Transcript Chapter 3 Spatial Vision

CHAPTER 3
GABOR PATCHES
Ryan Scott, Pete McGrath, Nate Hofman, Katy
Kolstad, Maria Peterson, and Katy Jenkins
POINTS OF DISCUSSION
Sine wave grating
 Gaussian window
 Spatial frequency
 Contrast
 Phase

WHAT IS A GABOR PATCH?
The figure on the right is a
Gabor patch. In essence, a
Gabor patch is a sine wave
grating, seen through a
Gaussian window.
WHAT ARE THEY USED FOR?

Gabor patches are mainly used in vision
laboratories because they have “characteristics
that match the receptive field properties of
neurons in a primary visual cortex”
ACTIVITY I
ACTIVITY II
SINE WAVE GRATING
“Light intensity alternates between its darkest
and lightest values according to a sine function”pg. 53
 If separate cones pick up the lightest and darkest
areas, grating is seen

THE GAUSSIAN WINDOW
SPATIAL FREQUENCY
Images in specific locations on the visual field are
transported to and interpreted in specific areas of
the cortex.
 Objects closer to the fovea are processed by
neurons in a large part of the striate cortex,
while images located close to the periphery are
processed in a small portion of the striate cortex.
 This distortion of the visual-field map on the
cortex is known as cortical magnification because
the cortical representation of the fovea is greatly
magnified compared to the cortical
representation of peripheral vision. This causes
decreased visual acuity (blurry vision) father
away from the fovea.

SPATIAL FREQUENCY CONT.
High resolution sight of the entire visual field
would require much larger eyes and brains to
process all of the information.
 Neurons in the striate cortex respond most
strongly to stripes, and individual neurons
respond to specific orientations of lines. More
cells are responsive to horizontal and vertical
orientations than to oblique lines.
 Individual cells of the striate cortex respond to
specific gratings of lines, allowing the brain to
distinguish the thickness of lines

Medium spatial frequency
High contrast
CONTRAST
High spatial frequency
High contrast
Definition:
**Contrast is the difference
between the lightest and
darkest portions of a Gabor
Patch.
•In
a high contrast region of a
Gabor Patch: the darkest
areas are black and the
lightest areas are white.
(there is a greater difference
between the two colors)
•In
a low contrast region of a
Gabor Patch: the lightest
areas are grey while the
darkest areas are going to be
dark grey. (there is a smaller
difference between the two
colors)
•When
the Gabor Patches
cycle through different
phases at varying
frequencies; they appear to
move laterally.
Low spatial frequency
High contrast
PHASES
Christina Enroth-Cugell & John Robson (1984)
were the first to record responses of retinal
ganglion cells to sinusoidal gratings.
 Cells responded to gratings of just the right size,
the response also depends on the phase of the
grating (its position within the receptive field).

PHASES

When shifted through a cycle the location of the
grating within the visual field shifts. The light
bar is desired to be in the center and the dark bar
on the surround of the center.
BIBLIOGRAPHY
J. Wolfe, K. Kluender, & D. Levi. Sensation and
Perception 2nd ed. Sinauer Associates, Inc. 2009
 http://www.michaelbach.de/ot/
 http://www.sinauer.com/wolfe2e/chap3/startF.
htm
