Visual associative memory
simulates the McCollough effect

Paul V. Maximov and Vadim V. Maximov

Institute for Problems of Information Transmission,
Russian Academy of Sciences, 101447 Moscow, Russia


A paper version of the poster was presented
at the 20th European Conference on Visual Perception
(Helsinki, Finland, 24-29 August, 1997)
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The McCollough effect
Adaptation

Look at the two coloured grids below for a few minutes, shifting your gaze from one grid to another from time to time. There is no need to stare at single point on a grid. Do not change a viewing distance significantly.

Vertical red grid Horizontal green grid

Testing

Originally the patterns below look as achromatic. After the inspection of two adapting chromatic grids displayed above, similarly oriented black-and-white test gratings appear tinted with complementary colours.

1st test grid 2nd test grid

Introduction

The orientation-contingent colour aftereffect, or the McCollough effect (ME) refers to the phenomenon that, after a few minutes' exposure to gratings differing in both orientation and colour, subjects perceive similarly oriented achromatic gratings as if they were tinted with complementary hues. The traditional explanation of the ME as an adaptation of detectors selective for colour and orientation suffers from a number of inconsistencies: Novelty filter These properties can be explained, however, in the framework of an associative memory and novelty filters. It is supposed that in the course of "adaptation" the colour grid patterns are stored in the memory. When testing with an achromatic grid, the associative image of the grid with same orientation is recalled from the memory and subtracted from the input image, leaving in the resulting image only novel feature, namely, a complementary colour of the grid.

The Model

A computational model of novelty filter has been developed which consists of
Model
Modification of synaptic efficacies wij conforms to the following rule: wijt+1 = wijt + exjtzit , where e is some constant, describing the synaptic plasticity.

Results


One-eyed version. Temporal properties

Random stimulation Adaptation to colour grids Random stimulation Stimulation by achromatic grids
Random stimuli Colour grids Random stimuli Achromatic grids
Time course
Time courses of the McCollough effect in the model during (1) an adaptation to alternating colour grids and (2) a subsequent desadaptation with random stimuli or (3) a clearing off the effect with black-and-white test grids. Before the adaptation the model was subjected to random stimulation (0).
The rate of decay in the case of tests with specific stimuli (3) is 20 times that of the random desadaptation (2).

Receptive fields structure

There are no predetermined specific detectors selective to orientation and colour in the model. Associative neurons with the properties of such detectors appear after adaptation to coloured grids.
Receptive fields structure
RF structure of a 'red' associative neuron after 1000 steps of adaptation to red vertical and green horizontal grids. RF structure of a 'green' associative neuron after the same adaptation.
The height of the bars represents the synaptic weight w of the contacts of the neuron with corresponding receptors. Inhibitory contacts are shown with bars oriented downwards.
Note the striped structure of the RFs: the red neuron makes vertically oriented excitatory zones with red receptors and random connections with green ones, and vice versa, the green neuron makes horizontally oriented zones with green receptors.

Spatial-frequency-contingent colour after-effect

Colour grids Besides the ordinary McCollough effect a spatial-frequency-contingent colour after-effect can be produced in the model by adaptation to coloured grids of the same orientation but differing in spatial frequency.
Receptive fields structure
RF structures of 'red' and 'green' associative neurons after 1000 steps of adaptation to close red and sparse green vertical grids.
In contrast to the ordinary ME here the green neuron makes broad alternating excitatory and inhibitory zones of contacts with green receptors oriented vertically.

Two-eyed version. Lack of the interocular transfer

In the model, in spite of the inherent connection of the associative neurons with both eyes
Random stimulation Adaptation to colour grids
(left eye occluded)
Adaptation to colour grids
(right eye occluded)
Random stimulation
left eye right eye
Random stimuli Random stimuli
left eye right eye
Black vertical red, horizontal green
left eye right eye
vertical green, horizontal red Black
left eye right eye
Random stimuli Random stimuli
Two-eyed version. Time course.

Independent decays of the ME in the eyes

Random stimulation Random stimulation
(left eye occluded)
Random stimulation
left eye right eye
Random stimuli Random stimuli
left eye right eye
Black Random stimuli
left eye right eye
Random stimuli Random stimuli
Independent decays

In the model, random stimulation of eyes causes nearly exponential decay of the ME that is completely arrested by occlusion of an eye.


Disparity-contingent colour after-effect

left eye right eye
Colour grids
In spite of the apparent independence of two eyes a specific binocular after-effect can be produced in the model by adaptation to coloured grids of the same orientation but differing in disparity.
Receptive fields structure
RF structure of a left-eye 'green' associative neuron after 1000 steps of adaptation to red and green vertical grids differing in disparity (as shown abowe right). The neuron makes alternating excitatory and inhibitory zones of contacts with green receptors of both eyes and random contacts with red receptors.
left eye right eye
Achromatic grid Achromatic grid This black-and-white test stimulus will 'look' green for the model after the adaptation.

left eye right eye
Achromatic grid Achromatic grid This black-and-white test stimulus will 'look' red for the model after the adaptation.

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Last Update: 23 February, 1999