lecture 6- action perception

Question 1

why is action perception important?

Answer 1

1. humans are highly social- living and interacting in social environments
2. successful gives evolutionary advantage- allows passing of genes to future generations (as good at making sense of each other)
3. interacting in social complex social environments (families, work, 1-on-1)
4. threat detection- see if we want to avoid
5. building alliances (understand when someone is giving you something)
6. interactions with potential mates
7. fast- enables us to make quick decisions

Question 2

how does functional specialisation in the visual cortex work?

Answer 2

• zeki discovered V4 and V5- anatomically different pattern in neurons
• anatomic difference = different functions
• V4 = colour
• V5 = direction and motion

Question 3

what is the motion pathway in the visual cortex?

Answer 3

eye -> LGN (thalamus) -> V1 (via optic radiation) -> V5 (connected directly to V1)

Question 4

what are the properties of V5 cells?

Answer 4

• larger receptive fields than V1 (4-5 degrees across)
• sensitive to moving dots/bars, (certain) direction, (optimal) speed
• contains retinotopic map of visual world- have cells that respond to all visual world/upper left/lower right etc.
• microstimulation of directionally selective V5 neurons biases perception of motion in the direction coded by the neurons
• respond to movement, but also if stimulate = sees movement (generates percept)

Question 5

what are properties of medial superior temporal (MST) cells?

Answer 5

• V5 -> MST
• larger receptive fields than V5 cells
• cells are sensitive to translation (left, right, up, down), expansion/contraction (optic flow- movement to/away a point in space that causes visual field to contract/expand)
• microstimulation of clusters of MST neurons influences perceived movement direction under many stimulus conditions

Question 6

what is biological motion?

Answer 6

type of stimuli where interaction between elements gives vivid percept of biological being- shows that motion can generate form information in mind

Question 7

what are the different percepts of biological motion stimuli?

Answer 7

1. actions- walking
2. hand actions, facial actions, sppech
3. gender- female/male walker
4. emotion- nervousness, happiness
5. body weight
6. identity- familiar/unfamiliar

Question 8

which brain region is responsible for biological motion perception?

Answer 8

posterior superior temporal sulcus (responds to biomotion figures)

Question 9

what similarites were found about biological motion stimuli to other complex stimuli?

Answer 9

• Pavlova & Sokolov 2000- inverted biological motion stimuli are difficult to recognise
• Saygin, Driver, de Sa 2008- sound improves biological motion recognition (e.g recognising walker by adding footsteps sound)

Question 10

what findings showed biological motion is pervasive?

Answer 10

• Fox & Mcdaniel 1982- infants preferentially observe biological motion
• Klin 2009- children with autism don’t
• Dittrich 1993- other social actions can be recognised
• Bassili 1978- emotion can be derived from biological motion faces
• Blake 1993- other animals (e.g cats) can discriminate biological motion

Question 11

what did Grossman (2000) find?

Answer 11

• STS activation to biological motion AND imagining biological motion
• ALSO STS activation to facial stimuli
• also involved in processing of motion of animate beings
• responds to articulated nature of moving human stimul-
• rigid, non-articulated motion = middle temporal gyrus (MTG- more posterior)

Question 12

what is implied motion?

Answer 12

stationary stimuli but stimulus captures mid-movement

Question 13

what did Zeki (1991) find?

Answer 13

• greater activity in V5 region of human cortex when viewing moving b&w squares than when they were stationary

Question 14

when is V5 also active?

Answer 14

• illusionary motion- compared BOLD response of V5 for illusionary vs. b&w similar non-illusionary -> active
• AND imaginary motion during mental rotation

Question 15

what did Kourtzi & Kanwisher (2000) do and find?

Answer 15

• compared BOLD response when figure implies motion vs. similar figures where motion not implied
• bigger response for implied in V5 and STS

Question 16

what is form-selectivity witin the STS?

Answer 16

STS responds to different views (e.g back/front view of body) in ventral pathway -> convergence in STS (info into comes from both V5 and AIT)

Question 17

what do STS cells merge?

Answer 17

• info about shape of body and motion info
• can respond to specific view and specific direction of movement (e.g sideways view of body walking forward i.e to the side of visual field)
• walking forward or backwards in the same direction aren’t the same
• which allows us to start to understand why they’re moving

Question 18

what is the function of the PIT and AIT

Answer 18

PIT = simple features
AIT = elaborate features

Question 19

what did Barraclough (2006) discover in monkey STS cells?

Answer 19

• respond to implied motion too (NOT to pictures standing stationary)
• link implied motion to walking direction from static pictures
• respond to someone walking in that direction AND someone that looks like they’re walking in that directio

Question 20

are there specialised action processing systems of single cells?

