Vision Final

Akinetopsia

•  A neurological condition characterized by the inability to perceive motion, often due to damage to the MT region, leading to a perception of the world in a series of still snapshots.

Aperture Problem

The ambiguity of direction signal for a straight edge when viewed through a limited aperture (or receptive field) and with limited context, causing it to appear to move orthogonally to its orientation.

Apparent Motion

•  The illusion of continuous motion created by rapidly presenting a series of still images in different positions, despite no actual continuous movement.

Corollary Discharge Theory

A theory explaining how the brain distinguishes between object motion and self-motion by comparing an "efference copy" (corollary discharge) of motor commands for eye movements with the image movement signal on the retina.

Dorsal Stream

• Also known as the "where" pathway, this hierarchical visual processing stream originates from magnocellular cells and is involved in spatial vision, including movement, spatial relations, location, and 3-D depth perception.

Direction Selectivity

The property of certain neurons (e.g., in V1 and MT) to fire only to stimuli moving in a particular direction but not others.

Emergent Property

•  In the context of motion perception, it refers to the idea that motion is not directly detected at the retina but rather emerges from cortical computations that build up extracted features into a complete perception.

Hassenstein-Reichardt Model

• A conceptual framework for how motion selectivity arises in invertebrate visual systems, proposing a circuit that uses a delay in signal transmission from one photoreceptor combined with a direct signal from an adjacent photoreceptor.

Image Movement Signal

The signal generated in the visual system due to the movement of images across the retina, which can be caused by either object motion or self-motion.

Induced Motion

• An illusion where a stationary object appears to move due to the movement of its surrounding context or background (e.g., a stationary moon appearing to move when clouds pass by).

Interblob

• Achromatic regions in V1 where magnocellular neurons project and simple cells involved in orientation and direction selectivity are found.

Isoluminant

• A condition where two different colors have the same intensity (luminance), making them appear to slow down or stop moving for the motion processing system because magnocellular neurons are insensitive to color differences at equal intensities.

Local Motion

Motion perceived within a small region of visual space, typically detected by V1 neurons due to their limited receptive fields and susceptibility to the aperture problem

Magnocellular Neurons/Pathway

• A pathway originating from the retina that is insensitive to color, responds primarily to changes in intensity, and is crucial for processing motion and detecting rapid temporal changes.

Motion Aftereffect (Waterfall Illusion)

The illusion where, after prolonged exposure to motion in one direction, a stationary object subsequently viewed appears to move in the opposite direction. Explained by the adaptation of neurons in opponent motion axes

MT (Middle Temporal Area)

•  An area in the dorsal stream where most neurons are direction selective and respond to global motion, playing a critical role in the conscious perception of motion.

Onset Transient

 A rapid, fleeting neural response that occurs when a light stimulus is switched on, particularly in LGN neurons

Offset Transient

A rapid, fleeting neural response that occurs when a light stimulus is switched off, particularly in LGN neurons

Opponent Motion Axes

The concept that motion perception is derived by comparing neural responses in opposing directions (e.g., left vs. right, up vs. down), where adaptation to one direction can lead to perceived motion in the opposite direction

Parvocellular Neurons/Pathway

A pathway originating from the retina that is sensitive to color and fine spatial details, primarily involved in object recognition

Polar Plot

A circular graph used to represent directional tuning of neurons, where the distance from the center indicates the strength of response for different directions.

Random Dot Kinematograms (RDKs)

Stimuli used to test global motion perception, consisting of multiple randomly positioned dots that move at various speeds and directions, often with varying levels of "coherence" (proportion of dots moving together).

Retinotopy

The topographical mapping of the visual field onto specific areas of the brain, meaning adjacent points in the visual field are represented by adjacent neurons in the cortex.

