Cognitive Neuroscience Lecture 8: Object Recognition

Recording info that wasn’t finished last class: ERP, EEG,
and MEG are very good temporal resolution but low spatial resolution. Useful
when you care about timecourse.

Connections beyond V1: we’ve studied what happens in V1 so
far

There’s more than just patches and bars that we understand.

EyeàLGNàv1àsplits to dorsal and
ventral path

Simplified to two pathways: further processing in
dorsal/ventral pathways

**dorsal**:
“where is the object”: spatial

**ventral**:  “what is the object”: identification of
object

Simplified because there are other things in between; not
always dichotomous

Monkey experiments are good because they have similar visual
systems to us

Also good bc can directly test function/role of area by
artificially lesioning brain region

What vs. where experiment

Task 1: What—**Object discrimination**

o
Food was hidden under one of them

Task 2: Where—**Landmark discrimination**

o
Same shape but distance between obj with food
and landmark was different than distance from non-food and landmark

Performance good for both tasks in a healthy
monkey

Performance bad in **landmark** task for monkey with **dorsal**
**lesion**

Performance bad in **object discrimination** task for monkey with **ventral** lesion

**This is**
double dissociation of object and landmark

Ventral àwhat,
dorsalà
where/spatial locations is shown by this experiment

Double dissociation in Humans

Can’t do artificial lesion, but using
neuropsych, studied people with preexisting lesions

Showed selective impairment of tasks

Ventral lesion

o
CO poisoning

o
Perception problem: “what” deficit

o
**Visual-form**
agnosia/object agnosia: **impaired object recognition NOTECARD**

o
**Prosopagnosia:**
**specific to faces**

Dorsal lesion

o
Stroke

o
Action problem: “where” deficit

o
**Optic**
Ataxia: **had trouble reaching to a spatial location NOTECARD**

Did similar double dissociation experiment

Task 1: Perception—are these identical?

Task 2: Action—reach out and grab this

Patient with ventral lesion was unable to do Task
1 (perception task), but was able to do Task 2 (action task)

Patient with dorsal lesion was unable to do Task
2 (action task), but unable to do Task 1 (perception task)

Basically, **dorsal**
important for action (since orientation is required) **and** ventral important for perception

Ventral lesion patient: object
agnosia—difficulty recognizing objects; but how do we know it’s this?

o
Alternative hypotheses: It could be a problem
with memory of word, difficulty articulating, vision problem, she just can’t
name them

o
We know it’s truly a **visual** object recognition problem because she was able to tactilely
recognize them when they were in her hands

o
This shows that she knows what they are but just
cannot VISUALLY recognize them

o
Further evidence:

§
Could draw pictures from memory

§
Could **not**
recognize or copy pictures given a model picture

§
Could **not**
**recognize her own drawings later on**

o
Matching orientation task in ventral lesion pt

§
**Explicit**
matching task **(perceptual orientation matching)**: **Couldn’t match something she was holding to something she was** looking **at**

§
**Action**
task **(visuomotor “posting”)**: **But**
when performing the **action**, she
could align the object to the slot

Dorsal lesion patient: optic ataxia (opposite of
ventral lesion patient)

o
Fine with recognizing and matching

o
Difficulty with visually-guided reaching

o
Make inappropriate grasping movements with hands
 (does not align hand with slot)

This was a double dissociation between the two
patients

**DORSAL/ACTION/WHERE:**
spatial action

**VENTRAL/PERCEPTION/WHAT**

**Main**
point: **visual processing involves several distinct pathways**

Further processing in dorsal/ventral pathways

**“Where”/action**:
Dorsal stream NOTECARD

Mostly parietal

V1àSuperior longitudinal fasciculusàposteroparietal cortex

**“What”/perception**:
Ventral stream NOTECARD

Mostly temporal

V1àInferior
longitudinal fasciculusàinferior
temporal cortex

Oversimplification—connections between them; feeds forward,
back to V1, and all directions

Despite this, fMRI shows that distinction is somewhat true

**Evidence for**
dorsal/ventral pathways **NOTECARD**

1.       Animal lesion studies (monkeys)

2.       Human neuropsychological cases
(DF&RV)

3.       Single unit recordings

**What**: **temporal neurons** fire for color, shape, faces

o   E.g. will fire for shape of hand
regardless of orientation, but will fire less when given a less detailed hand
shape

**Where**: **parietal neurons** fire for change in direction of motion, velocity,
control of movements of attention

o   E.g. change if you move your
attention to left side to right side

o   To know that something is moving is
to know that it has changed location (where)

4.       Human neuroimaging studies with
intact subjects

**Remembering what vs. where**

o   Healthy normal adults

o   **Position task:** “are the objects in the same locations”

o   **Object task:** “are
these the same objects”

o   Same stim, diff task: location vs.
identity

o   Object task lights up
ventral/temporal area

o   Position task lights up inferior
parietal area

o   **Position/object tasks light up different areas even in neurologically**
intact patients when they were looking at same stimuli

o   Results of PET study

§  Dot-location matching used parietal
more

§  Face matching used ventral/temporal
more

What/where:
color/motion

o   **Color:** compare
brain response of color vs. black&white sq

§  **ventral**

o   **Motion:** compare
brain response to stationary vs. moving black and white regions

