Sensory processes exam 1

step 1 of perceptual process

distal stimulus

distal stimulus

objects in the environment available to observer that they attend to, the stimulus impinges on receptors for an internal representation

step 2 of perceptual process

light is reflected and focused

proximal stimulus

when the eye focuses on the light and creates a 2D representation of the tree unto the retina

Principle of Transformation

When the stimuli and responses created by the stimuli are transformed, or changed, between the environmental stimuli and perception

camera obscura effect

when bright light passes through a small aperture into a small space, projecting an upside down copy.

step 3 of perceptual process

Receptor processes

receptor processes

rod and cone receptors line the back of the eye, change light energy into electrical energy and influence what we perceive. this results in electrical representation of the tree within the neural circuits of the retina

sensory receptors

cells specialized to respond to env energy

transduction

key event which changes env energy to nerve impulses, occurs during step 3 (receptor processes)

step 4 of perceptual process

neural processing

neural processing

the different processes that occur as signals are transmitted through the maze-like network of neurons from the retina to the brain

cortex primary receiving areas

occipital - vision

temporal - hearing

parietal - touch

step 5-7 of perceptual process

behavioral responses

behavioral responses

electrical signals transformed into conscious experience <→ person perceives object (perception)<→ recognizes it as a tree (placing it into a category)(recognition) <→ lets have a closer look (action)

knowledge

information the perceiver brings to a situation

bottom up/databased processing

processing based on incoming stimuli from the env

top down/knowledge based processing

processing based on perceivers previous knowledge

the intersection between topdown and bottom up processing

perception

psychophysics

showing someone something and then observing their behavior as we lacked sufficient physiological measures to peer into the brain

stimulus perception and stimulus physiology relationship experiment

neurophysiological activity should predict/correlate with perceptual performance; the finest line width that can be perceived by the subject indicates the subjects grating acuity

stimulus physiology relationship

copla - measures relationship between bar orientation stimuli and brain activity

oblique effect

phenomenon where oblique (angled) grating produces smaller levels of brain activity than vertical/horizontal grating

absolute threshold

smallest amount of energy needed to detect a stimulus

cross-over point

the threshold, found using method of limits (stimuli of different intensities presenting in ascending and descending orders which observer responds to whether or not they perceived the stimulus)

what is the identity of the stimulus

recognition testing

how quickly can i react to it

reaction time

How can i describe what is out there

phenomenological report

difference between physical and perceptual measures

subjects estimate that the magnitude is lower than it actually is

fovea rod and cone distributions

solely consists of cones

peripheral retina rod and cone distribution

both rods and cones, but more rods than cones

macular degeneration

fovea and small surrounding area destroyed, creating blind spot in center of field, common in older individuals

retinitis pigmentosa

genetic though everyone has it, rods destroyed in periphery then fovea attacked as well. in severe cases it leads to complete blindness

how many rods and cones are there in the eye

120 million rods to 6 million cones

the blind spot

where the optic nerve leaves the eye, on edge of visual field but is filled in from the other eye. located 12-15 degrees eccentricity, is 5.5×7.5 deg,1.5 deg below horizontal

cornea

fixed and unchanging; 80% of focusing

lens

adjusts shape for object distance; 20% of focusing when ciliary muscles tighten the lens thickens. light pass through lens more sharply, focus on objects near retina

near point

the closest focal point the lens can accommodate

presbyopia

the distance of the near point increases due to hardening of the lens and weakening of ciliary muscles → corrective lens needed for close activities

myopia

nearsightedness - inability to see distant objects clearly, focus point in front of retina. caused by refractive myopia: cornea or lens bends too much light or axial myopia: eyeball is too long

hyperopia

farsightedness - inability to see nearby objects clearly. focus point behind retina, usually caused by short eyeball. constant accommodation for nearby objects can lead to eyestrain and headaches

receptor cells

specialized cells in retina that convert light to electrical signals for visual perception

electromagnetic spectrum

a continuum of all possible forms of electromagnetic energy

what is most perceived light

reflected light, we are only able to see a very small range of existing wavelengths (380-740 nm)

phototransduction

the process of transferring energy from photons to the atoms and molecules of receptor photo-pigments in the retina, converting light into electrical signals for the brain to interpret as visual images

what happens during phototransduction

the retinal absorbs a photon (leads to isomerization)

Isomerization

the retinal changes shape after absorbing a photon, triggers the opsin to initiate an enzymatic chemical chain reaction (an enzyme cascade). isomerizing one pigment leads to the activation of a rod receptor

cascade reaction

single reaction leads to increasing numbers of chemical reactions

dark adaptation

the process of increasing sensitivity in the dark (measured by determining a dark adaptation curve)

process needed for transduction

1. retinal molecule changes shape

2. opsin molecule separates

3. retina shows visual pigment bleaching

4. retinal and opsin recombine to respond to light

5. visual pigment regenerates

light threshold

lowest in the middle of the spectrum, meaning most sensitive at around 580 nm

spectral sensitivity curve

1/threshold = sensitivity

rod spectral sensitivity (scotopic)

sensitive to short-wavelength light (500 nm)

cone spectral sensitivity (photopic)

