The visual system Martha Nari Havenith MPI for Brain Research Aug. 5th 2008 FIAS Summer School.

The visual system

Martha Nari HavenithMPI for Brain Research

Aug. 5th 2008FIAS Summer School

Receptive field

What and Where pathway

Change blindness

Bipolar cell

Striate cortex

Orientation column

Grandmother (Halle Berry) cell

Fusiform face area

Outline

Stuff we see – visual perception

Eye and retina

Tectum and thalamus

The visual cortices

Neuronal codes in the visual system

What I won’t really talk about: Depth, colour and motion perception; subcortical structures of the visual system, visual WM and attention

The visual

system I

Visual perception

Speed

→ 150 ms

Thorpe & Fabre-Thorpe (2001)

Speed

Thorpe & Fabre-Thorpe (2001)

20-40 ms

30-50 ms40-50 ms

50-70 ms

70-90 ms

80-100 ms

Speed

Acuity• Two-point acuity: 25 arc seconds = 3-4 mm at 50 cm distance =

diameter of a retinal photoreceptor

• Vernier acuity: 8 arc seconds ~= 1 mm at 50 cm distance

From Krauskopf & Forte (2002)

Context sensitivity

Figure segregation

From Schiffman (2000)

Figure segregation – Gestalt principles

Proximity

From Schiffman (2000)

Figure segregation – Gestalt principles

Similarity

From Schiffman (2000)

Figure segregation – Gestalt principles

Common fate

Figure segregation – Gestalt principles

From Schiffman (2000)

Closure

Figure segregation –What we can do

Figure segregation-What Windows cannot do

Invariance

Invariance

M.C. Escher

Top-Down controlof perceptual judgements

Top-Down controlof perceptual judgements

Kandel et al. (2000)

Top-Down controlof perceptual judgements

Kay & Kempton, 1984

Blue Green

Siyoname

Some limitations of visual perception - Awareness

Monkey: 77% correct - His V1: 96% correct!

Chen et al., 2008

Ideal observerMonkey

Some limitations of visual perception - Priming

HAPPINESS

Some limitations of visual perception - Priming

HAPPINESS

Some limitations of visual perception - Priming

HAPPINESS

Some limitations of visual perception - Priming

HAPPINESS

Some limitations of visual perception – Parallel processing

Adapted from Anne Treisman

Pop-out

Stimulus size

Automatic processing

Searc

h t

ime

Focused attention

No po

p-ou

t

Pop-out

Automatic

No Pop-out

Attentive

Some limitations of visual perception – Parallel processing

Visual memoryThe modal model

Sens

ory

mem

ory

(ico

nic

mem

ory)

Shor

t-te

rm m

emor

y (w

orki

ng m

emor

y)

Lon

g-te

rm m

emor

y

200-300 ms Several seconds or while rehearsing

Up to life long

Luck & Vogel, 1997

Set size

50

Pe

r c e

nt

Co

rrect

2 4 6

75 SizeGap

ColourConjunction

100

Orientation

Conclusion: the capacity of visual WM is about four objects, while every object can consist of multiple features.

- WM similar to attention.

Study Test

Wheeler & Treisman, 2002

Study Test

Conclusions:

- Feature dimensions are independent.

- Only four features per feature dimension.

- Attention binds features within WM.

- Proof: With distractors memory for conjunctions impaired.

Performance drops for conjunctions but not for features.

Some limitations of visual perception – Change blindness

Harborside.mov

Some limitations of visual perception Impossible objects

Summary I – Visual perception is…

• Fast and precise

• Highly specialized for extraction of contours

• Designed for detecting invariant features

• Modulated by top-down processes

• Limited by the capacity of attention and

visual WM