PSYC 212

Rosenblatt's Perceptron

Rosenblatt's Perceptron

A computer than can be trained to learn perceptual patterns; computers still can't perceive as well as humans

Perception

Identified with complex processes that involve higher-order mechanisms like interpretation and memory that involve activity in the brain; everything that invovles understanding how we experience the world through our senses; ex) identifying the food you're eating and remebering the last time you had it; the experiences that result from stimulation of the senses; smth you experience constantly; everything you see, hear, taste, feel, or smell is the result of activity in your nervous system and your knowledge gained from past experience; must activate sensory receptors designed to respond to light energy, sound energy, chemical stimuli, and perssure on the skin; a continuously changing process (dynamic); how we understand scenarios; interpreting external stimuli; making something out of something; giving meaning to stimuli; internal representations of things that are out there

Sensation

Involving simple "elementary" processes that occur right at the beginning of a sensory system. Ex) when light reaches the eye , sound waves enter the ear, or food touches your tongue

Perceptual process

Begins w stimulus in environment and ends with perceiving the stimulus, recognizing it, and taking action relative to it: Perceptual system starts with image on retina and its job is to determine object "out there" that created that image

Overview: stimulus (distal and proximal 1,2) , physiology (receptors and neural processing 3,4), behavior (perception, recognition, action 5,6,7)

Step 1) distal stimulus: distant/in the environment ex) a tree. The perceptions of the tree is based on light reflected from tree entering the eye and reaching the visual receptors and the pressure changes in the ear caused by the rustling leaves entering the ear and reaching the auditory receptors.

Step 2) light is transformed when it is reflected from the tree, when it travels through the atmosphere, and when it is focused on by the eye's optical system. Result is proximal stimulus: image of tree on retina, a representation of the tree

Step 3) receptor processes: sensory receptors receive info from environment and transform environmental energy into electric energy (transduction), and shape perception by the way they respond to different properties of the stimuli. Sensory receptors are bridge btwn external sensory world and your internal (neural) representation of that world; end result: an electrical representation of tree.

Step 4) neural processing: electrical signals travel through interconnected network of neurons that transmit signals from the receptors to/within the brain and change/process the signals as they are transmitted; signals can be reduced, prevented from getting through, or amplified, then travel to various places in the brain; electrical signals created through transduction are often sent to a sense's primary receiving area in cerebral cortex (creates perceptions). Primary receiving area for: vision=occipital lobe. Hearing=temporal lobe=what pathway. Skin senses=parietal lobe=where pathway. Frontal lobe=receives signals form all senses, important for coordinating perceptions from multiple senses together

Step 5) electrical signals transformed into conscious experience or perception (conscious awareness)

Step 6) recognition; placing object into category/giving it meaning

Step 7) action; motor activities in response to stimulus

Distal stimulus

Environmental stimuli are all objects in the environment available to the observer; stimulus impinges on receptors resulting in internal representation

Proximal stimulus

The representation of the distal stimulus on the receptors; stimulus is "in proximity" to the receptors

Principle of transformation

States that stimuli and responses created by stimuli are transformed, or changed, btwn the distal stimulus and perception. Ex) transformation of light hitting the tree and being reflected, then the reflected light enters eye and is transformed again by vision receptors

Principle of representation

States that everything a person perceives is based not on direct contact w stimuli but on representations of stimuli that are formed on the receptors and the resulting activity in the person's nervous system. Ex) distal stimulus (tree) is transformed into proximal stimulus and this image represents the tree in the person's eyes

Sensory receptors

Cells specialized to respond to environmental energy; each sensory systems receptors are specialized to respond to a specific type of energy —> visual receptors respond to light, auditory receptors respond to pressure changes in air, touch receptors respond to pressure transmitted through skin, and smell and taste receptors to chemicals entering nose/mouth

Transduction

Transformation of light/sound/thermal energy into electrical energy that can be understood by the brain; changing of one form of energy into another; ex) light energy transformed into electrical energy (how neurons function: they carry electrochemical signals to the brain that the brain can understand) ; visual transduction occurs by rod and cone receptors which change the environmental light energy into nerve impulses;

