Lecture 2 - Perceptual development

Question 1

perception

Answer 1

• tells us what is out there, allowing for adaptive decisions, actions and social interactions
• undergoes development post-natally: structure and function of sensory organs minor changes, but structure and function of sensory brain areas major change
• depend on sensory experience

Question 2

early visual abilities

Answer 2

• at birth:
  > poor accomodation, poor vergence, jerky eye movements. orients to patterns and faces but limited visual acuity and contrast sensitivity
• 1 - 3 months:
  > better accom, vergence and smoth eye movements for tracking moving targets. better acuity and contrast sensitivity. emerging ability to distinguish motion, orientation, pattern and binocular depth
• 4 - 8 months:
  > acuity and contrast sensitivity close to adult level. global organisation of stimuli (coherence form and motion, biological motion, depth from pictorial cues). discrim faces.

Question 3

early auditory abilities

Answer 3

1. birth
   - recognise sounds and mothers voice in utero. localise sounds in space
2. 1-3 months
   - distinguish speech sounds
3. 4 - 8 months
   - inc sensitivity to pitch
   - distinguish auditory patterns e.g. pitches, rhythms & melodies.
4. 9-12 months
   - begin to lose ability to discrim speech sounds not used in the language (perceptual narrowing)

Question 4

eye movements

Answer 4

• controlled by multiple cortical & subcortical networks
• disorders inc failure to develop proper vergence and nystagmus (unsteady fixation)
• can result from poor visual exp
• saccadic system allows orienting to one location
• smooth pursuit movements are slower tracking movements of eyes designed to keep a moving stimulus on the fovea

Question 5

visual acuity and contrast sensitivity

Answer 5

• VA: finest pattern one sees
• CS: lowest contrast one sees
• both work together to characterise basic visual abilities
• CS improves non linearly and levels off ay approx 12-15 weeks
• VA continues to improve with age
• explained by experience-dependent changes in neuronal connectivity: LGN to V1 and beyond
• visual deprivation (loss of acuity & contrast sensitivity) occurs if V1 does not acquire connections to input from affected eye

Question 6

visual evoked potentials

Answer 6

• VEP are an EEG method to assess if neurons are firing in response to a specific visual change e.g. orientation

Question 7

orientation

Answer 7

• cortical activity produced by specific orientation change at 3 weeks (braddick 1993)
• for direction there is behavioural discrim at 7 weeks and disparity at 11

Question 8

motion

Answer 8

• cortical activity produced in response to directional motion at 10 weeks for low speed and 13 weeks for high speeds
• experience important: kittens with no motion have no directional cells. normally gain in first 2-3m

Question 9

depth

Answer 9

• cortical responses emerge at 11-13 weeks
• depth detail (stereoacuity) improves within 4-5weeks of onset
• gives 3D sense of image (we compare discrepencies between L and R eye images)

Question 10

newborn face perception

Answer 10

• infants prefer standard faces over scrambled (Johnson et al 1991)
• driven by basic and early developing sub-cortical mechanisms
• by 2m face processing inc sub-cortical system (conspec) and cortical system (conlern) mechanisms working in parallel
• preferences may emerge in womb e.g. prefer two dots at top and one at bottom (face like) lights

Question 11

face perception neural

Answer 11

• specialised cortical response in adults, not seen at 6 months
• 9m old could distinguish between human faces but neither 9m or adults could distinguish monkey faces. 6m could discrim both human and monkey faces = infants specialise to human faces in first year
• by 6m we do not get a specialised response so treat upright and inverted faces similarly and monkey faces differently = cortical responses not yet tuned
• cortical systems develop longer than sub-cortical

Question 12

pattern perception

Answer 12

• petterns are processed in 2 parallel streams: dorsal stream (motion/space/action - where/how) & ventral stream (what/objects)
• ventral - temporal. dorsal - parietal.
• can compare coherence threshold of form and motion. can reliably tell until 20% (form coherence threshold)
• form coherence threshold gets lower until about 10 years so need fewer elements in line to be able to see the pattern.
• for motion need about 30% coherence vs 20% for form
• motion responses are poorer/later than form, also worse in autism, dyslexia & WS.
• dorsal stream has longer more vulnerable development than ventral and may depend more on experience.
• there is cross talk in reality

Question 13

perceptual narrowing

Answer 13

• young infants are sensitive to processing contrasting info
• english 6-8m discrim 2 hindi sounds that adult english cannot. english 10-12m cannot but hindi infants can.
• also other senses e.g. young infants discrim both human and monkey faces but by 9m respond more to a novel human face than a novel monkey face
• get perceptual narrowing for range of discrim occurring in other domains too = infants lose ability to make some subtle discriminations while they are gaining expertise in others. occurs with experience & limited brain resources.
• statistical learning - infants abilities to rapidly learn the co-occurrence statistics of the world around them (which items go together) even in artificial stimuli e.g. syllables and object elements

Question 14

multisensory development

Answer 14

• we often receive redundant info (same info from more than one sense) = can make faster/accurate decisions through flexibility (use one cue when other not available) and correlations (temporal which allow us to attend to important objects).
• events that go together have amodal features in common
• infants tune into amodal properties
• intersensory redundancy hypothesis = info presented in multiple senses at once is more easily attended, learned and remembered.
• e.g. 5 month see and/or hear hammer tapping, notice rhythm bettwe in the two cue condition. = multisensory ifno guides attention & learning.

Question 15

multisensory learning of own body

Answer 15

• 5m old looks longer at live feed of own legs than prerecording of own or others (bahrick & watson 1995)
• 3-5m look longer when legs move in opposite direction to own (richat & morgan 1995)
• while infants notice visuomotor correlation they may not relate it to their own body
• Zmyj et al 2011 - 10m old look longer at synchronous display of stroking of legs and viewing stroking than 7m.
• does not show sense of self as infants look in mirror at self at 2 years,