the visual system martha nari havenith mpi for brain research aug. 5th 2008 fias summer school
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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
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)
Some limitations of visual perception - Awareness
Monkey: 77% correct - His V1: 96% correct!
Chen et al., 2008
Ideal observerMonkey
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.
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