Occurs bc isomerization of retinal

Neural processing

Changes in the signals in perceptual process that occur as they are transmitted through maze of neurons; the interaction of the signals of many neurons; perception is outcome of neural processing

If problems in eye's focusing system deliver degraded images to retina, no amount of processing in brain can create sharp perception

Visual Object Agnosia

Inability to recognize (identify) objects ; not an issue of perception bc you still know smth is there

Knowledge

Any information that the perceiver brings to a situation; prior experience or expectations; can affect steps of perceptual process; rat/man demonstration shows how recently acquired knowledge can influence perception ; naming objects=categorizing them —> long term knowledge buildup influences perception

Bottom-up processing

Processing based on incoming stimuli reaching receptors; stimuli provide starting point; data based processing; to detect something

Top-down processing

Processing based on perceiver's previous knowledge (cognitive factors); our knowledge of how things usually appear in the environment, based on past experiences, can play an important role in determining what we perceive; knowledge based processing; to perceive something; ex) if you're given first few and last few letters of a word, you can still read an entire book of those misspelled words bc you're predicting what it will say even though it doesn't actually say it; causes optical illusion/bistable figure bc you expect smth from previous knowledge; know from experience

Computer vision

Object recognition: detection of objects in an image and then matching those objects to existing, stored representations of what those object are to create a scene

-Autonomous vehicles: require fast and precise identification of objects in order to smoothly navigate environment -cellphones: rely on object recognition: face recognition across different angles and lighting to unlock device -hard to design perceiving machine bc stimulus on receptors is ambiguous: inverse projection problem: an image on retina can be caused by an infinite number of objects; objects can be hidden or blurred; occlusions are common in environment; objects look different from different viewpoints; difficult task for computers to perform; ambiguity of image on retina

Dualism

Physical dimension=sound waves/electromagnetic spectrum. Psychological dimension=frequency (pitch), tone, amplitude (loudness), the image you develop etc

Oblique effect

Ppl see vertical and horizontal lines better than lines oriented obliquely (diagonally, not horizontal or vertical); exists bc we grew up in world where almost everything is horizontal or vertical

Stimulus-behavior relationship

Relates stimuli straight to behavioral responses; studied using psychophysics: measures relationships btwn the physical (stimulus) and the psychological (behavioral response); use grating acuity: finest line width at which you can perceive bars in a black/white grating stimulus; you're asked to indicate grating's orientations; ex) see/hear phone ring and immediately pick up phone

Stimulus-physiology relationship

Stimuli to physiological response like neurons firing; studied by measuring brain activity; ex) measure brain response size to line orientation bc horizontal/vert lines generate largest brain activity; optical imaging: electrical activity of neurons is related to local metabolic activity and blood flow, blood flow volume changes, blood oxygenation changes, light scattering changes caused by ion and water movement, brain response is bigger to vertical/horizontal orientation; bypassing perception and behavior

Physiology-behavior relationship

Studied by measuring brain response and behavioral sensitivity in same participants using fMRI; still lines idea

Absolute threshold

Smallest stimulus level that can be detected; grating acuity experiment ex) smallest line width that can be detected; thresholds measure the limits of sensory systems; measures of the minimums; Light intensity necessary for you to detect it

Methods for measuring the limit

-Method of limits: stimuli of different intensities presented in ascending and descending order, observer responds to whether she perceived the stimulus, crossover point is the threshold -method of constant stimuli: one after another tones say yes/no hear; time consuming; more accurate, person must detect stimuli over 50% of time so that it's above chance -Method of adjustment: participant adjusts stimulus intensity themselves unit it's barely detectable; faster; less accurate

Together called the psychophysical methods

Difference threshold

Smallest difference btwn 2 stimuli that enables us to tell the difference btwn them; intensity by which a stimulus has to change for a person to be able to detect the difference. Jnd=just noticeable difference

