VISION ADAPTATION & INDUCTION

• The nature, intensity, duration of the stimulating light

• Of the subsequent light

• The condition of the retina, as to its state of adaptation

• The particular region of the retina stimulated and its extent

• The stimulation of other parts of the retina

factors influencing

vision adaptation

and induction

VISION ADAPTATION

Gradual adjustment to a constant or changing light environment.

1.Stimulus Intensity and Abruptness, 2.Environmental Changes.

KEY POINTS ABOUT ADAPTATION

• Brightness adaptation

• Color adaptation

TYPES OF ADAPTATION

BRIGHTNESS ADAPTATION

This process allows the human visual system to adjust its sensitivity to varying light levels, enabling clear vision in both bright and dim environments. It involves rapid adjustments in pupil size and slower changes in photoreceptor sensitivity, optimizing vision across a wide range of luminance conditions

Driving on a dim highway at night with occasional oncoming headlights.

example of brightness adaptation

adaptation

In ______, however, we attain a stationary condition which may continue, with a given stimulus, for a long time.

adaptation

In _____, however, this is not due to previous work (as in fatigue) but to the adjustment of the protoplasm to a new and now steady state of the environment. This state has been called minothesis (minor, less; thesis, a placing).

fatigue

In ____ the condition is progressive, i.e., the longer the activity, the greater the _____

fatigue

in ____ there is a reduction in sensitivity due to its previous work.

Adaptation: Headlights cause temporary "blinding." Pupils constrict, retina adjusts, vision recovers.

Fatigue: Hours of driving lead to slowed reactions, blurry vision, and the need for rest due to constant visual processing.

Scenario: Driving on a dark highway at night with occasional oncoming headlights.

Adaptation: Initial blue tint lessens after 10-15 minutes. Colors appear more normal, allowing comfortable reading.

Fatigue causes increasing eye strain, difficulty focusing, headaches. Adaptation allows a stable visual state, whereas fatigue progressively worsens.

Scenario: Imagine you are reading a book under a strong blue light for an extended period.

COLOR ADAPTATION

This refers to the visual system's ability to adjust to the color content of a scene. Prolonged exposure to a particular color can lead to a decrease in sensitivity to that color and an increased sensitivity to other colors.

Red paper on white field

example of color adaptation

• Prioritizes Detection of Change

• Enables Efficient Processing of Diverse Stimuli

• Prevents Overstimulation

• Increases Sensitivity to New Stimuli

• Facilitates Rapid Information Processing

VALUE OF RETINAL ADAPTATION

VISION INDUCTION

The influence of prior light exposure and adaptation on the perception of a subsequent visual stimulus, resulting in after-images and altered color perception.

• Positive After-image

• Negative After-image

• Induced Colored After-image

(3) After-images

positive

A ___ after-image is what you see when you look at a bright light for about half a second and then close your eyes or shield them from light. The after-image appears in the same color as the original light and can vary in brightness and how long it lasts.

Growth of stimulation

When you briefly look at a bright light, the photoreceptors are highly activated, leading to a strong neural response. This initial activation corresponds to the "_____ ____ _______" phase—where the photoreceptors experience a surge in activity and send signals to your brain.

Decay of stimulation

Once you remove the light source (by closing your eyes or looking away), the photoreceptors and neural pathways begin to "___ _____ ______" or return to their resting state. However, this recovery process isn't instant, which leads to the lingering positive after-image.

"blind spot" (scotoma)

THE FLIGHT OF COLORS: When you look at a very bright light, like the setting sun, and then look away, the lingering after-image can change colors and include dark gaps in between. The order of the colors depends on how bright the light is and how long you look at it, so it doesn’t follow an exact pattern. However, for strong white light, the after-image often starts as blue, then shifts to yellow, green, red, and bluish-green. This process might even result in a temporary ___ ____ _____ ______.

blue, green, crimson

According to McDougall, a short burst of bright white light first appears as white in the after-image, but quickly transitions to ___, ___, and ____.

red-green, blue-yellow, black-white

Opponent-Process Theory:

Color perception is influenced by opposing color pairs: _____, ____, and _____. When one part of a pair is overstimulated, the other part can become dominant as the brain tries to balance the signal.

red, green

Opponent-Process Theory:

Initially, blue may dominate because the ___ and ____ cones are more fatigued, leaving the signal from the blue sensitive cones stronger.

yellow

Opponent-Process Theory:

Then, ___ may appear, as it is the opponent of blue and arises as the blue-sensitive cones recover and balance out.

Bright white light

contains all wavelengths of visible light.

perceived intensity of the after-image

The dark intervals you notice between color phases are moments when all cone signals briefly balance out or remain suppressed, reducing the _____________________.

the brain integrates all inputs dynamically

Neurological processing:

The transitions between colors may not be perfectly linear because __________, which can lead to seemingly spontaneous changes in after-image colors.

