ventral stream
DESCRIPTION
Object recognition and the ventral "what stream". Used for a university course on visual perception.TRANSCRIPT
What are you looking at?
Barbara Nordhjem
Visual Neuroscience Group
Laboratory of Experimental Ophthalmology
University Medical Center Groningen
Mechanisms of visual recognition.
Human recognition
• Gist of the scene at 7 images per second.
• Unpredictable random sequence of images
Potter 1971, 1975; Biederman 1972; Thorpe 1996 Movie by Jim DiCarlo
QuickTime™ and aSorenson Video 3 decompressorare needed to see this picture.
• Images change: object position, distance, pose, lighting and background clutter. Yet we know where to attend and what we are looking at.
Moving beyond V1
• What happens at the cellular level after V1?
Simple Cells
Hubel & Wiesel, 1959, 1962, 1965,1968
Gradual more complex preferred stimulus
Tanaka, 1996
Illustration from Rousselet et al., 2004
Parallel increase in invariance properties (position and scale) of neurons
Pathways in the brain
• Lesions parietal lobe (Newcombe, 1969)
• Ungerleider and Mishkin (1982) lesions in monkeys. Suggested regions organized in pathways
• Goodale and Milner (1992) distinguish between perception and action
Figure by Mike Cohen
• The case of DF: visual form agnosia• Carbon monoxide poisoning• Lesion of lateral occipital cortex
Goodale et al., 1991
Aglioti et al., 1995
Are people attending to both constellations when they grasp?
Patient (AT) with parietal lesions was better grasping familiar than novel objects – interaction of memory and action control (Jeannerod et al., 1994).
Aglioti et al., 1995
Modules in the brain
Figure by Mike Cohen
Processing areas with the ventral pathway:
Faces, Objects, Places
Face and form agnosia
Some patients show a specific deficit for recognizing faces, others show deficits for recognizing all other objects.
Faces and objects are processed in separate, perhaps non-overlapping, brain areas.
The idea of functionally specialized regions
Lateral Occipital (LO)
Grill-Spector et al., 1998Malach, Levy, & Hasson, 2002
Levels of recognition
Gauthier et al., 1999, 2000
Visual awareness
Andrews et al., 2002
Right FFA
One-category
Two-category
Two types of bistable figures
One-category Two-categories>
Different ways of seeing
Peripheral and central vision
Levy et al., 2001
Form and texture
Cant & Goodale, 2007
Cant & Goodale, 2007
Representation in ventral areas
Freeman& Simoncelli, 2011
Honey et al, 2008
Spatial scales: coarse and fine representation
Olivia, 2007
Fast saccade bias towards faces, event for phase scrambled images
More than one ventral pathway?
Summary
• Parallel increase in invariance to position and scale of neurons from V1 to IT
• Specialized information processing• Dorsal and ventral pathways for
action and perception• Keep in mind that the idea of
pathways and specialized regions is simplified
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