Final Exam Perception

Sensation

the ability to detect a stimulus and, perhaps, to turn that detection into a private experience.

Perception

·       The act of giving meaning to a detected sensation.

Materialism

The only things that exists is matter, and that all things, including mind and consciousness, are the results of interactions between bits of matter.

Psychophysics

The science of defining quantitative relationships between physical and psychological (subjective) events.

Just noticeable difference

The smallest detectable difference between two stimuli, or the minimum change in a stimulus that can be correctly judged as different from a reference stimulus; also known as difference threshold.

Absolute threshold

Minimum amount of stimulation necessary for a person to detect a stimulus 50% of the time.

Method of constant stimuli

Many stimuli, ranging from rarely to almost always perceivable, are presented one at a time.

Method of adjustment

Similar to the method of limits, but the participant controls the stimulus directly.

Magnitude estimation

The participant assigns values according to perceived magnitudes of the stimuli.

Cross modality matching

The participant matches the intensity of a sensation in one sensory modality with the intensity of a sensation in another.

Criterion

An internal threshold that is set by the observer.

Sensitivity

A value that defines the ease with which an observer can tell the difference between the presence and absence of a stimulus or the difference between stimulus 1 and stimulus 2.

Fourier analysis

: A mathematical procedure by which any signal can be separated into component sine waves at different frequencies; combing these component sine waves will reproduce the original signal.

Spatial frequency

·       The number of cycles of a grating per degree of visual angle.

Synapse

The junction between neurons that permits information transfer.

Neurotransmitter

: A chemical substance used in neuronal communication at synapses.

EEG

 A technique that, using many electrodes on the scalp, measures electrical activity from populations of many neurons in the brain.

fMRI

Variant of MRI. Measures localized patterns of brain activity. Activated neuron’s provoke increase blood flow, which can be quantified by measuring changes of oxygenated and deoxygenated blood to strong magnetic fields.

Fencher

founder of psychophysics.

Reflection

Energy that is redirected when it strikes a surface, usually back to its point origin.

Absorption

Energy (light) that is taken up and is not transmitted at all.

Refraction

Energy that is altered as it passes into another medium.

Aqueous humor

The watery fluid in the anterior chamber.

Vitreous humor

gel-like transparent fluid that fills the eye’s largest chamber (vitreous chamber), helps holds eye’s shape.

Pupil

·       The dark circular opening at the center of the iris in the eye, where light enters the eye.

Iris

The colored part of the eye, a muscular diagraph, that regulates light entering the eye by expanding and contracting the pupil.

Lens

Inside the eye, which focuses light into the back of the eye.

Retina

: A light-sensitive membrane in the back of the eye that contains rods and cones. The lens focuses an image on the retina, which then sends signals to the brain through the optic nerve.

Myopia

When light is focused in front of the retina and distant objects cannot be seen sharply; nearsightedness.

Presbyopia

Literally “old sight”, severely diminished ability of the lens to accommodate due to advanced age.

Rods

Photoreceptors specialized for night vision.

Cones

Specialized daytime vision, fine visual acuity, and color.

Fovea

2% total retinal area but 33% ganglion cells devoted to it.

Lateral inhibition

Antagonistic interaction between adjacent regions.

Ganglion cells

The projection neurons of the vertebrate retina, conveying information from other retinal neurons to the rest of the brain.

ON-center ganglion cell receptive field

Excited by light that falls on their center and inhibited by light that falls in their surround.

OFF-center ganglion cell receptive field

·       Inhibited when light falls in their center and excited when light falls in their surround.

P cells

small cells

M cells

large cells

Contrast

The difference in illumination between a figure and its background.

Acuity

The smallest spatial detail that can be resolved at 100% contrast; better in fovea, worse in periphery of vision.

Visual angle

Unit of measure expressing the size of an image on the retina.

Contrast sensitivity

Describes how spatial frequency and contrast interact to make a grating more or less visible.

LGN

In the thalamus.

Topographical mapping

Cells in each layer of LGN show an orderly representation of the retina.

Complex cells

Do not have well defined ON-OFF regions. Do have preference for orientations of stimulus. Properly oriented stimulus can be anywhere in RF to get strong response.

Simple cells

Receptive fields elongated (not circular). Simple relationship between RF layout and preferred stimulus. To get strong response, stimulus must be positioned exactly within RF.

Hypercolumn

A 1-mm block of striate cortex containing “all the machinery necessary to look after everything the visual cortex is responsible for, in a certain small part of the visual world.

Adaption

: A reduction in response caused by prior or continuing stimulation.

Strabismus

·       A misalignment of the two eyes.

Amblyopia

Reduced spatial vision in an otherwise healthy eye.

