NSCI 225 Learning Check #1

steps in the perceptual process

1. environmental stimulus

2. stimulus on the receptors

3. transduction

4. processing

5. perception

6. recognition

7. action

psychophysical level of analysis

stimulus and perception/behavior

-Fechner's Classical Psychophysical methods (method of limits, constant stimuli, adjustment)

-recognition testing

-reaction time

-phenomenological report

-physical tasks and judgement

physiological level of analysis

stimulus and physiology/physiology and perception

-neural recording

-brain imaging

absolute threshold

the smallest amount of a stimulus energy necessary to detect a stimulus

Gustav Fechner

developed methods to measure the relationships between stimuli and perceptions

why is it important to vary between ascending and descending trials and vary the starting point between blocks during the method of limits?

to limit response bias; this helps prevent subjects from recognizing a pattern

method of limits

stimulus is presented in ascending to descending order by an experimenter to a subject

method of adjustment

stimulus is adjusted by the subject themselves until they can barely detect it

-can be continuous or stepwise

-fastest to conduct

-most bias

method of constant stimuli

5-9 stimuli are presented in a random order a number of times

-threshold is the stimulus that is detected 50% of the time

-least bias

forced choice procedure

there are two time intervals, one with a stimulus and one without. the subject has to determine which interval the stimulus was presented in. if the subject doesn't know, it forces them to guess

-works for all senses (touch, taste, smell, audio, sight)

difference threshold

the smallest difference between two stimuli that can be detected by the subject

-studied by Ernst Weber

Weber's law

the difference threshold has a direct relationship with the intensity of the standard

DL = K*S

recognition testing

subject is asked to recognize an item seen earlier in the experiment

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dendrites

-shorter

-abundant

-receive signals

-passive signals

axons

-longer

-release signals

-myelinated

-active signals

general steps of how signals travel from neuron to neuron

1. neurons receive a signal that's either chemical (neurotransmitter/hormone) or physical (pain/sensory)

2. sodium diffuses down through the dendrites and cell body

3. the electrical signal is activated and travels quickly down the axon to the axon terminals

4. neurotransmitter release at the synapse

sodium-potassium pump

a carrier protein that uses ATP to actively transport sodium ions out of a cell and potassium ions into the cell

-along axons only

action potentials

-only in axons

-can travel at speeds up to 100 m/s

-remain constant in strength as they move, so signals are transmitted without loss

-propagated response: once the action potential is triggered, it travels down the axon without diminishing in size (when sodium ions get inside one part of an axon, the region of the axon opens its sodium channels to allow more sodium to enter the intercellular space)

-remain the same size no matter how intense the stimulus is

-once the difference in potential reaches +40 mV, the sodium channels close, and the potassium channels open, and potassium rushes out of the axon, so the charge becomes more negative

recording from single neurons

-important for understanding larger neural systems

-should record from multiple neurons individually

refractory period

a period of inactivity after a neuron has fired

spontaneous activity

action potentials that occur in the absence of a stimulus from the environment

excitatory response

inside of neuron becomes more positive and depolarizes

-increases the chances that a neuron will generate action potentials

-associated with increasing rates of nerve firing

inhibitory response

inside of neuron becomes more negative and hyperpolarized

-decreases the chances that a neuron will generate action potentials

-associated with lower rates of nerve firing

action potentials with myelinated axons

-no action potentials in myelinated area

-action potentials in nodes of ranvier (unmyelinated)

-passive current in myelinated areas

wavelength

determines the color of light

-long wavelength is red; short wavelength is violet

amplitude

determines the brightness of light

-higher amplitude is brighter light

purity

determines the amount of saturation of light

-greater purity is more saturated light

cornea

transparent layer at the front of the eye that is responsible for 70-80% of focusing the light/bending the light for the retina

sclera

opaque layer at the front of the eye that is a protective structure and makes the eyeball white; clear in front

iris

a ring of muscle tissue that forms the colored portion of the eye around the pupil and controls the size of the pupil opening

pupil

the adjustable opening in the center of the eye through which light enters

lens

the transparent structure behind the pupil that changes shape to help focus images on the retina

-the additional 20-30% of the focusing of light for the retina

-ciliary muscles are relaxed for distant vision (light rays are nearly parallel)

-ciliary muscles contract for close vision (light rays diverge and require more refraction for focusing)

aqueous humor

the clear fluid filling the space in the front of the eyeball between the lens and the cornea.

vitreous humor

jellylike substance found behind the lens in the posterior cavity of the eye that maintains its shape

retina

the light-sensitive inner surface of the eye, containing the receptor rods and cones plus layers of neurons that begin the processing of visual information

optic nerve

the nerve that carries neural impulses from the eye to the brain

-no rods and cones (no receptors, blind spot)

