Perception

chapter 4 of textbook

modalities

sensory brain regions that process different component of the perceptual world

sensation

simple awareness due to the stimulation of a sense organ

perception

the organisation, identification and interpretation of a sensation in order to form a mental representation

transduction

when many sensors in the body convert physical signals from the environment into neural signals sent from the central nervous system

transduction

occurs when many sensors in the body convert physical signals from the environment into neural signals sent to the central nervous system

psychophysics

methods that measure the strength of a stimulus and the observers sensitivity to that stimulus

absolute threshold

the minimal intensity needed to just barely detect a stimulus on 50% of the trials

just noticeable difference (JND)

the minimal change in a stimulus that can just barely be detected

webers law

states the just noticeable difference of a stimulus is a constant proportion despite variations in intensity

noise

all other stimuli from internal and external environment

signal detection theory

the response to a stimulus depends on a persons sensitivity to the stimulus in the presence of noise and on a persons response criterion

d-prime (d')

a statistic that gives a relatively pure measure of the observers sensitivity or ability to detect signals

hits, misses, false alarms and correct rejections are

signal detection theory features

sensory adaptation

sensitivity to prolonged stimulation tends to decline over time as an organism adapts to current conditions

length of a light wave

determines its hue or perceived colour

amplitude of a light wave

determines brightness

purity of a light waves (number of wavelengths)

saturation or richness of colour

how light passes through the eye

cornea - bending light wave, pupil

light adaptation

the recovery of the eye's sensitivity to visual stimuli in light after exposure to darkness

retina

light sensitive tissue lining the back of the eyeball

muscles in the eye

adjust the shape of the lens to focus objects at different distances. makes the lens flatter for objects that are far away and rounder for nearby

accomodation

the proccess by which the eye maintains a clear image on the retina

farsightedness

hyperopia
ability to see objects in the distance better than closer objects

nearsightedness

myopia
ability to see objects up close better than far away objects

cones

detect colour, operate under normal daylight conditions and allow us to focus on fine detail

rods

become active under low light conditions for night vision. provide no information about colour and sense only shades of grey

fovea

area of the retina where vision is the clearest and there are no rods at all

what does high concentration of cones in the fovea affect

visual acuity and explains why your peripheral vision isnt so clear

dark adaptation

cones adapt to the dark within about 8 mins but arent too sensitive at low light levels. rod require about 30 mins to completely adapt but provide better sensitivity in the dim light (no colour vision with the rods however)

bipolar cells

collect neural signals from the rods and cones and transmit them to the outermost layer of the retina

retinal ganglion cells (RGCs)

receive signals from the bipolar cells and organize these signals and send them to the brain

axons in photoreceptors/bipolar cells VS in the retinal ganglion cells

axons and dendrites of photoreceptors and bipolar cells are relatively short (a few microns long) VS axons of the retinal ganglion cells span several cm

optic nerve

the bundle of retinal ganglion cells axons which leaves the eye through a hole in the retina (the blind spot)

blind spot

contains neither rods nor cones therefore has no mechanism to sense light

receptive field

the region of the sensory surface that, when stimulated, causes a change in the firing rate of that neuron

lateral inhibition

within the receptive field - neighbouring photoreceptors respond to stimulation differently, some excited some inhibited, this means the signals sent through the bipolar cells to the rgc are based on differing levels of receptor activation

on centre ganglion cell

a central inhibitory zone surrounded by an excitatory zone

off centre ganglion cell

A retinal ganglion cell that is activated when light is presented to the periphery, rather than the centre, of the cell's receptive field.

how is the retinal ganglion cell a 'spot detector'

records relative changes in excitation and inhibition of receptive fields

visible spectrum of light

The part of the electromagnetic spectrum that can be seen. Visible light makes up only 35 percent of natural sunlight.

how many wavelengths of different cone receptors are there

s-cone (blue), m-cone (green), l-cone (red) 3 different types of pigment

additive colour mixing

the process of adding colours of light together to produce other colours

trichromatic colour representation

the pattern of responding across the three types of cones provides a unique code for each colour

colour deficiency

a genetic disorder in which one of the cones types are missing (in rare cases two or all three)

colour afterimage

staring too long at one colour fatigues the cones that respond to that colour

colour-opponent system

where pairs of visual neurons work in opposition
red vs green
blue vs yellow

right visual field and left visual field

objects in the right visual field stimulate the left half of each retina. vise versa

