2) Perception II

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Questions and Answers

What is the primary range of wavelengths for visible light?

300-500nm

700-900nm

400-700nm (correct)

100-300nm

What is the term used to describe the number of photons per unit space that contributes to the perception of brightness?

Illumination

Chrominance

Luminance (correct)

Intensity

Which of the following describes a way light interacts with the environment?

Diffusion through surfaces

Transmission passing through opaque surfaces

Absorption by transparent materials

Reflection striking opaque surfaces (correct)

How are brightness and color best described, according to the content?

As perceptual properties Signup and view all the answers

Which factor does NOT influence the perception of brightness?

Shape of the object Signup and view all the answers

What does colour constancy refer to in visual perception?

The maintenance of perceived color despite changes in light intensity Signup and view all the answers

Which part of the visual system is primarily responsible for converting light into electrical signals?

Photoreceptors Signup and view all the answers

What factors influence the perception of brightness?

Both bottom-up and top-down factors including environmental knowledge Signup and view all the answers

How does lateral inhibition contribute to vision?

It improves the contrast of visual signals in the retina Signup and view all the answers

What is the main role of the optic nerve in the visual system?

To relay visual signals from the retina to the visual cortex Signup and view all the answers

What color of objects reflects longer wavelengths of light?

Red Signup and view all the answers

Where are rods primarily located in the human eye?

In the peripheral retina Signup and view all the answers

Which statement about cones is true?

They contain three different photopigments. Signup and view all the answers

What is the first structure that visual information passes through after the retina?

Optic nerve Signup and view all the answers

Which process affects brightness perception that involves the eye's immediate response to light?

Bottom-up processing Signup and view all the answers

What kind of light levels do rods require to operate effectively?

Low light levels Signup and view all the answers

What is the role of retinal ganglion cells in the visual pathway?

They transmit signals to the optic nerve. Signup and view all the answers

How does the brain influence perceived brightness alongside light intensity?

It compares brightness to previous stimuli. Signup and view all the answers

What can cause errors in 2D images representing 3D scenes?

Interactions of light with 3D objects Signup and view all the answers

Which condition describes an individual with complete color blindness?

Monochromacy Signup and view all the answers

How does the perception of color result from cone photoreceptors?

Through a combination of excitatory and inhibitory inputs Signup and view all the answers

Which photopigment is found in rod photoreceptors?

Rhodopsin Signup and view all the answers

What is the primary effect observed in negative afterimages?

A specific color's absence creates the illusion of its complementary color Signup and view all the answers

Which type of cone is predominantly sensitive to short wavelengths?

S-cones Signup and view all the answers

What visual phenomenon is characterized by the perception of grey spots due to inhibition from surrounding areas?

Illusory gray spots Signup and view all the answers

Which type of color perception deficiency allows for only two functioning cone types?

Dichromacy Signup and view all the answers

Which color perception mechanism enables distinct pathways like Red/Green and Blue/Yellow?

Color opponency Signup and view all the answers

Which condition involves a defect in one of the cone types but allows for some color perception?

Anomalous trichromacy Signup and view all the answers

What does brightness constancy refer to?

The perception of consistent brightness despite changes in illumination Signup and view all the answers

How does light/dark adaptation affect the retina?

It constantly adjusts sensitivity based on surrounding luminance. Signup and view all the answers

What is the primary role of lateral inhibition in the visual system?

To detect changes in luminance and enhance edge perception Signup and view all the answers

What phenomenon can result from light/dark adaptation under certain conditions?

Negative afterimages Signup and view all the answers

In brightness perception, what does the term 'luminance' refer to?

The amount of light reflected off an object per unit area Signup and view all the answers

What type of configuration is formed by retinal ganglion cells in relation to lateral inhibition?

Centre-surround configuration Signup and view all the answers

What visual illusion demonstrates the effects of lateral inhibition?

Hermann grid illusion Signup and view all the answers

How does the retina respond to high mean intensity light conditions?

Reduces sensitivity Signup and view all the answers

What occurs when the reflectance of an object is low, such as black text on white paper outdoors?

Less light will be perceived compared to light surfaces Signup and view all the answers

What role does contrast play in brightness perception?

It helps encode the luminance ratio of an object Signup and view all the answers

In what way do neighbouring photoreceptors affect retinal ganglion cell responses?

They provide both excitatory and inhibitory inputs Signup and view all the answers

Which of the following best explains the term 'reflectance'?

The proportion of light that an object reflects from incident light Signup and view all the answers

Study Notes

Cognitive Psychology 1 - Perception II: Brightness and Colour

The stimulus for vision is visible light, a band of energy within the electromagnetic spectrum; its wavelength (difference in peaks of the electromagnetic waves) and intensity/luminance (amount of photons).
Light can be described as consisting of small packets of energy called photons.
Light intensity/luminance is associated with brightness perception. Different wavelengths of light are associated with different colour perceptions.
Brightness and colour are perceptual properties, not physical ones.
Light interacts with the environment through absorption, reflection, and transmission.
Different materials reflect and absorb different wavelengths of light, affecting our perceptions of brightness and colour.
The human eye has a single chambered structure with a convex cornea and lens projecting an image onto the retina.
This structure enables directional sensitivity—the ability to detect the spatial structure of light rather than just its total amount.
Photoreceptors, including rods and cones, transduce light into electrical signals.

