Midterm 2 perception

Action affordance

A response to an object that involves both its affordance (what it is for) and the action associated with it.

Action-specific perception hypothesis

Hypothesis that people perceive their environment in terms of their ability to act on it.

Affordances

The information specified by a stimulus pattern that indicates how the stimulus can be used. An example of an affordance would be seeing a chair as something to sit on or a flight of stairs as something to climb.They guide behaviors and interactions with objects.

Audiovisual mirror neurons

Neuron that responds to actions that produce sounds. These neurons respond when a monkey performs a hand action and when it hears the sound associated with this action. See also Mirror neuron. They are believed to play a role in understanding the intentions behind actions and in the development of social cognition.

Cognitive map

A mental map of the spatial layout of an area of the environment. It allows individuals to navigate and understand their surroundings, integrating various sensory information.

Ecological approach to perception

This approach focuses on specifying the information in the environment that is used for perception, emphasizing the study of moving observers to determine how their movement results in perceptual information that both creates perception and guides further movement.It highlights the relationship between perception and action, viewing perception as a dynamic process influenced by the observer's interactions with the environment.

Focus of expansion (FOE)

The point in the flow pattern caused by observer movement in which there is no expansion. According to J. J. Gibson, the focus of expansion always remains centered on the observer’s destination.It is crucial for understanding how we perceive motion and navigate through our environment.

Gradient of flow

In an optic flow pattern, a gradient is created by movement of an observer through the environment. The “gradient” refers to the fact that the optic flow is rapid in the foreground and becomes slower as distance from the observer increases. This gradient provides critical information about the speed and direction of movement, helping individuals to gauge their position relative to objects in their environment.

Grid cells

Cells in the entorhinal cortex that fire when an animal is in a particular place in the environment, and which have multiple place fields arranged in a gridlike pattern These cells are thought to contribute to spatial navigation and the understanding of an animal's position in its environment.

Invariant information

Environmental properties that do not change as the observer moves relative to an object or scene. For example, the spacing, or texture, of the elements in a homogenous texture gradient does not change as the observer moves on the gradient. The texture of the gradient therefore supplies invariant information for depth perception. This information remains constant regardless of the observer's position, aiding in the perception of spatial relationships.

Landmark

Object on a route that serves as a cue to indicate where to turn; a source of information for wayfinding.

Mirror neurons

Network of neurons hypothesized to play a role in creating mirror neurons. These neurons fire both when an individual performs an action and when they observe the same action performed by another, suggesting a role in understanding and imitating behaviors.

Mirror neuron system

Network of neurons hypothesized to play a role in creating mirror neurons. This system is involved in understanding and imitating actions by firing during both execution and observation of those actions.

Optic flow

The flow of stimuli in the environment that occurs when an observer moves relative to the environment. Forward movement causes an expanding optic flow, whereas backward movement causes a contracting optic flow. Some researchers use the term optic flow field to refer to this flow.

Parietal reach region (PRR)

A network of areas in the parietal cortex that contains neurons that are involved in reaching behavior.

Place cells

Neurons that fire only when an animal is in a certain place in the environment

Place field

Area of the environment within which a place cell fires.

Proprioception

The sensing of the position of the limbs.It provides feedback about body posture and movement, allowing for coordination and balance.

Size-weight illusion

Erroneously predicting weight when observing two differently sized objects that have the same weight. The error occurs when the perceiver predicts that larger object will be heavier, and therefore uses more force to lift it, causing it to be lifted higher and to feel lighter.

Spatial updating

Process by which people and animals keep track of their position within a surrounding environment when they move.

Visual direction strategy

A strategy used by moving observers to reach a destination by keeping their body oriented toward the target.

Visuomotor grip cells

A neuron that initially responds when a specific object is seen and then also responds as a hand grasps the same object.

Wayfinding

The process of navigating through the environment. Wayfinding involves perceiving objects in the environment, remembering objects and their relation to the overall scene, and knowing when to turn and in what direction.

Achromatic Colors

Colors such as white, gray, and black that occur when light is reflected equally across the spectrum.

Chromatic Adaptation

Prolonged exposure to chromatic color, which selectively reduces the sensitivity of cones to that color.

