Perception Chapter 2

Visible light is between _____ and ____ nm within the electromagnetic spectrum

400; 700

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 the horizontal, bipolar, amacrine, and ganglion cells.

Farsightedness

A condition causing poor vision in which people can see objects that are far away but do not see near objects clearly. Also called hyperopia.

Rod

A cylinder-shaped receptor in the retina that is responsible for vision at low levels of illumination.

Ganglion cells

A neuron in the retina that receives inputs from bipolar and amacrine cells. The axons of the ganglion cells are the nerve fibers that travel out of the eye in the optic nerve

Amacrine Cell

A neuron that transmits signals laterally in the retina. Amacrine cells synapse with bipolar cells and ganglion cells.

Rod monochromat

A person who has a retina in which the only functioning receptors are rods.

Absorption Spectrum

A plot of the amount of light absorbed by a visual pigment versus the wavelength of light.

Cone spectral sensitivity cure

A plot of visual sensitivity versus wavelength for cone vision. Often measured by presenting a small spot of light to the fovea, which contains only cones. Can also be measured when the eye is light adapted, so cones are the most sensitive receptors.

LASIK

A process in which the cornea is sculpted with a laser in order to achieve clear vision by adjusting the focusing power of the cornea so it focuses light onto the retina.

Retina pigmentosa

A retinal disease that causes a gradual loss of vision, beginning in the peripheral retina.

Bipolar cell

A retinal neuron that receives inputs from the visual receptors and sends signals to the retinal ganglion cells.

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.

Synapse

A small space between the end of one neuron (the presynaptic neuron) and the cell body of another neuron (the postsynaptic neuron).

Preferential looking technique (PL)

A technique used to measure perception in infants. Two stimuli are presented, and the infant's looking behavior is monitored for the amount of time the infant spends viewing each stimulus.

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.

Cone

Cone-shaped receptors in the retina that are primarily responsible for vision in high levels of illumination and for color vision and detail vision.

Electromagnetic spectrum

Continuum of electromagnetic energy that extends from very-short-wavelength gamma rays to longwavelength radio waves. Visible light is a narrow band within this spectrum.

The structure of the eye that provides about 80% of the eye's focusing power is the

Cornea

Individual suffering from myopia may have difficulty seeing _______ objects clearly. Often times they are also referred to as being _______.

Distant; nearsighted

Accommodation

In vision, bringing objects located at different distances into focus by changing the shape of the lens.

Refractive Myopia

Myopia (nearsightedness) in which the cornea and/or the lens bends the light too much. See also axial myopia.

Spontaneous Activity

Nerve firing that occurs in the absence of environmental stimulation.

Dendrites

Nerve processes on the cell body that receive stimulation from other neurons.

Visual pigment regeneration

Occurs after the visual pigment's two components—opsin and retinal—have become separated due to the action of light. Regeneration, which occurs in the dark, involves a rejoining of these two components to reform the visual pigment molecule. This process depends on enzymes located in the pigment epithelium.

Inhibitory response

Occurs when a neuron's firing rate decreases due to inhibition from another neuron.

Light can be described in terms of wavelength, or as consisting of small packets of energy called

Photons

D's mother is 60 years old. Because of the condition called ______, the closest distance at which she can focus an object is probably about ____ cm.

Presbyopia; 100

Action potential

Rapid increase in positive charge in a nerve fiber that travels down the fiber. Also called the nerve impulse.

_______ reacts to light to start the process of transduction.

Retinal

In the early stages of _______, peripheral rod receptors are destroyed leading to poorer peripheral vision.

Retinitis pigmentosa

Visual Acuity

The ability to resolve small details.

Visual pigment bleaching

The change in the color of a visual pigment that occurs when visual pigment molecules are isomerized by exposure to light.

Resting Potential

The difference in charge between the inside and the outside of the nerve fiber when the fi ber is not conducting electrical signals. Most nerve fi bers have resting potentials of about 70 mV, which means the inside of the fiber is negative relative to the outside

Near Point

The distance at which the lens can no longer accommodate enough to bring close objects into focus. Objects nearer than the near point can be brought into focus only by corrective lenses.

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.

Pupil

The opening through which light reflected from objects in the environment enters the eye.

Axon

The part of the neuron that conducts nerve impulses over distances. Also called the nerve fiber.

Rod-cone break

The point on the dark adaptation curve at which vision shifts from cone vision to rod vision.

As stimulus intensity is increased, recording from a single neuron shows

The rate of the firing nerve increases

Purkinjie Shift

The shift from cone spectral sensitivity to rod spectral sensitivity that takes place during dark adaptation. See also spectral sensitivity.

Neuron

The structure that transmits electrical signals in the body. Key components of neurons are the cell body, dendrites, and the axon or nerve fiber.

Refractory Period

The time period of about 1/1,000th of a second that a nerve fiber needs to recover from conducting a nerve impulse. No new nerve impulses can be generated in the fiber until the refractory period is over.

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.

Which of the following is true about the difference between the rods and the cones?

There are about 120 million rods in the human eye and about 5 million cones.

Convergence

When many neurons synapse onto a single neuron

To isolate the rod portion of the dark adaptation curve, researchers

use rod monochromats as the participants.

The blind spot is located

where the optic nerve leaves the eye