sensory sys. glossary terms (pt.1) Flashcards
(209 cards)
1
Q
Action …
A
Motor activities such as moving the head or the eyes, and locomoting through
the environment. Action is one of the major outcomes of the perceptual
process.
2
Q
Action potential .
A
Rapid increase in positive charge in a nerve fiber (axon) that travels down the
fiber. Also called nerve impulse or spike.
3
Q
Afferent neurons
A
Neurons that carry action potentials from receptors in the sensory organs
towards the central nervous system.
4
Q
Auditory perception
A
The sense of “hearing”, one of the five traditional senses.
5
Q
Bottom-up processing
A
Processing that is based on stimulation of the receptors. Also called data-based
processing. The antonym is top-down processing.
6
Q
Efferent neurons ..
A
. Neurons that carry action potentials away from the central nervous system to
effectors such as muscles.
7
Q
Environmental stimulus
A
The stimulus “out there”, in the external environment
8
Q
Homunculus ……..
A
A map-like representation of regions of the body in the brain.
9
Q
Perception .
A
The organization, identification, and interpretation of sensory information in
order to represent, understand, and interact with the environment.
10
Q
Primary receiving areas
A
Areas of the cerebral cortex that are first to receive most of the signals initiated
by a sense’s receptors.
For example, the occipital cortex is the site of the
primary receiving area for vision, and the temporal lobe is the site of the
primary receiving area for hearing.
11
Q
Receptive field
A
A neuron’s receptive field is the area on the receptor surface (e.g., the retina
for vision or the skin for touch) that, when stimulated, affects the firing of that
neuron.
12
Q
Receptor
A
A sensory receptor is a cell sensitive to environmental energy. Receptors
change this energy into electrical signals in the nervous system.
13
Q
Recognition
A
The ability to place an object in a category that gives it meaning – for example,
recognizing a particular red object as a tomato or giving a physical sound a
semantic meaning.
14
Q
Sensory organs
A
Specialized organs that interact with environmental stimuli and that contain
receptors that transduce a specific type of stimulus energy into nerve activity
(e.g., the eye in vision or the skin in touch).
15
Q
Top-down processing
A
Processing that starts with the analysis of high-level information, such as
knowledge a person brings to a situation. Also called knowledge-based
processing. Distinguished from bottom-up, or data-based processing, which is
based on incoming data.
16
Q
Topographic maps
A
The ordered projection of a sensory surface (e.g., the retina or the skin) or an
effector system (e.g., the musculature) to one or more structures of the central
nervous system. Topographic maps can be found in all sensory systems and in
many motor systems.
17
Q
Transducer
A
A “device” that converts a signal in one form of energy to another form of
energy.
18
Q
Transduction
A
In the senses, the conversion of environmental energy into electrical energy.
For example, receptors in the eye transduce light energy into electrical energy
19
Q
Autonomic nervous ………
system (ANS)
A
The part of the PNS that influences the function of internal organs. The ANS
acts largely unconsciously and regulates the heart rate, digestion, respiratory
rate, pupillary response, urination, and sexual arousal.
20
Q
Brainstem
A
The posterior part of the brain, adjoining and structurally continuous with the
spinal cord. In humans, it is usually described as including the medulla
oblongata, pons, and midbrain.
21
Q
Brodmann area
A
A region of the cerebral cortex that is defined by its cytoarchitecture, or
histological structure and organization of cells.
22
Q
Cerebellum .
A
A large, highly convoluted (in-folded) structure located dorsal to the brainstem
at the level of the pons. Also known as “little cerebrum”.
23
Q
Cerebral cortex
A
The layered sheet of neurons that covers the surface of the brain and contains
the machinery for creating perception, as well other functions, such as
language, memory, and thinking. It is divided in two (lateral) hemispheres,
each containing four major lobes.
24
Q
Contralateral .
A
On the opposite side of the body (antonym of ipsilateral).
25
Coronal plane
A plane that shows brain structures as seen from the front. Also called frontal
plane.
26
Distal
Located more distant from the point of origin or attachment (antonym of
proximal).
27
Dorsal .
Toward the back, away from the ventral (stomach) side. The top of the brain
is considered dorsal because it has this position in four-legged animals
(antonym of ventral).
