PSYC 212

Perceptual process

steps occur between time a person looks at stimulus in environment, perceives it, recognizes and takes action toward it

Distal Stimulus

object in environment available to observer
environmental stimuli

Proximal Stimulus

"in proximity" to receptors
representation of distal stimulus on receptors

Principle of Representation

everything person perceives based not on direct contact with stimuli but on representations of stimuli that are formed on receptors and resulting activity in person's nervous system

Principle of transformation

when stimuli and responses created by stimuli are transformed between environmental stimulus and perception

Step 1 and 2 of Perceptual Process

Distal stimulus is transformed into the proximal stimulus and this image represents the stimulus in person's eye

sensory receptors

cells specialized to respond to environmental energy

transduction

changes environmental energy to nerve impulses

Step 3 of Perceptual Process

receptor process
sensory receptors transduce signals and end result is electrical representation of stimulus

Step 4 of Perceptual Process

neural processing and sent towards the brain

neural processing

changes that occur as signals transmitted through maze of neurons

Primary receiving area

area of cerebral cortex that first receives most signals initiated by sense's receptors

Steps 5-7 of Perceptual Process

electrical signals transformed into conscious experience
perception
recognition
action

perception

conscious awareness of stimulus

recognition

placing an object in a category

action

involves motor activities in response to stimulus

knowledge

any information that perceiver brings to situation

Bottom-up processing:

processing based on incoming stimuli from environment

incoming data

data based processing

Top-down processing

processing based on perceiver's previous knowledge
knowledge-based processing

Studying Perceptual Process

stimulus-perception
stimulus-physiology
physiology-perception

oblique effect

The finding that vertical and horizontal orientations can be perceived more easily than other (slanted) orientations.

optical imaging

electrical activity of neurons related to local metabolic activity and blood flow
correlates brain activity
blood volume changes
blood oxygenation changes
light scattering changes caused ion water movement

Physiology Behavior relationship

decreasing intensity between dark and light bars until subject could no longer detect gratings

absolute threshold

smallest amount of energy ended to detect a stimulus

Method of limits

stimuli of different intensities presented in ascending and descending order
observer responds to whether she perceived the stimulus
cross-over point in threshold

Method of adjustment

adjust the volume until you can just barely hear the sound

Method of constant stimuli

different stimulus intensities are presented one at a time and participant must respond whether they perceive
stimulus intensities presented in random order

Difference threshold

smallest difference between two stimuli that enable us to tell the difference between them

Magnitude Estimation and Power Function

ask subject to estimate magnitude of the stimulus
at low intensities, detect difference
as intensity gets higher, ability to detect changes is less

cell body

contains mechanisms to keep cell alive

dendrites

branch out to receive electrical signals from other neurons

axon

filled with fluid that conducts electrical signals

Recording electrical signals in neurons

small electrodes used to record from single neuron
recording electrode inside nerve fiber
reference electrode outside fiber

resting potential

when there are no signals in neuron, at rest
-70mV

Properties of Action Potential

show propagated response
remain same size regardless of stimulus intensity
increase in rate to increase in stimulus intensity
have refractory period
show spontaneous activity that occurs without stimulation

propagated response

once triggered, travels all the way down axon without decreasing in size

Chemical Basis of Action Potential

sodium ions (Na+): positive chargerich outside neuron
chlorine ions (Cl-): negative chargerich outside neuron
potassium ions (K+): positive charge

Rising phase of action potential

-70 mV to 40 mV
inflow of Na+

falling phase of action potential

+40mV to -70mV
potassium rushes out

neurotransmitters

released by presynaptic neuron from vesicles
received by postsynaptic neuron on receptor sites
matched like key to lock

excitatory transmitters

depolarization
increase likelihood of action potential

depolarization

neurons become more positive

inhibitory transmitters

hyperpolarization
decrease likelihood of a action potential

hyper polarization

neuron become more negative

specificity coding

specialized neuron that responds only to one concept or stimulus
one neuron can represent one stimulus or concept