Magnitude estimation

You ask subject to estimate magnitude of stimulus; you also have the actual stimulus intensity; power functions; To determine relationship btwn physical stimuli and their magnitude; participant assigns loudness value to each sound intensity; the # for loudness is the perceived magnitude of the stimulus; for measuring perception above threshold

Recognition testing

Recognition=categorization/naming —> testing identity of stimulus such as with ppl w brain damage ; for measuring perception above threshold

Reaction time

Time btwn presentation of a stimulus and the person's reaction to it; for measuring perception above threshold

Electromagnetic spectrum

The waves (ultra violet, gamma, FM, etc) you give meaning to to get sight; vision is based on visible light (a band of energy within electromagnetic spectrum)

Sound

Sound waves; pressure changes that you make to represent sound; sound isn't actually out there

Smells/tastes

Come from representation of chemicals through receptors

Consciousness

Everything that we are experiencing through our senses in our brain

Neuron

Cell body: contains mechanisms to keep cell alive Dendrites: receive electrical signals from other neurons Axon/nerve fiber: filled w fluid that conducts electrical signals; electrodes used to record electrical signals in axons

Action potential

Propagated response; once response is triggered, it travels all the way down the axon without decreasing in size; increasing stimulus size increases rate and regularity of nerve firing in this fiber but doesn't affect size of action potentials; refractory period: the interval btwn the time one nerve impulse occurs and the next one can be generated in the axon; spontaneous activity: the few action potentials that occur before the stimulus arrives; Na+ starts outside, K+ inside, Na+ channels open and Na+ travels in, K+ travels out, Sodium Potassium Pump puts it back to normal; rising phase of action potential: quick and steep depolarization from -70 mV to +40 mV (inside gets more positive bc Na+ enters); hyperpolarization: +40 mV to -70 mV (increase in neg charge inside neuron; falling phase of action potential) ; when action potentials reach end of neuron, they trigger release of chemicals called neurotransmitters at synapse which bind to receptor sites that are sensitive to specific neurotransmitters which triggers either excitatory response (depolarization so inside is more positive) or inhibitory response (inside gets more negative, hyper polarized); excitation increases chances that neuron will generate action potentials and is associated w increasing rates of nerve firing; inhibition decreases chances that neuron will generate action potentials and is associated w lowering rates of nerve firing

Sensory code

Refers to how neurons represent various characteristics of environment

Specificity coding

Notion of a specialized neuron that responds only to one concept or stimulus; ex) one neuron can represent one perceptual experience, like the taste of salt; ex: for a specific person's face

Grandmother cell

A cell that only responds to your grandmother; highly specific type of neuron; even just thinking abt the idea of your grandma can make grandmother cell fire; neurons respond to both presence/visual input of someone, but also the concept of that particular person; no proof though— perhaps a number of neurons (not j 1) are involved in representing a perceptual experience

Sparse coding

When a particular stimulus is represented by a pattern of firing of only a small group of neurons with the majority of neurons remaining silent; more likely than specificity coding

Population coding

Proposes that our experiences are represented by the pattern of firing across a large number of neurons; large number of stimuli can be represented bc large groups of neurons can create a huge number of different patterns

Phrenology

Approach using shape/bumps/contours on a person's skull to conclude brain areas, abilities, and traits; debunked as a method later

Distributed representation

Idea that brain represents info in patterns distributed across cortex, not just one brain area; distributed approach to representation focuses on activity in multiple brain areas and the connections btwn those areas.

Modularity

Idea that specific brain areas are specialized to respond to specific types of stimuli/functions; each specific area is called a module; studied using brain imaging which creates pictures of the location of the brain's activity; not true bc multiple brain areas respond to different things; overlap

Broca's Area

Involved with speech production

Wernicke's Area

Involved in understanding speech

Neuropsychology

A field abt the relation btwn location of brain damage and specific effects on behavior

Magnetic Resonance Imaging (MRI)

Brain imaging technique that allows us to create images of structures within the brain

fMRI

Technique that displays how various functions activate different areas of the brain thru measurement of blood flow

Distributed representation

Says the brain represents info in patterns distributed across the cortex, rather than in 1 single brain area; emphasizes connections btwn brain areas and working together