Area V1 (primary visual cortex)

the part of the occipital lobe that contains the primary visual cortex, is the initial processing region

topographic visual organisation

adjacent neurons process adjacent portions of the visual field

how area v1 is specialised from encoding edge orientation

it contains populations of neurons, each 'tuned' to respond to edges orientated at each position in the visual field

visual streams

two functionally distinct pathways that project from the occipital cortex to visual areas in other parts of the brain (dorsal and ventral)

ventral (below) stream

travels across the occipital lobe into the lower levels of the temporal lobes. includes brain areas that represent an objects shape and identity

dorsal (above) stream

travels up from the occipital lobe to the parietal lobes, connecting with brain areas that identify the location and motion of an object

visual form agnosia

the inability to recognise objects by sight

optic ataxia

difficulty using vision to reach and manipulate objects. however can recognise what objects are. ventral stream intact, dorsal stream damaged

blinding problem

how features are linked together so that we see unified objects in our visual world rather than free-floating or miscombined features

illusory conjunction

a perceptual mistake where features from multiple objects are incorrectly combined

feature integration theory

proposes that attention binds individual features together to comprise a composite stimulus

synaesthesia

the perceptual experience of one sense that is evoked by another sense

modularisation

The process of relatively encapsulated function

perceptual constancy

even as aspects of sensory signals change, perception remains consistent

perceptual grouping rules

governs how the features of things fit together. simplicity, closure, continuity, similiarity, proximity, common fate

template

a mental representation that can be directly compared to a viewed shape in the retinal image

monocular depth cues

aspects of a scene that yield information about depth when viewed with only one eye

relative size

using the differences in retinal image size to perceive distance

linear perspective

parallel lines appear to converge with distance

texture gradient

the tendency for textured surfaces to appear to become smaller and finer as distance from the viewer increases

interposition

if one object partially blocks our view of another, we perceive it as closer

height in the image

objects closer to you are lower in your visual field

binocular disparity

the difference in the retinal images of the two eyes that provides information about depth

motion parallax

a depth cue based on the movement of the head over time

optic flow

the pattern of motion that accompanies an observer's forward movement through a scene, is a form of motion parallax.

apparent motion

the perception of movement as a result of alternating signals appearing in rapid succession in different locations

three dimensions of a sound wave

frequency, amplitude, complexity

frequency of a sounds wave

corresponds to perception of pitch

pitch

how low or high a sound is (frequency)

amplitude of a sound wave

corresponds to perception of loudness

loudness

a sound's intensity (amplitude)

complexity of a sound wave

corresponds to our perception of timbre

timbre (complexity)

a listeners experience of sound quality of resonance

cochlea

within the inner ear, a fluid-filled tube that is the organ of auditory transduction

basilar membrane of cochlea

a structure in the inner ear that undulates when vibrations from the ossicles (middle ear) reach the cochlear fluid

hair cells

specialised auditory receptor neurons embedded in the basilar membrane

area A1

a portion of the temporal lobe that contains the primary auditory cortex.

left hemisphere is responsible for analysing... (in relation to audio)

sounds related to language

right hemisphere is responsible for analysing... (in relation to audio)

rhythmic sounds and music

area A1 tonotopic organisation

similar frequencies activate neurons in adjacent locations

place code

mainly used for high frequencies, active when the cochlea encodes different frequencies at different locations along the basilar membrane

frequency in relation to basilar membrane movement

when frequency is low, the wide floppy tip (apex) of the basilar membrane moves the most.
when frequncy is high, the narrow stiff end (base) of the membrane moves the most

temporal code

registers low frequencies via the firing rate of action potentials entering the auditory nerve

visual orienting

a behavioural response to move the eyes towards a target (which may signal prey or predator)

mulitsensory integration

the perceptual representation of events from more than one sensory modality

haptic perception (touch)

active exploration of the environment by touching and grasping objects with our hands

thermoreceptors

nerve fibres that sense cold and warmth, respond when your skin temperature changes

pain pathways

1. sends signals to the somatosensory cortex, identifying where the pain is occuring and what sort of pain it is
2. sends signals to the motivational and emotional centres of the bran (hypothalamus and amygdala) motivates us to escape or relieve the pain

referred pain

sensory information from internal and external areas converge on the same nerve cells in the spinal cord

gate-control theory of pain

signals arriving at pain receptors in the body can be stopped or gated by interneurons in the spinal cord via feedback from two directions

vestibular system

the three fluid-filled semicircular canals and adjacent organs located next to the cochlea in each inner ear. maintaining balance depends on this

olfactory receptor neurons (ORNs)

receptor cells that initiate the sense of smell. theres about 10 million in the olfactory epithelium

olfactory bulb

a brain structure located above the nasal cavity beneath the frontal lobes