LECTURE 7

Question 1

Parvocellular Cells

Answer 1

Carries info primarily from cones. Primarily carries information about small, slow, colorful things

Question 2

Magnocellular Cells

Answer 2

Carries info primarily from rods (but also some from cone). Primarily carries information about large, fast things and is colorblind

Question 3

Parvocellular (Foveal) & Magnocellular (Peripheral) pathways to LGN

Answer 3

In left eye, right visual field is projected ipsilaterally (dotted lines) while left visual field is projected contralaterally (solid lines)

Question 4

Does the brain identify an object separately from determining its location?

Answer 4

yes (different pathways). Evidence:
* Non-human primate studies
* Train monkeys on task
* Lesion their brains
* Observe how they perform the task post- lesion
* Primate picks an option hoping for a reward
* Rewards can be hidden

Question 5

OBJECT VERSUS LANDMARK CUES

Answer 5

READ THE FRIGGIN SLIDE

Question 6

OBJECT DISCRIMINATION

Answer 6

Primates with lesions in temporal area (ventral stream) had difficulties with object discrimination task

Question 7

LANDMARK DISCRIMINATION

Answer 7

Primates with lesions in parietal area (dorsal stream) had difficulties with landmark discrimination task

Question 8

DUAL STREAM HYPOTHESIS

Answer 8

• Dorsal visual pathway involved in recognizing where objects are and how to interact with them - The WHERE pathway
• Ventral visual stream more involved in recognizing objects on the basis of shape, texture, color, detail, etc.
• The WHAT pathway

Question 9

SPARSE CODING AKA GRANDMOTHER CELL THEORY

Answer 9

Ventral pathways respond to increasingly complex objects. At some point in the pathway there are highly specialized cells that respond to specific objects

Problems
- How many neurons do we than have in our brain and where’s the limit
- If one cell dies do we forget everything aout the info it held

Question 10

POPULATION AKA COMBINATION CODING

Answer 10

• Uses hierarchical feature coding up to a point (still needed for early visual processing in V1, etc.)
• No “one neuron” that represents a concept
• Concepts/percept is the sum pattern of activation across a bunch of neurons

Probelms
* If a whole population of neurons is required to identify a single
percept, how do you link that percept to stored knowledge?
* There isn’t one cell to “connect”, there are many

Question 11

Perceptual constancy

Answer 11

we are able to perceive and identify objects as
being the same even when many of the visual cues are different

Question 12

How Does the Brain Identify Objects in Different Conditions?

Answer 12

• Form-cue invariance: The brain can identify objects as belonging to the same category despite differences in the visual cues across objects

Question 13

Is object perception based on mentally assembling
the individual parts of an object, or on holistic
representations?

Answer 13

• Left hemisphere is specialized for local/feature-based processing
• Right hemisphere is more specialized for global/holistic/configural processing

Question 14

Feature-based encoding

Answer 14

Is object perception based on mentally assembling the individual parts of an object

Question 15

Configural encoding

Answer 15

Is object perception based on holistic representations

Question 16

Objection recognition: Category perception

Answer 16

Humans have evolved to process visual information with a lot of detail
* Are we “hard-wired” to be able to recognize certain types of objects? Have some parts of the brain evolved to be specialized to recognize very specific stimuli?

• Face
• Words
• Location
  -Human body

Question 16

Thatcher Effect

Answer 16

Aka Inverse effect. Phenomenon where
recognition is poorer when an object is turned upside down

NOTE: if processing was entirely featural, you wouldn’t have any difficulty spotting the odd features when the face is inverted

Question 17

Fusiform face area (FFA)

[Objection recognition: Category perception - Faces]

Answer 17

Exhibits a greater response to faces than to other
objects

Question 18

Parahippocampal place area (PPA)

[Objection recognition: Category perception - Location]

Answer 18

Appears to process visual information related to places in the local environment

Question 19

Extrastriate body area (EBA)

[Objection recognition: Category perception - Human Body]

Answer 19

Responds preferentially to images of human bodies and body parts, compared to inanimate objects and object parts

Question 20

Visual word form area (VWFA)

[Objection recognition: Category perception - Words]

Answer 20

Especially responsive to written words

Question 21

Focus: Face Recognition

Answer 21

• Faces are a frequently encountered category of visual
  objects
• We process tons of different faces in our lives, all with similar configurations
• Innate preference for faces
• Yet we’re able to distinguish between them
• Face recognition is a really important task
• Important social/evolutionary process
• Evidence for specialized face processing in the brain:
• Non-human primate research
• Innate preference for face-like stimuli
• fMRI studies in humans
• Prosopagnosia

Question 22

Face Pareidolia

Answer 22

Tendency to perceive faces when there are none

Question 23

Prosopagnosia

Answer 23

• Selective inability to recognize or differentiate among faces
• Suggests that faces are special category of object recognition

Question 24

ERP During Face Processing

Answer 24

N170 Response ○ Spike in activity 170ms after exposure to face

Question 25

Greebles and the FFA

Answer 25

Participants trained on made-up stimuli called “greebles” - Participants trained on made-up stimuli called “greebles” ● Training on greeble discrimination prompted N170 responses that were not present prior ● FFA responded similarly ○ More evidence for the expertise hypothesis? ○ Maybe, but these results are not very reliable – other studies have found little/no response for non-face objects even among experts ○ Another confound: greebles are still kinda face-like

Question 26

Two hypotheses concerning FFA

Answer 26

* Hypothesis #1: FFA is specialized for FACE processing * Hypothesis #2: FFA is specialized for expert individuation

Question 27

Visual agnosia

Answer 27

An inability to recognize objects in the visual modality that cannot be explained by other causes. * Typically results from injury to the ventral stream * Two main types: apperceptive & associative

Question 28

Apperceptive Agnosia

Answer 28

* Fundamental difficulty in forming a percept (mental impression of something perceived by the senses) * Can’t copy drawings * Can’t process local elements * Cannot identify objects based on vision * Problem with scale (only pays attention to fragments) -Apperceptive agnosia: usually diffuse damage to occipital lobe

Question 29

Associative Agnosia

Answer 29

* Basic visual information can be integrated to form a meaningful perceptual whole * But that perceptual whole can’t be linked to store knowledge * Can copy drawings but not identify them * Can see and even reproduce objects * But can’t recognize them as what they are * No access to name, usage, or meaning * Damage is to ventral stream - Associative agnosia: usually damage to occipitotemporal regions of both hemispheres