Cognitive Neuroscience Lecture 13: Spatial Representation

*L13: Spatial*
Representation

What is the problem to be solved?

Need to know where things are so that:

Identification: move our eyes to them

o
ID what it is; face/word/unfamiliar

Action: interact with objs

o
Pick up, sit on them, avoid them, etc.

Navigation: find them when they are outside the
range of our senses

o
Your house, your car, supermarket

o

o   **What: STGàIFG (superior temporal gyrus to**
inferior frontal gyrus)

o   **Where: STGàSPLàSFG (STGàsup.**
Parietal lobeàsuperior frontal gyrus)

Visual pathways:

o
Superior longitudinal fasciculusàPosteroparietal cortex

o
Inferior longitudinal fasciculusàinferior temporal cortex

Representation of location

**Relative by reference**
to something else: reference point

Anything can be a reference point

Reference point is a defining aspect of a **frame of reference**

 What reference frames used by brain areas that encode
locations?

Cells in v1?

Cells in the doral/parietal (where) pathway?

Reference frames:

Retino-centered

Viewer-centered (ego centric)

Object-centered (allo-centric)

Frame of reference for V1 neurons

Calcarine fissure (v1)

Fovea most posterior

In goes out, up goes down, left goes right

V1 neurons only encode in terms of direction and
distance from fixation

o
**Retino-centric**
frame of reference (relative to fixation)

We know this because:

o
Objects in world that stim same location in
retina represented by same v1 neurons

§
If a cup is at point A on retina, and then a
phone is at point A, these will both activate same v1 neurons

o
When fixation moves, same objs represented by
diff v1 neurons (ie not obj centric)

Cortical blindness

Deficit defined relative to fixation

When fixation moves, same location in external
space represented differently

Frames of reference: evidence from visuo-spatial neglect

Visuo-spatial neglect/extinction

Difficulty in perceiving/attending/being
conscious of stim on contralesional side of space

Varieties:

Viewer centered

Object centered

Provides evidence for viewer-centered and object-centered
frames of reference in temporal/parietal areas

Neuropsychological cases: right temporal/parietal subsequent
to drug overdose

Line bisection: better for shorter line

Line cancellation: cross out all lines on page

Frames of reference: evidence from **visuospatial neglect**

Not cortical blindness; V1 is intact

Defecit persists despite eye mvt

o
Therefore **attentional**
defecit **due to parietal lobe lesion**

What frame of reference must we assume is disrupted?

Critical evidence:

o
V1 is intact

o
Neglect persists despite eye mvts

o
Left is not retinocentric but rather defined
relative to viewer

**Viewer**
centered neglect: person’s midline

Difficulty in processing **contralesional** side of midline regardless of eye position

Neuropsych: half of each obj missing (group of bow is an
obj)

Location defined with reference to **represented object** (not retina or
viewer): **object-centered frame of ref**

You’ll be able to see it when you flip the obj

What counts as an object?

o
Grouping/visual attributes

Locations defined relative to obj’s right and
left side

Difficulty processing/perceiving stim of
contralesional side of obj regardless of midline/eye pos

Scene copy and gap detectionà
viewer centered neglect associated with lesions to **inferior lobule**

Superior temporal gyrus: object centerd neglect

Monkey studies show:

To grab mug, refrence frame must be in common frame of ref