Week 11 Tapping parallel pathways & stages

Question 1

What are the two elements of using behavioural studies to tap parallel pathways and processes?

Answer 1

1. Behavioural study as a proxy for processing in these areas
2. Performance of stimulus is not the goal, it is to investigate areas

Question 2

Why is the description of being motion blind inaccurate?

Answer 2

To be completely blind to motion, other aspects of vision would also be impaired, since motion processing first occurs in V1. You cannot have a level of selectivity to be completely blind to motion due to the level that occurs in V1

Question 3

What are the 2 ways that we can test to see if motion system is blind?

Answer 3

Traditional Ishihara = the luminance is randomly assigned/no systematic between number and background, number is defined purely within colour

Isoluminance approach - make luminance the same and see if motion processing works

Question 4

How does the Traditional Ishihara test work to test if motion system is blind?

Answer 4

The luminance is randomly assigned - the number is defined purely within colour

Has both luminance and colour info in a stimulus

The system has to rely on colour information and not changes in luminance to discriminate the number vs. the background.

Question 5

What is the Isoluminance approach?

Answer 5

1. Aim Make luminance the same but colour different - and see if motion processing works

Use red dot on a green background and match in luminance contrast

if you can’t do the task, i.e. see luminance changes in motion, this means that motion processing is mediated by a colour blind system.

Question 6

What is the aim of the new Ishihara approach?

Answer 6

1. To keep luminance the same but arrange luminance so it doesn’t result in a percept of depth percept for motion, by adding noise to the isoluminance, so the background is covered in dots of different luminance levels

Question 7

What are the findings of the new Ishihara approach?

Answer 7

1. People cannot do motion processing in achromatic condition,
   but can do it in the chromatic/colour condition

If system is colour blind = you should be able to do both tasks

Shows that MS is not colour blind since you can only combine the stimuli at T1 and T2 in the chromatic condition - we are not using isoluminance we are using both isoluminance and also colour

Question 8

So is the motion system colour-blind?

Answer 8

The motion system is not colour blind, ie. studies show we use both m and p cells and double duty cells that are sensitive to both luminance and colour

Question 9

What 2 designs do we use to test form processing/recognition in the ventral pathway?

Answer 9

1. Static Glass patterns - identity the global pattern over the noise dots in two alternative forced choice
   What is the minimum number of signal elements you need to perceive the global pattern?
2. Contour integration
   Extract the overall shape of the object from the smoothness of the contour in a sea of mess

Question 10

What 2 designs do we use to test form processing/recognition in the ventral pathway?

Answer 10

1. Global motion stimulus - signal strength - What are the minimum no. of dots moving in the signal direction needed to determine the global motion? (normally about 10-15, ie. evolved to solve the aperture problem)
2. Global gabor stimulus - looking at complex issues of motion pooling with spatial frequency tuning