Psyc375 Andre Test 2

Outer Segment (Photoreceptors)

contains photo-pigment; catches the light

Inner Segment(Photoreceptors)

Contains mitochondria; helps power the eye

Number of cones per eye

6-8 million

Number of rods per eye

120-130 million

Geographic distribution of cones

Mostly in fovea

Geographic distribution of rods

Mostly in periphery

Acuity of cones

Great

Acuity of Rods

bad

Acuity

smallest spatial detail that can be resolved at 100% contrast

Color in cones

They can see it

Color in rods

they can not see it (achromatic)

Peak wavelength in cones

About 550 nm

Peak wavelength in rods

About 500 nm

Purkinje Shift

Photopic (Day)= reds are brighter than greens; Mesopic= Greens are brighter than reds; Scotopic (Night)= greens turn into dark grey and reds turn into black

Motion in cone

Very sensitive

Motion in rods

not so sensitive

Luminance in cones

Day; not so sensitive; "photopic"

Luminance in rods

Night; High sensitivity to light; "scotopic"

Dark adaption in cones

quick (about 5 minutes)

Dark adaption in rods

slow (about 30 minutes)

Dark adaptation

Below your average threshold of what you're used to, you will not be able to see
Your pupil constricts to reduce the amount of light arriving at your retina

Time Course

the speed and the time spent traveling in a known direction from a known position, rather than a direct observation

Rhodopsin

Found in the rods of the retina; Extremely sensitive to light and therefore allows for good vision in low-light conditions

"Kinked" function on adaption graph

When the cones and rods are the most sensitive at any given point

Two parts of pigment

The protein and vitamin A derivative

Protein (ospin)

Found in the photoreceptor cells of the retina; Mediating the conversion of a photon of light into an electrochemical signal

Vitamin A derivative

actually catches the light

Transduction

changing physical energy into neural energy

Photo-isomerization

chromophore changes shape and releases energy when photon is absorbed; changes in flow of electrical current surrounding the photoreceptor occurs; takes <1 msec

Sign inverting (sign-reversing) connections

when light is absorbed it hyperpolarizes; rods and cones become more negative and cells become more positive

"Backwardness of eye"

no receptors on outside of eye

order of cells in the retina

photoreceptors--> horizontal --> bipolar--> amacrine--> retinal ganglion cells

Retinal Ganglion cells processing (RGC)

Light--> retinal ganglion cells--> amacrine cells--> bipolar cells

Two main types of RGC

Parvo-cellular (P-cells) and Magno-cellular (M-cells)

lateral inhibition

when neurons fire, they inhibit neighboring cells

Mach bands

differences in edges; darker on the dark side and lighter on the light side; exaggerating the edges

Microelectrodes and single cell recording

Microelectrodes are used in measuring single cells; they look for ways they get excited (EX: MRIs)

Optic Chiasm

x-shaped structure formed at the point below the brain where the two optic nerves cross-over each other

Temporal retina

visual track on the out side of the eyes and stays on the same side (Ipsilateral)

Nasal retina

visual track on the inside of the eyes; cross over; left nasal retina processes in the right hemisphere of brain and visa versa (Contralateral)

Superior Colliculus characteristics

Older; used to find where, not what
Layered multi-sensory structure

Superior Colliculus functions

the upper layer receives visual signals from the retina; lower layer processes multiple signals from various other parts of the brain

Jay and Sparks Superior Colliculus study

Found auditory cells in the Superior Colliculus; found that they fire when you aren't looking at where the noise is coming from and do not fire when you are look at where the noise is coming from ("Annoying little brother cells"

Lateral Geniculate Nucleus (LGN) characteristics

Small, ovoid, ventral projection at the terminal of the optic tract on each side of the brain; all about organization

Layers of LGN

6 layers- Layers 1 & 2 (bottom layers) are Magnocellular; Layers 3, 4, 5, & 6 (top layers) are Parvocellular

Magnocellular layers of LGN

Large; rods; necessary for the perception of movement, depth, and small differences in brightness ; Rapid and transient

Parvocellular layers of LGN

Small; Cones; long and medium wavelength; necessary for the perception of color and form (fine detail); Slow and sustained

LGN functions

Receives information directing from ascending retinal ganglion cells via optic track and from the reticular activating system; Receives many strong feedback connections from the primary visual cortex; Main connection for the optic nerve to the occipital lobe

Topographical mapping

The orderly mapping of the world in the lateral geniculate nucleus and the visual cortex

Primary Visual cortex (V1) or the Striate Cortex

The area of the cerebral cortex of the brain that receives direct inputs from the lateral geniculate nucleus, as well as feedback from other brain areas

Orientation tuning

the tendency of neurons in striate cortex to respond optimally to certain orientations and less to others

Filter

an acoustic, electrical, electronic, or optic device, instrument, computer program, or neuron that allows the passage of some range of parameters and blocks the passage of others