Answer 20

• monkey STS cells code selectively to an action
• hand: picking, tearing, placing, hitting
• body: walking, bending knees, arms
• face: eye movements, grasping with teeth
• face/hand combos- hand to mouth
• bigger response of a specific cell = more likely that action is occurring
• NOT grandmother cell coding- more likely to be population coding of actions

Question 21

how do we perceive actions under different low-level conditions?

Answer 21

• lighting, size, position in space, instance
• STS cells seem to respond to action irrespective of these qualities

Question 22

how do we perceive actions under different views from which action is seen?

Answer 22

• visual characteristics are different, but still grasp action
• gives action about who is performing the action (you, someone else)
• some STS cells respond to action from one view -> view-dependent coding (egocentric)
• some STS cells respond to action from any view -> object-centered coding (allocentric)

Question 23

what is possible organisation of neurons in the STS?

Answer 23

lower-level inputs -> view-dependent stage -> view-independent stage

Question 24

how do we distinguish who is doing the action?

Answer 24

• low level info may be useful to determine who is doing the grasping action
• e.g shape of hand, texture of hand, colour, view
• e.g only specific views of self-actions are possible

Question 25

what is the evidence in humans for specialised action processing systems?

Answer 25

Downing 2001- bodies > other objects in the EBA = whole bodies > body parts > face parts > other objects > object parts

Question 26

what the brain regions in the specialised action processing systems?

Answer 26

- extrastriate body area (EBA) = body selective - fusiform body area (FBA) = body face selective BUT FOR STATIC BODIES AND BODY PARTS - OFA = face selective (close by)

Question 27

what did Pitcher (2009) find using TMS?

Answer 27

- TMS study of visual processing - targeting occipital face area (OFA), lateral occipital area (LO) and EBA temporarily disrupts processing in visual cortex - performed object discrimination task - disruption of OFA = impairs face processing - disruption of LO = impairs object processing - disruption of EBA = impairs body processing

Question 28

what did Rizzolatti (1996) find?

Answer 28

- observations of hand actions -> PET activity in STS and inferior frontal gyrus

Question 29

what did Allison (2000) find?

Answer 29

- STS consists of several subregions and nearby related areas (pSTS, TPJ, STG) - responds to biological motion, static images of hands and body, hand actions, face actions, eye movements

Question 30

why do we need perception of intention?

Answer 30

- bodies are special object of perception- can integrate multimodal info (visual, tactile and kinesthetic) to understand where our bodies are - bodies are the only way we can intentionally influence the world and interact with it - our language ascribes intention to our own and other people actions (we are always conscious of our goals, in other there is speculation the goal is functional and of the phenomenal state) - intention needs both ends and means

Question 31

what constitutes perception of action intentio?

Answer 31

action movement and information beyond the stimulus -> infants attend to human bodies, toddlers understand goal-directed action, pre-schoolers have a 'theory of mind'

Question 32

what is the theory of mind in social action perception?

Answer 32

behind an action, there is a phenomenal state -> the ability to differentiate- 1. object of the mental state- what the mental state is about and goal of the action 2. content of the mental state- how the mental state is actually represented allows us to understand how other peoples mental representations relate to reality (might differ)

Question 33

what are the roles of the different brain regions in social action perception?

Answer 33

EBA- representation of bodies pSTS- representation of body movement, goals and intention TPJ (temporal parietal junction)- representation of specific contents on mental states, ToM

Question 34

what did Allison (2000) find about perception of mouth movements?

Answer 34

- patient watched movies of mouth movements and images of faces - ERPs recorded from STS- responded better to mouth movements

Question 35

why are mouth movements important?

Answer 35

- perception of auditory speech- observing movement of others face improves intelligibility of speech - deaf people can use mouth movements to understand speech without sound (lip-reading)

Question 36

what did Calvert (1997) do and find?

Answer 36

- compared brain activity during 1. sounds (listening to number list read aloud) and 2. vision (watching lips of reading list) - vision: V1/V2/V5 - sounds: auditory cortex - both: common activation in STS and auditory cortex - auditory cortex (A1- primary auditory) also responds to visual -> multimodal response

Question 37

why do we need perception of hand gestures?

Answer 37

- during speech, people often use concurrent hand gestures (often clear semantic relationship) - can see and interpret hand gesture to better understand speech - blind children also use hand gestures even though can't see them- so it might be an integral part of speech

Question 38

what has been found about sign language?

Answer 38

- specific hand movements used instead of speech - profoundly deaf people can see hand gestures and fully communicate using them - fMRI scan of noncongenitally deaf participants fluent in ASL (Neville 1998) -> STS more active to ASL

Question 39

why is perception of 'emotional body language' important?

Answer 39

- we are able to make inference about perception of peoples emotions from their actions

Question 40

what the brain structures involved in processing emotional body language and how do they link together?

Answer 40

STS, amygdala, body processing network (EBA, FBA, STS), emotion processing network (amygdala, anterior cingulate) NOTE: STS and amygdala are highly and reciprocally connected -> emotional body language increases activity in the STS (occurs when trying to understand others emotions)