PA wk 7- motion perception. - ESSAY LEC

Question 1

Motion after-effect

Answer 1

When viewing a stationary object ‘up’ and ‘down’ detectors fire equally
Prolonged viewing of downward motion causes reduced firing of ‘down’ detectors (adaptation)
Viewing a stationary object post-adaptation results in greater ‘up’ activation than ‘down’, hence we perceive upward motion.

Question 3

Local Motion

Answer 3

Motion of individual (local) elements

Question 4

Global motion

Answer 4

We can group the motion of many individual elements to perceive a complex pattern of global motion

Question 5

motion coherene threshold

Answer 5

minimum proportion of signal dots (dots moving in same direction) compared to noise dots (random direction) to detect coherent motion.

For humans this is 10% (5% if trained)

Question 6

what do these global motion tests suggest ab our motion detectors

Answer 6

we have:
Local motion detectors: mall receptive field
and
Global motion detectors: large receptive field

Question 7

how brain processes motion.

Answer 7

MT (middle temporal) or V5 specialised in processing motion

Question 8

single cell recording evidence for MT/V5 area in processing motion

Answer 8

found nearly all cells have a preferred direction and respond to motion

Question 9

Artificial stimulation research as evidence for MT/V5 area in processing motion

Answer 9

when stimulated area of downward motion cells in monkeys when presenting random movement, monkeys reported downwards motion

Question 10

Tootell et al (1995): fMRI study of the motion after-effect

Answer 10

When we adapt to motion, then view stationary test, we experience motion in the opposite direction

2 conditions. 1 showed only expanding. 2 showed expanding + contacting (which resulted in no after effect)

Results:
When no after effect, the activity in MT took less time to reduce compared to when there was an after effect.
MT remains active during period of after-effect (i.e. no direct stimulation, but motion still perceived)

Question 11

lesion study of MT

Answer 11

Newsome and Paré (1988) introduced small lesion to monkey MT
Undamaged coherence thresholds = 5%
Damaged coherence threshold = 80%

(big threshold is bad)

Question 12

Optic flow

what motions create which retinal movements

Answer 12

pattern of retinal motion produced when we move

e.g. moving forwards, everything expands

backwards, everything contracts##

Rotation = horizontal motion

lateral movement = horizontal movement (but with motion paralax

Roll = created by eye, head, or body roll.

Question 13

optic flow

complex movements

Answer 13

e.g. forward translation and head rotation combined

Question 14

Imaging Optic Flow

(MST predicted to be important)

Answer 14

Measure response of MT and MST to 5 types of motion:
Complex
Expansion
Rotation (Roll)
Translation
Random
Interested in the difference in response to optic flow compared to random motion

The difference in response to optic flow compared to random motion is greater in MST than MT
Suggests MST is more specialised for processing optic flow motion than MT

(i.e the difference removes the activity explained by random motion)

Question 15

what is optic flow used for

Answer 15

• navigation in world
• postural stability
• perceiving object motion during self motion

Question 16

Gibson proposed we use optic flow to tell us

Answer 16

where we are heading and to control locomotion

Question 17

Optic flow might not be the only information used for heading
e.g.

Answer 17

Driving – Land & Lee (1994) showed we don’t look at FOE when driving, we look at other parts of the scene e.g. When on a curved path we look at the tangent

Question 18

how is optic flow used for postural stability

evidence fir this

Answer 18

provides info on how posture is changing

they slid walls of a room to appear as if you were leaning forwards .
Found that todlers fell over

Question 19

Perception of object motion during self-motion

how is this calculated
what is this called

Answer 19

Flow-parsing hypothesis:
Optic flow due to self movement subtracted from total optic flow.

This gives optic flow due to object movement

Question 20

Biological Motion

Answer 20

= the motion of another person’s body creates a complex pattern of movement
Local motion signals need to be integrated to recover the global pattern of motion
* We appear to be particularly adept at perceiving biological motion

Question 21

what do fMRI studies show about biological motion processing

Answer 21

Area STS (superior temporal sulcus) more active for biological motion compared to scrambled

Question 22

Grossman et al (2005) TMS experiment

Answer 22

Applied TMS to STS and MT

Task –is the stimulus biological
motion or scrambled?
Found:
TMS to STS caused significant decrease in ability to distinguish biological motion from scrambled
TMS to MT had no effect on biological motion perception