Sensation and Perception Exam 3

motion aftereffect (MAE)

The illusion of motion of a stationary object that occurs after the prolonged exposure to a moving object. The existence of MAE implies an opponent process system, like that of color vision.

Interocular Transfer

The transfer of an effect (such as adaption) from one eye to another. MAW exhibits an interocular transfer. MAE must occur in neurons that respond to both eyes.

How would you build a motion detector?

Motion = change in spatial position over time. Two adjacent receptors incorporating a temporal delay.

Apparent motion

The illusory impression of smooth motion resulting from the rapid alteration of objects that appear in different locations in rapid succession. Motion detector circuit does not need real motion in order to fire.

Correspondence problem (motion)

The problem faced by the motion detection system of knowing which feature in frame 2 corresponds to which feature in frame 1.

Aperture

An opening that allows only a partial view of an object.

Aperture Problem

The fact that when a moving object id viewed through an aperture (or a receptive field), the direction of motion of a local feature or a part of an object may be ambiguous.

Lesions in Magnocellular Layers of LGN

Impair the perception of large, rapidly moving objects.

Middle Temporal Area (MT)

The vast majority of neurons in MT are selective for motion in a particular direction.

Newsome and Pare (1988)

Conducted a study on motion perception in monkeys. They trained monkeys to respond to correlated dot motion displays. The MT area of the monkeys was lesioned.

Result of Newsome and Pare's 1988 monkey experiment

Monkeys needed about ten times as many dots to correctly identify the direction of motion.

Disadvantages of using lesion studies to study motion

It's invasive and lesions may be incomplete or may influence other structures.

Electrical stimulation of MT neurons

Avoids problems of lesion studies. Biases motion detection in the direction of MT neuron normally responds to.

Akinetopsia

A rare neuropsychological disprder in which the affected individual has no perception of motion. It is caused by distributions to cortical area MT.

First-order motion

The motion of an object that is defined by changes in luminance.

Luminance-defined object

An object that is delineated by differences in reflected light

Second-order motion

The motion of an object that is defined by changes in contrast or texture, but not by luminance

texture-defined object or contrast-defined object

An object that is defined by changes in contrast or texture, but not by luminance.

Optic array

The collection of light rays that interact with object in the world in front of a viewer.

Optic flow

The changing angular position of points in a perspective image that we experience as we move through the world.

Focus of Expansion (FOE)

The point int he center of the horizon from which, when we are in motion, all points in the perspective image seem to emanate. This is one aspect of optic flow. The focus of expansion tells the observer which way they are heading.

Avoiding imminent collision

How do we estimate the time to collision (TTC) of an approaching object?

Tau

Information in the optic flow that could signal TTC without the necessity of estimating either the absolute distance or velocity. It equals the ratio of the retinal image size at any moment to the rate at which the image is expanding TTC is proportional to tau.

Biological motion

The pattern of movement of all animals

Motion-induced blindness (MIB)

A moving surface can cause stationary objects to "disappear" - no clear explanation.

Efference copy (corollary discharge signal)

When an eye movement is issued, the motor command is copied and sent to other areas of the sensory cortices.

Comparator

Receives the efference copy (the other copy goes to the eye muscles) and compensates for eye movements.

Stevens (1976)

Paralyzed himself with curare and tried to move his eyes - the world subsequently shifted in the opposite direction.

Smooth persuit

Voluntary eye movement in which the eyes move smoothly to follow a moving object

Saccade

A type of eye movement, made both voluntary and involuntary, in which the eyes rapidly change fixation from one object to another.

Vergence

A type of eye movement, both voluntary and involuntary, in which the two eyes move in opposite directions.

Convergent

Eye movements turn the eyes inward

Divergent

Eye movements turn the eyes outward

Reflexive

Automatic and involuntary eye movements

How many muscles make up the eye?

Six and are arranged in three pairs

Superior colliculus

A structure in the midbrain that is important in initiating and guiding eye movements. When the structure is electrically stimulated, eye movements result.

Saccadic suppression

The reduction of visual sensitivity that occurs when we make saccadic eye movements. Eliminates the smear from retinal image motion during eye movements.

How else do we compensate for eye movements to preserve the stability of the visual world?

Dynamic remapping of receptive fields. Receptive fields are already processing information from a new location before the eye lands there.

What is sound?

Sounds are created when objects vibrate. object vibrations cause molecules in the surrounding medium to vibrate, creating pressure changes in the medium. Speed depends on the medium.

Amplitude or Intensity

The magnitude of displacement (increase or decrease) of a sound pressure wave.

Frequency

For sound, the number of times per second that a pattern of pressure change repeats.

Hertz (Hz)

A unit of measure for frequency. 1 Hz equals 1 cycle per second

Decibel

A unit of measure for the physical intensity of sound. Define the difference between two sounds as the ratio between two sound pressures.

Logarithmic scale

Small dB changes can correspond to large physical changes.

Sine wave ("pure tone")

The waveform for which variation as a function of time as a sine function.

Spectrum

Complex waves that displays how much energy is present in each frequencies of the sound.

Harmonic spectrum

The spectrum of a complex sound in which energy is at integer multiples of the fundamental frequency. Typically caused by a simple vibrating source.

Fundamental frequency

The lowest-frequency component of a complex periodic sound.

Timbre

The psychological sensation wherein two sounds with the same loudness and pitch are dissimilar. Timbre quality is conveyed by harmonics and other high frequencies.

Outer ear

Sound waves are collected from the environment by the pinnae, then funneled by the pinnae into the ear canal.

Ear canal

Funnels sound waves to the tympanic membrane (the eardrum).

