Visualizing Visual Adaptation

Summary

This article describes a novel method for simulating and studying adaptation in the visual system.

Abstract

Many techniques have been developed to visualize how an image would appear to an individual with a different visual sensitivity: e.g., because of optical or age differences, or a color deficiency or disease. This protocol describes a technique for incorporating sensory adaptation into the simulations. The protocol is illustrated with the example of color vision, but is generally applicable to any form of visual adaptation. The protocol uses a simple model of human color vision based on standard and plausible assumptions about the retinal and cortical mechanisms encoding color and how these adjust their sensitivity to both the average color and range of color in the prevailing stimulus. The gains of the mechanisms are adapted so that their mean response under one context is equated for a different context. The simulations help reveal the theoretical limits of adaptation and generate "adapted images" that are optimally matched to a specific environment or observer. They also provide a common metric for exploring the effects of adaptation within different observers or different environments. Characterizing visual perception and performance with these images provides a novel tool for studying the functions and consequences of long-term adaptation in vision or other sensory systems.

Introduction

What might the world look like to others, or to ourselves as we change? Answers to these questions are fundamentally important for understanding the nature and mechanisms of perception and the consequences of both normal and clinical variations in sensory coding. A wide variety of techniques and approaches have been developed to simulate how images might appear to individuals with different visual sensitivities. For example, these include simulations of the colors that can be discriminated by different types of color deficiencies^1,2,3,4, the....

Protocol

NOTE: The protocol illustrated uses a program that allows one to select images and then adapt them using options selected by different drop-down menus.

1. Select the Image to Adapt

1. Click on the image and browse for the filename of the image to work with. Observe the original image in the upper left pane.

2. Specify the Stimulus and the Observer

1. Click the "format" menu to choose how to represent the image and the observer.
2. Click on the "standard observer" option to model a standard or average observer adapting to a specific color distribution. In this case, ....

Results

Figures 2 - 4 illustrate the adaptation simulations for changes in the observer or the environment. Figure 2 compares the predicted appearance of Cezanne's Still Life with Apples for a younger and older observer who differ only in the density of the lens pigment²⁸. The original image as seen through the younger eye (Figure 2a) appears much yellower and dimmer through the more densely pigmented lens (

Discussion

The illustrated protocol demonstrates how the effects of adaptation to a change in the environment or the observer can be portrayed in images. The form this portrayal takes will depend on the assumptions made for the model — for example, how color is encoded, and how the encoding mechanisms respond and adapt. Thus the most important step is deciding on the model for color vision — for example what the properties of the hypothesized channels are, and how they are assumed to adapt. The other important steps are.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Computer
Images to adapt
Programming language (e.g., Visual Basic or Matlab)
Program for processing the images
Observer spectral sensitivities (for applications involving observer-specific adaptation)
Device emmission spectra (for device-dependent applications)