Sensation & Perception (unit 4)

psychology

Sensation v. Perception 

S: detect enviormental stiumi → convert to neural signals, bottom up 

P: select/organize/interpret sensations, top down 

Bottom up Processing

• sensory receptors relay info to brain

• brain interprets

Top down processing

• previous experience/expectations affect analysis of info from senses 

• explains visual illusions 

Transduction

sensors in body convert phys signals from enviorment into encoded nerual signals (sends to CNS)

Psychophysics

methods measure strength of stimulus + observers sensitivty to it

Absolute Threshold? Subliminal?

A: minimum stim nedded to detct particular stimulus 50% of time

S: below threshold for concious awarness 

Difference Threshold/JND

minimal change in stimulus

Weber’s Law

in order to percieve difference

• 2 stimuli must differ by constant proportion instead of amount 

Sensory Adaptation

• diminished sensitivty as consequence of constant stiumulation (unchanging stim) 

• benefit: focus on important changes, dont focus on uninformative background stim 

Vision

• transform light en → neural signals

• represents objects in enviorment → shapes/size/colour/location 

Light Energy: Wavelength

distance from one peak to other → effects colour 

• short: high frequency, bluish colour 

• long: low frequency, reddish colour 

Light: Intensity

amplitude 

• great amp: bright colours

• small amp: dull colours

3 light wave properites

1. wavelength = colour/hue 

2. amplitude = brightness 

3. purity = saturation 

Cones

• center of retina

• bright light

• sensitive to colours/detail

Rods

• greater than cones 

• periphery of retina

• low light

• not colour/detail sensitive

Normal Vison? Nearsighted? Farsighted?

norm: nearby/far objects focused on retina (back of eye)

near: far objects focused in front of retina 

far: nearby objects focused beyond retina 

Visual Cortex

• nerve cells respond to specific features

• visual association areas put together combos of visual properties

Colour Vision: Trichromatic Theory

3 receptors that are sensitive to red/blue/green

(red/green colour blindness) 

what happens if all visible wavelengths are present

we see white

Oponent Colour Processing Theory

• explains complementary colour afterimage

• brain processes colours in pairs (ex. green v. red) 

ex. fatigue of pathways promoting red → produce green 

Pathway of Information in Vison

• photoreceptors fire 

• optic nerve passes impulse to thalamus 

• thalamus → visual cortex (occipital lobe) 

Feature Detection

• Hubel & Wiesel 

• disovered feature detector cells in visual cortex 

Properties of Sound Waves

1. frequency: pitch

2. amplitude: loudness

3. complexity: timbre

Sound waves: Frequency

low: low pictched

high: high pitched

Sound: Amplitude

high: loud 

low: soft 

Sound Waves: Complexity

simple: pure tone 

complex: mix of frequencies 

Ear: Outer? Middle? Inner? Hair Cells?

O: sound waves collected

M: waves amplified

I: waves transducted into coded neural msgs

HC: sensory receptors for sound 

Measure of Sound 

• decibel: measures intensity of sound (ear is sensitive)

• smallest audible sound: 0 dB

• 100 times more powerful = 20 dB (increase by 10)

Auditory Cortex: 2 Regions

Spatial (where): features locate source of sound, back/caudal auditory cortex 

Nonspatial (what): features locate temp aspects of sound, lower/ventral cortex

Cochlear Implant

• micorphone detects/sends sounds to speech processing computer behind individuals ear 

• elec signals from speech processor transmited to implanted reciever → sends signals via elctrodes to cochlea (stimulates auditory nerve) 

Touch? Proprioception?

T: pressure, warmth, cold, pain
P: info about body position

Kinesthesis? Vestibular Sense? 

K: position/movement of parts of body
V: balance, sensing orientation of head/body in space

Proprioception: Brain? Vestibular Organs? Eyes? Stretch Receptors?

B: receive/interpret info
V: inner ear, send info about rotation/acceleration/postion 
E: send visual info 
S: in skin, muscles/joints send info about position of body parts 

Touch Sensors 

Mecanoreceptors: tickle 

Nociceptors: respond to chem/mech/thermal stim

Thermo/Mechanoreceptors: combo → wet 

Thermoreceptors: searing hot 

Pain

unpleasent sensory/em experience

warns of acutal/potential tissue damage

• C fibers: longer lasting dull pain

• A-Delta fibers: fast acting, sharp pain 

• Nociceptors: pain receptors 

Gate Control Theory

• non painful input → closes gate to painful input (prevents pain from travelling to CNS) 

• stim by non-harmful imput able to suppress pain 

5 taste types? Their Survival Impact?

• Sweet: energy

• Sour: potentially toxic

• Umami: protein growth/repair tissue 

• Bitter: posion 

• Salty: Na for physiological processes 

Olfaction

• olfactory neurons = only neurons that directly link brain → outside world

• connect to temp lobe (involved in rec of smells) 

• limbic system structures: help reg em reactions to smell 

Synesthesia

perceptual experience of one sense envoked by sensation of another (ex. hearing colours)

Gestalt

• form/whole 

• Wertheimer (1 of main founders) 

• organize sensations into meaningful whole 

Depth Perception

• judge distances

• learn from infancy 

• ex. visual cliff 

Retinal Disparity

images from 2 eyes differ

• object far: disparity on both retina is small 

• near: is large

Relative Size? Interpostion?

S: smaller = farther away
I: blocked by other objects = father away

Relative Height? Relative Motion?

H: higher in field of vison = father away
M: moving slower = father away

Linear Perspective? Light & Shadow? 

P: converging lines = father away 
L/S: dimmer one = farther away 

Perceptual Constancy

percieve objects as unchanging even as retinal images change (colour constancy)

Cataract Surgery

= sensation restored, recognition of faces/objects not

for: distinguish features, cant percieve whole pic

ex. kittens raised seeing only V lines, later diff to perceive H lines

Perceptual Adaptation

can adjust to artificially displaced visual field