28
Gray matter
A major component of the central nervous system that contains primarily
neuronal cell bodies.
29
Inferior
Below another part (antonym of superior)
30
Ipsilateral
On the same side of the body (such as two parts on the left, antonym of
contralateral).
31
Lateral
Toward the side, away from the midline (antonym of medial).
32
Occipital lobe .
One of the four major lobes of the cerebral cortex, which holds amongst
others the primary visual cortex.
33
Parietal lobe ........
One of the four major lobes of the cerebral cortex, which holds amongst
others the primary somatosensory cortex.
34
Peripheral nervous ...........
system (PNS)
The part of the nervous system apart from the brain and the spinal cord.
35
Proximal
Located close (approximate) to the point of origin or attachment (antonym of
distal).
36
Sagittal plane .
A plane that shows brain structures as seen from the side.
37
Somatic nervous system
The part of the PNS that is associated with body movements through the
control of skeletal (voluntary) muscles and with the reception of external
stimuli.
38
Temporal lobe
One of the four major lobes of the cerebral cortex, which holds amongst
others the primary auditory cortex.
39
Thalamus
A group of nuclei, which provide primary sensory relay for somatosensory,
gustatory, auditory, visual, and vestibular sensory inputs to the cerebral
cortex.
40
Transverse plane
A plane that shows brain structures as seen from above. Also called horizontal
plane.
41
White matter
A major component of the central nervous system that contains millions
myelinated axons (i.e., the wires between neuronal cell bodies).
42
Dendrite
Branching extensions of the neuron’s plasma membrane that increase the
surface area of the neuron and collect neuronal activity from other cells.
43
Equilibrium potential
The membrane potential at which a particular type of ion has no driving force
to diffuse through the plasma membrane in either direction. At the equilibrium
potential, chemical and electrical gradients are equal in magnitude.
44
glia cells
Non-neuronal cells in the nervous system that provide support and protection
for neurons. Among many other functions, Glia cells are responsible for the
myelination of axons.
45
Graded potential .
A relatively small change in membrane potential, for example by opening
ligand-gated ion channels. The strength of a graded potential is given relative
to the strength of stimulation (compare action potential).
46
Ligand-gated channels .
A group of ion channels, which open to allow ions such as Na+
, K+
, Ca2+, or Cl−
to pass through the membrane in response to the binding of a messenger.
47
membrane potential
The difference in electric potential between the interior and the exterior of a
biological cell
48
neuron doctrine
. The concept proposing that the neuron is the fundamental unit of the nervous
system. Compare Reticular theory
49
neurotransmitter
Chemical messenger released by neurons onto a target cell with an excitatory
or inhibitory effect.
50
oligodendrocytes
A type of glia cells in the central nervous system (CNS). Oligodendrocytes cells
wrap around axons to form the myelin sheath (equivalent to Schwann cells).
51
resting potential
......... The membrane potential in the absence of stimulation. The resting potential
of neurons is typically around -70 mV (inside negative). It depends on the
equilibrium potentials of contributing ions and the selective membrane
permeability for these ions
52
reticular theory
An obsolete scientific theory in neurobiology that stated that the nervous
system is made up of a single interlinking network. Compare Neuron doctrine.
53
schwann cells
The principal glia of the peripheral nervous system (PNS). Schwann cells wrap
around axons to form the myelin sheath (equivalent to Oligodendrocytes).
54
vesicles
Small membrane compartments that store and release neurotransmitters at
the synapse.
55
Cutaneous senses
The ability to perceive sensations, such as touch, temperature, and pain that
are based on stimulation of receptors in the skin
56
Kinesthesis .
The perception of body movements. It involves being able to detect changes
in body position and movements based on proprioception and the vestibular
system (the latter will be discussed in the lectures on audition).
57
Mechanoreceptor
Receptor that responds to mechanical stimulation, such as pressure,
stretching, or vibration.
58
Meissner corpuscle .........
(RA1)
A rapidly adapting mechanoreceptor in the skin. It has been proposed that the
Meissner corpuscle is important for perceiving tactile slip and for controlling
the force needed to grip objects.
59
Pacinian corpuscle (RA2)
A mechanoreceptor in the skin with a distinctive elliptical shape. It transmits
pressure to the sensory neurons inside it only at the beginning and the end of
a pressure stimulus. Associated with the perception of vibration and the fine
textures that are perceived when moving the fingers over a surface.