Structural connectivity

The "roadmap" of fibers connecting different areas of the brain

Functional activity

The neural activity associated with a particular function that is flowing thru structural network ; fMRI measures functional activity

Mind-body problem

How do physical processes like nerve impulses (the body part) become transformed into the richness of perceptual experience (mind part)? ; causation not just correlation; bc nerve impulses can represent things in environment

Vision

Light reflected from objects in environment enters eye thru pupil and is focused by cornea and lens to form sharp images of the object on the retina; the network of neurons that covers the back of the eye and that contains the receptors for vision (photoreceptors); you focus image onto retina but see image in brain (you don't actually have vision in retina) ; before brain can create vision, the light on the retina must activate photoreceptors in retina; from light energy (energy emanating from electromagnetic spectrum)

Photoreceptors

Rod and cones; the outer segments contain visual pigments that react to light and trigger electrical signals which go thru neuron network in retina and emerge from optic nerve at back of eye; optic nerve fibers conduct signals toward brain

Fovea

Contains only cones; highest visual acuity; firing rate is higher than spontaneous firing in fovea bc center surround; smaller receptive fields, less inhibition; center of retina

Peripheral retina

Contains cones and rods; periphery of retina has larger receptive fields; they are smaller towards fovea (center) so they can be more accurate; more convergence at periphery than fovea (which have smaller receptive fields and less convergence); more inhibition around periphery than in enter

Stephen Kuffler

Father of neuroscience; measured ganglion cell receptive field in cat and discovered ganglion cells have center surround receptive fields; on=pos=excitatory, off=neg=inhibitory

Hartline

Discovered ganglion cells have receptive fields

Macular degeneration

Condition that destroys cone-rich fovea creating a blind region in central vision; Only have peripheral vision; center is blurred; cones are lost in fovea; macula (middle of retina full of cones) damaged

Retinitis pigmentosa

Condition that attacks peripheral rod receptors and leads to poor vision in peripheral visual field; Periphery is blurred; can only see center; loss of rods

Blind spot

Area in retina with no photoreceptors bc it's where the optic nerve fibers leave the eye; we aren't usually aware of our blind spot bc it's to the side of our visual field and we aren't looking for it and a mechanism in our brain "fills in" the place the image disappears; we don't notice bc we have 2 eyes w blind spots that don't line up and our brain fills in what you don't see based on surrounding image

Cornea

Transparent covering of front of eye; fixed in place=can't adjust focus

Lens

Can change its shape to adjust the eye's focus for object located at different distances; ciliary muscles increase focusing power of lens by increasing it's curvature; lens uses accommodation process to prevent blurring; focuses light reflected from object onto eye onto the retina

Accommodation

The change in the lens' shape that occurs when the ciliary muscles at the front of the eye tighten and increase curvature of lens so it gets thicker; increased curvature increases bending of the light rays passing thru lens so focus point shifts to create a sharp image on the retina; when you look around at different objects, your eye is constantly accommodating to adjust its focus; accommodation adjusts vision for different distances; object near=accomodation thicker lens and more curvature;

Refractive errors

Errors that can effect the ability of cornea/lens to focus the visual input onto the retina

-Presbyopia -Myopia/nearsightedness -hyperopia/farsightedness

Presbyopia

Old age related loss of the ability to accommodate; lens becomes more rigid with age; trouble seeing near objects due to aging

Astigmatism

Irregularly shaped lens; nearsighted and farsighted depending on how light falls bc misshapen lens

Myopia

Nearsightedness; inability to see distant objects clearly

Axial myopia: eyeball too long Refractive myopia: cornea and lens over bend the light

Hyperopia

Farsightedness; trouble seeing nearby objects; usually bc eyeball is too short

Parts of visual pigment

Opsin (long) and retinal (smaller but more important) : the 2 together result in a molecule that absorbs visual light; absorbing light causes retinal to go from bent to straight.

Isomerization=change of shape; creates chemical chain reaction that activates charged molecules to create electrical signals in receptors; entire photoreceptor activated= electrical signal is created= transduction.