§  **Dorsal**

o
Results:
Color is medial (V4), motion is lateral (MT)

**Lateral occipital**
complex: object recognition

Lesions in people who cannot do obj recognition
are same as location of LOC in intact people

Selectively responds to object information (e.g.
not scrambled objects)

Further processing in dorsal/ventral

Computational problems in object recognition:

**Object constancy**
(car from different views, diff background)

o
We can recognize objects across changes in
illumination, size, occlusion, and viewing position

o
diff image on retinaàhow do you still recognize?

o
Does take more time to recognize noncanonical

**Grouping**
of features and parts of objects
(Gestalt principle)

è Help determine what bits of an
image belong together

o   Proximity: closer things get
grouped as 1  object

o   Similarity: similar get grouped

o   Closure

o   Good continuation: 2 lines, not
scattered

o   Good form (e.g., regularity,
symmetry)

**Use of**
stored object knowledge

o
We can still identify objects even when there
aren’t local cues for grouping

o
**Top-down**
processing **to ID obj**

§
If you already know it’s a dog, you can tell
it’s a dog

How do we achieve object recognition? Some theories:

**Template matching: exemplars**

o
Compare input to stored template of an object;
yes or no

§
Then respond whether a match or not

§
E.g. stored template ‘B’ would match ‘B’ but not
‘A’

o
What’s the problem with this?

§
Doesn’t work for novel objs

§
You could have something that is still a capital
B but is a different font

o
You can recognize it as something different in a
different context

o
What’s the template for a chair? You recognize
many things as 1 type of obj

o
Also you can categorize things that aren’t
evolutionarily coded in a template

o
**Problems**
in template matching

§
Variability of exemplars

§
New objects

§
Changing viewpoints

§
The idea of a grandmother cell rejected

·
Grandma changes over time, but you can still
recognize her; must not have 1 cell for 1 exact face, then.

**Recognition by components: Geons**

o
“Alphabet” of vision

§
Sphere, block, prisms, etc.

§
**Geons**:
basic building blocks of all object recognition

§
**Objects =**
Geons + Spatial relationships

o
What geons can’t do:

§
Some things can’t be reduced to geons easily

§
Fine with general categories, but not
individuals: all would break down into same set of geons, so how do we tell
difference between dogs

Deficits in object recognition:

Visual agnosia (DF)

o
Different from memory loss; tactile enables
recognition in agnosia, meaning that they *know*
*the object but just can’t recognize it* visually

Stroke patient: could see visual details and make
appropriate hand gestures

o
Could not describe obj **functions** though; used particular parts to infer it was something
else like phone

§
Could not put parts together into whole

o
**Apperceptive**
Agnosia

§
Right lateralized (found in people with right
damage)

§
Posteriorà
earlier in visual processing stream

§
Failure in basic perceptual processing

·
We can tell things from fragmented line
drawings, but they cannot

o
**Associative**
Agnosia

§
Left hemisphere

§
Anterior à
Higher level processing failure

§
Can perceive obj but cannot assign meaning

§
Fail at matching-by-function

·
Only can match by form

§
Category specificity shown by HSV patient

·
He got common obj 90% correct

·
but live things only 6%

§
What are implications of category specific associative
agnosia?

·
We interact more with inanimate things
(sensorimotor regions also used, not just vision)

o
G.S. motor activation to manmade obj

o
Left premotor, sensory becomes active when
viewing tools

o   Regions:

§  Extrastriate Body Area (bodies)

§  Fusiform face area (faces)

§  Middle Temporal (Motion
processing)

§  Lateral occipital complex
(Objects)

§  Parahippocampal place area
(places)

§  Superior temporal sulcus-face
area (faces)

·
Visual areas are segregated by living vs.
inanimate obj

o
Specificity in ventral visual stream

o
Large scale segregation in ventral stream for
living vs nonliving

·
Summary of category-specific agnosia: 2
explanations

o
Motor system engaged when viewing inanimate obj à agnosics ID these
better than animate

o
Ventral visual system is segregated by animate
vs inanimate shown in fMRI

§
Vasculature implies that animate regions more
prone to damage in encephalitis/stroke

§
Animate is usually one lost; we’ve never seen
only inanimate lost

o
**Integrative**
Agnosia

§
Right/left hemisphere

§
Cannot put features into parts, or integrate
parts as whole

Category-specific defecits

o
Apperceptive agnosia

o
Integrative agnosia – object recognition

o
Associative agnosia

o
**Alexia**—written
word recognition (reading) deficit

o
**Prosopagnosia**—face
recognition deficit

§
Sometimes following damage to FFA

§
Sometimes congenital

§
Can recognize that it *is* a face, but not identity of face

§
To ID, use non-facial info like hair/clothes

o
What’s special about faces?

§
More accurate at identifying whole face than
parts

·
Not true for other obj; just faces

§
Holistic processing of faces: upside down is
hard bc holistic effect disappears

§
Evidence from object agnosia

·
Obj recognition difficulties

·
Normal objects are confusing, but agnosia pts
see face

·
Obj recognition is diff from face recognition

§
Evidence from single cell recording

·
There are cells that respond more than others to
faces

§
Fusiform gyrus: Right fusiform, Fusiform Face
Area

Faces activate it more than scenes