Ocular Dominance

The property of the receptive fields of striate cortex neurons by which they demonstrate a preference, responding somewhat more rapidly when a stimulus is presented in one eye than when it is presented in the other

Simple Cells

A cortical neuron whose receptive field has clearly defined excitatory and inhibitory regions

Complex cells

A cortical neuron whose receptive field does not have clearly defined excitatory and inhibitory regions

End Stopping

The process by which a cell in the cortex first increases its firing rate as the bar length increases to fillip its receptive field, and then decreases its firing rate as the bar is lengthened further

Column

A vertical arrangement of neurons. Neurons within a single column tend to have similar receptive fields and similar orientation preferences

Hyper-column

A 1-millimeter block of striate cortex containing two sets of columns, each covering every possible orientation, with one set preferring input from the left eye and one set preferring input from the right eye

Cytochrome Oxidase (CO)

An enzyme used to reveal the regular array of "CO blobs," which are spaced about 0.5 millimeter apart in the primary cortex

Cortical Magnification

The amount of cortical area (usually specified in millimeters) devoted to a specific region in the visual field

Perceptual consequences of Cortical Magnification

Visual Crowding- The deleterious effect of clutter on peripheral object recognition

Schneider's Experiment

Used hamster to investigate if the midbrain was involved with eye movement. They used hamsters because their brains aren't fully developed and they are easily manipulated with sunflower seeds

What did the Schneider experiment find

Focal vision was used to identify what and ambient vision was used to determine where

Differences in focal and ambient vision

retinal location; awareness (ambient needs it); Luminance (focal requires a lot); refractive error (Ambient is okay with some); optical rearrangement; spatial frequency

Civil Twilight

The time between day and night when the sun is below the horizon but its rays still light up the sky (brightest of the three phases)

Civil Twilight times

About 30 minutes before sunrise and about 30 minutes after sunset

Applied vision with driving

Uses both focal and ambient visual processes

Andre & Owens ciil twilight distance

the distance in front of the vehicle where the dark limit of civil twilight is reached and focal vision can be considered useful

How far down the road is the dark limit of civil twilight

225 feet at ground level (can vary)

Spatial Frequency Analysis

The number of cycles of a grating per unit of visual angle (usually cycles per degree)

Cycles per degree

The number of pairs of dark and bright bars per degre of visual angle

On-Center receptive fields

A cell that depolarizes in response to an increase in light intensity in its recepetive-field center; Wants the light in the center of the receptive field and dark on the outside (chocolate donut)

Off-Center receptive fields

A cell that depolarizes in response to a decrease in light intensity in its receptive-field center; Wants it dark in the center and light on the outside

Contrast

The difference in luminance between an object and the background, or between lighter and darker parts of the same object; represented by the waves amplitude

Fourier Analysis

Mathematical procedure by which any signal can be separated into component sine waves at different frequencies. Combining these sine waves will reproduce the original signals (Square waves are made up of a ton of separate sine waves)

Sine-Wave Graph physiology

Different cells = different size receptive fields = different spatial scare

Receptive fields

the region on the retina in which visual stimuli influence a neuron's firing rate

What are Sine-wave gratings

Visual stimulus with alternating darker and lighter areas with a sinusoidal luminance profile (gradual transitions into light and dark)

Sine-Wave characteristics

Higher Specific frequencies = thinner strips (finer detail)

Color vision cones

S-cones; m-cones; l-cones

S-Cones

peak at 420 nm

M-cones

peak at about 535 nm

L-cones

peak at about 565 nm

Principle of Univariance

the fact that an infinite set of different wave length intensity combinations can elicit exactly the same response from a single type of photoreceptor

Hue

divides blues, reds, greens, etc

Brightness

Related to the amount or intensity of light (lightness or darkness of the color); the more light absorbed the darker the surface will appear

Saturation

Amount of hue; pale or vivid

Color spindle

Circumference = hue; radius = saturation; height = bightness

Young-Helmholtz trichromatic receptor theory

a theory that the color of any light is defined in our visual system by the relationships of three cones (S,M,L); a "lower" theory = the actual sensation

Opponent Processing theory (Hering)

color is from the output of three mechanisms, each of them resulting from an opponency between two colors (red-green, blue-yellow, and black-white); a "higher" theory = where the processing occurs

Complementary colors

Orange and blue, Yellow and Purple, red and green

Additive color mixing

Light; approaching white when you mix

Subtractive color mixing

Pigments; The typical idea of mixing blue and yellow to get green

Color Vision Deficiencies in gender

More males than females have color deficiencies

Achromatopia

Missing all cones

Abnormal Trichromats

Red-Green Protanomaly, Red- Green Deuteranomaly

Dichromats

red-green protanipia, red-green deuteranopia, blue-yellow tritanopia

Red-Green Protanomaly

Abnormal L pigments

Red- Green Deuteranomaly

Abnormal M pigments

Red-green protanipia

Missing L pigments