Two Types of Photoreceptors: Rods and Cones

Rods are located primarily in the peripheral retina and are sensitive to low light levels. They can detect single photons.
Cones are concentrated in the centre of the retina (fovea) and require higher light levels (daylight) and respond to light.
Cones have 3 different photopigments, each sensitive to different wavelengths of light (short, medium, and long).

The Visual Pathways

Visual information is transmitted from the retina to the brain via the optic nerve.
The pathway includes the optic chiasm, lateral geniculate nucleus (LGN), and primary visual cortex (V1).

Brightness Perception

Light intensity is linked to perceived brightness (higher intensity regions usually appear brighter).
Brightness perception is influenced by both bottom-up and top-down processes.
Bottom-up factors include: light intensity and processes like light/dark adaptation and lateral inhibition.
Top-down factors include the brain's use of knowledge about how light interacts with objects, including identifying shadows.

Brightness Perception - Light/Dark Adaptation

The retina's sensitivity is constantly adjusted to compensate for changes in mean luminance.
Sensitivity is reduced with high light intensity and increased in low light.
Light/dark adaptation refers to this process. It dictates how contrast (the ratio of object's luminance to the background/mean luminance) affects brightness perception, playing a crucial role in brightness constancy.

Brightness Perception - Negative Afterimages

Light/dark adaptation produces illusions.
For example, staring at a red object might create a green afterimage.

Brightness Perception - Lateral Inhibition

Lateral inhibition is an early information processing form in the retina.
Retinal ganglion cells receive excitatory and inhibitory input from neighboring photoreceptors (thus arranged in a centre-surround) influencing perception of edges and borders of objects.
The effect of lateral inhibition can be seen in the Hermann grid illusion.

Brightness Perception - Top-Down Influences

Visual systems use knowledge about how light interacts with three-dimensional objects to perceive brightness (e.g., shadows affecting brightness constancy).
This process can lead to perceived errors in 2D images portraying 3D scenes, such as the checker-shadow illusion.

Colour Perception

Colour is a perceptual property associated with the wavelength of light.
Normal human colour perception relies on the relative output of three types of cones (trichromacy).
Colour perception is influenced by bottom-up processing (e.g., photopigments in cones) and top-down processing (e.g., knowledge of the environment).

Colour Perception - Trichromacy

Cone photoreceptors contain one of three different photopigments, each with different wavelength sensitivities: S-cones (blue), M-cones (green), and L-cones (red).
The relative outputs of these three cone types allow for unambiguous signalling of wavelength.

Colour Perception - Variations from Trichromacy

Monochromacy: individuals with either 0 or 1 functioning cone type, resulting in complete colour blindness.
Dichromacy: individuals with only 2 functioning cone types (protanopia, deuteranopia, tritanopia).
Anomalous trichromacy: a more common form of colour perception deficiency, characterized by a defect in one of the cone types. Individuals with such differences are sometimes diagnosed using Ishihara colour tests.

Colour Perception - Opponency

Retinal ganglion cells receive excitatory and inhibitory input from different cone types, creating distinct red/green and blue/yellow pathways.

Colour Perception - Negative Afterimages

Colour opponency is demonstrated through negative afterimages (e.g., staring at red creates a green afterimage).

The "Lilac Chaser" Revisited

This illusion is a demonstration of colour perception, likely due to retinal processing and adaptation and lack of constancy.

Colour Perception - Top-Down Influences

Visual systems account for the intensity and composition of light hitting different surfaces, affecting colour perception. This can create illusions where the same wavelength of light is perceived differently due to how light interacts with and reflects on objects.

#TheDress Revisited

This phenomenon highlights individual differences in colour perception and variations in the brain's interpretation of the interplay of light reflected off objects and the surrounding light.

Summary of the Learning Objectives

Understand the stimulus for vision and basic structure of the human visual system
- Visible light is a band of energy
- Wavelength and intensity are components
- Eye structure (cornea, lens, retina, rods, cones)
Describe the factors that shape the perception of brightness
- Bottom-up: Light intensity, adaptation, lateral inhibition
- Top-down: Knowledge of environment (shadows)
Understand the principles of normal and abnormal colour perception
- Trichromacy (3 cones)
- Variations (monochromacy, dichromacy, anomalous trichromacy) and tests (Ishihara)

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Description

Explore the fascinating aspects of visual perception in this quiz. Test your knowledge on the nature of light, its interaction with the environment, and how the human visual system processes brightness and color. Dive deep into concepts like color constancy and the roles of different photoreceptors.