Binding problems and feature integration theory. Feature detectors Neurons that fire to specific...

Binding problems and feature integration theory

Feature detectors

• Neurons that fire to specific features of a stimulus

• Pathway away from retina shows neurons that fire to more complex stimuli

• Cells that are feature detectors:– Simple cortical cell– Complex cortical cell– End-stopped cortical cell

Single cell recording of neurons in the temporal lobe

An electrode is inserted in this area, and measure neural responses when stimuli are changed gradually

Neurons in this area respond to complex stimuli like those shown on the left.

Selective adaptation

Selective adaptation to size

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Figure 3.30 How neurons that respond best to narrow (N), medium (M), and wide (W) bars respond to the medium-bar grating on the right of Figure 3.28. (a-b): Response before adaptation. (c) Response after adaptation to the wide-bar grating at the top left. (d) Response after adaptation to the narrow-bar grating on the bottom left.

After Image

After images:

Red Green

Green Red

Blue Yellow

Yellow Blue

R G B Y

Color perception

R G B Yadaptation

adaptation

After image After image

Binding problem

Two visual pathways (what & where/how systems)

Image from Neuroscience, 2nd Ed. (2000).

Columnar organization

• Neurons that respond to the same orientation are packed in the same column

Image courtesy of Dr. Paul Wellman and Neuroscience, 2nd Ed. (2000).

Distributed coding; then what do you need?

Combining input

• Feature integration theory by Treisman & Gelade– Attention plays a central role in solving the

binding problem.– Attention helps organize information.

Attention and Figure-ground segregation

Depending on where you look at, the figure and the ground switch rapidly.

Attention plays some role in determining the figure and the ground.

Attention and 3D structure

Depending on where to look at, you get different 3D structures.

Damage to the parietal lobe creates binding errors.

Copies of the black (A) and

the white (B) vertical contour.

Copies of the black (A) and

the white (B) diagonal contour.

Copies of the left sub-figure (A)

The right subfigure (B)

And the central sub-figure (C)

Feature integration theory

• Attention is the “glue” that combines the information from the what and where systems.

What can you predict from this theory?

• If you can’t attend, you can’t combine information.

Illusionary conjunction

Demonstration• I will show you a scene quickly.

• Report first the black numbers.

• Report what you see at each of the 4 locations.

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Mask

+++++

• Report first the black numbers.

• Report what you saw at each of the 4 locations.

Illusionary conjunctions

• We tend to put different features from different objects together.

• Some brain damaged patients (parietal lobe) show illusionary conjunctions even when the patients were allowed to view the stimuli for 10 seconds.

Visual search experiments

• Feature search– This is easy because you

find the target by looking for a single feature.

you don’t need attention

• Conjunction search– For this you need to combine

two or more features (color and orientation)

you need attention

• Looking for the target

• Conjunction search– For this you need to

combine two or more features (color and orientation)

you need attention

– Because you can attend an item one at a time, the difficulty in the conjunction search increases proportional to the number of items in the stimulus frame.

– This is not the case in the feature search.

Find Which is more difficult?

Find Which is more difficult?

Feature binding and attention (Treisman, 1988)

Experiments:Task

Given a stimulus frame containing visual items, subjects were asked to indicate whether or not a target item was present in the frame.

Target:

Target:

Target:

Target:

Feature search vs. conjunction search

• Feature search– The target item has a unique feature.

• Conjunction search– You need to combine features to find the target.– You need attention.– Because you can attend only one item at a time,

the conjunction search becomes more difficult when more items are in the stimulus frame.

Generality of the results:

Feature search Conjunction search

Experiments:

• Measure accuracy and response times (conjunction cases vs. non-conjunction cases)

Response time

# of distractors

1000 ms

500ms

Response time

# of distractors

1000 ms

500ms

The physiology of attention

• How do you combine features?

• Synchrony hypothesis• When neurons in different parts of the cortex are

firing to the same object, the pattern of firing is synchronized (they fire at the same time, and in the same manner).

• So when neurons are firing in synchrony, the corresponding features are bound together.

• Separate neurons respond to color (green, blue, white), contours (orientations), textures, so on.

• Synchrony hypothesis: – When the features come from

the same object (i.e., the woman), these neurons fire at the same time in the same manner.

– When the neurons fire at the same time and in the same manner, we perceive “binding” of features.

• Attention is likely to increase synchrony

Attention

• Selecting information

• Enhancing information

• Combining information