60
Merkel receptor (SA1)
A disk-shaped mechanoreceptor in the skin connected to slowly adapting
sensory neurons. Associated with the perception of fine details.
61
Nociceptor
A sensory neuron that responds to stimuli that are damaging to the skin.
62
Phantom limb .
A person’s continued perception (often including pain) of a limb, such as an
arm or a leg, even though that limb has been amputated.
63
Proprioception
The sensing of the position and movement of the limbs.
64
Rate code
A neuronal coding principle in which the firing rate of a neuron carries
information about the stimulus. It is often associated with neural coding of
magnitude (intensity of pressure, stretch, light intensity, or loudness).
65
Rapidly adapting (RA) ....
receptor
Mechanoreceptors that respond with bursts of firing just at the onset and
offset of a pressure stimulus. The Meissner corpuscle and the Pacinian
corpuscle are rapidly adapting receptor.
66
Ruffini cylinder (SA2)
A mechanoreceptor structure in the skin connected to slowly adapting sensory
neurons. It has been proposed that the Ruffini cylinder is involved in perceiving
“stretching”.
67
Slowly adapting (SA) ......
receptors
Mechanoreceptors located in the epidermis and the dermis that respond with
prolonged activity to continued pressure. The Merkel receptor and the Ruffini
cylinder are slowly adapting mechanoreceptors.
68
Somatosensory system
The system that includes the cutaneous senses (senses involving the skin) and
proprioception (the sense of the position and movement of the limbs).
69
Two-point threshold
The smallest separation between two points on the skin that is perceived as
two points; a measure of acuity on the skin.
70
amygdala
A subcortical structure that is involved in emotional responding and in
processing olfactory signals.
71
Chemotopic map
The pattern of activation in the olfactory system in which chemicals with
different properties create a “map” of activation based on these properties.
For example, there is evidence that chemicals are mapped in the olfactory bulb
based on carbon-chain length. Also called odor map.
72
Flavour
The perception that occurs from the combination of taste and olfaction.
73
Glomeruli .
Small structures in the olfactory bulb that receive signals from similar olfactory
receptor neurons. One function of each glomerulus is to collect information
about a small group of odorants.
74
Mitral cell ..
A neuron in the olfactory bulb that receives signals from olfactory receptor
neurons and relays them to the brain. There are about 50,000 mitral cells in
the human olfactory bulb.
75
Odorant
The structure that receives signals directly from the olfactory receptors. The
olfactory bulb contains glomeruli, which receive these signals from the
receptors.
76
Olfactory epithelium .
The region inside the nose that contains the receptors for the sense of smell.
77
Olfactory receptor .
A protein string that responds to odor stimuli. Different olfactory receptor
neurons are equipped with different olfactory receptors.
78
Oral capture
The condition in which sensation from both olfaction and taste are perceived
being located in the mouth.
79
Papillae .
Ridges and valleys on the tongue, some of which contain taste buds.
There arethree types of papillae:
fungiform,
foliate,
and circumvallate.
80
Population coding
A general principle of sensory processing, according to which different values
of perceptual attribute are coded by different patterns of activity in a whole
population of neurons.
81
Recognition profile
The pattern of olfactory activation for an odorant, indicating which olfactory
receptor neurons are activated by the odorant.
82
Retronasal route
The opening from the oral cavity, through the nasal pharynx, into the nasal
cavity. This route is the basis for the way smell combines with taste to create
flavor.
83
Tastant
sny stimulus that can be tasted
84
Taste bud
A structure located within papillae on the tongue that contains the taste cells.
85
Taste cells ..
Cells located in taste buds that cause the transduction of chemical or electrical
energy when chemicals contact receptor sites or channels located at the tip of
this cell.
86
Taste pore
An opening in the taste bud through which the tips of taste sells protrude.
When chemicals enter a taste pore, they stimulate the taste cells and result in
transduction.
87
Acoustic signal
The pattern of frequencies and intensities of the sound stimulus.
88
Amplitude
In the case of a repeating sound wave, such as the sine wave of a pure tone,
amplitude represents the pressure difference between atmospheric pressure
and the maximum pressure of the wave.
