VISION

, vision is also often implicated in a blending-of-sensations phenomenon known as

synesthesia.

Visual information might be processed in parallel pathways which can generally be described as the

"what pathway" (the ventral pathway) and the "where/how" pathway (the dorsal pathway).

Cones

- Cones are types of photoreceptors that work best in bright light conditions. - Cones are very sensitive to acute detail and provide tremendous spatial resolution. - involved in our ability to perceive color.

While cones are concentrated in the fovea; where images tend to be focused,, RODS, another type of photoreceptor, are

- Rods are located throughout the remainder of the retina. Rods are specialized photoreceptors that work well in low light conditions - they lack the spatial resolution and color function of the cones - they are involved in our vision in dimly lit environments as well as in our perception of movement on the periphery of our visual field.

Wavelength

- refers to the length of a wave from one peak to the next. - is directly related to the frequency of a given waveform

The optic nerve from each eye merges just below the brain at a point called the

- the optic chiasm is an X-shaped structure that sits just below the cerebral cortex at the front of the brain. - At the point of the optic chiasm, information from the right visual field (which comes from both eyes) is sent to the left side of the brain, and information from the left visual field is sent to the right side of the brain.

Frequency refers to the number of

- waves that pass a given point in a given time period - is often expressed in terms of hertz (Hz), or cycles per second.

Axons from the retinal ganglion cells converge and exit through the back of the eye to form the

Axons from the retinal ganglion cells converge and exit through the back of the eye to form the

There is a point in the visual field called the

Blind Spot

COLOR VISION

COLOR VISION

Normal-sighted individuals have three different types of cones that mediate

Color Vision

DEPTH PERCEPTION

DEPTH PERCEPTION

The "what pathway" "where/how pathway" EXAMPLE

For example, when you see a ball rolling down the street, the "what pathway" identifies what the object is, and the "where/how pathway" identifies its location or movement in space.

vestibulo-ocular reflex.

It is achieved by integrating information from both the visual and the vestibular system (which knows about body motion and position). EXAMPLE when you move your head in one direction, your eyes reflexively move in the opposite direction to compensate, allowing you to maintain your gaze on the object that you are looking at.

LIGHT WAVES

LIGHT WAVES

Longer vs. Shorter Wavelengths

Longer wavelengths will have lower frequencies, and shorter wavelengths will have higher frequencies

Rods and cones are connected (via several interneurons) to

Retinal ganglion cells

the portion of the larger electromagnetic spectrum that we can see

The visible spectrum

The eye is the major sensory organ involved in

VISION

As mentioned above, light enters your eyes as a

WAVE

In humans, light wavelength is associated with perception of color

Within the visible spectrum, our experience of red is associated with longer wavelengths - greens are intermediate, and blues and violets are shorter in wavelength: - mnemonic ROYGBIV: red, orange, yellow, green, blue, indigo, violet.) - The amplitude of light waves is associated with our experience of brightness or intensity of color, with larger amplitudes appearing brighter.

lens

a curved, transparent structure that serves to provide additional focus. - is attached to muscles that can change its shape to aid in focusing light that is reflected from near or far objects

Young-Helmholtz trichromatic theory of color vision

all colors in the spectrum can be produced by combining red, green, and blue. The three types of cones are each receptive to one of the colors.

Two physical characteristics of a wave are

amplitude and wavelength

We use a variety of cues in a visual scene to establish our sense of depth. Some of these are;

binocular cues, which means that they rely on the use of both eyes.

example of a binocular depth cue is

binocular disparity (binocular disparity: the slightly different view of the world that each of our eyes receives.)

The optic nerve carries..

carries visual information from the retina to the brain

the electromagnetic spectrum

cause or have all of the electromagnetic radiation that occurs in our environment and includes gamma rays, x-rays, ultraviolet light, visible light, infrared light, microwaves, and radio waves.

opponent-process theory.

color is coded in opponent pairs: black-white, yellow-blue, and green-red. - The basic idea is that some cells of the visual system are excited by one of the opponent colors and inhibited by the other. So, a cell that was excited by wavelengths associated with green would be inhibited by wavelengths associated with red, and vice versa - we do not experience greenish-reds or yellowish-blues as colors - Another implication is that this leads to the experience of negative afterimages.

An afterimage describes the

continuation of a visual sensation after removal of the stimulus. EX when you stare briefly at the sun and then look away from it, you may still perceive a spot of light although the stimulus (the sun) has been removed.

Light waves are transmitted across the

cornea

monocular cues

cues that require only one eye

Our ability to perceive spatial relationships in three-dimensional (3-D) space is known as

depth perception.

The cornea is the transparent covering over the

eye - It serves as a barrier between the inner eye and the outside world - it is involved in focusing light waves that enter the eye

In a normal-sighted individual, the lens will focus images perfectly on a small indentation in the back of the eye known as the

fovea, which is part of the retina,

The amplitude of a wave is the height of a wave as measured from the

highest point on the wave (peak or crest) to the lowest point on the wave (trough).

with depth perception we can describe things like

in front, behind, above, below, or to the side of other things.

The pupil's size is controlled by muscles that are connected to the

iris,

The "what pathway"

is involved in object recognition and identification,

"where/how pathway"

is involved with location in space and how one might interact with a particular visual stimulus

iris,

is the colored portion of the eye.

photoreceptor cells

known as cones, are light-detecting cells.

After passing through the pupil, light crosses the

lens

An example of a monocular cue would be what is known as

linear perspective (Linear perspective refers to the fact that we perceive depth when we see two parallel lines that seem to converge in an image)

Once inside the brain, visual information is sent via a number of structures to the

occipital lobe at the back of the brain for processing.

Synesthesia occurs when

one sensory signal gives rise to two or more sensations. - most common type is grapheme-color synesthesia. EXAMPLE taste and color or music and color: the taste of chicken might elicit a sensation of green, for example, and the timbre of violin a deep purple.

The fovea contains densely packed specialized photoreceptor cells;

photoreceptor cells

Light waves are transmitted across the cornea and enter the eye through the

pupil

trichromatic theory applies:

the cones are responsive to three different wavelengths that represent red, blue, and green. But once the signal moves past the retina on its way to the brain, the cells respond in a way consistent with opponent-process theory (Land, 1959; Kaiser, 1997).

retina

the light-sensitive lining of the eye

The pupil is

the small opening in the eye through which light passes - the size of the pupil can change as a function of light levels as well as emotional arousal - When light levels are low, the pupil will become dilated, or expanded, to allow more light to enter the eye. - When light levels are high, the pupil will constrict, or become smaller, to reduce the amount of light that enters the eye.

The visible spectrum in humans is associated with

wavelengths that range from 380 to 740 nm