STUDIES OF THE DEVELOPMENT OF PERCEPTUAL ABILITIES

Are we born with ability (nature, bottom up, nativist) or is it acquired through experience (nurture, top down, empiricist). Can look at infants abilities and /or people living in different environments to try and answer this.

GENERAL AO2 limitations
Infant studies. (Neonate)
Abilities not present at birth not necessarily learned – may require later development. Some may actually get experience in the womb i.e. not innate even if present at birth.
Assessment very difficult – e.g. motor skills and acuity – acuity 10-30 times poorer than for adult therefore difficult to assess e.g. depth perception
Techniques may not be reliable- may respond to inadvertant cues from experimenter – experimenter bias (cannot ask them)
Methods used • Habituation • Sucking rate • Preferential looking • Conditioning • Heart and breathing rate • PET scans

Infant studies
AO1
Gibson and walk visual cliff – used infants 6 – 14 months old –most refused to cross onto deep side even when enticed by parents – suggests innate ability

AO2
Infants 6+months so could have learnt –when done on new born mobile animals – they wouldn’t cross – but animals not humans. Compos – babies placed on both sides heart rate measured. On deep side decreased in very young suggesting they could perceive depth i.e. an innate ability, but not worried, older infants heart rate increased suggests not only perceive depth but understand implications i.e. could fall. So may be innate ability to perceive depth but need to learn the relevance.
Yonas – on video object seen moving towards infant, avoidance behaviour seen e.g. flinching in 2 month olds suggesting innate ability. Yonas 6 week old infants – one group born on time other 4 weeks late. Both had same experience but post term babies more likely to show avoidance behaviour – again suggests innate.
Visual cliff – a controlled lab experiment – therefore objective

Hofsten
Used habituation method with 3 month olds using three rods and baby moved in a chair. When bored changed position of rods. Showed they used cue of motion parallax
BUT have had 3 months to learn

Bower
Presented different images to each eye to give 3D image to infants as young as 1 week old, they tried to reach for image showing they could use cue of retinal disparity.
Babies shielded eyes at approaching objects - innate

Granrud and Yonis
Objects (dice) using cue of overlap in one condition. 7 month olds reached for the nearest showing they could use cue of overlap but 5 month olds didn’t. Suggests overlap cue is learnt at around 6-7 months old

VISUAL CONSTANCIES
Infant
AO1
Size constancy Bower
Infants 40-60 days old – conditioned to respond to 30cm cube 1m away.
|Size |30cm |30cm |90cm |90cm |
|Distance |1m |3m |1m |3m |
|Retinal image | |smaller |larger |same |

Looked at same size not same retinal image – concluded babies have innate size constancy. Also looked at cues
Condition 1 texture gradient and motion parallax
Condition 2 texture gradient
Condition 3 texture gradient and retinal disparity

Couldn’t judge size/distance in condition 2, suggests don’t use texture gradient, best in condition 1 intermediate in condition 3. Suggests they use mainly motion parallax and retinal disparity to a limited extent.

AO2
Infants approx. 2 months old so could be due to experience. Results have been hard to duplicate. Not easy to obtain conditioned response and their behaviour can often be misinterpreted. Slate and Morison found shape constancy in new-borns. Supports Gibsons view of direct perception – i.e. if innate suggests no involvement of cognitive processes – view that sufficient data in optic array to perceive visual constancy’s.

Kaye and Bower
1 day old infants trained that when they sucked a dummy it would show a particular picture.
2 pictures the dummy they were sucking (familiar) an unfamiliar dummy.
Found they sucked to show familiar dummy. Suggesting shape constancy innate.
Bower – reinforcement used to train 2 month olds to turn and look at a tilted rectangle, found could distinguish between this shape and others – shape constancy

Evaluation

• Overall difficult to know whether it is nature or nurture, as eye may need to mature – visual system is not well developed at birth • Even if only one day old may still be learning – could be sensory learning in the womb- most studies use older infants – they could have learned • Many studies suggest abilities are present at birth or soon after – suggesting ability is innate – support for Gibson • Ethical considerations of informed consent and causing distress e.g. visual cliff where mother encourages baby to crawl off an apparent vertical drop • Vulnerable to researcher bias – infant cannot tell researcher what they see.l • Perceptual completion appears later e.g. Kanizsa square. We can see things that aren’t really there babies cannot. They can see shapes but cannot integrate them until the age of about 3 months. Will see 2 cards one partly behind the other as one shape. Suggests completion and occlusion are learned abilities – support for Gregory. • But Bottom up – suggest ability to “see” occlusion etc. is not a perceptual process but a cognitive process • Distinction between bottom up and top down may lie in deciding what is perceptual development and what is cognitive development.