89
Auditory canal
The canal through which air vibrations travel from the environment to the
tympanic membrane.
90
Auditory response area
The psychophysically measured area that defines the combinations of
frequencies and sound pressure levels (SPLs) over which hearing functions.
91
Complex tone
A tone that consists of two or more pure tones. In music instruments, the first
harmonic of a complex tone is the pure tone with the lowest frequency in the
frequency spectrum. The other components, called higher harmonics, have
frequencies that are multiples of the fundamental frequency.
92
Decibel (dB) ...
A unit that indicates the pressure of a sound stimulus relative to a reference
pressure: dB = 20 log (p/p0)
where p is the pressure of the tone and p0 is the
reference pressure.
93
Frequency
The number of times per second that pressure changes of a sound stimulus
repeat. Frequency is measured in Hertz, where 1 Hertz is one cycle per second.
94
Frequency spectrum
A plot that indicates the relative energy (or amplitudes) of the various
frequencies that make up an acoustic signal.
95
harmonics
Pure-tone components of a complex tone that have frequencies that are
multiples of the fundamental frequency.
96
Hertz (Hz)
The unit for designating the frequency of a tone. One Hertz equals one cycle
per second.
97
incus
The second of the three ossicles of the middle ear. It transmits vibrations from
the malleus to the stapes.
98
Inner ear
The innermost division of the ear, containing the cochlea and the receptors for
hearing.
99
Loudness
The perceived quality of sound that ranges from soft to loud. For a tone of a
particular frequency, loudness usually increases with increasing decibels.
100
Malleus
The first of the ossicles of the middle ear. Receives vibrations from the
tympanic membrane and transmits these vibrations to the incus.
101
Middle ear
The small air-filled space between the auditory canal and the cochlea that
contains the ossicles.
102
Middle ear muscles
Muscles attached to the ossiclesin the middle ear. The smallest skeletal muscle
in the body, they contract in response to very intense sounds and dampen the
vibrations of the ossicles.
103
Ossicles .
Three small bones in the middle ear that transmit vibrations from the outer to
the inner ear
104
Outer ear
the pinna and auditory canal
105
Pinna ..
The part of the ear that is visible on the outside of the head
106
Oval window .
A membrane covered hole in the cochlea that receives vibrations from the
stapes.
107
Pitch
The perceived quality of sound, ranging from low to high, that is most closely
associated with the frequency of a tone.
108
Pure tone
A tone with pressure changes that can be described by a single sine wave.
109
Sound (perceptual) .
The perceptual experience of hearing. The statement “I hear a sound” is using
sound in that sense.
110
Sound (physical) .
The physical stimulus for hearing. The statement “The sound’s level was 10 dB”
is using sound in that sense.
111
Sound pressure level .....
(SPL)
A designation used to indicate that the reference pressure used for calculating
a tone’s decibel rating is set at 20 micropascals, near the threshold in the most
sensitive frequency range for hearing.
112
Sound spectrogram .
A plot showing the pattern of intensities and frequencies of a sound stimulus.
113
Sound wave
Pattern of pressure changes in a medium. Most of the sounds we hear are due
to pressure changes in the air, although sound can be transmitted through
water and solids as well.
114
Stapes .
The last of the three ossicles in the middle ear. It receives vibrations from the
incus and transmits these vibrations to the oval window of the inner ear.
115
Timbre .
The perceived quality that distinguishes between two tones that sound
different even though they have the same loudness, pitch, and duration.
Differences in timbre are illustrated by the sounds made by different musical
instruments.
116
Tympanic membrane
A membrane at the end of the auditory canal that vibrates in response to
vibration of the air and transmits these vibrations to the ossicles in the middle
ear. Also called eardrum.
117
Acoustic prism
The way the cochlea separates frequencies entering the ear to create activity
at different places along the basilar membrane.
118
Apex of the cochlea .
The end of the cochlea farthest from the middle ear.
119
Auditory space .
Perception of where sounds are located in space. Auditory space extends
around a listener’s head in all directions, existing wherever there is a sound.
120
Azimuth
In hearing, specifies locations that vary from left to right relative to the listener.
121
Base of the cochlea
The part of the cochlear nearest to the middle ear.
