Lecture 3- Spatial Vision
The retina processes information similar to a computer. Which neurons in which
pathways play a role? Describe some of the functions of the pathways. In which
important way does retinal information processing differ from that of a usual computer?
One bipolar cell connects to a photoreceptor
Inhibitation and facilitation:
Spatial vision refers to our ability to resolve or discriminate spatially defined features.
• Natural Scene Statistics: Why Care About Gratings?
• What Is Visual Acuity?
• The Primary Visual Pathway
• Functional Properties of the Striate Cortex
• The Girl Who Almost Couldn’t See Stripes
Natural scene statistics: why care about gratings?
– Gutenberg’s printing press
– Gratings and their characteristics
– What is a Fourier transform?
– The independent components of the visual world
Printing press metaphor
– 1439 Johannes Gutenberg invented a printing press with movable types.
– Huge impact on 15 century Europe (1424 Cambridge 122 books!) –
“Greatest invention in the last 1000 years”.
– Similar technology in ancient China & Korea had no comparable impact. Why?
not much cultural exchange. In China and Korea, movable types not as
important as Europe
The simpler the alphabet, the easier to recreate text (China has THOUSANDS
of characters) A page of text can be pieced together from a small set of simple elements.
– Similarly, visual images can be described/ represented as compositions
of simple elements.
– Each of these elements can be separately filtered out.
Word document is much smaller than BITMAP (bitmap: notice or memorize what each
pixel value is)
Three types of gratings
– Rectangular grating
– Sine wave (sinusoidal) grating
• Gabor (sine wave viewed through a circular aperture defined by a 2D gaussian)
Three characteristics of gratings
• Cycles per second = Hz
• Cycles per visual degree = cpd
Sine wave gratings
– who cares?
– Patterns of stripes with fuzzy boundaries are quite common
– The edge of any object produces a single stripe, often blurred by a
shadow, in the retinal image
– Any image can be decomposed into sine wave gratings and other
• Important cues for visual recognition
• Efficient coding.
– (This is what the visual system appears to do.) Fourier transform: an operation that breaks down a function/an image into sine waves
of different frequencies.
– Music can be decomposed into sine waves with different temporal frequencies.
- Images can be decomposed into sine waves with different spatial
frequencies (get rid of extra frequencies)
you still see the animals but have difficulty seeing the details
image of zebra: low frequency tells body of the zeb