Grandmother cell

jaragon of the field to stan for any cell that seems to be selectively responsive to one specific object.

Agnosia

Failure to recognize objects despite the ability to see them.

Feed-foward process

A process that carries out a computation one neural step after another, without the need for feedback from a later stage to an earlier stage.

Illusory contours

·       A contour that is perceived even though nothing changes from one side of the contour to the other.

Gestalt psychology theory

The whole is greater than the sum of its parts.

Gestalt principle, common region

 Items will group if they appear to be part of the same larger region.

Gestalt principle: synchrony

Elements that change at the same time tend to group together.

Bayesian theory

: A formal, mathematical system that combines information about the current stimulus with prior knowledge about the world

Prosopagnosia

An inability to recognize faces.

Re-entrant process

·       If multiple invocations can safely run concurrently on multiple processors.

 

 Geon

In Biederman’s recognitions, which holds that objects are recognized by the identities and relationships of their component parts.

Structural model of object recognition

A description of an object in terms of the nature of its constituent parts and the relationships between those parts.

Principle of Univariance

The fact that an infinite set of different wavelength-intensity combinations can elicit exactly the same response from a single type of photoreceptor. One photoreceptor type cannot make color discriminations based on wavelength.

Metamers

Stimuli that are physically different but produce the same perception.

Number of lights needed to match any: color humans can see

3

Cone-opponent cells

Conveys information about the color of a broad area. Example the cells are most excited by red and not green.

Opponent color theory

Ewald Hering. One member of the color pair suppresses the other color. For example, we do see yellowish-greens and reddish yellows, but we never see reddish-green or yellow-blue color hues.

Color-opponent pairs

3 opponent channels, each comprising an opposing color pair: red versus green, blue versus yellow, and black versus white.

Where double-opponent cells are first found

The visual cortex

Deuteranope

An individual who suffers from color blindness that is due to the absence of M-cones.

Additive color mixing

A mixture of lights. If light A and Light B are both reflected from a surface to the eye, in the perception of color the effects of those two lights add together.

Subtractive color mixing

A mixture of pigments. If pigments A and B mix, some of the light shining on the surface will be subtracted by A, and some by B. Only the remainder will contribute to the perception of color.

Rod monochromat

Has no cones of any type; truly color-blind and very visually impaired in bright light.

Color contrast

A color perception effect in which the color of one region induces the opponent color in a neighboring region.

Color constancy

The tendency of a surface to appear the same color under a fairly wide range of illuminants.

Color assimilation

A color perception effect in which two colors bleed into each other, each taking on some of the chromatic quality of the other.

Steps in color perception

1. Light is differentially absorbed by three photopigments in the cones. 2. Differences are taken between cone types, creating cone-opponent mechanisms, important for wavelength discrimination.  3. Further recombination of the signals creates color-opponent processes that support the color-opponent nature of color appearance.

Binocular summation

The combination of signals from each eye in ways that make performance on many tasks better with both eyes than with either eye alone.

Binocular disparity

·       The differences between the two retinal images of the same scene.

Metrical depth cues

A depth cue that provides quantitative information about distance in the third dimension.

Nonmetrical depth cue

A depth cue that provides information about the depth order but not depth magnitude.

Texture gradient

: A depth cue based on the geometric fact that items of the same size form smaller, closer spaced images the farther away they get.

Familiar size

A cue based on knowledge of the typical size of objects.

Vanishing point

The apparent point at which parallel lines receding in depth converge.

Convergence

The ability of the two eyes to turn inward, often used to focus on nearer objects.

Linear perspective

Lines that are parallel in the three-dimensional world will appear to converge in a two-dimensional image as they extend into the distance.

Pictorial depth cue

A cue to distance or depth used by artists to depict three-dimensional depth in two-dimensional pictures.

Motion parallax

Images closer to the observer move faster across the visual filed than images farther away.

Accommodation

The process by which the eye changes its focus (in which the lens gets fatter as gaze is directed toward nearer objects).

Free fusion

The technique of converging or diverging the eyes in order to view a stereogram without a stereoscope.

Random dot stereogram

A stereogram made of a large number of randomly places dots.

Correspondence problem

In binocular vision, the problem of figuring out which bit of the image in the left eye should be matches with which bit in the right eye.

Stereopsis

The ability to use binocular disparity as a cue to depth.

Attention

Any of the very large set of selective processes in the brain.

cue

A stimulus that might indicate where or what a subsequent stimulus will be.

Distractor

In visual search, any stimulus other than the target.

Feature search

Search for a target defined by a single attribute, such as a salient color or orientation.

Salience

The vividness of a stimulus relative to its neighbors.

Parallel search

In visual attention, referring to the processing of multiple stimuli at the same time.