What experimental apparatus has been used to study depth perception in infants?

Memory Strategy – Child Psychology – Perceptual Development:

• Fantz – Faces
• Ayres – Autism and SI
• Lashley – Little rats
• Lang – Lacks usefulness
• Spalding – Speedy chicks
• Habituation – Familarisation
• Blakemore & Cooper – Cats
• Compos – Cardio
• Fantz – Focus = Interest
• Gibson & Walk – The ledge

FALLS Happen Because Children Fail to Gauge

Perception is the process by which our minds organise, process and make sense of sensory data.

Depth perception is the visual ability to perceive the world in 3D, coupled with the ability to gauge how far away an object is.

Depth perception, size, and distance are ascertained through both monocular (one eye) and binocular (two eyes) cues. Monocular vision is poor at determining depth. When an image is projected onto a single retina, cues about the relative size of the object compared to other objects are obtained. In binocular vision, these relative sizes are compared, since each individual eye is seeing a slightly different image from a different angle.

Visual perception: Information that enters our pupils and the ability to recognise objects, colours and depth. Below are a number of sensory skills that develop over the first year of life:

Acuity: this is the sharpness of or vision; the ability to detect fine detail. It is determined by how quickly our eye muscles are able to contract and relax in order to focus. Infants can see 6 metres clearly, but an adult can see between 100-125 metres!!

Binocular vision: eyes have to be aligned and coordinated in their movements in order to achieve accurate depth perception. Newborns eyes have poor muscle definition and so struggle to do this.

Colour: cones are cells that are found in the retina and are responsible for colour vision. Young babies have been found to prefer bold colours or highly contrasting ones such as black and white. Because their eyes are in the early stages of development, perceiving colours may be more difficult for them.

Pattern Perception:

Fantz (1963) found that babies prefer complex patterns compared to simple patterns suggesting that babies can differentiate between patterns. He also found that newborn babies preferred patterns that resembled a human face compared to other patterns, suggesting an innate perceptual ability to recognise faces. He looked at children under 5 days old and found that they spent more time looking at faces and patterns compared to plain colours.

How perceptual development can be studied in babies:

Habituation:

A new born any will look at something if it is a new stimulus. If you present the same thing to a baby many times, eventually it will lose interest; if you then present something similar but different in some way, the child will show interest again. For example, if you show a baby a picture of a square many times, the amount of time the baby will look at the square will gradually decrease. If you show a series of squares until no interest is shown, and you then show a rectangle, if the child shows interest in it, we can infer that the child can tell the difference between a square and a rectangle.

Compos (1900’s)

Compos showed that 6 week old babies placed on a visual cliff had a decreased heart rate. At 7 months old infants were lowered down on a visual cliff their heart rate rapidly increases and they started to whimper, showing a fearful response.

Fantz (1950) A child was placed in front of 2 stimuli whilst a researcher looked through the aparatus to time how long the child spent looking at a particular stimulus. The longer the gaze, the more the child preferred that stimulus

How perception is measured in animals:

Spalding (1873) kept chicks in a black sack made from a soft flannel material. They were in the bag when they hatched. When he released them several days later, they could run to their mother, avoiding obstacles, implying that they had the innate skill to identify where objects were and how to avoid them.

Lashley (1934) used rats and kept them in the dark for 3 months, when tested they used more effort to jump large gaps than small gaps, implying that they knew when something was further away. However, when rats were kept in the dark for 300 days, rats did not have depth perception. This shows how perception may be innate, but without interaction with light, this is a skill that can be lost.

Other research which looked at the effect of light on perception was achieved by sewing up the eyelids on kittens and baby monkeys. When the eye lids were unstitched, this would show what innate perception skills that the animals had.

Blakemore and Copper (1970) can also be used as background research.

Key Research – The Visual Cliff: Gibson, E.J & Walk P. D (1960)

Aim:

• The study also aimed to show support the idea that both humans’ and other species’ depth perception is innate.

