Development of infants perceptual abilities during the first 18 months of life

How has the use of new research methods contributed to a greater understanding of the development of infants’ perceptual abilities during the first 18 months of life? Perception is the experience of our environment gathered via our sensory organs. Effective navigation of these experiences requires the ability, not only to recognise, but also to act upon sensory stimuli, as it is through this process that we come to interpret the nature of our environment.

As a basis for the acquisition of knowledge, understanding what and how we perceive can provide insight into developmental progress and a comprehensive understanding of human limitations and developmental milestones. Influencing scientific research are the theoretical perspectives of nativism and empiricism. Do we learn to perceive through direct experience with our surroundings as an empiricist believes, or is the nativist position that we have innate perceptual capabilities correct?

Increasingly, the amassed evidence suggests that neither position is entirely accurate in of itself and a more authentic view posits that infants are born with some rudimentary knowledge which experience then refines and enhances. This essay aims to evaluate a small contribution of the research available, primarily visual and auditory studies. Individually, the separate perceptive senses of vision and hearing have been extensively studied, however in reality total perception is rarely the product of one sensory organ in isolation.

The presence of so many potential confounding variables creates challenges for researchers trying to devise studies that have true relevance but still provide unambiguous and conclusive answers. Further adding to that challenge are the subjects themselves. Physiological immaturity will have some impact on how a baby perceives its universe and as long as explicit communication of those perceptual differences is not possible, inferences from observable behaviour become the window into the infant perceptual world.

Pioneering visual ability testing through behavioural responses, Robert L. Fantz devised an experiment that refuted popular claims of the time that infant visual ability was at best poor. The viewing chamber apparatus he created, capitalised on human visual propensity to actively seek out and select what we want to look at, our eyes are not just passive receivers of information. Fantz reasoned that visual fixation duration for one stimulus over another was affirmation that babies can perceive a difference. His studies confirmed that infants have reasonably acute pattern vision and a preference for ‘face type’ stimuli (Fantz 1962).

Further testing on younger subjects of 10 hours old suggested that these abilities are innate (Fantz 1963). Again, the longest fixation periods favoured the face shape, but Fantz cautioned against using these results to assume the innateness of facial recognition as similar shaped patterns evoked similar responses. He ventured that a stimulus representative of something that holds social familiarity and importance might be the key to interest response whatever the underlying mechanism for that interest is. Fantz’s studies gave some remarkable information on the capabilities of very young subjects.

Despite their physical underdevelopment, he managed to show that infants are born with a more sophisticated level of ability than one might ordinarily have ascribed. Critics have argued that the real world validity is somewhat limited as the visual world is rarely static and two dimensional but in the context of it’s time, Fantz did provide answers to questions without which, more comprehensive research might not have been possible. Without knowing the extent to which an infant can visually differentiate, it would not be feasible to exclude the possibility that subjects simply couldn’t see the difference between more elaborate stimuli.

Our facility to perceive the environment in three dimensions comes from depth perception and it is these visual cues that are synthesised into intelligence about distance. Eleanor Gibson explored the possibilities of depth perception being an innate or learnt ability through her ‘visual cliff’ experiments (Gibson and Walk 1960) which engaged the subject as an active participant in their perceptive experience. A ‘visual cliff’ is created by suspending a glass floor over a checkerboard surface on one side of which, the surface is immediately below the glass.

On the other side, the surface is one metre below. The subject is placed on a covered runway in the centre of the apparatus and mothers then encouraged their babies to move into either the shallow or cliff sides successively. Of the 27 subjects that crawled to their mothers, all did so across the shallow side but only three crawled off the ledge. Gibson observed infants crawling away from their mothers when she was positioned at the cliff side leading to the conclusion that babies can discriminate depth as soon as they can crawl.

Although the question of innateness is asked, the evidence cannot show this as subjects were already six months old. By this age, a baby’s experience of heights from being carried would in all probability be quite pronounced and depth perception at this point could very well be learnt.

Gibson noted that depth perception is limited by loco motor function as some less experienced crawlers backed over the edge in their attempt to reach their mothers and similar studies by Campos et al. (1992) found that new crawlers were happy to cross the cliff whereas experienced crawlers almost always would not.

This suggests that there is a learning process that takes place. As crawling ability improves a more accurate understanding of the visual cues can be processed. Vital for language comprehension and therefore communication, auditory ability in infants has also been extensively studied but as orientation of the ears towards the stimulus is not essential for hearing, observation of the sensory organ alone cannot provide any evidence of ability.

Infants do however turn their heads towards sound and this skill is demonstrated soon after birth. This behavioural response was used by Fernald (1985) on infants of 4 months old who were exposed to recordings of normal voices versus recordings of ‘motherese’. Motherese is the definition given to the type of speech adults typically use when communicating with babies. It is usually of a higher pitch, slower tempo and emphasises intonation.

Fernald’s study included a wide sample of 48 infants and the voice recordings were all unfamiliar female voices. Her results showed that given a choice, infants chose more often to listen to ‘motherese’ even when it is not spoken by the mother. Again, the age of the subject limits the inferences that can be made about innateness of ability. At four months old, babies have considerable experience of human voices, particularly the voice patterns of their care givers which would most likely have a high content of ‘motherese’.

Similarly to the interest observed in Fantz’s studies to the face stimuli, it’s plausible that the importance of attending to a ‘motherese’ speaking figure is not lost on a baby however young they are and that the innate ability is …

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