Sensation & Perception Exam #1

Absolute Threshold

Minimum stimulus intensity needed to evoke a sensation

Difference Threshold

Minimum change in intensity that leads to a noticeably different stimulus

Axon

A long, thin fiber that transmits signals away from the neuron cell body to other neurons, or to muscles or glands.

Cell body

Largest part of a typical neuron; contains the nucleus and much of the cytoplasm

Bleached/Unbleached

Refers to rods and cones; when photopigments are exposed to too much light, they become bleached. It takes time for the bleached pigment to revert to the unbleached state. Rods take longer to recover than cones do.

Center-On

Cell shows excited response if light hits center and an inhibited response of light hits the surround area

Center-Off

Cell shows excited response if light hits surround area and inhibited response if it hits the center

Convergence

The ability for multiple presynaptic neurons to "speak" to a single postsynaptic neuron. Rods have high convergence on a ganglion cell. Cones have low convergence on a ganglion cell.

Convex Lens

Focuses light onto a single point in the eye (fovea) where there is a high concentration of cones. The lens is adjustable via surrounding muscles to change its shape and refocus. (lens gets thicker when looking at close objects)

Correct Rejections

When subject indicates no stimulus is present and is correct

Dark-Adapted

The process by which our eyes adjust to darkness after being exposed to light; made possible by the dilation of our pupils and changes in the rods and cones of our retinas. Rods detect form and motion, and cones detect color. So in darkness our rods kick into high gear while our cones take a backseat.

Dendrite

Branchlike parts of a neuron that are specialized to receive information

Dual nature of light

light has properties of both particles and waves; Light is useful as a wave because of reflection and refraction.

Duplex Solution

Two types of cells: one for sensitivity and one for resolution; when rods have higher convergence, sensitivity is higher; when cones have higher convergence, resolution is higher

Eccentricity

the distance between the retinal image and the fovea

Excitation

When a stimulus or a presynaptic neuron increases the chance of a postsynaptic neuron to fire an action potential

False Alarms

When subjects claim stimulus is present when in fact it is not

Sensation

Faculty of perceiving by the senses, physical sensibility; information brought in through senses

Perception

Process of becoming aware of physical objects, phenomena, etc, through the senses; process of organizing/using info recorded from senses

Transduction

The change from external stimulus (EM waves, pressure changes) to neural information

Levels of Analysis

Computational, Representation & Algrorithim, and Hardware Implementation

Computational Analysis

What does the device do? Why does it do it this way? What problem is it solving? (cash register: Addition, subtraction, multiplication)

Representation & Algorithim

What strategy is it using? How is it represented? (cash register: Arabic numerals; algorithm- start with cents and move to tenths, dollars)

Hardware Implementation

What is the electronic circuitry/mechanical parts? (cash register: positions on a ten-notch metal wheel; binary coded decimal numbers)

Neuron

A cell that carries information through the nervous system.

Signal Detection Theory

A theory predicting how and when we detect the presence of a faint stimulus ("signal") amid background stimulation ("noise"). Assumes there is no single absolute threshold and detection is subjective.

if the signal is very strong, there is little to no overlap of the 2 distributions (noise & noise+signal). If the signal is not very strong, there is overlap of the 2 distributions. Overlap = Chance of Error.

Psychophysics

the bridge between the physical world and the perceptual world

Physical vs. Perceptual Characteristics

Light intensity vs. Brightness

Surface Reflectance vs. Lightness

Amplitude of acoustic wave vs. loudness

temperature vs. warmth

mass vs. heaviness

Weber's Law

Difference threshold is a fixed proportion of stimulus intensity

2 lbs->3 lbs = noticeable

12 lbs->13 lbs = not noticeable

Weber's Law Equation

(Difference Threshold) = (K constant) x (stimulus intensity)

Just Noticeable Difference

The difference threshold at that stimulus intensity (in units of sensation)

Method of Adjustment

The observer or the experimenter adjusts the stimulus intensity continuously until the observer can just barely detect the stimulus.They control the stimulus themselves, they do not have to tell the experimenter "yes" or "no"

Method of Constant Stimuli

A psychophysical method in which a number of stimuli with different intensities are presented repeatedly in a random order; subject has to report stimuli absence or presence

Method of Limits

Start at noticeable stimulus and present less of it until it's no longer noticeable, or start at unnoticeable and do the opposite

Concerns about detection experimental diagrams

-No objectively correct answer

-honesty

-motivation

Forced Choice

Instead of "is the stimulus present?" you answer something about the stimulus.

Light Advantages vs. Disadvantages

Advantages: preserves high resolution; travels long distances; interacts with surface

Disadvantages: can't use in the dark; can't see around opaque objects (chalkboard example)

Focal Length

The distance between the focal point and the lens

Functions of the eye

Transduction; produce sharp image; start image processing

Optics of the Eye

1. Lens

2. Cornea ->70% of the power of the system

Cornea

A clear, protective layer covering the lens and the front portion of the eye; it holds 70% of the focusing power.

Optic Nerve

A bundle of axons from the ganglion cells of the retina; information from the retina is carried through this to the brain to continue the perception process.

Photoreceptors

Light-sensitive cells (neurons) in the retina that convert light energy to neural impulses. Consist of rods and cones

Collector Cells

1. Horizontal

2. Bipolar

3. Amacrine

Inhibition

When a presynaptic neuron decreases the chance of a postsynaptic neuron to fire an action potential.

Rods

See in greys; need dim light; don't need much light; many, all over retina; one kind of rod

Cones

See in color; can react to bright light; need more light than rods; fewer than rods, very tightly packed; 3 kinds of cones

Sensitivity

A measurement instrument's ability to accurately measure variability in stimuli or responses

Resolution

The clarity of an image; the ability to distinguish one point from another point on an image.

Ganglion Cells

In the retina, the specialized neurons that connect to the bipolar cells; the bundled axons of the ganglion cells form the optic nerve; has the "target shape"; most of the visual field has no response, small circular center field has excitatory response, and donut-shaped surrounds have inhibitory response

3 types of cells in retina

Ganglion, collector cells, photoreceptors

Hits

Claiming a stimulus is present and being correct

Integration

When a neuron adds up the inputs from presynaptic cells (inhibitory and excitatory inputs). If the threshold is met, an action potential is fired. The action potential is the output.

Materialism

idea that the only thing that exists is matter, and everything is a response of tiny bits of matter interacting

Panpsychism

all matter has consciousness

Photopigment

chemically changed by light, in rods and cones, can be bleached or unbleached, reduce electrical current

Rate Law

# of neurons firing; higher stimulus has higher rate. number of spikes / unit of time.

Receptive Field

visual field in which the ganglion cells in question respond

reflection

To redirect something that strikes a surface- especially light, sound or heat- usually back toward its point of origin.

Refraction

The change in the direction of a wave when it passes into a different medium. Light waves refract through a lens, such as the lens in our eye.

Rhodopson

the visual pigment found in rods

Specific Nerve Energies

Formulated by Muller- says the nature of a sensation depends on which sensory fibers are stimulated, not on how fibers are stimulated

Stimulus

something that excites an organism to functional activity

Terminal

The point at which a neuron passes information to the neurons with which it contacts.

Transducer

translates one form of energy to another