The visual system Martha Nari Havenith MPI for Brain Research Aug. 5th 2008 FIAS 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) ms ms ms ms ms 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
M.C. Escher Top-Down control of perceptual judgements
Kandel et al. (2000)
Top-Down control of perceptual judgements Kay & Kempton, 1984 BlueGreen Siyoname
Some limitations of visual perception - Awareness Monkey: 77% correct - His V1: 96% correct! Chen et al., 2008 Ideal observer Monkey
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 Search time Focused attention No pop-out Pop-out Automatic No Pop-out Attentive Some limitations of visual perception – Parallel processing
Visual memory The modal model Sensory memory (iconic memory) Short-term memory (working memory) Long-term memory ms Several seconds or while rehearsing Up to life long
Luck & Vogel, 1997 Conclusion: the capacity of visual WM is about four objects, while every object can consist of multiple features. - WM similar to attention. StudyTest
Wheeler & Treisman, 2002 StudyTest 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
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