Dark adaptation

Increasing sensitivity to the dark; you can see after being in a dark room for a while; measured by dark adaptation curve; when light is out, no more isomerization so visual pigment concentration increases and causes increase in sensitivity during dark adaptation; rods better in the dark

Dark adaptation curve

Function relating sensitivity to light to time in the dark, beginning when lights are extinguished; rod and cone receptors control ability of visual system to adjust to dim levels illumination; shows as adaptation proceeds, participants becomes more sensitive to the light; first part of dark adaptation curve caused by cones and second by rods = 2 stages; as soon as light is extinguished, sensitivity of both cones and rods begins increasing

Pigment absorption spectra

Amount of light energy the pigments can absorb; different wavelength cones respond better to different wavelength stimuli; rods respond maximally to shorter wavelengths; S/M/L cones respond better to larger wavelengths

Visual pigment bleaching

Retinal change in shape (bent to straight) and separation from opsin causes molecule to be lighter in color

Visual pigment regeneration

Retinal returns to bent state and becomes reattached to opsin bc when pigment is in lighter bleached state, it's not useful for vision; cone pigment regenerates faster than rod pigment; the speed at which our sensitivity increases in dark depends on regeneration of visual pigment (chemical reaction);

Detached retina

Visual pigments presented from regenerating bc retinal and opsin can't recombine so person becomes blind in area of visual field served by separated area of retina

Spectral sensitivity

The eye's sensitivity to light as a function of the light's wavelength; measured by determining spectral sensitivity curve: relationship btwn wavelength and sensitivity; use spectrometer to create light of various wavelengths; can measure cone spectral sensitivity or rod spectral sensitivity; threshold is lower in middle of spectrum bc less light needed to see wavelengths in middle of spectrum than to see wavelengths at either short or long wavelength end of spectrum; Perceiving color thru various wavelengths

Monochromatic light

Light of a single wavelength

Purkinje shift

Enhanced perception of short wavelengths during dark adaptation; increased sensitivity determined by properties of rod and cone pigments; ex) green foliage more prominent at dusk

Absorption spectra

A plot of the amount of light absorbed versus the wavelength of the light; causes difference in rod and cone spectral sensitivity; also determined by rod and cone properties

Neural circuits

Interconnected groups of neurons (in retina); signals generated in receptors travel to bipolar cells then to ganglion cells — H-B-G

Ganglion cells

Have long axons that transmit signals out of retina in optic nerve; have center-surround receptive fields (pos in center, neg surround and respond differently); center-excitory area bc presenting it w a spot of light increases firing; surround=inhibitory area bc stimulation of is causes a decrease in firing; excitatory center, inhibitory surround receptive field; respond best to small spots but will also respond to other stimuli; receptive fields overlap; input ganglion cells receive from many different photoreceptors

Horizontal cells

Connect neurons across retina w amacrine cells; signals travel btwn receptors thru horizontal cells

Amacrine cells

Connect neurons across retina w horizontal cells; signals can travel btwn bipolar cells and btwn ganglion cells thru amacrine cells

Neural convergence

Occurs when a number of neurons synapse onto a single neuron; shapes perception; lots of convergence in retina bc lots of photoreceptors and not as many ganglion cells; signals from rods converge more than signals from cones

Takes less incoming light to stimulate a ganglion cell that is receiving input from rods bc many rods converge onto 1 ganglion cell; takes much more light to stimulate a ganglion cell that receives input from cones since fewer cones converge onto each ganglion cell.