Sparse coding

when particular stimulus is represented by pattern of firing of only a small group of neurons

most neurons remain silent

evidence that code for representing objects may involve pattern of activity across relatively small number of neurons

population coding

proposes that our experiences are represented by pattern of firing across large number of neurons
large number of stimuli can be represented because large groups of neurons can create huge umber of different patterns

modularity

idea that specific brain areas are specialized to respond to specific types of stimuli or functions
each specific area is module
can be studied by recording brain responses

distributed representation

idea that brain represents information in patterns distributed across cortex, not just one brain area
focuses on activity in multiple brain areas and connections between those areas

structural connectivity

road map of fibers connecting different areas of brain

functional connectivity

neural activity associated with particular function that is flowing through this structural network

wavelength

distance between peaks of electromagnetic waves

visible light

energy that humans can perceive at certain range

pupil

light enters eye

retina

network of neurons that covers back of eye and contains receptors for vision

visual pigment

light sensitive proteins

fovea

contains only cones

small receptive field

peripheral retina

outside fovea with both cones and rods with more rods

larger receptive fields

macular degeneration

cone-rich fovea destroyed and creates blind region in central vision

retinitis pigmentosa

degeneration of retina and attacks peripheral rod receptors

blind spot

absence of photoreceptors
brain creates perception that matches surrounding pattern

cornea

transparent covering of front eye accounts for 80% of eye focusing power
can't adjust its focus

lens

can change shape to adjust eye's focus for objects

ciliary muscles

increase focusing power of lens by increasing curvature

accommodation

change of lens shape when ciliary muscles tighten and increase curvature of lens to adjust for light

Myopia

nearsightedness
trouble seeing distant objects
refractive and axial

refractive myopia

cornea and lens overbend the light

axial myopia

eyeball is too long

hyperopia

farsightedness
trouble seeing near objects
focus point beyond the retina
eyeball too short

presbyopia

trouble seeing near objects due to aging
lens becomes more rigid with age

visual pigment and transduction

opsin and retinal
visual pigment absorbs light and causes molecule to isomerize (change shape)
this creates chemical chain reaction that activates charged molecules to create electrical signals

dark adaptation

process of increasing sensitivity in the dark

measuring dark adaptation curve

look at fixation point and pay attention to flashing light and adjust until barely seen
measure sensitivity: high threshold \= low sensitivity
then turn off lights and adjust until test light barely seen

threshold

minimum amount of energy necessary to just barely see light is converted to sensitivity

dark adaptation curve

as adaptation proceeds, participant becomes more sensitive to light
higher sensitivity at bottom of graph so movement downward means sensitivity increases

visual pigment bleaching

change in shape and separation from opsin causes molecule to become lighter in color

spectral sensitivity

eye's sensitivity to light as a function of light's wavelength

Spectral Sensitivity Curve

present wavelength one at a time and measure sensitivity
rods more sensitive to short wavelength than cones (500 nm)
cones most sensitive to wavelengths around 560 nm

purkinje shift

enhanced perception of short wavelengths during dark adaptation

absorption spectrum

plot of light absorbed vs. wavelength of light

pigment absorption spectrum

rods best absorb blue-green area of spectrum
short wavelength pigment absorbs best at 419 nm
medium wavelength pigment absorbs best at 531 nm
long wavelength pigment absorbs best at 558 nm

Neural convergence

number of neurons synapse onto single neuron

rod convergence

rods result in better sensitivity than cones
greater sensitivity of rods→ takes less light to generate response form individual rod receptor than individual cone receptor
ex: five rod receptors converge onto one ganglion cell

ganglion cell receiving more

cone convergence

cones result in better detail vision in rods
cones have better visual acuity
cones and ganglion cells converge 1:1
highest visual acuity in fovea

Hartline's Discovery of Receptive Field

isolated single ganglion cell axon in opened eyecup of frug
illuminated different areas of retina and found that cell he was recording from responded only when small area of retina was illuminated→ RGC
receptive field covered area greater than single photo
receptorreceptive fields overlap

Kuffler's Discovery of Center-Surround

measured ganglion cell receptive field in cat and reported property of these fields
ganglion cells have center-surround receptive fields that are arranged like concentric circles in center-surround organization

center surround antagonism

when light covers inhibitory areas, this counteracts excitatory response causing decrease in neuron's firing rate

Lateral Inhibition

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

edge enhancement

increase in perceived contrast at borders between regions of visual field

Mach bands

illusory light and dark bands near a light-dark border

resting-state fMRI

measure functional connectivity and resting state activity of brain

task-related fMRI

measured activity of brain as person engaged in specific task

reaction time

time between presentation of stimulus and an observer's or listener's response to stimulus

optic chiasm

x-shaped bundle fibers on underside of brain

superior colliculus

structure involved in controlling eye movements

pathway to brain

signals cross over
90% travel to lateral geniculate nucleus
10% travel to superior colliculus
LGN to occipital lobe

lateral geniculate nucleus

neurons have center-surround receptive field

signal sent from LGN to cortex smaller than input LGN receives from retina

feedback

backward flow of information

occipital lobe

also known as visual receiving area or striate cortex or V1

Hubel and Wiesel

• stimulate retina with patterns of light while recording single cells at various points along visual pathway

• cells in striate cortex have inhibitory and excitatory areas