Successive Contrast, Temporal Induction, or Negative After-images

occur when light affects the way we see things after the initial exposure

Positive after-images

happen because the retina remains excited from the first light, while negative after-images occur when the retina becomes temporarily less sensitive to stimulation where the first light was focused. Meanwhile, other parts of the retina, like those that were exposed to the black background, stay highly sensitive. That’s why the contrast between the black square and white background looks stronger in the negative after-image.

Induced colored after-images

happen when either the first light (primary) or the second light (secondary), or both, are colored.

colored, white, opposite

If the primary light is ___ and the secondary light is ___, the after-image will show the color ___ to the primary light.

colored

When both the primary and secondary lights are ____, their effect changes.

primary

If the secondary light isn’t the same or opposite of the primary light, the ____ light still influences how you see it.

• Relation between Positive and Negative After-images

• Binocular Effect

• Effect of Eye Movement

• Cause of After-images

(4) IMPORTANT CONSIDERATIONS

original, reversed or complementary colors

Relation between Positive and Negative After-images

Positive and negative after-images may seem completely opposite since one shows the same colors as the ____light, while the other shows _________. However, they are closely connected and can even appear one after the other under certain conditions.

McDougall

Binocular effect:

_____ discovered that after-images in one eye can affect the other eye.

Binocular Effect

For example, if the right eye is exposed to bright light for 30 seconds and then both eyes are covered completely to block out all light, the positive after-image in the right eye fades away. If a small amount of light is allowed through the left eyelid for two seconds, it brings back the positive afterimage in the right eye for about five seconds.

sudden eye movements, focusing on different distances (accommodation), blinking

After-images seem to form in the retina, which is the light-sensitive layer at the back of the eye. Certain actions like ______, ________, or ____ can disrupt or stop these after-images from forming. However, if you move your eyes gently while looking at an after-image, the image will move along with your eyes.

retina adjusts its sensitivity to the light it has been exposed to

Negative after-images happen because the _________. This adjustment was once thought to be caused by "fatigue, " but evidence disproves this.

adaptive normalization

The retina is constantly adjusting its sensitivity to light and color—this is called ______. When you stare at a color for an extended period, the retina and higher visual pathways adapt to the incoming signals, effectively recalibrating themselves. This recalibration makes the originally exposed cone cells' signals relatively weaker when you look away, shifting the balance in favor of signals from the other cone types.

• Brightness Contrast

• Chromatic Contrast

• Border Contrast

• Surface Contrast or Induction

• Colored Shadows

• Irradiation

SIMULTANEOUS CONTRAST: SPATIAL INDUCTION (6) factors

Brightness contrast

_____ happens when the way we see one part of an image is influenced by the areas around it.

simultaneous contrast, spatial induction

This effect, where the stimulation of one part of the retina affects how we see the neighboring areas, is called ______ or _____.

Chromatic contrast

occurs when the color of a background influences how we perceive the colors placed on it. One of the simplest and easiest ways is that of Meyer.

The color of the background

_______ is the inducing color; that which it gives rise to is called the induced color. The induced color is therefore complementary, at least approximately so, to the inducing color.

Spatial induction

happens most strongly at the edges where two different colors meet, which is why it’s also called border contrast. If you add a black or white line between the two colors or move them farther apart, the effect becomes weaker or disappears.

similar texture, light intensity, strong color saturation

Border contrast:

For the best results, the test area (where the effect is observed) should be small, and the inducing area (the surrounding color) should be large and completely cover the test area. Both colors influence each other, but the effect is usually stronger in the smaller area. Factors like _____, ______, and _____ help enhance the effect.

Surface Contrast or Induction

This happens when colors next to each other influence how we see them. For example, if you place a large blue sheet next to a white sheet and focus on the edge, the white area starts to look bluish while the blue area appears more whitish. Over time, both areas might even look the same. Instead of creating complementary colors, the blue makes the white look blue too. If you use blue and red areas instead, their colors combine to create violet.

mutual induction

This effect, called _______, happens more quickly in the outer parts of the retina than in the center (fovea).

color-blind

Interestingly, the outer parts of the retina respond so quickly to induction that they are sometimes considered "______. "

green, red, blue, yellow

surface contrast or induction:

Research also shows that some colors are affected differently, with ____ disappearing first, followed by ____, then ___ and ____. These differences are thought to be due to adaptation and induction.

colored shadow experiment

The ________ demonstrates how light and colors interact to create fascinating effects.

Irradiation

happens when brightly lit objects look bigger than darker ones, even if they are the same size.

Irradiation

This effect is more noticeable with higher light intensity and smaller objects.

• Hering’s Theory

• Opponent-Process theory

• Sherrington’s Perspective

• Haldane’s Perspective

THEORIES & PERSPECTIVES