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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
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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
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The visual system I Visual perception
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Speed
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→ 150 ms Thorpe & Fabre-Thorpe (2001) Speed
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Thorpe & Fabre-Thorpe (2001) 20-40 ms 30-50 ms 40-50 ms 50-70 ms 70-90 ms 80-100 ms Speed
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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)
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Context sensitivity
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Figure segregation
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From Schiffman (2000) Figure segregation – Gestalt principles Proximity
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From Schiffman (2000) Figure segregation – Gestalt principles Similarity
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From Schiffman (2000) Figure segregation – Gestalt principles Common fate
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Figure segregation – Gestalt principles From Schiffman (2000) Closure
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Figure segregation – What we can do
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Figure segregation- What Windows cannot do
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Invariance
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M.C. Escher Top-Down control of perceptual judgements
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Kandel et al. (2000)
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Top-Down control of perceptual judgements Kay & Kempton, 1984 BlueGreen Siyoname
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Some limitations of visual perception - Awareness Monkey: 77% correct - His V1: 96% correct! Chen et al., 2008 Ideal observer Monkey
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Some limitations of visual perception - Priming HAPPINESS
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Some limitations of visual perception - Priming HAPPINESS
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Some limitations of visual perception - Priming HAPPINESS
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Some limitations of visual perception - Priming HAPPINESS
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Some limitations of visual perception – Parallel processing
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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
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Visual memory The modal model Sensory memory (iconic memory) Short-term memory (working memory) Long-term memory 200-300 ms Several seconds or while rehearsing Up to life long
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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
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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.
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Some limitations of visual perception – Change blindness
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Some limitations of visual perception Impossible objects
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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
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