122
Basilar membrane
A membrane that stretches the length of the cochlea and controls the vibration
of the cochlear partition. Physical properties of the basilar membrane play a
critical role for the frequency tuning
123
Binaural cue
Sound localization cue that involves both ears. Interaural time difference and
interaural level difference are the primary binaural cues.
124
Characteristic frequency
The frequency at which a neuron in the auditory system has its lowest
threshold.
125
Cilia
Fine hairs that protrude from the inner and outer hair cells of the auditory
system. Bending the cilia of the inner hair cells leads to transduction.
126
Cochlea
The snail-shaped, liquid-filled structure that contains the structures of the
inner ear, the most important of which are the basilar membrane, the tectorial
membrane, and the hair cells.
127
Cochlear amplifier
Expansion and contraction of the outer hair cells in response to sound
sharpens the movement of the basilar membrane to specific frequencies. This
amplifying effect plays an important role in determining the frequency
selectivity of the auditory nerve fibers.
128
Cochlear partition
A partition in the cochlea, extending almost its full length, that separates the
scala tympani and the scala vestibule. The organ of Corti, which contains the
hair cells, is part of the cochlear partition.
129
Distance .
How far a stimulus is from the observer. In hearing, the distance coordinate
specifies how far the sound source is from the listener.
130
Elevation
In hearing, sound locations that are up and down relative to the listener.
131
Frequency tuning curve
Curve relating frequency and the threshold intensity for activating an auditory
neuron.
132
Hair cell
Neuron in the cochlea that contains small hairs, or cilia, that are displaced by
vibration of the basilar membrane and fluids inside the inner ear.
There are
two kinds of hair cells: inner and outer.
133
Inner hair cell
Auditory receptor cell in the inner ear that is primarily responsible for auditory
transduction.
134
Interaural level .................
difference (ILD)
The difference in the sound pressure (or level) between the left and right ears.
This difference creates an acoustic shadow for the far ear. The ILD provides a
cue for sound-localization for high frequency sounds.
135
. Outer hair cell
Auditory receptor cells in the inner ear that amplify the responses of the inner
hair cells by amplifying the vibration of the basilar membrane.
136
Organ of Corti .
The major structure of the cochlea partition, containing the basilar membrane,
the tectorial membrane and the receptors for hearing
137
Place theory of hearing
The proposal that the frequency of a sound is indicated by the place along the
organ of Corti at which nerve firing is highest.
138
Tectorial membrane ....
A membrane that stretches the length of the cochlea and is located directly
over the hair cells. Vibrations of the cochlear partition cause the tectorial
membrane to bend hair cells by rubbing against them.
139
Tonotopic map .
An ordered map of frequencies created by the responding of neurons within
structures of the auditory system. There is a tonotopic map of neuron along
the length of the cochlea, with neurons in the apex responding best to low
frequencies and neurons at the base responding best to high frequencies
140
Traveling wave .
In the auditory system, vibrations of the basilar membrane in which the peak
of the vibrations travels from the base of the membrane to its apex.
141
Otolith organ .
Either of two mechanical structures (utricle and saccule) in the vestibular
organs that sense both linear acceleration and gravity.
142
Semicircular canals .
Any of the three toroidal tubes in the vestibular organs that sense angular
motion.
143
Vestibular organs
The set of five organs –three semicircular canals and two otolith organs–
located in each inner ear that sense head motion and head orientation with
respect to gravity.
144
Vestibular system .
The mechanism in the inner ear that is responsible for balance and sensing the
position of the body.
145
Absolute threshold . (psychpphy)
The minimum stimulus energy necessary for an observer to detect a stimulus.
146
Bias ...
A measure for the extent to which one response is more probable than
another (e.g., a subject may be more likely to respond that a stimulus is
present). Bias is independent of sensitivity.
147
Correct rejection
In a signal detection experiment, saying “No, I don’t detect a signal” on a trial
in which the signal is not presented (a correct response).
148
False alarm
In a signal detection experiment, saying “Yes, I detect the signal” on a trial in
which the signal is not presented (an incorrect response).
149
Hit
In a signal detection experiment, saying “Yes, I detect the signal” on a trial in
which the signal is present (a correct response).
150
Miss
In a single detection experiment, saying “No, I don’t detect a signal” on a trial
in which the signal is present (an incorrect response).
