PSY 506 - Midterm SP25

lecture 10/10 done

Sensory Neurons

Bring IN information

Motor Neurons

Send information OUT

Sensation

Collection of data by our sensory receptors

Perception

Brain’s interpretation of sensory data

Perceptual Process (7 Steps)

1. Environmental Stimulus

   1. Must pay attention to stimulus to sense it

2. Light is reflected and focused

   1. Light is focused on back of eye (retina)

3. Receptor Processes

   1. Transduction

   2. Principle of Representation

4. Neural Processing

   1. Transmission

   2. Interaction

5. Perception

   1. Conscious experience

6. Recognition

   1. Categorizing stimuli/giving it meaning

7. Action

   1. When perceiver initiates motor activity in response to recognition

   2. NOT ALWAYS NEEDED

Transduction

part of step 3 of perceptual process

Physical energy → Electrical Energy

Principle of Representation

part of step 3 of perceptual process

Perception is NEVER due to direct contact with stimuli

ALWAYS a result stimuli acting on receptors which affect various neural processes

Transmission

part 1 of step 4 of perceptual process

Signals from receptors travels to brain (travels in chain like a game of telephone)

Interaction between neurons

In brain

Info is processed in web and spread to neurons

Interconnection of neurons:

• info is passed along and modified between neurons; individual experiences

Knowledge

Existing knowledge influences our perception

(existing knowledge biases our interpretation)

Bottom-Up Processing

Purely data driven (ex: lines, angles, contrast, etc.)

Top-Down Processing

Knowledge-driven; what you interpret?

Psycho-physical Approach

Stimulus←→ Perception

participants describes experince

Physiological Approach

Stimulus ←→ Physiology

Observer actually sees what is going on in the brain

Absolute Threshold

Energy needed to just detect something

ex: candle light at 10 miles → can just barely pick up the light

Difference Threshold

Energy needed to tell the difference between two things

ex: 1g/2g vs 1kg/2kg

10% of the total weight

Limits method of measuring thresholds

Incremental (increasing or decreasing)

in the middle of the three

Adjustment method of measuring thresholds

Participant turns the dial up or down

Less precise, but easier to do

Constant Stimuli method of measuring thresholds

random presentation of various levels of presentation

more precise, but longer

Compression: estimating the magnitude of stimuli

involving light; underestimation; double intensity = quieter/darker

Expansion: estimating the magnitude of stimuli

involving electrical shock; overestimation; double intensity = louder/more intense

Communication within a neuron

Ions → charged particles inside/outside cell

At rest, always more Na+ outside, K+ inside; the Na+ wants in

Resting Potential

-70mV

Why does Na+ want inside?

1. diffusion

2. electrostatic pressure

incoming stimulus opens channel, RP must go down to threshold of excitation to trigger action potential (change in polarity)

Threshold of Excitation

-55mV

5 Steps of Action Potential

1. Incoming stimulus causes Na+ channels to open

2. Na+ rushes in; temporarily makes inside positive and outside negative

3. Na+ channel closes, K+ channel opens

4. K+ rushes out; restores in=neg, out=pos

5. Na+K+ pump restores original ion concentration

5 Steps of Synaptic Transmission

Communication between Neurons

1. Arrival of action potential (in cell A)

2. Calcium ions enter terminal button

3. Neurotransmitter is released into synapse (synaptic gap)

4. NT binds to post synaptic receptor (dendrite of cell B)

5. Binding of NT causes changes in post-synaptic cell (cell B)

3 Properties of Neural Processing

Rate Law: Action potential’s RATE increases SIZE stays same

Excitation/Inhibition: more likely/less likely for action potential

Neural Integration: excitation + inhibition = how neuron fires

Parts of the eye

Sclera: Tough white outer coating

Cornea: Transparent, curved, refracts light

Iris: Ring of muscles around pupil

Pupil: Hole that lets light into eye

Lens: Convex, between the cornea and the pupil, for accomodation

Ciliary body: muscles that contract the lense

Choroid: thin layer between the sclera and the retina that contains blood vessels

Retina: Back of eye, has five layers, where transduction happens

Fovea: Thinnest layer of retina, contains most of the cones → best color vision and acuity

Optic Nerve: Sends into to brain, made up of ganglion cell axons

Presbyopia

Condition where ciliary muscles weaken with age and the “near point” (how close and object must be to see it clearly) gets further away

Breakdown of how light focuses on retina

Cornea = 80%

Lens = 20%

Myopia

Image is focused in FRONT of the retina

Nearsightedness

Hyperopia

Image is focused BEHIND the retina

Farsightedness

What does LASIK do?

