@11 on Monday, 11 Oct 99
perception
of shapes & pattersn
familiarisation/habituation
technique
Prelims = an intro to psych in Ox
1. developmental
2. perception
3. physiological basis for behaviour
4. cognition
D in
the way people behave � mainly through childhood (birth � late adolescence)
perception channels � learn about the world
can babies perceive in a systematic fashion?
or do they learn (over time) to discriminate?
i.e. do they learn establish ways of perceiving before learning about their subjective world
what does a newborn baby perceive � hear/see/feel etc.
very difficult to get direct evidence � can�t test/talk to them easily � answer until recently based on very indirect evidence, eg:
1. based on blind adults who gain power of sight (seen as analogous to new-borns)
2. another line of evidence � animal species � newborn animals often easier than babies
but both methods unsatisfactory
blind � had the powers of touch & hearing their whole lives
recent evidence: they can perceive
tests need measurable responses � hard to find in babies � they don�t talk, press bars, run down alleys etc.
don�t sit up till 6 months, don�t crawl till 9 months
they fall asleep, they cry
can't be repetitive, not last for ages
soln: Robert Fantz (American)
possible to measure how long the child looks at objects
babies look at some things more than others
\ must discriminate them in some way
babies of 1-20 weeks � pairs of shapes to look at in diff 30sec trials
if systematic pref of A over B � demonstrates some kind of discrimination
breakthrough experim � in method, more than results
some results were positive � pref of one over another
some �ve (no difference), e.g. cross vs circle
problem: -ve results are ambiguous � could be that the babies cannot distinguish cross & circle
alternatively: can discriminate perfectly well, but don't find one more interesting/engaging than the other
but no way of distinguishing those 2 results
soln: Fantz suggested soln, though didn't carry it out
Alan Slater�s version
preference for novelty � seems to be universal
novel events/stimuli attract attention much more than familiar � very reliable/universal features of behaviour theory
incorporate it into the experim
make one more/less interesting than the other on the basis of familiarity/novelty- now standard technique
1. familiarise babies with one of t shapes � when thorougholy familiar/bored, then show them 2 shapes: t familiar and the novel one
2. argued that if did that, and if true that babies are more interseted in novel shapes than familiar shapes, then to discrim, they will look more at t new shape
series of habituation trials � shown shape �F' repeatedly until they don't look at it much any more
when they look away, it�s taken away � repeat until the viewing time is typically half of what it was initially
post-habituation trials
�F' presented together with a novel shape (N)
will babies look more at N than at F?
if so, then must be discriminating
neonates � avge 36 hours old
4 shapes in diff combinations spent 65.3% of time looking at N
\ demonstrates preference (consistent across babies � 26/30 babies)
we see in 3D: use many cues to perceive depth
� is this built-in or learnt? (do children originally see a flat world?)
depth perception = different from shape perception cos the retina = 2D � depth perception depends on depth cues (which could be innate or might have to be learned)
main method for testing depth perception in the young = avoidance (cliff)
but actual cliffs may give non-visual cues for depth
=> the visual (only) cliff
very tough glass surface � 2 parts: shallow end CBS and deep end
goats & babies � crawling baby > 9 months old
baby on glass � shallow end
if put on shallow end, not even mother can induce them to � deep
gibson & walk� established inate depth perception in many animals
but these animals all move around actively soon after birth
\ could possibly have already learnt about depth (same with babies)
soln: Joe Campos � use different reaction, e.g. fear of fallings � heart rate
heart rate 8> when distressed/frightened, down when interested in novel
6 weeks old babies � long before they�re crawling � fairly early perception
???
perceptual categories; discontinuities along a continuum
many perceptual continue which we treat as discont: e.g. reds/yellows/blues
although they�re merely different points along same continuum of wavelength, subj = differentiated
mechanisms to break up continua into categs (e.g. in the visual categs of colour, shape, angle)
also in speech
VOT � voice onset time
consonant � release breath and make articulatory movements, all different for the different consonants � also vibrate the vocal chord
variations in the interval bewteen rleease of breath & vocal cord movement
VOT = continuum
sounds involving the same articulatory movements vary along the VOT continuum
can distinguish between but not within perceptual categories, e.g. �b� vs �p� (30ms = cut-off point)
HAS � high amplitude sucking
looking at speec catgories in infants
HAS babies given a dummy wired up so that sucking maintains sound
babies learn this very quickly, and they do suck more for new sounds
if they hear the same sound, they suck less
if they hear a new sound, they start sucking more
Eimas � possibility of �b� and �p� speech categories in 1 and 4 montha� infants in 3 group experiemnt
1. 20 � 40, 40 � 20 (between �b� and �p�)
2. 0 � 20, 40 � 60 (within, indistinguishable to us)
3. control � sound unchanged
cross-changes � big increases in rate of sucking
within � 1-month babies slight increase, 4-month decrease
no change � decreases
newborn babies able to make discrims which english adults cannot make � they drop categories
infants are born with array of perceptual mechanisms
(presumably) to allow them to learn about the properties of their environment