3a. motion perception

how do we detect motion

cells in the V1 area love motion and respond to bars of moving light

they start firing when they see downwards motion because they love this the most

explain motion after effect

viewing loads of downwards motion causes reduced firing of downwards detectors (because we just get used to it)

when we stop viewing this downwards movement, we have higher activation of upwards detectors - making us perceive upward motion that isn’t real

what is local motion

motion of smaller elements on a smaller part of the retina

what is global motion

grouping many elements of motion to perceive a bigger complex pattern of global motion (i.e. someone running)

how do we process global motion/build a global motion detector

pool together the visual fields of loads of cells tuned to the same direction of motion, so when the cells fire, the global motion detector fires

explain motion coherence paradigm and what the level is for humans

the minimum amount of dots moving in the same direction for us to recognise it as global/coherent motion

we need 10% to recognise the pattern, 5% if practiced

what does the motion coherence paradigm suggest about global motion

since we only need a tiny proportion of dots to be moving coherently to detect a global motion pattern, it suggests our brain is secretly looking out for global motion

which area of the brain is involved in motion processing

Middle temporal (MT) area / V5

how do we know the MT is involved in motion processing

most cells in the MT are tuned in to respond to motion of preferred directions

Explain a study that used artificial stimulation

directly (artificially) stimulating cells in the MT that have the same preferred direction (i.e. down) made monkeys perceive random motion of dots as downward motion

what did tootell et al find in their fMRI study

when we view motion and then a stationary object, the MT stays active and we experience motion in the opposite direction

explain what lesion studies found about the MT?V5

monkeys with MT lesions needed 80% of movement to be coherent to detect global motion, compared to the normal 5%

what is optic flow

patterns of retinal motion produced when we move, all motion emanates from one point

what is optic flow expansion

created by forward movement

all motion comes from a central point called the focus of expansion

objects closer to the centre move slower than things closer to us

explain contraction in optic flow

everything seems to move towards an inwards point

created by backwards movement

what is horizontal (constant speed) optic flow

all objects move across the retina at the same speed regardless of depth when we rotate our head/eyes

what is horizontal (parallax) optic flow

created by lateral movement (moving sideways)

things closer to us move quicker, things further away move slower

what is roll in optic flow

creates a spiral field of vision - happens when we roll

what are complex motions optic flow

happens when we have multiple different patterns of motion going on at the same time

i.e. forward moving and head turning

creates a combined image of movement on retina

explain what duffy and wurtz found from single cell recording

the MST and MT’s neurons respond preferentially to global optic flow patterns

what did smith et al find in their study of mst and mt

MST is more specialised for processing global optic flow because it likes structured motion

and the MT just likes all motion

what is optic flow used for

balance (postural stability), to tell us where we are heading

explain the swinging room experiment

floor is fixed but the walls of the room move side to side

simulates the same optic flow someone would experience from swaying side to side

toddlers would compensate for the optic flow and lean in the direction the room is swaying in - making them sometimes fall over lol

what are the 2 sources of retinal motion

self-motion

object motion

how to calculate retinal motion when perceiving object motion during self-motion

object motion + self motion

explain the flow-parsing hypothesis

when we are moving and also witnessing object movement, subtracting self-movement leaves the remaining movement attributed to the object

explain biological movement

we are particularly well adapted to perceiving biological movement (the movement of another person’s body)

what part of the brain is involved in processing biological movement

superior temporal sulcus