presentations\MonaChapter 2

Visual Perception:
It Is All In Your
Mona Moshtaghi
Beginnings of Human Perception
Perception of a real object is
based on “sensory data
representing the physical
properties of the object such as its
weight, reflectance, rigidity,
stiffness and texture.”
– “Platonic Solids”
– “There is nothing in the mind that
was not first in the senses.”
David Marr
– Vision
James J. Gibson
• Psychologist in the field of visual perception
• Introduced texture gradient
• Visual texture  cue to the 3D structure of surfaces
• Texture studied as 3D cue (computational and
computer vision)
Decompositions of Texture Gradients Into Different Components
David Marr
Three Levels of Understanding Complex
Information-Processing Devices
Computational Approach
Most abstract level
Describes the problem the system
is trying to solve & the constraints
it uses in order to solve it
Representation and
Addresses the questions of
Involves the details of the
hardware in which the algorithm is
Marr’s “2.5D Sketch”
Opaque cube
7 of the 8 vertices
9 of the 12 edges
More than half of the 3D shape can be seen
when represented by contours or vertices
Computational Geometry
• Vertices:
0-dimensional cells
• Edges:
1-dimensional cells
• Regions or Faces:
2-dimensional cells
A, B: In the Ponzo illusion, the two converging lines provided the depth
impression that the two physically identical objects were located at
different distances from the observer, and the distant object looks larger
than the object that appears closer in space.
C: In the Ebbinghaus illusion, the object surrounded by small items
looks larger than a physically identical object surrounded by big items.
Cayetano Ferrer
Mary Temple
Latex paint on walls
Illusion of light coming from a window into a room
How does the brain accomplish
diverse functions of scene
 Where
Disentangling scene content from spatial boundary:
complementary roles for the parahippocampal place area and
lateral occipital complex in representing real-world scenes.
•Analysis of the visual scene account for the objects and the
spatial layout of surfaces in a scene
• Parahippocampal place area (PPA)
 same spatial boundaries
• Lateral occipital complex (LOC)
 same content
New approach to the perception of 3D shape
based on veridicality, complexity, symmetry
and volume.
• 3D shape is unique in perception
– Complexity  identification of objects
• 3D shape perception is veridical (car, chair, etc)
Hide & Seek That Beer…
Thank You