Cross-cultural Studies
General AO2 • Could still be biological e.g. different genes. So could be nature. E.g in U.S.A. etc older people are less likely to be fooled by Muller Lyer illusion possible because as you get older retinal pigment gets darker. If a culture has darker retinal pigment this could explain why not fooled by illusion rather than the environment they live in ~(non carpentered) • Imposed etic (cultural specific task and assume it will be suitable in all other cultures) • Most evidence rather anecdotal/poor controls. • Participants may not be representative of the whole culture. • If relying on translators – do they really understand each other. • Manly natural experiments so cannot control I.V. so difficult to conclude cause and effect only association. • Few cultures not exposed to carpentered /western environment.

Anecdotal e.g.
Anthropologist Turnbull visited tribe of pigmies in a dense forest in the Congo. Took one member – Kenga out of the forest. Saw Buffalos far away in the distance. Kenga said what are those strange insects? As they got closer he was able to recognise them as buffalos and thought Turnbull was a magician. But could suggest as he lived in a dense forest he would not have had a chance to develop depth perception and visual constancy. Suggesting these must be learnt –nurture not nature.
BUT
• Anecdotal not scientific • Could be language problems

AO1
Use of pictorial cues
Hudson drawing of elephant, etc shown to children from Bantu, Europe, India and S Africa. Spear points at both elephant and antelope, but depth cues (size, linear perspective etc.) suggest pointing at antelope, by age 10 half Europeans got it right but Bantu still tended to see 2D picture.
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AO2
Hudson – schooling didn’t seem to make a difference, experiences outside classroom probably played larger role. So monocular cues appeared to be learned not innate, but may be cues fairly weak. Or they are not used to interpreting 2D drawings i.e. could use depth cues in real life.

Jahoda and McGurk
Participants given training task – shown silhouettes of a girl(5.0cm) and a women (7.5cm) and asked to construct wooden models of them. Then shown pictures of them, one in foreground and other in background – depth cues used – linear perspective and/or texture gradient. In middle distance small bird. For each picture asked to place their models in correct position. Tested children from Scotland and Ghana – found did better the more depth cues, older children did better than younger and overall Scottish children did better. Some depth cues are innate but get better with experience

Shape constancies
Allport and Pettigrew
Tested Zulu people in S.Africa with trapezoid window, rural Zulus didn’t live in houses with square windows, whereas Zulus living in more urban areas did. Found Rural Zulus less likely to be fooled by illusion than Urban Zulus suggesting ability learnt.
Size constancies
AO1
Segall – European groups more susceptible to Muller Lyer illusion than non-European.
Pollack suggests may be biological factor – susceptibility declines with age, older people also find it more difficult to detect contours. In a further study found that the denser the retinal pigmentation the poorer the contour detection. Therefore darker pigmentation may be responsible for susceptibility to Muller Lyer and dark skinned people may have denser retinal pigmentation i.e. Biological not environmental.
Stewart – Muller Lyer and Sander Illusion.

| |Zambezi Valley |Lusaka |Illinois (black) |Illinois (white) |
|Muller Lyer |4.36 |5.81 |6.1 |6.1 |
|Sander |4.24 |5.33 |5.59 |5.4 |
| |Same culture and different environment |Different cultures but same environment |

Support idea that nurture (environment) responsible not innate.

AO2
Possible non-Europeans may have been confused by the instructions and be responding to experimenter cues and act according to expectations. Generally support notion that environmental experiences responsible, unlike infant studies that suggests innate

Differences may be perceptual or due to ignorance of techniques or aesthetic i.e. not due to perceptual ability.

Evaluation • Most cross cultural studies support Gregory - nurture • More recent studies suggest fewer differences between cultures e.g. pictorial depth perception but this could be due to the fact that methods are now more scientific and rigorous so results more reliable and/or that now it is very hard to find a tribe who have never seen a carpentered environment. • Language – Page did a study like Hudson’s but rephrased the question and more seemed to understand and get it right • Myopia (short-sightedness) if eyeball is too long image doesn’t focus properly on retina – blurry image. Evidence that myopia runs in families, also more common in environments where you have formal education – doing close up work e.g. reading. This is an example of where biology and environment may interact. • Lack of understanding of 2 dimensional depth cues. Deregowski suggested there is an important distinction between epitomic images (no depth cues e.g. silhouettes) and eidolic images (illustrations that look 3D even if impossible figure. He suggested Hudsons pictures more epitomic and Jahoda and McGurk more eidolic – these are more easy to interpret. Problem not interpreting real world depth cues but using culturally relative depth cues in pictures. Might just be convention they dodn’t understand e,g, when show pictures in colour (more realistic) more seemed to understand and get it right than in black and white, Western style pictures (see elephant) • Research focuses mainly on visual illusions and 2D drawings which may not relate to more everyday perceptual abilities • Nature nurture argument not fully resolved – we have to combine innate and learned factors in order to perceive the world and attach meaning to what we see. We appear to be born with certain ‘hard wired’ abilities which require interaction with environment to develop appropriately – this makes sense from an evolutionary perspective. • Research focuses mainly on visual illusions and 2D drawings which may not relate to more everyday perceptual abilities