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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
