Lecture 5: object recognition

Question 1

Object constancy

Answer 1

the ability to maintain a stable and consistant perception of an object or persion, despite changes in their physical presence, appearance or emotional state.

visual information emanting from object varies
- viewing position
- illumination
- context

Question 2

What & Where pathways

Answer 2

Ventral stream: specialized in object perception and recognition (What we are looking for)

Dorsal stream: specialized in spatial perception (Where is the object located in space)

Question 3

What & where pathways in auditory domain

Answer 3

ventral stream: what is the sound

Dorsal stream: where is the sound coming from

Question 4

Inferior temporal cortex (IT)

Answer 4

neurons in the IT cortex rarely respond to simple stimuli such as lines or spots of light. they respond to more complex objects such as hands.

Question 5

agnosia

Answer 5

inability to process sensory information even though the sense organs and memory are not defective

Question 6

visual agnosia

Answer 6

deficit in recognising objects even when the processes for analysing basic properties such as shape, color and motion are relatively intact

Question 7

Patient D.F

Answer 7

impairment in naming objects but when object was placed in her hand, she identified it & visual acuity was intact.

performed poorly on explicit matching task (match orientation of card and the slot) but showed normal performance in the action task (insert card in slot)

impairment in explicit matching task showed that D.F could not recognize orientation of a three dimensional object, yet when asked to insert the card in box (action task) DF performed well.

D.F impaired in the ‘what’ but not in the ‘where/how’

Question 8

Lateral occipital complex (LOC)

Answer 8

important for object recognition

Question 9

optic ataxia

Answer 9

patient can recognize objects, but cannot use visual information to guide their actions

lesions in the parietal cortex

example: patient cannot move towards an object to grasp it, but rather moves hands around like a person searching for light switch in the dark.

Question 10

Functional near-infrared spectoscopy (FNIRS)

Answer 10

in infants revealed the role of LOC in processing objects with shape and texture being manipulated

LOC is sensitive to shape but not to other visual features

Question 11

Binocular rivalry

Answer 11

Binocular rivalry is a visual phenomenon that occurs when two different images are presented simultaneously to each eye. Instead of seeing a blended image, your perception alternates between the two distinct images, meaning you can only consciously perceive one at a time.

Question 12

The hierarchical coding hypothesis

Answer 12

elementary features are combined to create objects that can be recognized by gnostic units.

at the first level of the hierarchy depicted are edge detectors (simple cells)

these feature units combine to form corner detectors, which in turn combine to form cells that respond to even more complex stimuli such as surfaces

Question 13

the grandmother cell hypothesis

Answer 13

also known as gnostic cell.

proposes that individual neurons or very small groups of neurons, respond specifically to highly particular objects faces or concepts.

example: there might be a single neuron that activates only when you see your grandmother’s face.

suggests:
highly specificity: certain neurons respond to specific, unique stimuli.
all or nothing response: if you lose the grandmother cell you might lose the ability to recognize your grandmother al together

Question 14

The ensemble coding hypothesis

Answer 14

object recognition results from activation across complex feature detectors. an ensemble of cells respond to your grandmother. thus, recognition is not due to one unit but rather to collective activation of units.

predicts:
distributed representation: a network of neurons work together to represent an object or concept. each neuron in the ensemble might respond to different features of the object.

greater felxibility: losing one neuron would not erase the ability to recognize an object as recognition emerges from the combined activity of the ensemble.

Question 15

Top down effects on object recognitionBar and colleagues (2006)

Answer 15

Used MEG to examine top-down influence on object recognition.

They compared frontal regions with those in temporal

provided evidence for top down influence of frontal regions over more posterior regions during object recognition.

Question 16

Mind reading: decoding and encoding brain signals

Answer 16

decoding: predicting the stimulus that is being viewed based on brain activity.

encoding: how stimulus features are represented in neural activity.

Voxels (measured with fMRI) might contain neurons that are tuned to one specific orientation (aggregate of many neurons measured in that voxel).
> showed the ability to decode what images people view based on brain activity.

yet this simple model is based on V1, V2 and V3 and thus does not include information represented in higher order visual areas

Question 17

Specificity of object recognition in higher visual areas

Are faces special? what was the evidence found from monkey research?

Answer 17

research showed some cells in the superior temporal suclus (STS) respond specifically to faces.

STS: regions that respond to faces
Functional MRI = fusiform face area (FFA): activation whilst seeing faces.

BOLD signal in FFA was stronger during intervals in which faces (vs. objects) or intact faces (vs. scrambled faces) were presented.