Chromatic Colors

Colors such as blue, green, and red, also known as hues.

Color Constancy

The perception of an object's color as being relatively constant even under changing illumination.

Color Matching

A psychophysical procedure in which observers adjust the amounts of three different wavelengths of light to match a reference color.

Color Solid

A three-dimensional space that organizes colors systematically according to their hue, saturation, and value.

Dichromacy

A form of color deficiency in which an individual has only two types of cone pigment.

Hue

The chromatic color (e.g., red, blue, green).

Illumination Edge

An edge where the lighting changes.

Ishihara Plates

Color vision test that uses stimuli consisting of a circular array of dots of slightly different colors.

Isomerization

The change in shape of the retinal part of a visual pigment molecule when it absorbs light.

Lightness Constancy

The perception of an object's lightness as being relatively constant even under changing illumination.

Memory Color

The effect of prior knowledge of the typical colors of objects on their perception.

Metamerism

The phenomenon where physically different stimuli appear identical in color.

Monochromatism

A rare form of color blindness in which an individual has no functioning cones and sees only in shades of lightness.

Neutral Point

The wavelength at which a dichromat perceives gray.

Nonspectral Colors

Colors that do not appear in the spectrum because they are mixtures of other colors, such as magenta.

Opponent Neurons

Neurons that respond with an excitatory response to light from one part of the spectrum and with an inhibitory response to light from another part.

Penumbra

The fuzzy border at the edge of a shadow.

Reflectance Edge

An edge where the reflectance of two surfaces changes.

Reflectance Curve

A plot of the percentage of light reflected from an object at each wavelength in the visible spectrum.

Saturation

The intensity or purity of a color.

Selective Reflection

The process by which chromatic colors are created when some wavelengths are reflected more than others.

Selective Transmission

The process by which the color of transparent objects is created when only some wavelengths pass through the object.

Spectral Colors

Colors that appear in the visible spectrum, such as red, orange, yellow, green, blue, indigo, and violet.

Transmission Curve

Plots of the percentage of light transmitted at each wavelength.

Trichromacy of Color Vision

The idea that color vision depends on the activity of three different receptor mechanisms.

Univariance

Once a photon of light is absorbed by a visual pigment molecule, the identity of the light's wavelength is lost.

Value (Lightness)

The light-to-dark dimension of color.

Wavelengths

Different colors correspond to specific wavelengths of light: violet (400-450 nm), blue (450-490 nm), green (500-575 nm), yellow (575-590 nm), orange (590-620 nm), and red (620-700 nm).

Reflectance

The property that determines which wavelengths an opaque object reflects, creating its perceived color.

Selective Reflection

Occurs when an object reflects some wavelengths more than others, resulting in chromatic colors.

Selective Transmission

The process where only certain wavelengths pass through a transparent object.

Subtractive Color Mixing

Mixing paints where absorption of wavelengths occurs. For example, when yellow and blue paints mix, they absorb most wavelengths except green.

Additive Color Mixing

Mixing lights where wavelengths are reflected. Combining blue and yellow lights results in the perception of white.

Hue

Commonly referred to as 'color,' representing distinct colors such as red, blue, and green.

Saturation

Describes the intensity or purity of a color. Desaturated colors appear faded or washed out.

Value (Lightness)

The light-to-dark dimension of color that describes how light or dark a color appears.

Cone Receptors

There are three types of cone receptors in the eye: S cones (maximal absorption at 419 nm), M cones (531 nm), and L cones (558 nm).

Metamerism

A phenomenon where two physically different stimuli appear identical in color because they produce the same response in cone receptors.

Opponent-Process Theory

A theory suggesting that color vision is based on opposing color pairs: red-green and blue-yellow.

Color Constancy

The perception of colors as stable and relatively constant despite changes in illumination.

Chromatic Adaptation

The phenomenon where prolonged exposure to a chromatic color alters color perception by reducing sensitivity to that color.

Memory Color

The influence of prior knowledge about typical colors of objects on color perception.

Color Perception

The experience of color created by the brain's response to different wavelengths of colorless light.

Chromatic Adaptation

The eye adjusts its sensitivity to different wavelengths to maintain approximately constant color perception as illumination changes, allowing novel colors to stand out.

