M2, T1, object recognition processes and models

Question 1

Why is object recognition important?

Answer 1

• Recognise objects regardless of: Orientation, Distance, Lighting conditions
• Objects encountered everyday under a variety of circumstances
• Impaired viewing conditions: object recognition more difficult but can do it
• Two-dimensional images: photos, paintings i.e.. depth is absent
• Brain’s object recognition system automatically “copes” with a number of object transformations

Question 2

Object recognition, description and storage

Answer 2

Object descriptions of structures of all known objects must be stored in the brain/mind

Object recognition involves a comparison of the seen object with the stored structural description of the object.

• what the item is, what it is used for, other objects it is associated with

Question 3

Object recognition system - stored information

Answer 3

• Visual knowledge of an object’s shape
• Can process an object from various alternative viewpoints that it might be presented in
• Knowledge of semantic functions and object’s associates
• Knowledge of verbal names (labels) for objects

Question 4

Models of object recognition

Answer 4

Marr’s (1980) model of object recognition

Ellis and Young (1988) model of object recognition

Riddoch and Humphreys (2001) model of object recognition

Question 5

Marr’s (1980) model of object recognition

Answer 5

*look up image

Question 6

Marr’s object recog model - Primal Sketch

Answer 6

• Initial object representation, initial stage
• Brightness changes across the field of vision allowing for perception of 2D geometry of images
• See edges because they result in sharp changes in brightness (luminance)

Question 7

Marr’s object recog model - 2.5D Sketch

Answer 7

• Combines information such as textures and shading (depth information) from the primal sketch to construct and determine the spatial locations of visible surfaces from the viewers point of view
• Describes the object from only one view-point

Question 8

Marr’s object recog model - 3D model

Answer 8

• Real shape of objects and surfaces and how they relate to one another
• Independent of view-point of viewer
• Could use this “standard” information to look up our list of known descriptions of objects for recognition

Question 9

Ellis and Young (1988) model of object recognition

Answer 9

*look up image

Question 10

Riddoch and Humphreys (2001) model of object recognition

Answer 10

*look up image

A hierarchical model of object recognition and naming, specifying different component processes which, when impaired, can produce varieties of apperceptive and associative agnosia

Question 11

Ellis and Young object recog model - initial raw visual representation

Answer 11

Initial representation (Marr - primal sketch)

• intensity (brightness) changes across field of vision
• features such as edges, colours, etc

Question 12

Ellis and Young object recog model - viewer centred description

Answer 12

Viewer centred representation (Marr 2.5D sketch)

• spatial locations visible surfaces
• uses information such as depth and location
• object only represented from the viewpoint of viewer

Question 13

Ellis and Young object recog model - object centred description

Answer 13

Object centred representation (Marr - 3D model)

• real shape of objects and surfaces
• independent of view-point of viewer
• could use this ‘standard’ information to look up object in object store

Question 14

Ellis and young object recog model - object recognition units

Answer 14

Object recognition units

• stored structural object representations
• comparison of viewer and object centred representation
• interface between visual and semantic object representations
• one recognition unit for each known visual object
• describe what an object looks like

Question 15

Ellis and young object recog model - semantic system

Answer 15

Semantic representation
- Describes object properties and attributes
- Object Recognition Units access semantic representations if match between visual representation and stored object description at levels of object recognition unit
- Access to Semantic representation occurs at number of levels
- Number of different types of input gain semantic access
object, picture, written name, spoken name

Question 16

Ellis and Young object recog model - speech output lexicon

Answer 16

• Name codes for objects not contained within semantic system
• Object Name is represented in separate store – Lexicon
• Must access object name via semantic system
• Object naming task is typically used with neuropsychological patients

Question 17

Ellis and Young object recog model - Perceptual Classification Stage Evidence

Answer 17

• Perceptual classification involves matching viewer-centred and object-centred representations
• Repetition Priming: items, which have been previously encountered at an earlier phase of an experiment, are more easily recognised than those that have not been previously encountered
• Repetition Priming effects are modality specific

Question 18

Warren and Morton (1982) - priming

Answer 18

Briefly presented pictures of objects – task naming aloud

• Found that subjects were able to identify a picture of an object at a shorter exposure duration if they had either …
• > Seen the same object in a picture previously or
• > A different picture of the same object previously in the experiment
• prior exposure to object label had no effect on recognition performance
• repetition priming is modality specific - only occurs if first and second presentation appear in same modality

Question 19

Ellis and Young object recog model - semantic processing stage

Answer 19

Semantic System: stage at which object’s functions and associates are retrieved from memory
Access to semantics occurs – object seen, heard, felt or if written name or spoken name encountered
Why would this be important?
Semantic Priming – effect of related item context on performance i.e., presenting related items facilitates responding to the second item
-> e.g. nurse - butter slower than bread - butter

Question 20

Ellis and Young object recog model - Name retrieval stage/speech output lexicon

Answer 20

• Access names of objects (verbal labels) via semantic system
• Objects and pictures have direct access to their meanings but an indirect access to their labels which occurs via semantics
• > classification of pictures faster than decisions requiring access to object labels (Potter & Faulconer, 1975)
• > word recognition – words named faster than they are categorised
• > interference effects – irrelevant names interfere with object naming but not with picture classification (Glasser & Glasser, 1995)