 Research Method:

• The main study was a laboratory experiment
• The independent variable (IV) was whether the infant was called by its mother from the cliff side or the shallow side (of the visual cliff apparatus).
• The dependent variable (DV) was whether or not the child would crawl to its mother.
• This was a repeated measures design because the infant was called from both the cliff side and the shallow side of the apparatus.
• The studies using other species are quasi-experiments. The naturally occurring independent variable (IV) was the animal species. The dependent variable (DV) was whether the animal preferred the shallow side or the deep side.

 Sample:

• 36 infants ranging for 6-14 months. Their mothers also participated in the experiment. Unspecified number of a variety of animal species e.g. cats, rats, goats, sheep, turtles and chickens

Procedure:

• Each child was placed on the centre board, and his mother called him from the cliff side and then afterwards called the child from the shallow side.
• Similarly chicks, turtles, rates, lambs, kids, and kittens were placed on the visual cliff apparatus
• A number of control experiments were conducted to ensure the design of the visual cliff apparatus had no hidden bias e.g. reflections from the glass were eliminated. In some experiments the patterned surface was replaced with a plain grey surface and finally, alterations were made in order to determine which of the two visual cues play the decisive role in depth perception, either motion parallax or relative size/size constancy.
• To determine whether depth perception in rats and kittens is innate, groups of light-reared and dark-reared rats were tested using the visual cliff experiment.

Baby findings:

• 27 infants who crawled off the board crawled out on the shallow side at least once.
• Only 3 of the 27 children who moved off the board crawled off the brink onto the glass suspended above the pattern on the floor.
• Many of the infants crawled away from the mother when she called to them from the cliff side and some cried when their mother stood on the cliff side because they could not get to her without crossing the cliff.
• Often the infants would peer down through the glass on the deep side and then back away.
• Some infants patted the glass with their hands, yet despite this tactual assurance of solidity would refuse to cross.

 Animal findings:

• Overall, findings suggest that depth perception develops once the animal becomes mobile – suggesting survival purposes shown in Lambs, Kids and chicks who become mobile within 24 hours.
• Kittens at 4 weeks old choose the shallow side and freeze when placed on the cliff side.
• Overall, most of the species behaved in a similar way to the children in the sense that they preferred the shallow side.
• The poorest performance on the visual cliff was shown by turtles where 24% of the aquatic turtles crawl towards the cliff side.
• When placed on glass over the deep/cliff side, Dark-reared kittens did not back off like light-reared (normal) kittens, but showed the same behaviour that they had exhibited on the shallow side.
• Once exposed to the light the dark-reared kittens were tested daily. After a week they showed preference for the shallow side.
• At the age of 90 days both light-reared and dark-reared rats showed the same preference for the shallow side. These results support the idea that depth perception in rats is innate.

 Control experiments:

• Overall, the variations of the experiment found no hidden bias.

Separation of depth perception cues:

• With only motion parallax to guide them, day old chicks, and rats reared in both light and dark conditions showed a strong preference for the shallow side. However, this was not the case when they only had object size to guide them. This finding suggests that motion parallax may be an innate visual cue, but that object size develops as a result of maturation.

Conclusions:

• Both nature and nurture influence the development of depth perception
• Binocular cues such as motion parallax are innate, while monocular cues such as size constancy are learned
• Humans and other animals have developed depth perception by the time of the onset of mobility, which is specifically suited to the habitat and skills of the species.

Debates and methodological issues in Gibson & Walk:

Methodological and ethical issues:

Gibson and Walk created conditions that were distressing in babies who felt they could not reach their mothers safely. there are also ethical issues when researching perception using animals as it could cause suffering to the animals and cause irreversible effects e.g. Blakemore and Coopers sensory deprivation research.

Looking at perceptual processes involves inferring meaning that is made from their senses and behaviour. Therefore researchers will make certain assumptions about what the participants are thinking – and this may not necessarily be valid – especially when there is no verbal communication to support the assumptions made.

Although the procedures and instructions were highly standardised, it is possible that the verbal cues provided by mothers may have changed when calling the child from the shallow side compared to the cliff side. This may evoke extraneous variables.

Usefulness of research:

This research has been useful in creating an time line for visual perception in order to track ‘normal’ development in newborns and infants. Findings like this help to identify abnormalities in perception or vision. This is extremely important as a child may need intervention such as glasses or hearing devices or strategies such as Braille may need to be taught.

