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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