Simple Cells (V1)

Neurons in V1 that are orientation selective, have distinct ON and OFF regions (phase sensitive), are retinotopic, and are direction selective. They are considered the first definite site of direction sensitive cells in the primate visual system

Smooth Pursuit

An eye movement in which the eyes track a moving object to keep its image stable on the fovea, even though the eyes are moving, the perceived world remains stable

Spatial Opponency

• The organization of receptive fields with distinct ON and OFF regions, where light in one region excites the neuron and light in the other inhibits it.

Temporal Transients

• Fleeting neural responses (onset or offset) that occur quickly when a stimulus changes, reflecting sensitivity to temporal changes in light intensity.

Two-Stream Hypothesis

The theory proposing two hierarchical visual processing pathways: the dorsal ("where") stream for spatial vision and motion, and the ventral ("what") stream for object recognition

Vection

• The illusory sensation of self-motion despite actually being stationary, often induced by large-scale visual motion that spans much of the visual field, leading to conflict with vestibular information.

Absolute Binocular Disparity

The difference in the positions of an object's image on the two retinas, measured relative to the foveas. It indicates an object's depth in relation to the fixation point

Aerial Perspective (Atmospheric Perspective)

A monocular depth cue where distant objects appear blurrier, hazier, and often bluer due to light scattering by atmospheric particles over longer distances

Amblyopia (Lazy Eye)

• A neural problem where the brain suppresses or "shuts down" vision from one eye, typically due to abnormal visual development in early childhood (e.g., uncorrected strabismus).

Autostereogram

A single-image stereogram designed to create a 3-D perception when viewed with a specific technique (e.g., crossing eyes or diverging gaze), relying on the brain's ability to fuse disparate patterns

Binocular Cues

Depth cues that require the use of both eyes, deriving information from the slight differences between the images projected onto each retina.

Binocular Disparity

• The difference in the image positions of an object on the two retinas, caused by objects existing in depth. It is the primary cue for stereovision.

Binocular Neurons

• Neurons in the visual cortex (e.g., V1 superficial and deep layers) that receive input from both the left and right eyes, allowing for the combination of information necessary for stereovision.

Complex Cells

• A type of neuron in V1 (found in superficial and deep layers) that responds to bars and edges anywhere within their receptive fields. Unlike simple cells, they are typically binocular and disparity-tuned.

Correspondence Problem

• The challenge faced by the visual system in correctly matching corresponding points or features in the left and right retinal images to compute binocular disparity.

Crossed Disparities (Near Disparities)

• Binocular disparities created by objects that are nearer to the observer than the horopter. Conventionally assigned negative values.

Diplopia

Double vision, occurring when the brain cannot fuse the images from the two eyes into a single percept, resulting in separate images

Emergent Property of the Cortex

• A characteristic or function (like 3-D vision) that arises from the complex interactions and computations of many different brain areas, rather than being directly encoded or extracted by a single, simple mechanism.

Emmert's Law

A principle stating that the perceived size of an afterimage or an object is proportional to its perceived distance from the observer, given the same retinal image size

Fusion

The phenomenon of combining images from both eyes into a single, unified visual percept. It is a prerequisite for stereovision within Panum's fusional area.

Global Disparities

Binocular disparities associated with whole objects or patterns, which require pooling information from many local disparities and are processed in extrastriate areas (e.g., MT) to solve the correspondence problem.

Horopter

An imaginary curve in visual space where objects, when fixated upon, project corresponding points onto the two retinas, leading to zero disparity or images that are equidistant from the foveas. Objects on the horopter are perceived as being at the same depth as the fixation point.

Interocular Distance (Interpupillary Distance)

• The distance between the centers of the two eyes. This lateral separation is fundamental to binocular disparity.

Linear Perspective

• A monocular depth cue based on the geometric principle that parallel lines in 3-D space appear to converge at a vanishing point in the distance on a 2-D image.

Local Disparities

Binocular disparities detected by individual V1 neurons, typically related to small segments of contours or features within their limited receptive fields

Monocular Cues

Depth cues that can be perceived with only one eye, present in the image of a single eye alone.