151
Difference threshold ..
The minimal detectable difference between two stimuli. Also called just
noticeable difference (JND).
152
Fechner’s law
A principle describing the relationship between a stimulus and the resulting
sensation that says the magnitude of subjective sensation increases
proportionally to the logarithm of the stimulus intensity.
153
Psychophysics
Traditionally, the term psychophysics refers to quantitative methods of
measuring the relationship between properties of the stimulus and the
subject’s experience.
154
Receiver operating ..........
characteristic (ROC)
curve
In a signal detection experiment, the graphical plot of the hit rate as a function
of the false alarm rate. If these are the same, observers cannot distinguish
between signal and noise.
As the observer’s sensitivity increases, the curve
bows toward the upper left corner –a point that represents perfect sensitivity.
155
Response criterion
In a signal detection experiment, the subjective magnitude of a stimulus above
which the participant will indicate that the stimulus is present.
156
Sensitivity
A measure for how hard or easy it is for a subject to detect that a target
stimulus is present. It can be computed based on hit- and false alarm rates.
Also call d’ (pronounced “dee prime”).
157
Signal detection theory
A theory stating that the detection of a signal depends both on the
participant’s sensitivity to the signal and on the participant’s response bias.
158
Weber’s law
A law stating that the ratio of the difference threshold (I) to the stimulus
intensity (I) is constant.
According to this relationship, doubling the value of
the stimulus intensity will cause a doubling of the difference threshold. The
ratio I/I is called Weber’s fraction.
159
Accommodation (focus)
In Vision, bringing objects located at different distances into focus by changing
the shape of the lens.
160
Blind spot
The small area where the optic nerve leaves the back of the eye. There are no
visual receptors in this area, so small images falling directly on the blind spot
cannot be seen.
161
Cones .
Cone-shaped photoreceptors in the retina that are primarily responsible for
vision in high levels of illumination and for color vision and detailed vision.
162
Cornea
The transparent focusing element of the eye that is the first structure through
which light passes as it enters the eye. The cornea is the eye’s major focusing
element.
163
Eccentricity
The distance between a position on the retina and the center of the fovea.
164
Electromagnetic ................
spectrum
Continuum of electromagnetic energy that extends from very-shortwavelength gamma rays to long-wavelength radio waves. Visible light is a
narrow band within this spectrum.
165
Emmetropia
The condition in which there is no refractive error, because the refractive
power of the eye is perfectly matched to the length of the eyeball.
166
Eye
The eyeball and its contents, which include focusing elements, the retina, and
supporting structures.
167
Eyelid .
A thin fold of skin that covers and protects the eye.
168
Fovea .....
A small area in the human retina that contains only cone receptors. The fovea
is located on the line of sight, so that when a person looks at an object, the
center of its image falls on the fovea.
169
Hyperopia
A condition causing poor vision in which people can see objects that are far
away but do not see near objects clearly. Also called farsightedness.
170
Myopia
An inability to see distant objects clearly. Also called nearsightedness.
171
Iris
The colored part of the eye, consisting of a muscular diaphragm surrounding
the pupil and regulating the light entering the eye by changing the pupil size.
172
Illuminance .
A photometric measure of the light incident on a surface (per unit area).
173
Lens
The transparent focusing element of the eye through which light passes after
passing through the cornea and the aqueous humor. The lens’s change in
shape to focus at different distances is called accommodation.
174
Luminance
A photometric measure of the luminous intensity per unit area of light
travelling in a given direction.
175
Optic nerve
Bundle of nerve fibers that carry impulses from the retina to the lateral
geniculate nucleus and other structures. Each optic nerve contains about 1
million ganglion cell fibers.
176
Peripheral retina
The area of the retina outside the fovea.
177
Photon
A quantum of visible light (or other forms of electromagnetic radiation)
exhibiting wave-particle duality (i.e., demonstrating properties of both waves
and particles).
178
Photopic vision
Vision under well-lit conditions (i.e., with light intensities that are bright
enough to stimulate cone receptors and bright enough so saturate the rod).
179
Photoreceptor
A light sensitive receptor in the retina of the eye.
180
Presbyopia
The inability of the eye to accommodate due to a hardening of the lens and a
weakening of the ciliary muscles. It occurs as people get older.
