psy 214 lecture 11 (10/19/2011) – (perceiving motion & color)...

PSY 214 Lecture 11 (10/19/2011) – (Perceiving Motion & Color) Dr. Achtman

Written by: Aubrey Tucker, [email protected] of 4

Corrections: • None Needed. Announcements:

• Thank you for all of the feedback, she has read it and the class seems to be going well but some people seem to think that it is going along a little quickly (she will try to slow down). We, as students, control the class and we must be active and ask questions if we do not understand something; she challenges us to ask questions.

• The next midterm is on Wednesday, October 26th. • There will be a review period Monday, October 24th at 5:30 in a room to be announced.

Please bring questions. • She also has office hours for those of you who cannot attend on Monday.

Lecture Notes: Review from last time: (motion perception) Motion happens if only the MS and CDS OR the IDS are stimulated. If all three of them are stimulated then we comprehend no movement. Aperture Problem

• An aperture is like a window into the world; it only shows a small spot. Every individual neuron only sees a small piece of the world.

• The way to demonstrate this is to make the ‘ok’ sign with your thumb and forefinger and to view a pencil. This demonstrates the potential view of one single neuron:

PSY 214 Lecture 11

Topic: Perceiving Motion & Perceiving Color Chapters 8 & 9, pages 177-198 & 201-227



• The problem with this limited view is that the one neuron alone cannot differentiate between a pencil that is moving only from left to right and a pencil that is moving both from left to right and slightly up in a diagonal motion.

How do we solve this problem? • The responses of a number of V1 neurons are pooled to make sure they are all seeing the

same thing (ex: like asking all the other neurons if they all saw the pencil moving sideways) It takes thousands of neurons to find out with is actually happening.

• Evidence of this is found in monkeys in the MT Cortex; we know this. But why do we use a bar of light to measure it?

• The world is complicated and bars are the easiest thing controlled Moving dots Display (bunch of dots and arrows pointing direction and speed; longer arrow for faster and shorter arrow for slower)

To be able to correctly understand the direction of the dots, a person only needs between 12 & 13% in one coherent motion. Determining direction of fields of oriented bars Lesion experiment by Newsome and Pare: they removed the MT cortex (the part that detects motion) from the monkey’s brain and the monkey had a hard time recognizing the correct direction of motion.



Micro stimulation experiment by Movshon & Newsome: They trained a monkey to move a lever in whatever way the dots were moving in (only 20% of the dots were in a cohesive direction). By stimulating cells in a specific neuron they want to see if they can make the trained monkey move the lever the wrong way.

• Let’s say the dots are moving left and they stimulate the ‘up’ neurons, depending on how much stimulus you provide the monkey could move it left, up, or most likely in a diagonal motion.

Biological motion

• In the video we saw that if we put receptors on all of the major joints and video tape a person moving then when we view only the receptors on a black background it is clearly a person moving. You can also spot the difference between a man and a woman moving.

CHAPTER 9- Perceiving Color

Outline for today and Monday

1. function of color vision 2. the color experience 3. trichromatic theory 4. color deficiencies 5. opponent process theory 6. perceiving color under changing illumination

Functions of color vision

• foodappeal (what color something is changes how you interact and interrupt it) • we see in the visual spectrum (400nm[blues]- 700nm[reds]) • light is reflected off of everything (black absorbs most and reflects least, white reflects most

and absorbs least) Trichomatic theory of color

• Proposed by Young and Helmholtz (late 1800’s) although they never worked together they both get credit because they came up with it at relatively the same time.

o 3 different receptor mechanisms are responsible for color vision (3 different cones we don’t need a different cone for every single different color.

o Behavioral experiments Color matching experiments subjects were shown test fields and were told

to change the comparison field by changing the intensity of blue, red, and yellow-green lights.

• Normal color vision people CAN make any color using this technique



For more information: • Lesion Experiment: http://www.youtube.com/watch?v=pG6NaqwUTv8

• Shows the experiment in more detail and gives a new opportunity to see the experiment. Real-life example: • A real life example of perceiving motion is so that we can tell if we are in danger of an object

flying at our heads. And perceiving color is important for us to be able to notice if food has gone bad or as a way to attract a spouse with what we wear.

psy 214 lecture 11 (10/19/2011) – (perceiving motion & color)...

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