Chapter 3: Spatial Vision (Part the Second)

Question 1

Simple cells

Answer 1

responds primarily to oriented edges and grating

Question 2

With even DIRECTION sensitivity:

Answer 2

only respond to motion in one direction!

Question 3

Complex cells

Answer 3

respond primarily to oriented edges and gratings, however they have a degree of spatial invariance.

Question 4

Simple cells in the primary visual cortex can be formed by the linking of outputs from concentric lateral geniculate nucleus (LGN) cells with adjacent receptive fields.

Answer 4

In addition to signaling the presence of an edge, simple cells are selective for orientation.

Question 5

Each LGN cell responds to one eye or the other….

Answer 5

…but never to both

Question 6

Ocular dominance in V1

Answer 6

Each striate cortex cell can respond to input from both eyes with preference for one eye’s input.

Question 7

COMPLEX cells

Answer 7

sensitive to motion.

Respond to bar regardless of location, as long as within RF.

Question 8

two flavors of simple cells

Answer 8

an edge detector and a stripe detector

Question 9

End Stopping

Answer 9

Process by which cells in the cortex first increase their firing rate as the bar length increases to fill up its receptive field, and then decrease their firing rate as the bar is lengthened further.

HYPERCOMPLEX cells: IMPORTANT for LUMINANCE BOUNDARIES and discontinuities.

LAST: cells can respond differently due to feedback from other visual areas.

Question 10

Column

Answer 10

A vertical arrangement of neurons

Question 11

Columns:

Hubel & Wiesel’s Discoveries

Answer 11

Found systematic, progressive change in preferred orientation;

All orientations were encountered in a distance of about 0.5 mm;

Same orientation preference in columns perpendicular to the surface of cortex.

Question 12

Column Arrangement

Answer 12

Each of the 200 million cells in the Striate Cortex responds to a stripes or edges, gratings, oriented at a particular angle, with a particular width, perhaps moving in a specific direction.

But they are not arranged randomly…

Once they had the orientation of a neuron, Hubel & Wiesel pocked a bit harder and the neurons below would be sensitive to the same orientation.

If pocked tangentially, all orientations in succeeding manner…

Question 13

Hubel and Wiesel’s Columns:

Summary

Answer 13

Found systematic, progressive change in preferred orientation; all orientations were encountered in a distance of about 0.5 mm

Question 14

Hypercolumn

Answer 14

A 1x1-mm block of striate cortex containing “all the machinery necessary to look after everything the striate cortex is responsible for, in a certain small part of the visual world” (Hubel, 1982)

Question 15

COLOR PROCESSING

Answer 15

Regular array of “CO blobs” in systematic columnar arrangement (discovered by using cytochrome oxidase staining technique)

cytochrome oxidase blobs

Question 16

Method of Adaptation

Answer 16

The diminishing response of a sense organ to a sustained stimulus.

Question 17

TILT AFTEREFFECT

Answer 17

Look for a long time (about one minute) to the fixation bar, keeping your eyes on the line between left gratings, maybe moving , but always on the bar.
Then, quickly move your eyes to the point between right gratings. Keeping your eyes on the dot, try to judge the orientation of the bars.

demonstrates selective adaptation.

Question 18

Demonstration of Adaptation that is specific to Spatial Frequency

Answer 18

ADAPT to top panel. 1 minute
Then switch to panel immediately below.
Same spatial frequency, but lower contrast: you won’t see it.

Repeat testing with panel on right or left and the dim panel will not disappear.
After adaptation: contrast sensitivity is reduced, so that you need a STRONGER (higher contrast) stimulus to be detected.

Neurons responding to different enough spatial frequencies are not affected by the fatigue.

Question 19

Tilt aftereffect

Answer 19

Perceptual illusion of tilt, provided by adapting to a pattern of a given orientation.

Supports the idea that the human visual system contains individual neurons selective for different orientations.

Question 20

Selective Adaptation

Answer 20

Evidence that human visual system contains neurons selective for specific stimulus properties (e.g. orientation, frequency, motion, color)

Question 21

Other aftereffects: Motion 1, Motion 2

Answer 21

If adaptation to a stimulus occurs, then it must be that a group of neurons was coding that stimulus and became fatigued.

Easy non-invasive method of measuring what the human visual system is sensitive to.

Question 22

Spatial frequency channel

Answer 22

Pattern analyzers, implemented by a group of neurons with each set of neurons tuned to a limited range of spatial frequencies.

Why would the visual system use spatial frequency filters to analyze images?

Different spatial frequencies emphasize different types of information

Question 23

IOW, sets of groups extract from image different “aspects” of the image:

Answer 23

how much left tilt at a high frequency,

how much horizontal at a lower freq…

Question 24

Why sine waves?

Answer 24

Many stimuli can be broken down into a series of sine wave components using Fourier analysis
Any sound, including music & speech
Any complex image, including photographs, movies, objects, and scenes
Any movement, including head & limb movements

Also, our brains seem to analyze stimuli in terms of their sine wave components!

• Vision
• Audition

Question 25

Period or wavelength

Answer 25

The time or space required for one cycle of a repeating waveform.

Question 26

Phase

Answer 26

1) In vision, the relative position of a grating

2) In hearing, the relative timing of a sine wave

Question 27

Amplitude

Answer 27

The height of a sine wave, from peak to trough, indicating the amount of energy in the signal

Question 28

Even something as complicated and artificial as a square wave can be reproduced by adding the correct sine waves together.

Answer 28

….

Question 29

Joseph Fourier

Answer 29

(1768–1830) developed another useful tool for analyzing signals

Question 30

Fourier analysis

Answer 30

A mathematical procedure by which any signal can be separated into component sine waves at different frequencies.

Combining these component sine waves will reproduce the original signal.

Question 31

Sine wave:

Answer 31

1. In hearing, a waveform for which variation as a function of time is a sine function.
   Also called a “pure tone”
2. In vision, a pattern for which variation in a property, like brightness or color as a function of space, is a sine function.

Question 32

Show high spatial-frequency mask: Guess who?

Answer 32

lincoln