640 likes | 677 Vues
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
E N D
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.
1 2 3 4 5 6 7 8 9 10 11 12
1 2 3 4 5 6 7 8 9 10 11 12
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 images: Red Green Green Red Blue Yellow Yellow Blue R G B Y Color perception
R B Y G adaptation adaptation After image After image
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.
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. 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 • Looking for the target • 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
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.