Reshapes the cornea to allow light to properly hit the retina/correct vision

Layers of Retina: PHBAG

Photoreceptors: cones and rods (where transduction begins)

Horizontal cells: Allows photoreceptors to talk to each other

Bipolar cells

Amacrine cells: Allows bipolar cells to talk to eachother, and allows ganglion cells to talk to each other

Ganglion Cells: their axons come together to form the optic nerve, which is the back of the eye

Rods

Scotopic vision, dim light

All in the peripheral retina, NONE in fovea!

120 receptors converge into 1 ganglion cell

High sensitivity to light, low acuity, slow adapt to dark

1 type of opsin = NO COLOR VISION

Peaks at 500-510nm (cyan)

Cones

Photopic Vision; well-lit

Mostly in the Fovea, a few in the peripheral retina (rest of retina)

6 receptors converge into 1 ganglion cell

Low sensitivity to light, high acuity, fast adapt to dark

3 types of opsin = COLOR VISION

peaks at 550-580nm (yellow)

Where does the transduction process happen?

Outer segment of retina (closest to back of eye)

Contains visual pigment molecules

• Opsin: Large protein

• Retinal: Light-sensitive Molecule

Transduction process (simple 4 steps)

1. Photon triggers retinal to be isomerized

2. A series of complex physiological changes occur

3. Membrane is hyperpolarized in receptors

4. Action potential happens in the ganglion cells and a signal is sent to the brain

Isomerization (4 steps)

Retinal absorbs one photon of light and changes shape (this starts the transduction process)

Isomerization is followed by regeneration

1. Retinal absorbs light

2. retinal changes shape

3. opsin bleaches

4. the pigments regenerate and retinal reattaches to the opsin

Blind spot of eye

Where the optic nerve leaves the eye; has no photoreceptors

NOT a gap in vision, the eyes compensate for each other

Is located at the edge of visual field, and the brain “fills it in”

Fundus

The interior of the eye

Macular degeneration

Common condition from retina damage

Cones are affected

Macula = the area around the fovea

Causes a blurry CENTER of vision

Retinitis Pigmentosa

Rare condition from retina damage

Rods are affected

Slowly destroys the retina

Peripheral vision is gone causing TUNNEL VISION, center of vision may eventually go to

Retinal Detachment

Retina is pulled loose, results in hemorrhaging in the eye, spots in vision or complete vision loss; can also cause flashes of light

Purkinje Shift

Shift from cone vision to rod vision

Things look blueish in hue

Left visual field

Right primary visual cortex (V1)

Right Visual Field

Left primary visual cortex (V1)

Primary Visual Pathway

1. Optic Nerve

2. Optic Chiasm

3. Lateral Geniculate Nucleus (LGN)

4. Optic Radiation → relays info

5. Primary Visual Cortex (V1/Striate Cortex)

6. Superior Colliculus → orientation, visual movement

   1. Part of the brain stem

Cortexal Blindness

Blindness due to V1 damage

Modularity

Brain is made up of different modules and module systems;

Interconnected networks with distinct functional areas

Hierarchy of Brain Modularity

Simple → Complex

Lines → Faces

Ventral Stream

“What” Pathway

Processes object identification

To Temporal lobe

Dorsal Stream

“Where” Pathway

Works with motor system

To Parietal Lobe

Fusiform Face Area (FFA)

How faces are represented in the brain

In the temporal lobe, since face = object

Prosopagnosia

Face-Blindness

Damage to FFA

Cerebral Achromatopsia

Type of color-blindness due to bilateral brain damage to cortex

Feature Detectors

Neurons in V1 that fire to specific features of stimuli

V1 Neurons

Simple cells → Respond best to LINES in specific orientations

Complex cells → respond best to MOVEMENT of lines in specific orientations

End-Stopped cells → Respond best to movement of CORNERS

Specificity Coding

“Grandmother Cell”

Every stimulus has a neuron that responds to it

ex: one neuron, one stimuli

Population Coding

Different firing patterns across neurons

ex: Neurons respond to stimuli differently

Sparse Coding

Small Group of neurons respond to stimulus

ex: Little group of neurons

Why do we struggle to make a perceiving machine?