Motion Parallax

A monocular depth cue that arises from the relative movement of objects in the visual field when the observer moves their head. Objects closer than the fixation point move in the opposite direction to head movement, while farther objects move in the same direction.

Occlusion

A monocular depth cue where one object partially blocks the view of another, indicating that the occluding object is closer than the occluded one.

Ocular Dominance Columns

Columns of neurons in V1 that predominantly respond to stimulation from either the left or the right eye, although they also contain binocular neurons

Ocular Dominance Index (ODI)

A measure of how strongly a V1 neuron responds to stimulation from one eye versus the other.

Panum's Fusional Area

• The small region of visual space around the horopter where binocular disparities are small enough to be fused into a single percept, enabling stereovision.

Perceptual Constancy

• The ability of the visual system to perceive an object as being constant (e.g., in size, color, brightness) despite changes in its retinal image due to varying viewing conditions.

Phase Shifted Complex Cells

A type of disparity-tuned complex cell in V1 where the receptive fields in the two eyes cover the same retinal position but have different ON-OFF subregion configurations, contributing to disparity detection

Pictorial Cues

Monocular and stationary cues to depth that can be inferred from the arrangement of objects in a 2-D image, such as occlusion, shading, linear perspective, and texture gradients

Position Shifted Complex Cells

• A type of disparity-tuned complex cell in V1 where the receptive fields in the two eyes are identical but are shifted in their positions on the retina, contributing to disparity detection.

Shading and Shadows

Monocular depth cues based on the patterns of light and dark on an object's surface and the shadows it casts. We typically infer light comes from above, influencing our perception of convexity or concavity.

Sighting Dominance

A person's behavioral preference for using one eye over the other for tasks requiring precise aiming or viewing. Distinct from a neuron's ocular dominance.

Size Constancy

The ability to perceive the actual size of an object as constant, regardless of its distance from the observer and the resulting changes in its retinal image size

Spatial Frequency

A measure of the number of cycles of a grating (e.g., light and dark bars) per unit of visual angle. In depth perception, texture gradients show higher spatial frequencies with increasing distance.

Stereoblindness

• A condition in which an individual is unable to perceive depth from binocular disparities (stereovision), often due to early childhood visual abnormalities like strabismus or amblyopia.

Stereopsis (Stereovision, Stereoscopic Vision)

The 3-D depth perception achieved by the brain combining and fusing slightly different images of objects from the two eyes, utilizing binocular disparity.

Strabismus

A muscular problem characterized by the misalignment of the eyes, where they do not point in the same direction, often leading to diplopia if not corrected early

Texture Gradients

A monocular depth cue where textures appear progressively finer and denser as they recede into the distance, providing a gradient of spatial frequency.

Uncrossed Disparities (Far Disparities)

Binocular disparities created by objects that are farther from the observer than the horopter. Conventionally assigned positive values

Acuity

The sharpness of vision; the ability to resolve fine details. Often refers to visual acuity, the highest visible spatial frequency at maximum contrast

Cardiff Acuity Test

An improved preferential looking test that uses engaging pictures with varying patterned edges and contrast to assess visual acuity and contrast sensitivity in infants, reducing boredom

Contrast Sensitivity

The lowest contrast visible at a particular spatial frequency. It refers to the ability to detect differences in lightness and darkness, especially for fine patterns

Critical Period

A specific, limited temporal window during which a given behavior or visual function is especially susceptible to, and indeed requires, specific environmental influences (e.g., normal visual experience) to develop normally. Failure to receive appropriate stimuli leads to permanent impairment.

Differentiation (Cellular)

The process by which a less specialized cell becomes a more specialized cell type. In neural development, this refers to neurons developing their specific structures and functions.

Electro-encephalogram (EEG)

A non-invasive neurophysiological technique that measures electrical activity from the brain by placing electrodes on the scalp.

Form Deprivation

A type of visual deprivation where the eye receives blurry, low-contrast images, thus lacking high spatial frequency and high contrast information.