3 types:

sensitive to short wavelength (419)

sensitive to medium wavelength (531)

sensitive to long wavelength (559 nm)

purkinje shift

enhanced sensitivity to short wavelengths during dark adaptation when the shift from cone to rod vision occurs

key components of neurons

cell body - dendrites - axon or nerve fiber

sensory receptors

specialized neurons that respond to specific kinds of energy

electrical signals in neurons

light energy enters the eye → (through the optic nerve) lateral geniculate nucleus in thalamus → visual receiving area (V1 or striate cortex)

recording electrical signals in neurons

2 small electrodes used to record from single neurons (1 inside and outside) difference in charge of -70 mV (resting potential)

resting potential

negative charge of neuron relative to its surroundings (-70 mV)

action potentials

show propogated response, 1 ms refractory prd (500-800 max upper firing rate), increase in stimulus intensity means increase in rate as size of action potential remains the same regardless of intensity. spontaneous activity of action potential occurs w/o stimulation

chem basis of action potentials

sodium flows into axon making it more positive (40 mV), positively charged potassium flows out of the axon making, charge returns to resting level

synapse

small space between neurons

neurotransmitters

released by presynaptic neurons from vesicles, received by postsynaptic neuron on receptor sites, matched into receptor sites, and used as triggers for voltage change in the post synaptic neuron

depolarization

caused by excitatory transmitters. neuron becomes more positive increasing likelihood of action potential

hyperpolarization

caused by inhibitor transmitters, neurons become more negative and decreases the likelihood of action potentials

convergence

process of multiple neurons sending signals to a single neuron to combine and process info from diff sources

high convergence

126 mill rods and cones to 1 mill ganglion cells (rods converge more than cones 120+6!!)

moderate convergence

120 rods and 6 cones to each ganglion cell

no convergence

1 cone to 1 ganglion cell (happens in fovea)

how does light pass through the eye

ganglion cells → bipolar cells → receptors

rod sensitivity

rods have greater convergence and sensitivity but cannot distinguish as much detail

Cone sensitivity

high visual acuity, incredible detail but need more light to respond than rods

lateral inhibition

neural mechanism in which an excited neuron reduces the activity of its neighbors, enhancing the contrast in sensory input

receptive field

the area of receptors that affects the firing rate of a given neuron in the neural circuit. determined by monitoring single cell responses

center on vs off cells

Con - light in center leads to highest firing rate

Coff - light in surround leads to highest firing rate

signal travel through the brain

1. lateral geniculate nucleus

2. primary visual receiving area in occipital lobe (striate cortex/V1)

3. 2 pathways to temporal and parietal lobes

   1. frontal lobe

major function of LGN

regulate neural information from retina to visual cortex, signals received from retina, cortex, brain stem, and thalamus. signals organized by eye, receptor type, type of env info

what cells are feature detectors

simple cortical cells (orientation)

complex cortical cells (orientation and direction)

end stopped cortical cell (orientation direction and length)

simple cortical cell

excitatory and inhibitory areas arranged side by side. responds best to bars of particular orientation

orientation tuning curve

shows how impulse is measured as a function of orientation for simple cortical cells

optic nerve fiber (ganglion cell)

center-surround receptive field responds best to small spots but will respond to other stimuli

lateral geniculate cell

center-surround receptive field similar to ganglion cell

complex cortical cell

responds best to movement of a correctly oriented bar across the receptive field. responds best to particular direction of movement

end-stopped cortical cell

responds to corners, angles, or bars of particular length moving in a particular direction

selective adaptation

neurons tuned to specific stimuli fatigue when exposure is long; firing rate decreases and fire less when stimulus immediately presented again. only neurons that respond to specific stimulus adapt

gratings

alternating light and dark bars

selective rearing

neural plasticity shows that when not shown some types of stimuli those types of neurons do not grow as much and thus lose ability to see these stimuli

prosopagnosia

inability to recognize faces, occurs due to damage in FFA (fusiform face area)

sensory coding

a representation of perceived objects through changes in neural firing of multiple individual neurons

specificity coding

specific neurons responding to specific stimuli, leads to grandmother cell hypothesis (each person gets own neuron)

problems - too many different stimuli to assign specific neurons

most neurons respond to a number of different stimuli

population coding

the pattern of firing across many neurons encodes specific objects, a large number of stimuli can be coded by a few neurons

sparse coding

only a small subset of neurons is active at any given time to represent specific stimuli

contextual modulation

response to stimulation within the receptive field can be affected by outside the receptive field

Topology

the study of geometric properties and spatial relations unaffected by the continuous change of a shape or the size of figures. refers to the way in which constituent parts are interrelated or arranged. topological maps are more concerned with relative than absolute positions

cochlea

tonotopic resonance along linear surface, representation of ears membrane, transduces sound and wired with receptors that have distinct topologu

auditory cortex

tonotopic map of cochlea surface

retinotopic map

electron map of the retina on the cortex

cortical magnification

small area of fovea is represented by large area on visual cortex, most of the visual field periphery has little computing power

positron emission tomography

radioactive tracer that moves through bloodstream and measures radioactivity in blood flow. Changes in blood flow → changes in brain activity