181
Pupil
The opening through which light reflected from objects in the environment
enters the eye.
182
Reflectance ...
The percentage of light reflected from a surface.
183
Reflectance curve
A plot showing the percentage of light reflected from an object as a function
of wavelength.
184
Retina
A complex network of cells that covers the inside back of the eye. These cells
include the receptors, which generate an electrical signal in response to light,
as well as horizontal, bipolar, amacrine, and ganglion cells.
185
rod
A cylinder-shaped photoreceptor in the retina that is responsible for vision at
low levels of illumination.
186
Scotopic vision .
Vision under low light conditions (i.e., with light intensities that are bright
enough to stimulate the rod receptors but too dim to stimulate the cone
receptors).
187
Selective reflection
When an object reflects some wavelength of the spectrum more than others.
Selective reflection is associated with the perception of chromatic color.
188
Visible light
The band of electromagnetic energy that activates the visual system and that,
therefore, can be perceived. For humans, visible light has wavelength between
about 400 and 700 nanometers.
189
Visual angle
The angle of an object relative to an observer’s eyes. This angle can be
determined by extending two lines from the eye – on to one end of an object
and the other to the other end of the object. Because an observer’s visual
angle is always determined relative to an observer, its visual angle changes as
the distance between the object and the observer changes.
190
Wavelength .
. For light energy, the distance between one peak of a light wave and the next
peak.
191
Absorption spectrum
A plot of the amount of light absorbed by a visual pigment versus the
wavelength of light.
192
Amacrine cell .
A neuron that transmits signals laterally in the retina. Amacrine cells synapse
with bipolar cells and the ganglion cells.
193
Bipolar cell
A retinal neuron that receives inputs from the visual receptors and sends
signals to the retinal ganglion cells.
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Centre-surround ..............
organization
Arrangement of a neuron’s receptive fields in which one area is surrounded by
another area, like the hole in a donut (corresponding to the centre) and the
donut (the surround). Stimulation of the centre and surround causes opposite
responses.
195
Ganglion cell
A neuron in the retina that receives inputs from bipolar and amacrine cells.
The axon of the ganglion cells are the nerve fibres that travel out of the eye in
the optic nerve.
196
Horizontal cell
A neuron that transmits signals laterally across the retina. Horizontal cells
synapse with receptors and bipolar cells.
197
Lateral geniculate ............
nucleus (LGN)
A structure in the thalamus that receives input from the retinal ganglion cells
and has input and output connections to the visual cortex.
198
Lateral inhibition
Inhibition that is transmitted laterally across a nerve circuit. In the retina,
lateral inhibition is transmitted by the horizontal and amacrine cells.
199
M cells .
Ganglion cells with large centre-surround receptive fields that are rather
indifferent to the wavelength of light and adapt rapidly.
200
Optic chiasma
The part of the brain where the optic nerves partially cross. The optic chiasm
is located at immediately below the hypothalamus.
201
Optic nerve
A paired nerve that transmits visual information from the retina to the LGN
and superior colliculus.
202
Outer segment
The part of the rod and cone visual receptors that contains light-sensitive
visual pigment molecules (the retinal bound top membrane proteins).
203
P cells
Ganglion cells with small centre-surround receptive fields that are sensitive to
the wavelength of light and adapt slowly.
204
Phototransduction
The process by which light energy is transduced into electrical energy in the
rod and cone cells in the retina of the eye.
205
Retinal
A molecule bound to membrane proteins in photoreceptors that can absorb
photons. It is hence the chemical basis of animal vision.
206
Retinotopic map .
A map on a structure in the visual system, such as the lateral geniculate nucleus
or the primary visual cortex that exhibits a spatial correspondence to the
retina. In retinotopic maps, locations adjacent to each other correspond to
locations adjacent to each other on the retina.
207
Superior colliculus .
An area in the brain that is involved in controlling eye movements and other
visual behaviours. This area receives about 10 percent of the retinal ganglion
cell fibres that leave the eye in the optic nerve.
207
Striate cortex
The primary visual cortex, also called V1 or Brodmann area 17.
207
Spontaneous activity
Neural activity in the absence of an explicit task, such as sensory input or motor
output. It is also referred to as resting-state activity.