Viewpoint Invariance: things look different and different angles

Also: stimulus on retina is ambiguous, and objects can still be partially hidden or blurred

Gestalt Approach

“Whole is different from the sum of its parts”

10 Laws

10 Gestalt Laws

Similarity: similar things grouped together

Simplicity/Pragnanz: structures are simply as possible

Good Continuation: lines follow smoothest path

Proximity: objects that are near each other are grouped

Common Region: regions are grouped together

Uniform connectedness: connected items are grouped

Synchrony: things happening at same time are grouped

Common Fate: items moving in same direction are grouped

Familiarity: items that are meaningful are grouped together

Closure: We see things are fully enclosed

Criteria for Figures

“Thing-like”, symmetrical, memorable, closer to bottom, “owns” the border

Perceptual Segregation

Figure vs Ground

Bistable Images

Recognition by Components (RBC)

Combining geons to make 3-D objects

36 total identified geons

How do we perceive Scenes?

Gist of scene: 250 msec is enough

Using global image features (color, openness, etc) and regularities in our world (light from above, etc)

Voxel

Small bit of brain tissue

Selective Attention

focusing on specific objects while ignoring others

Visual Attention

Directing gaze through visual scanning

Visual attention WITHOUT gaze

distracted without looking at the distracter

Gaze WITHOUT visual attention

Looking at something without paying attention to it

Inattentional Blindness

Failure to perceive a stimulus that is in full view because it was NOT attended to

No interruptions, just didn’t notice

the fucking gorilla video!!!!!!!!!

Change blindness

Difficulty in detecting changes in scenes

Break in stimuli/attention

flicker paradigms

Binding

Different features are combined to create perception

Feature Integration Theory

Binding Explanation, 2 parts

Preattentive Stage: Occurs very quickly, extracts SPECIFIC features (what, where, color, etc.)

Focused Attention Stage: Attention is “glue” that COMBINES together features

Synchrony Hypothesis

Binding Explanation

Neurons activated at the SAME TIME may be perceiving the SAME THING

Ecological Approach to Action

Measuring perception in dynamic environments with optic flow

Optic Flow

Appearance of objects as an observer moves past them

• moving TOWARDS stimulus → info moves PAST observer

• moving AWAY from stimulus → info comes from BEHIND

Focus of Expansion

What you are looking at

NO optic flow!

Affordances

Info that indicates what an object is used for

ex: a chair affords sitting

JJ Gibson

Object agnosia

when someone can’t recognize objects, but still knows how to use them

Middle Temporal Area (MT area)

Where we process (visual) movement

Superior Temporal Sulcus

where we process Bio Motion

(also for various social processes)

Real Motion

when something moves across out visual field

ex: deer crossing the road

Apparent Motion

When stimuli in slightly different positions are flashed one after another

ex: “chasing” lights

NO actual movement!

Induced Motion

when moving objects make stationary object appear to move

ex: the clouds moving at night can cause the moon to appear to move as well

NO actual movement

Motion Aftereffects

When viewing moving stimulus can make stationary stimulus move

ex: optical illusions

a brain process, NOT eye

NO actual movement

Why do we perceive motion?

Gestures, navigation, survival

Motion Agnosia

When a person can’t perceive motion

AKA Motion blindness or akinetopsia

Physical dimensions of color

Wavelengths of light

Purity

Intensity

Perceptual Dimensions of Color

Hue (color name)

Saturation (level of white/black)

Brightness (value)

3 functions of color vision

Identify objects

Classify objects

Evolutionary advantage in foraging for food and safety

Wavelengths

400-700nm = Visual Spectrum

Short waves → Blue

Medium waves → Green

Long waves → Red

How are colors of objects determined?

By the wavelengths that are reflected

200+ colors across the spectrum, millions more with changes in saturation and brightness

Trichromatic Theory of Color Vision

Young-Helmholz Theory

Cones have 3 opsin types → R,G,B

• Short wavelength sensitive (blue)

• Med. wavelength sen. (green)

• Long wavelength sen. (red)

Opponent Procession Theory of Color Vision

Hering Theory that challenged trichromatic to help explain after images

Proposed that blue/yellow and red/green are perceptually related

Thought yellow was elmental (necessary to describe perception)

Subtractive color mixtures

Mixing pigments (red, yellow, green)

Only reflect the hue in common between the colors

ex: blue is short and med wavelengths, yellow is M&L, green is medium