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Vision

Vision

Vision is the result of light being detected and transduced into neural signals by the retina of the eye. This information is then further analyzed and interpreted by the brain. First, light enters the front of the eye and is focused by the cornea and lens onto the retina—a thin sheet of neural tissue lining the back of the eye. Because of refraction through the convex lens of the eye, images are projected onto the retina upside-down and reversed.

Visual System

Visual System

Light enters the eye through the cornea, a transparent, dome-shaped surface covering the surface of the eyeball that helps to direct and focus incoming light. This light is then channeled toward the pupil, an adjustable opening whose size is controlled by the iris. The iris, a pigmented muscle, regulates the amount of light entering the eye by contracting or dilating the pupil, thereby ensuring optimal light levels for clear vision.
Once through the pupil, the light passes through the lens, a...

Color Vision

Color Vision

Color perception begins in the retina, the light-sensitive layer at the back of the eye. Two main theories explain how colors are seen: the trichromatic theory and the opponent-process theory. The trichromatic theory, proposed by Thomas Young in 1802 and extended by Hermann von Helmholtz in 1852, suggests that color vision is based on three types of cone receptors in the retina. These cones are sensitive to different but overlapping ranges of wavelengths corresponding to red, blue, and green.

Photoreceptors and Visual Pathways

Photoreceptors and Visual Pathways

At the molecular level, visual signals trigger transformations in photopigment molecules, resulting in changes in the photoreceptor cell's membrane potential. The photon's energy level is denoted by its wavelength, with each specific wavelength of visible light associated with a distinct color. The spectral range of visible light, classified as electromagnetic radiation, spans from 380 to 720 nm. Electromagnetic radiation wavelengths exceeding 720 nm fall under the infrared category,...

Focusing of Light in the Eye

Focusing of Light in the Eye

Light rays enter the eye through the cornea, a transparent dome-shaped tissue that is the eye's outermost layer. The cornea bends or refracts, light rays traveling to the pupil. The shape of the cornea determines how much of the light is bent and whether the image will be focused correctly on the retina at the back of the eye. Once the light has passed through both refraction layers, it converges into a single focal point onto a small area. This is where photoreceptors start transforming...

Anatomy of the Eyeball

Anatomy of the Eyeball

The eye is a spherical, hollow structure composed of three tissue layers. The outer layer — the fibrous tunic, comprises the sclera — a white structure — and the cornea, which is transparent. The sclera encompasses some of the ocular surface, most of which is not visible. However, the 'white of the eye' is distinctively visible in humans compared to other species. The cornea, a clear covering at the front of the eye, enables light penetration. The eye's middle...

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Related Experiment Video

Updated: Apr 28, 2026

A Method for Investigating Change Blindness in Pigeons Columba Livia

A Method for Investigating Change Blindness in Pigeons Columba Livia

Published on: September 7, 2018

Visual stimulus compounding with pigeons.

M A McDevitt¹, E Fantino

¹Department of Psychology, 0109, University of California, 9500 Gilman Drive, La Jolla, CA 92093, USA.

Behavioural Processes

|June 5, 2014

Summary

This summary is machine-generated.

Pigeons learned to respond to visual stimuli predicting rewards. Compound stimuli, when presented together, did not always produce additive effects, challenging simple models of stimulus compounding.

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Area of Science:

Behavioral psychology
Animal cognition
Visual perception

Background:

Additive models of stimulus compounding are widely used in psychology.
Previous research suggests that combining stimuli can lead to predictable changes in responding.
However, the generality of these models with complex visual stimuli needs further investigation.

Purpose of the Study:

To investigate how pigeons respond to compound visual stimuli.
To test the predictions of additive models of stimulus compounding.
To explore the effects of stimulus arrangement (superimposed vs. spatially separated) on responding.

Main Methods:

Eight pigeons were trained on color and line stimuli associated with different reinforcement likelihoods (100%, 50%, 10%).
An intertrial interval was used during training for half the birds.
Tests involved presenting superimposed and spatially separated compound stimuli.

Main Results:

Responding to superimposed compound stimuli was variable but intermediate to individual components.
Responding to spatially separated compound stimuli was intermediate or even lower than individual components.
Results indicate limitations in applying additive models to visual stimulus combinations.

Conclusions:

Additive models may not fully capture responding to complex visual stimulus compounds.
The spatial arrangement of stimuli significantly influences responding.
Further research is needed to refine models of stimulus compounding in visual perception.