[PS222] Midterm 1

9/23 (Tuesday)

1. Light

2. Sound

3. Chemicals

4. Pressure/heat

4 Physical Stimuli

Receptor cells

Cells that can detect physical stimuli

Transduction

The process of translating physical stimuli to neural signals

Receptive Field

an area on the sensory surface containing receptor cells which, when stimulated, change the activity of a neuron

equal

A neuron that receives signals from multiple neurons will have a receptive field size ______ to the total receptive field size of those neurons.

small, large

A receptive field with a small number of receptor cells will be _______, a receptive field with a large number of receptor cells will be _______.

• few receptor cells

• high resolution

• low sensitivity

Characteristics of a smaller receptive field

• many receptor cells

• low resolution

• high sensitivity

Characteristics of a larger receptive field

Resolution

The amount of information a neuron can convey, detail

Sensitivity

The level of receptiveness to weak or intense stimuli

smaller

Low-intensity stimuli cause a _______ change from baseline neuron activity

larger

High-intensity stimuli cause a _______ change from baseline neuron activity

1. Neuronal Level

2. Systems Level

3. Behavioral Level

Three levels of measuring how we perceive

Neuronal level of measuring perception

Use electrodes to measure deviation from baseline neuron activation

Systems level of measuring perception

Measuring response to stimulus of specific areas of the brain (ex. fMRI and EEG)

Psychophysics

Measuring the relationship between stimulus (physical) and experience (psychological)

Absolute Threshold

The level of intensity at which we can detect a certain stimulus (lowest/highest)

Difference Threshold

The amount of change in intensity required to detect a change in stimulus

Weber’s Law

The difference threshold is a constant proportion of the comparison stimulus

more, greater

As a stimulus gets _____ intense, we need a _______ intensity stimulus to detect change

proportional

The relationship between stimulus and perception is…

Method of Limits

Way of measuring absolute threshold; Play an intense stimulus, then lower intensity systematically until the observer can’t detect the stimulus (and inverse, start low and raise until they can detect it)

Method of Constant Stimuli

Way of measuring difference threshold; Present a “standard” stimulus (ex. 100hz, 20dB tone), then present a comparison stimulus (ex. 100hz, 30dB tone) and ask observer to judge whether the comparison is more intense than the standard.

wave, particles

Light is both a ____ and a stream of _______

Wave

An oscillation that travels through a medium by transferring energy from one particle point to another

Photon

A particle of light consisting of one quantum of energy

400nm-700nm

Portion of electromagnetic radiation we can see, visible light

Binocular Vision

The overlap of the eyes, allows for better depth perception

Improved spacial detail

The benefit of depth perception

Eye Movements

Allows us to point our eyes at things that are important to look at

Rectus Muscles

Controls movements on cardinal directions of the eye

Oblique Muscles

Controls eye rotation, in between directions

Superior rectus/obliques

Muscles at the top of the eye

Inferior rectus/obliques

Muscles at the bottom of the eye

Lateral rectus

Muscles at the outer portions of the eye (closest to the ear)

Medial rectus

Muscles at the inner portions of the eye (closest to the nose)

Why we don’t need to see short wavelengths

Most short, high energy wavelengths are reflected by the atmosphere (UV, X-Rays)

Why we don’t need to see long wavelenths

Long wavelengths are long enough that they go around physical objects and are not reflected off of them

Why we can see 400-700nm

Medium wavelength light is reflected off of objects and travels at immensely high speeds while also retaining spacial information; helps us understand visual information extremely fast and accurately

Choroid Layer

provides nutrients and blood to the retina and optic nerve; absorbs light

Iris

muscle that adjusts the amount of light that enters into the eye

Pupil

hole in the iris that allows light into the eye that hits the retina

Cornea

crucial for bending light to enter through the pupil; a protective layer for the eyes from UV light and debris

Aqueous humor

liquid between cornea, iris and lens; maintains shape of cornea by applying constant pressure through constant movement, leaving the outer eye/leaving the inner eye

Vitreous humor

liquid behind the lens and inside the eye; maintains the shape of the eye

Lens

located behind the pupil and connected to the zonules of zinn; focuses light let in by the pupil through thinning and fattening based on the distance of the light

Pigment epithelium

creates a barrier that regulates the transport of nutrients from the choroid layer to the retina

Retina

where transduction happens, all photoreceptors are located here

1. optical power of the cornea

2. optical power of the lens

3. size and shape of the eyeball

Three factors that impact focus

Optical power

the amount something bends (converges/diverges) light

Optical power of the cornea

Does the heavy lifting of bending light into the lens; tears reflect a good amount of light as well

uniform, unsystematically

The cornea must be a ______ shape, otherwise light from different sources will bend ___________

Optical power of the lens

dynamically bends light more, lens changes shape based on how far away light is

relaxes, tight, thin

If light comes from further away, the ciliary muscle _______, fibers are ______, and the lens is ______.

contracts, slack, fat

If light comes from a closer source, the ciliary muscle _______, fibers are ______, and the lens is ______.

Presbyopia

lens loses flexibility over time, becomes slower to accommodate to light; solved with reading glasses

Ciliary muscle

muscle that controls the shape of the lens via fibers than slack and tighten called the zonules of zinn

Zonules of zinn

fibers that connect the ciliary muscle to the lens

Focal length

distance from the retina to the cornea/lens

Why size and shape of the eyeball impacts focus

If the eyeball isn’t shaped correctly, light will not converge perfectly on the retina, creates a blurry image

Myopic

near sighted, lens decreases optical power to correct vision

Hyperopic

far sighted, lens increases optical power to correct vision

upside down, mirror image

How does light fall on our retina?

photosensitive

Photoreceptors contain a _________ pigment known as photopigments

Photosensitive

responding to light

How PRs send excitatory signals

PRs constantly emit glutamate, which is an inhibitory NT. Photopigments isomerize when interacting with light, which means they change shape and disrupt the flow of that glutamate. This means the photoreceptor becomes more positive, sending an excitatory signal to the RGCs.

1. S (short wavelength)

2. M (medium wavelength)

3. L (long wavelength)

Three kinds of cones

positive, negative

Receptive fields in the RGC can cause a _______ or a _______ response.

On Center Off Surround RF

Shining light in the center increases APs, light in the surround decreases APs

Off Center On Surround RF

Shining light in the center causes decreased APs, light in the surround increases APs

Retinal Ganglion Cells

first cells in the eye to fire action potentials; crucial for transduction and edge detection (center surround RFs)

Horizontal Cells

regulate input from photoreceptors, send inhibitory signals to opposite area of center surround RF (ex. light in center, inhibitory sent to surround)

Parasol RGCs

largest RF, most connections to PRs. more convergence (rods)

Small RGCs

smallest RF, less connections to PRs, less convergence (M and L cones)

Small Bistratified RGCs

wide range, medium connection to RGCs, moderate convergence (S cones)