Memory Color

Knowledge of the typical colors of objects influences color perception, making familiar objects appear richer and more saturated compared to unfamiliar ones.

Taking Illumination into Account

Color constancy is enhanced when an object is surrounded by various colors, allowing the visual system to estimate illumination characteristics and make corrections.

Lightness Constancy

Achromatic colors are perceived as remaining consistent in shade under varying illumination, with perception based on reflectance rather than light intensity.

Ratio Principle

The perceived lightness of an object depends on the ratio of its reflectance to the reflectance of surrounding objects when evenly illuminated.

Information in Shadows

The visual system distinguishes between reflectance edges and illumination edges by taking uneven illumination from shadows into account; the penumbra indicates a shadow's border.

Opponent-Process Theory

A theory suggesting that color perception is based on opposing color pairs: red-green and blue-yellow.

Core Idea of Opponent-Process Theory

Color perception is structured by pairs of colors that have opposite responses.

Chromatic Color Pairs

The primary pairs are red-green and blue-yellow, while black and white represent an achromatic pair.

Hering's Color Circle

A visual representation where similar colors are arranged together, and opposing colors cancel each other out to create white or gray.

Hue Cancellation Experiments

Experiments measuring how much of one color is needed to cancel out the perception of another color, confirming the strength of color mechanisms.

Physiological Evidence for Opponent-Process Theory

Opponents neurons react with excitation to one part of the spectrum and inhibition to another, supporting the theory's validity.

Receptive Field Layouts

The configurations of opponent neurons, which include circular single opponent, circular double opponent, and side-by-side single opponent.

Neural Circuits in Color Vision

Opponent neurons are formed through the inputs from L-cones, M-cones, and S-cones, creating excitatory and inhibitory responses.

Initial Challenges to Opponent-Process Theory

Challenges included the prominence of Helmholtz's trichromatic theory, lack of quantitative data, and absence of known neural mechanisms for opposing responses.

Support for Opponent-Process Theory

Results from hue-cancellation experiments and the identification of opponent neurons bolster Hering's theory of color perception.

Trichromacy of Color Vision

The principle that color perception is based on the activity of three receptor mechanisms in the eye.

Young-Helmholtz Theory

The theory proposed by Thomas Young and expanded by Hermann von Helmholtz that suggests color vision relies on three primary colors.

Color Matching Experiments

Tests that demonstrate how individuals with normal color vision can match any wavelength of color by combining at least three different wavelengths of light.

Short-wavelength (S) Cones

Cone receptors in the human retina that absorb maximally at approximately 419 nm, crucial for perceiving blue colors.

Middle-wavelength (M) Cones

Cone receptors that have a peak absorption at around 531 nm, important for perceiving green colors.

Long-wavelength (L) Cones

Cone receptors that absorb maximally at about 558 nm, essential for perceiving red colors.

Microspectrophotometry

A technique that confirmed the existence of three types of cone cells in the human retina, each with unique absorption spectra.

Metamerism

The phenomenon where two different stimuli are perceived as identical in color due to producing the same response in the three cone receptors.

Monochromacy

A type of color vision deficiency where only one type of cone pigment is present, allowing perception only in shades of gray.

Dichromacy

A color vision deficiency characterized by two types of cone pigments, leading to confusion between certain colors, requiring only two wavelengths for color matching.

Distributed Processing in Color Perception

Color processing occurs across several cortical areas rather than a single 'color center', allowing for complex interactions among different types of visual information.

Location of Color Areas

Color-responsive areas are located near regions responsible for face and place processing, specifically sandwiched between these areas to facilitate interactions.

Independence of Shape and Color Processing

Studies of brain damage show that shape and color are processed independently, demonstrated by 'double dissociation' cases such as patient D.F., who had color perception intact but impaired object recognition.

Relationship of Color to Face and Place Processing

Despite independent processing, color, face, and place areas are closely adjacent in the brain, which may explain why many patients with color blindness also experience difficulties with face recognition.

Role of Color in Perceptual Processes

Color influences perceptual organization, attention, and motion perception, highlighting its importance beyond mere visual experience.