NEUR1020 Module 3

Motion Aftereffect

Illusion of motion of a stationary object that occurs after prolonged exposure to a moving object

why is blindsight possible

there are multiple visual pathways to brain. one is primary visual pathway. other pathway projects visual info from SC to medial temporal lobe (V5 or MT)

what is the dual visual streams hypothesis

theory that humans have 2 visual systems. one for perception and one for action

what are the 2 visual streams in the dual visual streams hypothesis

ventral stream - pathway from v1 into temporal lobes. important for semantic memory and verbal naming

dorsal stream - pathway into parietal cortex where premotor and motor cortexes are. important for action

what is D prime (d’)

a number which shows sensitivity to visual targets

what are some important d’ values and what do they mean

d’ of 0 = no evidence of sensitivity

d’ of 1 or greater = evidence of sensitivity i.e. more hits than misses

d’ of less than 0 = bias towards reporting negative

what are on centre/off surround retinal ganglion cells

respond positively to input from central region (lots of activity) and either display less activity or inhibition to input in peripheral region of cell.

describe the crossing of signals in the primary visual pathway

signals that relate to the right side of VISUAL SPACE go to the left side of your brain (regardless of which eye ‘saw’) and vice versa

why is the crossing of signals helpful

helps to diagnose whether issue is with eye, or optic nerve (before crossing), or brain (after crosssing)

what is in the retina

photoreceptors

what are in photoreceptors

light sensitive chemicals called pigments which absorb photons of light

what is the optic nerve made out of

ganglion cells. carries visual signals from eye - brain

where are the pigments (light sensitive chemicals) in photoreceptors

outer segments at back of retina FURTHER AWAY from light.

where is the physiological blind spot?

where the optic nerve passes through the retina. there are NO photoreceptors here

what is perceptual filling in?

brain assumes that whatever is on either side of the blind spot is also within it. If there is space after the blind spot, bain assumes that extends forever until its given info otherwise

what do perceptual filling in and neon colour spreading show

human vision is a construct

what do sense organs do

transduce objective energy into signals that construct not-objective perception

visual adaptation

as our brain gets suppperrr used to the input it reduces the 'salience' of that input. demonstrated by troxler fading

why is adaptation important?

makes sure we're more alert to new things

what is a quality of sensory after-effects

usually opposite relative to the adator (e.g. opp colour, direction of movement etc)

what is sensory adaptation

after prolonged exposure to sesory inputs ppl can experience after-effects.

Troxler Effect

When one fixates on a particular point for even a short period of time, an unchanging stimulus away from the fixation point will fade away and disappear.

Perceptual Aftereffect

Demonstrates that we do not have veridical experience of sensory input. experiences are simply a product of neurological activity

Sensory adaptation shows that

perception is useful but not accurate

McGurk Effect

Error in perception that occurs when we misperceive sounds because the audio and visual parts of the speech are mismatched. perceptual experience is SUM of sensory info.

Frequency

Increase/decrease in air pressure over time (pitch)

High pitches

more rapid fluctuations of air pressure (higher frequency)

Amplitude

The magnitude of changes in air pressure. determines volume

big changes in amplitude

loud

Neon Colour Speading

Type of optical illusion where you see a neon blue square, even though the background is white

Humans absorb .... amount of wavelength

400-700nm

Trichromats

Having three classes of photoreceptors

How many cones do humans have

three. short (up to 430nm), medium (up to 530nm), long (up to 600nm)

what are dichromats and tetrachromats

have 2 classes of cones; have 4 classes of cones

why are males more likely to be colourblind

gene for colour blindness is carried on the X chromosome

are the number of cones in every person the same

no. Ppl all have diff amounts of long, short and medium cones.

Colour Constancy

Ability to perceive the colour of an object as constant even if it appears to change with changes in lighting. happens bc objects refract diff wavelengths throughout the day

Naive Realism

Belief that people everywhere see the world in the same way

Sensation

Ability to detect sensory input

Perception

Subjective experiences of sensory input

Auditory Hair Cell

located in cochlear of inner ear. chemicals are released when there is noise. this is bc the liquid vibration causes stereocilia to bend. chemicals bind to auditory nerve cells which creates the electrical signal

what is stereocilia

bundles of auditory hair cells. they extend into surrounding liquid

primary sensory modality

vision

Opponent Process Theory

After protracted viewing of certain colours you can see oppositely coloured afterimages

Face Aftereffect

Prolonged exposure to an adaptor face causes a test face to take on the opposite characteristics

Primary Visual Pathway process

Signal leaves the eye via optic nerve —> travels to the optic chasm —> signals travel to LGNs (sub-cortical brain structures)—> cross so info from either side of visual space goes to either primary visual cortex

If the problem is specific to one eye...

The problem must be in the eye itself or in the optic nerve

If the problem is specific to info from one side of the visual space...

The problem must be due to brain damage

Primary Visual Cortex (V1)

First cortical region of the brain to receive visual signals travelling along the primary visual pathway. humans have 1 V1 in each hemisphere of brain

V1 in each hemisphere of the Brain

Responds to all input from one side of the visual space. If portions of the V1 are damaged, you will report being blind to the region of the visual field.

what are mapping of V1 responses called

retinotopic bc they correlate with where in the visual field the info came from

cortical scotoma

results from damage to either V1. means that person cannot see inputs usually encoded for by damaged region of V1

Flicker Fusion Threshhold

Describes how many times a second light source can switch between different colours before we stop seeing flicker and instead a constant light source. In humans it is ~30Hz aka 30 times/second

Blindsight

Condition in which a person can respond to a visual stimulus without consciously experiencing it. can occur when ppl suffer damage to parts to V1 aka : visual sensitivity to inputs people insist they cannot see

what happens if whole V1 is destroyed?

patient will report blindness on one side of visual input opposite to side of brain damage

 

If V1 destroyed on both sides people will report blindness.

what is an example of a signal detection task?

2-alternative-forced-choice tasks

Participants have to guess between 2 choices even if they 'don't know'

Ppl w/ V1 damage who couldn't see performed well above chance.

Signal Detection Theory

Describes how to measure sensory activity in conditions of uncertainty

Issue of Blindsight

We cannot simply take people's subjective opinions at face value

Receptive Field

Position on the retina that images must fall upon to make that visual neuron respond

Response Selectivity

Type of input to which a cell will respond

Cortical cells

Responds to orientated inputs, instead of spots of light

which cortical regions respond to faces?

• Superior temporal sulcus

• Occipital face area

• Fusiform face area

Middle temporal visual area (V5)

Responds selectively to complex pattern of motion

Extrastriate visual cortex (V4)

Tuned to specific colours but not all cells are direction-oriented

Cerebral Achromatopsia

Loss of color vision caused by damage to both V4s. can be complete or partial

Prosopagnosia

Inability to recognise faces. seems to correlate w damage to OFA

Cerebral Akinetopsia

Inability to perceive smooth motion

Functional Modularity

Brain contains multiple regions that are specialised for processing different visual properties

Steady-State Mis-Binding

Visual bindings of colour and motion are disproportionally shaped by central vision. brain assumes that whatever bindings prevail in the central vision also apply to the peripheral vision