Eardrum

Thin sheet of skin at the end of the outer ear canal. Vibrates in response to sound.

Middle ear

Consists of three tiny bones (ossicles) that amplify and transmit sound to the inner ear.

Malleus

Receives vibrations from the typanic membrane and is attached to the incus.

Incus

The middle ossicle

Stapes

Connected to the incus on one end and the oval window of the cochlea on the other.

Oval window

The border between the middle and inner ear.

Tensor tympani and stapedius

Two muscles in the middle ear that decrease ossicle vibrations when tensed - muffle loud sounds and protect the inner ear (acoustic reflex)

Inner ear

Fine changes in sound pressure transduced into neural signals.

Cochlea

Spiral structure of the inner ear containing to organ of Corti. It is filled with watery fluids in three parallel canals - Vestibular, tympanic, and middle canal. Separated by Reissner and Basilar membranes.

How does sound get to the cochlea?

Vibrations are transmitted through tympanic membranes ("eardrum") and middle-ear bones (malleus and incus) causing the stapes to pus and pull the flexible oval window in and out of the vestibular canal at the base of the cochle.

Organ of corti

A structure on the basilar membrane of the cochlea that is composed of hair cells and dendrites of auditory nerve fibers.

Hair cells

Cells that support the sereocilia

Stereocilia

Transduce mechanical movement in the cochlea into neural activity sent to the brain cell. It is connected by a tiny filament-tip link.

Inner hair cells

Conver almost all information about sound waves to the brain (using afferent fibers). One row of cells

Outer hair cells

Receives information from the brain (using efferent fibers). They are involved in an elaborate feedback system. 3 rows of cells

Tectorial membrane

A gelatinous structure, attached on one end, that extends into the middle canal of the ear, floating above inner hair cells and touching outer hair cells. Vibrations cause displacement of the tectorial membrane, which bends stereo-cilia attached to hair cells and causes the release of neurotransmitters.

Place code

Tuning of different parts of the cochlea to different frequencies

Auditory nerve (AN)

Responses of individual AN fibers to different frequencies are related to their place along the cochlear partition.

Frequency selectivity

clearest when sounds are very faint

threshold tuning curve

a graph plotting the thresholds of a neuron or fiber in response to sine waves with varying frequencies

Two-tone suppression

A decrease in the response (firing rate) of one auditory nerve fiber to one tone when a second tone is presented at the same time.

Isointensity curves

A chart measuring an AN fiber's firing rate to a wide range of frequencies, all presented at the same intensity level.

Rate-intensity function

A graph plotting the firing rate of an auditory nerve fiber in response to a sound of constant frequency at increasing intensities.

Phase locking

Firing of a single neuron at one distinct point in the period (cycle) of a sound wave at a given frequency. Its existence means that the firing pattern of an AN fiber carries a temporal code.

Rate saturation

Maximum neural firing rare. neurons can only fire ~1000 Hz per second, but we can hear up to ~20,000 Hz.

Temporal code

Tuning of different parts of the cochlea to different frequencies, in which information about the particular frequency of an incoming sound wave is coded by the timing of neural firing as it relates to the period of sound.

the volley principle

multiple neurons can provide a temporal code for frequency if each neuron fires at a distinct point in the period of a sound wave but does not fire on every period - solves the problem of rate saturation

Cochlea nucleus

the first brainstem nucleus at which afferent auditory nerve fibers synapse

Superior olive

An early brainstem region in the auditory pathway where inputs from both ears converge.

Inferior collliculus

A midbrain nucleus in the auditory pathway

Medial geniculate nucleus

The part of the thalamus that relays auditory signals to the temporal cortex and receives input from the auditory cortex

Primary auditory cortex (A1)

The first area within the temporal lobes of the brain responsible for processing acoustic organization

Belt area (A2)

A region of cortex, directly adjacent to the primary auditory cortex (A1), with inputs from A1, where nuerons respond to more complex characteristics of sound

Parabelt area

A region of cortex, lateral, and adjacent to the belt area, where neurons respond to more complex characteristics of sounds, as well as to input from other senses.

Tonotopic organization

An arrangement in which neurons that respond to different frequencies are organized anatomically in order of frequency. Starts in the cochlea, Maintained all the way through the primary auditory cortex (A1)

Auditory system

A large proportion of processing is done before A1

Visual system

A large proportion of processing occurs beyond V1

Psychoacoustics

the branch of psychophysics that studies the psychological correlates of the physical dimensions of acoustics in order to understand how the auditory system operates.

Audibility threshold

the lowest sound pressure level that can be reliably detected at a given frequency

Equal-loudness curve

A graph plotting sound pressure level (dB SPL) against the frequency for which a listener perceives constant loudness

Temporal integration

the process by which a sound at a constant level is perceived as being louder when it is of greater duration of the light

Masking

Using a second sound, frequency noise, to make the detection of another sound more difficult

White noise

Noise consisting of all audible frequencies in equal amounts. White noise is hearing is analogous to white light in vision, for which all wavelengths are present.

Critical bandwidth

The range of frequencies conveyed within a channel in the auditory system

Presbycusis

Age-related hearing loss. Young people range from 20-20,000 Hz. By college age: 20-15,000 Hz.

Hearing aids

the earliest devices were horns

Interausual time differences (ITD)

The difference in time between a sound arriving at one ear versus the other.

Azimuth

The angle of a sound source on the horizontal plane relative to a point in the center of the head between the ears. Measured in degrees. 0 being straight ahead, 180 being behind the person.

Medial superior olive (MSO)

A relay station in the brainstem where inputs from both ears contribute to detections of ITDs.