Nature vs nurture:

Humans appear to have innate reflexes which help their sensory system e.g. the moro reflex, walking reflex etc. Most psychologists agree that perception is a result of both nature and nurture. Other research by Sugita (2004) have shown that although sensory capability may be present, without the right environmental stimulation, depth perception and colour perception can’t develop.

Gibson and Walk may be seen as supporting an innate explanation of depth perception due to the fact that the participants were so young that it is presumed it is mainly biological. However, we are aware that depth perception changes extremely quickly after birth, and this would imply environmental influences. Research has even shown that babies can be capable of sensing some light and sound from the womb therefore showing again, environmental effects.

Reductionism vs holism:

Many psychologists look at something called neuroanatomy, cognitive processes and environmental exposure. This is seen as more holistic as it tries to explain perception through the complex interaction of the above.

Psychology as a science:

Research in this field tends to use lab conditions and is therefore objective and standardised. Gibson and Walk reduced potential bias and extraneous variables by getting rid of light reflection in order to improve validity. In addition the materials and instructions during the visual cliff task was standardised and would appear to be easy to replicate.

Application: a play strategy to develop perception in young children:

Sensory and Perceptual difficulties:

People with Attention Deficit Hyperactive Disorder or Autism may struggle to receive, process and make sense of information provided by their senses. These individuals are mostly recognised to have such difficulties at a very young age. Some people with autism have difficulty with bright lights and are sensitive to certain stimuli. Therapists have been working to use play to help facilitate their perceptual development.

Sensory integrative play (SI Therapy):

Ayres (1988) theory of sensory integration outline how our senses are neurologically organised for use and allow us to move, learn and function in our environment. Ayres believed that developing a multi sensory perception was the best strategy in helping those who struggled to perceive the world accurately.

SI works by:

1. providing an initial assessment of the child’s sensory issues using a number of standardised tests.
2. developing a personalised treatment programme that uses effective techniques and tools to meet the individual needs of the child. These techniques are designed to be fun and, to the child seem like everyday play, rather than a therapy session.

For SI to be effective, the child must have intrinsic motivation, they should see it as rewarding, not as a chore.

Some examples of the playful activities include:

• using brushes on the skin – encouraging touch and hand-eye co-ordination
• sitting or rolling on a bouncy ball to encourage vision and balance
• being squeezed between exercise pads or wearing a weighted vest to encourage an understanding of pressure and movement
• dancing to different types of music to encourage an understanding of sound and movement

The effectiveness of SI therapy is measured through verbal feedback from the child or from behavioural outcomes such as improved tolerance for stimulation, attention building, improvements in perceptual abilities or general functioning. In a nutshell, this therapy works by providing stimulation of the senses in order to encourage the development of them. 

Even though Ayres highlights the success of her therapy, Lang (2012) carried out a meta-analysis of 25 studies using SI therapy and found that only a few studies showed clear positive results and that most studies used small samples.

Toys that encourage perceptual development:

Children’s play is an essential part of a child’s interaction with their environment and stimulates the development of these skills. The more opportunities that a child has to use their skills, the more developed they will become

A mobile has brightly coloured moving objects and can help to stimulate visual perception. Through the movement of the mobile babies will start to co-ordinate their eye movements i.e. binocular vision. The child will try to reach out for the objects and grab the toys on the mobile. This develops their understanding of distance e.g. motion parallax and size constancy.

A mobile is most appropriate for newborn babies 

Dot-to-dot can help develop visual perception. The child begins to develop hand eye co-ordination by joining the dots together. By completing various dot-to-dot activities, the child has experience of different shapes and this helps to develop their shape constancy i.e. the ability to see objects differently from different angles and orientations, and understand that objects remain the same shape even when they get bigger or smaller in size. Dot-to-dot is suited to children aged 4-6 years

Sensory develop the perception of touch. By feeling different materials, it enables them to understand different textures. The colourful nature of sensory books helps children to learn and differentiate between colours. It also develops acuity, through the smaller details in the books. Finally, it develops depth perception due to the 3D nature of the book. the child can develop binocular vision by using both eyes to look at the pictures. Suited to newborns-1 year