incidence was much higher in RH lesions in the occipital and temporal cortices
  32. 32Baylis et al (1985)Single cell recordings in monkeys in the STS while presented with stimuli of either monkey faces, human faces or face like stimuli. Some were highly selective and only responded to a full front profile monkey face. Non facial stimuli hardly activated neurons, and compared to spontaneous firing, activity decreased for some stimuli. Resembles grandmother cells
  33. 33What two regions are associated with face perception?Superior temporal sulcus and Inferotemporal gyrus (Rolls, 1992). Cannot be concluded that they respond only to faces, but the degree of specificity is quite striking
  34. 34Tsao et al(2006) Studied individual cells in the STS and found 97% of neurons exhibited a strong face preference showing responses to any face containing stimuli compared to non face stimuli
  35. 35McCarthy et al (1997)Subjects presented with stimuli of faces, inanimate objects and random texture patterns. Faces led to strong blood oxygen level dependent (BOLD) responses in the fusiform gyrus. Responses in the RH were significant compared to other conditions. Region called the fusiform face area (FFA)
  36. 36Expertise theoryGauthier (1999) the FFA is recruited when people have to make fine perceptual discriminations among highly familiar stimuli. Imaging studies entail the confound of expertise.
  37. 37Gauthier et al(2000) Investigated to see if the FFA would activate for people who are trained experts in discriminating cars and birds. Activation of the FFA was greater when people view objects for which they are experts in. The more expertise, the greater the response from the FFA. However, it activated a much broader region of the ventral occipitotemporal cortex (Rhodes et al, 2004).
  38. 38Perception of placesThe parahippocampus is consistently engaged when stimuli contain information about spatial relations or when people are asked to clarify objects on the basis of some spatial property.
  39. 39Epstein & Kanwisher(1998) named it the parahippocampal place area (PPA)
  40. 40Habib et al (1987)People with lesions in the PPA become disorientated in new environments
  41. 41Epstein et al (2001)Lesions in PPS have difficulty learning new places
  42. 42Valyear et al(2006) Investigated changes in BOLD activity as pps viewed two pictures which were either the same, differed in location, identity or both. The parieto-occipital cortex showed an increase for changes in object orientation and temporo-occipital cortex had increases for changes in identity
  43. 43Mishkin et al(1994) evidence from monkey studies support the hierarchical theory along the ventral pathway extending from V1 to the inferior temporal cortex. Neurons in V1 code for local orientations and other basic visual features, whereas neurons in IT show selectivity for more complex shapes and faces
  44. 44McCarthy & Warrington(1986) single patient with associative agnosia who was impaired at recognising common objects. MRI scan showed a unilateral deficit in the LH in the occipito-temporal lobe
  45. 45Nielson (1946) what did Konorski (1967) do with these findings?Patient with a greater difficulty identifying animate objects from inanimate objects. Konorski (1967) extrapolated from these dissociations to distinguish 'gnosic fields', one of which was living things. He also speculated the small manipuble objects form a separate category from non manipuble objects

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Biological Karteikarten am Object Recognition, erstellt von eloisefeeney27 am 07/05/2014.
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