Image Deprivation

A severe form of visual deprivation where the eye sees nothing, effectively equivalent to closing one eye

Monocular Deprivation

Experimental procedure (e.g., suturing one eye closed) that deprives visual experience from one eye during the critical period, leading to abnormal development of cortical representation for that eye

Preferential Looking

• A behavioral technique used to assess vision in infants, based on their natural tendency to look longer at patterned or novel stimuli compared to blank or familiar ones.

Presbyopia

Age-related farsightedness, a condition in which the eye's lens loses its ability to focus, making it difficult to see objects up close

Sensitive Period

• A temporal window following a critical period where the developing system is still influenced by environmental experience, but to a lesser extent than during the critical period itself.

Teller Acuity

A method using preferential looking to measure visual acuity in infants, typically by presenting grating patterns of varying spatial frequencies

Vernier Acuity

The ability to detect the smallest lateral displacement of one line segment relative to another. It is a measure of hyperacuity, often superior to visual acuity

Visual Cliff

• A classic experimental setup used to test depth perception in infants, consisting of a sheet of glass extending over a patterned surface, with a "deep" side and a "shallow" side.

Adaptation Aftereffects

Perceptual phenomena where prolonged exposure to a stimulus alters the perception of a subsequent, typically neutral, stimulus (e.g., staring at an angry face makes a neutral face appear happier).

Amygdala

A subcortical brain region, part of the limbic system, that plays a key role in processing emotions, particularly fear, and is involved in facial expression recognition

Caricature Effect

• The phenomenon where exaggerating a person's distinguishing facial features (creating a caricature) can make them more recognizable and identifiable than their actual photograph.

Categorical Perception

• A mode of perception where continuous variations in a stimulus are perceived as distinct categories, with poor discrimination within categories but good discrimination across category boundaries (e.g., facial expressions, colors).

Chimera Faces

Stimuli created by combining the top half of one person's face with the bottom half of another's. Used to demonstrate holistic face processing

Composite Effect

• The difficulty in perceiving the individual halves of a chimera face when they are aligned, illustrating that faces are processed as a whole rather than as separate features.

Contrast Inversion Effect

• The severe impairment in face recognition when the contrast of a face is inverted (like a photographic negative), despite intact edge information, suggesting the importance of intensity information.

Delusional Misidentification Syndrome

• A psychiatric condition where an individual recognizes familiar people but believes they have been replaced by imposters (e.g., Capgras delusion).

Face Inversion Effect

• The robust finding that recognizing inverted faces is significantly more difficult than recognizing upright faces, indicating specialized processing for upright facial configurations.

Fusiform Face Area (FFA)

•  A region in the fusiform gyrus of the extrastriate cortex, widely regarded as a primary area for face processing, particularly identity recognition and discrimination.

Greebles

• Novel, computer-generated objects used in experiments to study the development of perceptual expertise and test the specificity of brain areas like the FFA.

Holistic Processing

• A perceptual strategy where the brain processes a stimulus as an integrated whole, rather than breaking it down into individual features or parts. Faces are thought to be processed holistically.

Imprinting

•  A rapid and innate form of learning that occurs at a critical period early in life, often involving the recognition of caregivers in animals.

Magnocellular Inputs

Pathways in the visual system that are sensitive to motion and low spatial frequency information, and transmit rapidly

Neural Doctrine

An earlier, largely disproven, theory suggesting that there might be specific neurons that respond exclusively to highly complex stimuli, such as a "grandmother neuron."

Occipital Face Area (OFA)

•  A region in the occipital lobe of the extrastriate cortex, considered a subsidiary area to the FFA for face processing, often thought to provide input to the FFA.

Pareidolia

A psychological phenomenon involving a vague and random stimulus (often an image or sound) being perceived as significant, such as seeing faces in inanimate objects

Parvocellular Neurons

Pathways in the visual system that are sensitive to color and fine detail (high spatial frequency information), and transmit more slowly