Human vision

Human vision

Jitendra MalikU.C. Berkeley

Cerebral Cortex

Monocular Visual Field: 160 deg (w) X 175 deg (h)Binocular Visual Field: 200 deg (w) X 135 deg (h)

Cones and Rods

Receptor density vs eccentricity

Processing in the retina

ON and OFF cells in retinal ganglia

Visual Processing Areas

The visual system performs

• Measurement of light and spatial relations• Perceptual Organization• Active interaction with environment

Measurement of light and spatial relations

• Measuring light– Sensitivity over high dynamic range– Gain control results in “Weber Machine”– Sensitivity to contrast rather than absolute

luminance level—discounting the illuminant• Measuring Spatial relations

– Contrast sensitivity function– Vernier Acuity

Threshold vs. Intensity

Weber Contrast Cw = ΔL/LMichelson Contrast CM = (Lmax – Lmin)/2 Lmean

Why contrast is the right variable..

Simultaneous Contrast

Mach Band

A Mach Band in 1D profile

Craik-O’Brien-Cornsweet

Contrast Sensitivity Function at different luminances

Receptor density vs eccentricity

CSF as function of eccentricity

Cortical Magnification Factor

Mapping from Retina to V1

Physiological Optics 1840-1894

The Empiricist-Nativist debate

The debate..(and sometimes both were right !)

• Helmholtz argued that perception is unconscious inference. Associations are earned through experience.

• Hering proposed physiological mechanisms—opponent color channels, contrast mechanisms, conjunctive and sisjunctive eye movements..

The Twentieth Century..

• The Gestalt movement emphasized perceptual organization.– Grouping– Figure/ground – Configuration effects on perception of

brightness and lightness

Grouping factors

Grouping Factors

The Figure-Ground Problem

Transparency

Wallach’s Brightness ratios

Gibson’s ecological optics (1950)

• Emphasized richness of information about shape and surface layout available to a moving observer– Optical flow– Texture Gradients– ( and the classical cues such as stereopsis etc)

Measuring Surface Orientation

Accomodation

Depth of field of human eye

Convergence

Convergence angle vs. distance

Binocular Stereopsis

Optical flow for a pilot

Some Pictorial Cues

Shading

Cast Shadows

Geometry of cast shadows