Cones

Receptor concentrated near center of retina; better detail vision than rods; better visual acuity (detail) bc less convergence; better at color in daylight; no convergence (1:1 ratio)

Rods

Receptors around periphery of retina; better sensitivity than cones; night vision; signals converge more; more sensitive to light than cones; used in low light conditions

Acuity test

Hold baby up to see gray circle or grated black and white striped circle; they prefer novel things so they should look at new grating; gradually increase similarity btwn granting and if they have good acuity, they should look more at new grating

Receptive field in ganglion cells

The retinal region over which a cell in visual system can be influenced (excited or inhibited) by light; causes firing in ganglion cells in optic nerve; they overlap so stimulating a particular point on the retina will generally activate a number of fibers in optic nerve

Center-surround antagonism

Ganglion cells respond best to specific patterns of illumination; stimulation of inhibitory surround counteracts the center's exciters response, causing decrease in neurons firing rate; neuron responds best to a spot of light that is the size of the excitatory center of receptive field

Huber and Wiesel Nobel Prize receptive Fields in Visual Cortex

Had cats look at stimulus and visual fields are not center surround; found neurons in visual cortex (simple cells) responded to bars of light in center and peripheral fashion, not center surround which is a circle; simple cells fire when bar of light in center, but when bar is turned sideways, hits periphery so simple cell fires less; shows that there are cells in visual cortex that are selective to orientation; the more it rotates form vertical orientation, the less the cells fire; also found that complex cells fire to movement of bars of light in a particular direction; complex cells are movement direction sensitive

Lateral inhibition

Inhibition that is transmitted across retinal; in center surround ganglion cell; horizontal and amacrine cells transmit inhibitory signals laterally across retina; excitatory signal from center counteracts inhibitory signals form surround thru lateral inhibition; underlies center surround antagonism; inhibition coming from the sides

Hermann grid

Grid of squares and at the intersections, you see grey circles at the part you aren't staring directly at; looking straight at intersection you don't see circle but when you look away to a different intersection, you see the other one; looking right at intersection, you use fovea, receptive field is small so whole thing is illuminated by light so you dont see dark spot in middle; whereas if you're using periphery, you see dark spot bc extra fovea representation=large receptive field=inhibition; caused by lateral inhibition

Edge enhancement

An increase in perceived contrast at borders btwn regions of visual field; help make edges more distinct so they're easier to see

Mach bands

Light and dark bands created at fuzzy borders; vertical stripes of increasing color darkness (white to dark gray); right side of stripe is lighter and left side is darker; it's not actually there, it's just your perception of lightness; edge enhancement explained by center surround receptive field; to perceive contrast; different shades; caused by lateral inhibition; 2 colors side by side you get light line and dark line on border.

Preferential looking (PL) technique

Used to measure infant visual acuity; they can't talk; give infant 2 stimuli and see where infant chooses to look; infants have spontaneous looking preferences (they prefer to look at certain types of stimuli); visual acuity poorly developed at birth ( bc undeveloped photoreceptors, cones far apart, visual area in brain poorly developed at birth); then rapid improvement and levels off around 1 year old

Visual evoked potentials (VEP)

Electrical signal recorded by disc electrodes; if stimuli (ex: stripes) is large enough to be detected, VEP is generated; provides objective measure of visual systems ability to detect details

Magnitude estimation and power function graph

Ppl's ability to estimate the magnitude of a stimulus is not linear (ex: when you double brightness, ppl will perceive that it's only a little more which is incorrect); electric shock ex

Snake infrared detection

Snakes can "see" in the dark bc they have protein channels activated by heat from bodies of their prey; can detect infrared radiation (heat signatures) of their prey

Fermi Gamma-ray space telescope

Converts what it detects (black holes, nebula, etc, that emit high energy radiation) into wavelengths we can perceive; we can see super high energy objects in space

Optic chiasm

X shaped bundle of fibers; visual signals from both eyes leave the back of the eye in the optic nerve and meet at optic chiasm; fibers corresponding to right visual field end up on left side/hemisphere and vice versa bc fibers cross over; each hemisphere of brain corresponds to opposite/contra lateral side of visual field

Lateral geniculate nucleus

Signals proceed from optic nerve to to LGN, in thalamus (relay station where incoming sensory info takes a stop before reaching cerebral cortex) of each hemisphere; neurons in LGN have center-surround receptive field; LGN function unclear; potentially could regulate neural info as it flows from retina to cortex; also relieves a lot of feedback (signals from cortex) hinting at regulation of info flow; then info goes to visual cortex and feedback from cortex back to LGN for more processing