Question 18

Electrophysiological evidence for face processing: N170

Answer 18

faces elicit a large negative response in the EEG signal around 170ms after stimulus onset (the N170)

cofound: we see faces much more than other objects, so could it be the level of expertise that explains the N170?

Question 19

Facial perception

Chang & Tsao (2017)

Answer 19

they were able to determine how different each face was from the average face.

they found that neurons in the lateral (LAT) and anterior (ANT) face areas within the IT cortex showed different tuning profiles.

Question 20

Are there regions that are specialized?

Answer 20

Parahippocampal place area (PPA) is particularly responsive when people make judgements about spatial properties or relations.

Extrastriate body area (EBA) is responsive when making judgements about the body

Question 21

Testing causality:

Afraz (2006)

Answer 21

showed that stimulation cells in IT cortex made monkey biased towards seeing faces versus seeing a flower

Question 22

Testing causality:
Moeller

Answer 22

Let monkey look at two faces and judge them whether they were the same or different.

When IT was stimulated the monkeys almost always judged the faces to be different.

Parivizi found that stimulating the FFA in epilepsy patients. they reported seeing distorted faces

Question 23

Testing causality:
Duchaine, pitcher (2009)

Answer 23

applied TMS to the rOFA, rLO and rEBA whilst participants did a judgement on faces.

TMS over rOFA: participants performed worse in discriminating faces
TMS over rEBA: participants performed worse in discriminating bodies.
TMS over rLO: participants performed worse in discriminating objects.

Question 24

Failures in object recognition:
visual agnosia

Answer 24

difficulties in recognizing objects that are presented visually or require the use of visual based representation

although patient can recognize objects, their ability to do so diminishes when the perceptual input is limited or does not include the most salient features.

damage to posterior regions in right hemisphere performed worse than either patients with anterior lesions (no agnosia) or patients with agnosia arising from the left hemisphere lesions.

Question 25

failures in object recognition:

apperceptive visual agnosia

Answer 25

the recognition problem is one of developing a coherent percept; the basic components are there but they cant assembled.

patients can allocate attention to object and percieve its parts but are unable to group togehter these parts and name the objects.
example:
at legoland they see the lego bricks instead of seeing buildings or cars.

Question 26

failures in object recognition:

integrative visual agnosia

Answer 26

patients do not see object holistcally. They perceive the parts of an object but are unable to integrate them into a coherent whole
example:
at legoland they may see doors, walls, windows but not a house

Question 27

failures in object recognition:
associative visual agnosia

Answer 27

perception occurs without recognition.
A patient with associative visual agnosia can perceive objects with her visual system but cannot understand them or assign meaning to them
example:
at legoland, the patients may perceive a house and be able to draw a picture of that house but still unable to tell that it is a house or describe what a house is for.

Question 28

sensory functional hypothesis

Answer 28

conceptual knowledge is organized around representations of sensory properties (form, motion, color) as well as motor properties associated with an object and that these representations depend on modality-specific neural subsystems.

hypothesis proposes that our knowledge of objects is organized based on sensory and functional attributes.

different types or information (sensory or functional) are processed in different areas of the brain.

Question 29

sensory functional hypothesis:

sensory attributes vs. functional attributes

Answer 29

sensory attributes: relate to how an object looks,sounds,smells or feels.
example: we recognize a lemon by its yellow color, round shape or rough texture.

functional attributes: relate to what an object is used for or its purpose.
example: we understand a lemon can be squeezed to make juice or add flavor.

Question 30

Domain-specific hypothesis

Answer 30

conceptual knowledge is organized primarly by categories or domains that are evolutionairy relevant to survival and reproduction.

the idea is that our brains evolved specialized mechanims for recognizing objects in specific categories due to their importance for survival.

Question 31

prosopagnosia

Answer 31

impairment in face recognition.
associated with lesions in the ventral pathway, especially occipital regions associated with face perception (FFA)

Question 32

congenital propopagnosia (CP)

Answer 32

lifetime impairment in face recognition that cannot be attributed to a known neurological condition.

Question 33

face recognition in Autism (ASD)

Answer 33

individuals with autism show a marked reduction in areas that are most activated by face stimuli compared to house and objects

post mortem examinatiions revealed that people with ASD have fewer neurons and less neuronal density in the layers of the fisuform gyrus.

Question 34

holistic face processing

Answer 34

holistic processing is a form of processing that emphasized the overall shape of an object.
is particularly present during face perception: we recognize a face by overall configuration of its features and not by the individual features themselves.