Object Recognition

Question 1

Ventral visual processing stream

Answer 1

Processes information related to object recognition

Question 2

Inferotemporal cortex:

Answer 2

PIT: Posterior Inferotemporal cortex
CIT: Central Inferotemporal cortex
AIT: Anterior Inferotemporal cortex
- They interact back and forth to aid perception
- Expectations can influence what you see (cognitive processes can influence what you percieve)

Question 3

?!? Posterior Inferotemporal Cortex

Answer 3

Responds to relatively simple stimuli
Cells further along the ventral stream respond to more complex and specific stimuli

Question 4

Receptive feilds

Answer 4

Area of space that a cell is sensitive to
Becomes larger as we move further along to ventral stream
A larger receptive field allows an object to be identified regardless of size or location

Question 5

Visual Agnosia

Answer 5

Inability to recognize objects in the visual modality
- Inability to recognize the object
- Apperceptive and Associative

Question 6

Apperceptive Agnosia

Answer 6

Cannot form a mental impression of something
Sensory information is processed, but the brain cannot put the details together in a meaningful way
- Caused by damage to the occipital lobe and associated areas (more visual regions, beginning of ventral stream)

Question 7

Associative Agnosia

Answer 7

Basic visual information can be integrated and put together to form a meaningful whole
That particular whole cannot be linked to stored knowledge
- Caused by damage to the occipitotemporal regions of both hemispheres and subadjacent white matter
- damage occurs further along down the ventral stream compared to apperceptive agnosia

Question 8

Prosopagnosia

Answer 8

Agnosia specific to faces
- “selective inability to differentiate between or recognize different faces”
- Damage to the ventral stream in the right hemisphere
–> individuals can determine basic information (i.e. “this is a face”)
- Developmental (congenital) prosopagnosia is thought to be present in ~2% of the general populations
- The anterior temporal lobe (near the end of the ventral stream) is shown to not be as activated by images of faces

Question 9

Word vs. Face recognition

Answer 9

Faces: right side
Words: left side

Question 10

Sparse Coding

Answer 10

Theory that a small, specific group of cells responds to the presence of a given object/ stimuli

Question 11

Grandmother Cell theory

Answer 11

Extreme version of sparse coding
- the idea that there is a specific cell in the brain that, for example, fires only when your grandmother is present
- thought to be incorrect

Question 12

Population Coding

Answer 12

Theory that the pattern of activity across a large population of cells codes of individual objects
Extreme: every cell fires for every object

Question 13

How do we explain cell function in object recognition using theories?

Answer 13

Likely something between sparse coding and population coding

Question 14

Invariance in recognition

Answer 14

Humans can identify objects under many different conditions
2 ideas:
- Form-cue invariance- the brain’s categorization is constant regardless of the form of the cue that represents the object
- Perceptual constancy: the ability to recognize objects from different angles, lighting, size, position, etc.
Suggest that at some level, our mental representation of objects is abstract/ conceptual

Question 15

Lateral Occipital Complex (LOC)

Answer 15

Involved in form-cue variance and perceptual constancy
May be the stage in visual processing where
abstract shape representations are formed.
- Supports recognition of objects despite differing
conditions

Question 16

Are neural representations viewpoint-dependent or viewpoint-independent?

Answer 16

There seems to be some amount of viewpoint dependency
- can recognize objects regardless of viewpoint, but more familiar viewpoints cause faster and more accurate recognition
It’s a bit of both
» some ventral stream cells change depending on orientation, and others respond the same regardless of angle
> recognition likely depends on on comparison with stored abstracts in the brain
Viewpoint dependence takes place in the earlier stages of the ventral stream and viewpoint independence in further stages of the ventral stream

Question 17

Hemispheric Differences in Processing

Answer 17

Distinct Neural mechanisms involved in object recognition:
- left ventral stream: parts of the object
- right ventral stream: analyzing whole forms/ configuration of parts

Question 18

Inversion Effect

Answer 18

Recognition is poorer when view upside-down
» suggests we rely on how features are put together/ related to each other
»»> especially important for categories with which we have more expertise

Question 19

Nonlocal binding

Answer 19

Model for how shapes are recognizing
- whole object is represented by the co-activation of cells that represent the parts of an object in different locations
- no separate unit represents the whole; the whole is perceived when these units are all firing together

Question 20

Conjunctive Encoding

Answer 20

Model for how whole shapes are recognized
- Lower-level regions represent features and send output to higher-level regions representing the shapes that result from the joining of those features
- separate unit represents the whole, beyond just the ones that represent the parts
Evidence leans towards this model

Question 21

Object recognition based on tactile and auditory modalities

Answer 21

Humans can also recognize objects by touch and sound
- Similarities in brain organization emerge across modalities:
»>Early cortical areas code basic features
»>Higher-level areas organize sensations into representations
of recognizable objects

Question 22

Auditory Agnosia

Answer 22

The inability to recognize the meaning of sounds

Question 23

Somatosensory agnosia/ tactile agnosia

Answer 23

Inability to recognize an object by touch

Question 24

(may not be necessary) What vs. Where across modalities

Answer 24

All modalities across all senses must distinguish between what and where
There is a distinction between “what” and “where” pathways in
the brain that seems to be a basic organizational feature for all
modalities.
»> ventral (what) and dorsal (where) streams for the visual system