Grip study

Question 1

Ebbinghaus illusion

Answer 1

Perceptually different, physically identical. Used to test vision for action versus perception by studying grip aperture.

When perceptually identical, one is actually bigger. In a trial, when asked, respondents will say; equal, but the grip aperture DOES go to the right size. Not fooled by perceptual input

• Perception suffers from the illusion
• Visually guided action does not

Question 2

Size-contrast illusion

Answer 2

Size-contrast illusion is similar, dot seems smaller if next to bigger object. Again, fingers were not fooled.

BUT if the stimuli disappeared and response was delayed, they did observe difference in grasp. The perceptual illusion influenced the action

The memory delay causes size contrast illusion

Question 3

Possible explanation

Answer 3

At short distance, we use stereopsis/disparity to judge distance/size. At longer distance there’s no difference in images between the two eyes so you don’t use disparity.

Use of monocular depth cues causes you to see it larger/smaller. They’re very context dependent like what you do when looking in the distance.

• Also; objects in the distance are not dealt with immediately, but after some delay. So if you use this info you’ll be fooled.