Chapter 4 - Sensation and Perception

Sensation

detection of physical energy by the sense organs

external stimuli is converted by sense receptor into neural activity via transduction

activation is highest initially and then sensory adaptation occurs

Perception

brain’s interpretation of raw sensory data

Illusion

perception which does not match reality

Psychophysics

study of how we perceive sensory stimuli based on their physical characteristics

lowest level of stimulus we can detect at above chance performance is referred to as absolute threshold

Just Noticeable Difference

smallest amt of stimulus change humans can detect

Weber’s Law

constant proportional relationship b/w JND and stimulus intensity

stronger stim = higher JND

weaker stim = lower JND

Signal Detection Theory

how stimuli are detected under different conditions

McGurk Effect

auditory illusion

Ga vs. Da vs Ba

Multimodal Perception

process where brain combines info from multiple senses to create unified understanding of the world

Grapheme-colour

phenomenon where letters and numbers are associated w/ specific colours

Synesthesia

cross-modal sensations

sounds w/ colours

colours w/ taste

Selective attention

process of selecting one sensory channel and ignoring/minimizing others

Cocktail Party Effect

ability to focus on a single stimulus while filtering out other sounds

Role attention

poor at detecting stimuli in plain sight if our attention is focused elsewhere

Inattentional blindness

someone doesn’t notice an unexpected stimulus that’s clearly visible

Monkey illusion - focus on observing bouncing ball will miss monkey on screen

Change blindness

failure to detect changes in your environment

role in traffic accidents is intensively studied

Binding problem

how our brains combine all the various stimuli around us into a coherent whole

rapid coordinated activity b/w brain areas may make binding possible

Visual system

respond to a narrow spectrum of light

Brightness

amt of light reflected back to the eye

mixing lights produces white (additive)

mixing pigments produces black (subtractive)

Hue

color of light r/t wavelength

maximally sensitive to blue, green, and red

Sclera

white portion of eye

Iris

coloured portion that controls how much light enters the eye

Pupils

hole where light enters

cornea

protective

transparent cells that focus light on the back of the eye

lens

keeps image in focus

changes curvature (accommodation) to reflect light onto back of eye

important as we adjust for distance of objects

retina

responsible for transduction

membrane at the back of the eye

fovea

is in the center of the eye and is responsible for acuity (sharpness of vision)

Rods

low-light vision

dark adaptation

absent fovea

more of them

carry rhodopsin

Cones

high light requirement

color vision

less of them

carry opsins

Optic nerve

exits back of eye and is composed of axons of ganglion cells

causes blindspot

most axons go to thalamus then visual (V1) cortex then midbrain

Feature detector cells

allow us to detect lines and edges

Simple (V1) cells

orientation-specific slits of light in a particular location

Complex (V1) cells

orientation-specific but less dependant on location

Trichromatic theory

colour vision is based on our sensitivity to 3 primary colours: blue, green, red

consistent w/ 3 types of cones in eye

explains colour blindness

Dichromats

tend to be male

polygenetic on X chromosome

red + green colourblindness

Monochromats

rare

see on one tone

Opponent process theory

sees colour vision as a fxn of complementary, opposing colours

red vs. green vs. blue vs. yellow

Echolocation

might improve following blindness

Visual Agnosia

object recognition deficit

damage to higher visual cortical areas

Blindsight

above-chance visual performance of cortically blind individuals w/ damage to V1 area

Amplitude

larger the amplitude, the higher the intensity (light = bright, loud = sound)

Hearing

sense we rely on most after sight

perception based on physical properties of sound waves - physical form of energy

Pitch

wave frequency (Hz)

loudness

amplitude of sound waves (dB)

timbre

complexity of sound

nature of sound

Ear

transduction happens from the oval window onwards

hair cells —> acoustic info —> transduce into AP —> neural impulses down length of auditory nerve

Outer ear

includes pinna and ear canal

funnels sound waves into the ear drum

Middle ear

ossicles (hammer, anvil, stirrup) vibrate and transmit sounds to the inner ear

Inner ear

cochlea converts vibration into neural activity

inside are the organ of Corti and basilar membrane —> bottom, closest to the oval window

Pitch perception

different tones excite different areas of the basilar membrane and primary auditory cortex

Place theory

specific location along basilar membrane matches a specific tone and pitch

low pitch = top

high pitch = bottom

Frequency theory

rate of AP is r/t pitch

Smell and Taste

Olfaction and gustation

Work together

known as “chemical senses” b/c sense receptors are stimmed by chemicals

Odours

airborne chemicals that interact w/ lining of nasal passage

5 basic tastes

sweet (carbs)

salty

sour

bitter

umami (protein)

some evidence for “fatty” as well

Sense receptors

olfactory neuron contains a single type of receptor - recognizes odourants based on their shape

taste buds - for each basic taste

Orbitofrontal cortex

smell and taste senses converge here

Pheromones

odourless chemicals that serve as a social signal to members of the same species

vomeronasal organ in humans (used to sense pheromones) not well developed

Somatosensory system

responds to stim applied to skin, temp, and injury

Gate control model

argues neural mechanisms in spinal cord regulate conscious awareness of pain

Phantom pain

pain that feels like it's coming from a limb or organ that's no longer there

may be responsive to mirror tx

Proprioception

kinesthetic sense

helps us keep track of where we are and move efficiently

Vestibular sense

sense of equilibrium

enables us to sense and maintain balance as we move

d/t fluid in semi-circular canals in inner ear

Parallel processing

when attending multiple senses at once

Bottom-up processing

whole is constructed from the parts

Top-down processing

whole is modified by experiences, expectations, and goals

Perceptual sets

occur when our expectations influence our perceptions

Perceptual constancy

allows us to perceive stim consistently across conditions

Gestalt Principles

rules that govern how we perceive objects as wholes w/in their overall context

Visual perception

to determine motion, brain compares visual frames of what is to what was

Phi phenomenon

an optical illusion that makes still images appear to be moving

Monocular depth

cues rely on one eye:

relative size

texture gradient

interposition

linear perspective

height in plane

light and shadow

Binocular depth

require both eyes:

disparity

convergence

Visual cliff

hesitation as young as 6 mths

demonstrates depth perception is partly innate and a result of experience

Muller-Lyer Illusion

a famous optical illusion that makes two lines of the same length appear to be different lengths

Ponzo Illusion

an optical illusion that makes two parallel lines appear different in length when surrounded by converging lines

Horizontal-vertical illusions

an optical illusion that makes a vertical line appear longer than a horizontal line of the same length

Ebbinghaus-Titchner illusions

a classic optical illusion that makes two identical circles appear different in size

Subliminal Perception

processing sensory info that occurs below the level of conscious awareness