Activity: View Michael Bach’s Color aftereffect at .

View the stimulus both with and without fixating on the target in the middle. What happens under each viewing condition? Why?

Three effects may become apparent when you fixate
1. The magenta/lilac spots appear to be chased by a greenish spot
negative color afterimages

2. The magenta/lilac appearing spots disappear

3. Is this a Troxler fading effect?
integration of coherent or patterned stimulus changes
apparent movement phenomenon (is the illusion beta or phi movement?)

Use the controls to change the:
color appearances
observe that the complementary color appearance to red is not green but blue-green
saturation
speed

Write a 5 or more page paper in which you:
Provide a detailed description of the physical attributes of the stimuli and viewing conditions

You can use a paint program to identify the RGB values used to produce the discs.

What is the viewing distance? Do the effects change with viewing distances?

Provide a detailed description of your experiences and how those correspond to and differ from physical attributes
Discuss why Bach calls the color aftereffect a negative retinal aftereffect
Does the aftereffect transfer between eyes and thereby indicate a cortical rather than retinal effect?

What experiential differences result when you use:
color appearance control
saturation control
speed control

What do the differences in experiences say about how you are built to respond?

Discuss the implications of:
seeing the color aftereffect when you fixate on the X and not seeing the color aftereffect when you don’t fixate
the aftereffect having a predictable relationship to the inducing stimulus color appearance (e.g. magenta appearing stimulus induces greenish appearing aftereffect)

Present and discuss how the color aftereffects influenced Hering’s conclusions about the structure of our visual systems

Relate the aftereffects to R+G-, R-G+, B+Y-, and B-Y+ neural channels in color opponent process theory
the color aftereffect continuing to appear even when the inducing stimulus isn’t seen
the faded blobs reappear when the eye(s) are moved even slghtly
What is necessary to experience an aftereffect?
try monocular and binocular viewing. What happens? What are the implications?
when the inducing stimulus appears magenta/lilac and the background appears white, the green appearing aftereffect occurs, but when the background appears black, the green appearing aftereffect doesn’t occur €¦ Why is stimulation necessary for an aftereffect to occur and what does the experience of the aftereffect from the stimulation tell us? €¦ What happens with various color appearance backgrounds?
Read the Zaidi et al. article that you can find in the at https://www.uic.edu/depts/vpl/reprints/QasimCurrBio2012.pdf. What does the article help us to understand about the Lilac Chaser?