-made of axons from basal ganglia

-cells father in the back of the retina and exit towards the brain

-exit towards the brain at the optic disc

astigmatism

a condition in which the eye does not focus properly because of uneven curvatures of the cornea

cataracts

clouding of the lens due to protein buildup

-surgery involves using lasers to remove the cloudy lens and allow for the placement of a clear, artificial lens

myopia

objects viewed at distances appear blurry and out of focus (nearsightedness)

-light that is entering the eye from far away is bent too much and image is focused in front of the retina

hyperopia

farsightedness

-light is not bent enough and the image is focused behind the retina

presbyopia

over time, the lens becomes stiff and loses its ability to accommodate

glaucoma

the flow of the aqueous humor is obstructed, pressure builds up in the eye and puts pressure on the optic nerve, damaging it

macular degeneration

progressive damage to the macula of the retina

-only thing you can't see is the thing you are trying to look at

-opposite is retinitis pigmentosa

order of light hitting the retina

1. ganglion cells

2. bipolar cells

3. receptor cells (rods and cones)

travels in the reverse way back into the brain through the optic nerve

rods

-retinal receptors that detect black, white, and gray

-each little disc within the rod contains rhodopsin

rhodopsin

pigment in rods made of retinal and opsin

-when retinal absorbs a photon of light, it changes shape (isomerization, cis/trans), and it detaches from the opsin, making them separate entities

-"bleaching " of rhodopsin is also just known as transduction; this creates retinal and opsin

are there more rods or cones in the fovea?

cones

-everywhere else (besides the blind spot), there are more rods than cones

-there are about 120 million rods and about 5 million cones in the retina

-rods are much more sensitive to light while cones have better acuity (rods have higher convergence than cones)

the purkinje shift

blues and greens become lighter and reds become darker as we shift into night vision

-this was seen with the flower picture example, as the red flower became darker, and the green leaves became lighter as we shifted into a black/white photo (resembling night vision)

-this is due to rods having a maximum sensitivity to wavelengths of around 507 nm (shorter than 555 nm, which is the maximum sensitivity wavelength for cones)

maximum wavelength for scotopic vision (rods)

about 507 nm

maximum wavelength for photopic vision (cones)

about 555 nm

photoreceptor convergence

-126 million rods and cones converge to 1 million ganglion cells

-there is a higher convergence of rods than cones (about 120 rods to one ganglion cell and about 6 cones to one ganglion cell)

-one to one convergence of cones to ganglion cells in fovea

lateral inhibition

the pattern of interaction among neurons in the visual system in which activity in one neuron inhibits adjacent neurons' responses

-allows us to see edges

-horizontal cells connect to multiple cells across a line and allow for our lateral inhibition

-amacrine cells are also involved in lateral inhibition

ganglion cells

-the retinal output

-respond to visual stimulus features with action potentials

-about 1 million ganglion cells make up the optic nerve

-bipolar and ganglion cells give the same type of microelectrode recording

receptive field

the region on the receptors in which stimulation causes that cell to change its activity

-start out small in the fovea and increase as you move out towards the periphery

lateral plexus

in the limulus's (horseshoe crab) eye, the structure through which lateral inhibition is occurring

light hitting the off-center or off-surround causes

hyperpolarization

light hitting the on-center or on-surround causes

depolarization

lateral geniculate nucleus (LGN)

a structure in the thalamus, part of the midbrain, that receives input from the retinal ganglion cells and has input and output connections to the visual cortex

-each LGN has 6 layers

-layers 1, 4, and 6 are contralateral, so the opposite side controls the opposite eye

-layers 2, 3, and 5 are ipsilateral, so the same side controls the same eye

-M ganglion cells have a large cell body and fire in bursts. they control movement and are in layers 1 and 2

-P ganglion cells have a small cell body and sustained firing. they control color, fine texture and pattern, and depth and are in layers 3, 4, 5, and 6

-processing in the LGN is known to occur before we have conscious perceptions

-information passes from the LGN to the primary visual cortex (PVC)

which sense does not have a nucleus in the thalamus?

smell

other names for PVC

-V1

-striate cortex

-BA 17

-calcarine fissure

blindsight

-damage to V1

-LGN connections are not fully functional, so there are no conscious perceptions

what is the receptive field of the visual pathway?

the retina

simple cells

-found in the V1/PVC

-receptive field of cells consists of excitatory and inhibitory areas arranged side by side

-cells respond best to bars of a particular orientations

complex cortical cells

-found in the V1/PVC

-cells respond best to movement of a cortically oriented bar across the receptive field

-many cells respond best to a particular direction of movement

end-stopped cortical cells

-found in the V1/PVC

-cells respond to corners, angles, or bars of a particular length moving in a particular direction

top-down processing

the use of preexisting knowledge to organize individual features into a unified whole

-processing, perception, recognition

bottom-up processing

analysis that begins with the sensory receptors and works up to the brain's integration of sensory information

-transduction

Visual information that is presented to the ________ visual field is processed first by the left half of each retina and then by the ________ hemisphere of the brain

right; left