Visual acuity is the ability to make fine discriminations between the elements in the visual array. Infants’ vision is poorer than that of an adult. Visual accommodation is the ability to focus on objects irrespective of their distance from the eye. Infants are not good at this either. There are several ways to test infants their vision:

1. Visual preference method
   Infants are shown two objects and the object they look the longest at is the one they have a preference for.
2. Habituation techniques
   Habituation shows the existence of visual memory and this tests whether infants can discriminate between two objects by presenting them sequentially and seeing whether dishabituation occurs.

Infants are able to discriminate between simple shapes. This even occurred in new-borns, showing that new-born infants perceive simple shapes as a whole and not just as a collection of parts.

Size constancy is the understanding that an object remains the same size despite its retinal image size changing as it moves closer to or away from us. Shape constancy is the understanding that an object remains the same shape even though the retinal image shape changes when it is viewed from different angles. New-borns already understand the principle of size constancy and shape constancy. Object unity is the understanding that an object is whole or complete even though part of it may be hidden. 4-month-olds perceive object unity already. It is likely that infants use common motion to perceive object unity. New-borns do not perceive object unity. 6-month-olds perceive trajectory-continuity, whereas 4-month-olds only do so when the occlude is narrow. Subjective contour is when only parts of an object are presented, the remaining contours are filled in, in order that the complete shape can be perceived. 4-month-olds perceive subjective contour, especially when the object is in motion. They also perceive this as an occlude.

Face perception emerges at around 2 months, although evidence suggests that a form of facial perception is present at birth. The two-process account of newborn face perception states that new-born preference for faces stems from an innate subcortical mechanism that leads new-borns to attend preferentially to faces of the same species. After the second month of life, this is replaced or supplemented by an experientially based mechanism that involves a diffuse network of cortical areas and allows for continues cortical specialisation and tuning to specific faces. An alternative view is that new-borns prefer certain properties of stimuli that are not face specific.

Infants have a preference for the face of their mother and can discriminate between their mother and other faces. 2-month-old infants and even new-borns will look longer at a face rated attractive by adults than non-attractive faces. The preference for attractiveness may stem from the preference for prototype faces. General abilities become more narrowly tuned as a result of experience. Infants are able to imitate already and this might play an important role in language development.

Very young infants are able to discriminate between certain speech distinctions that exist in other languages but not in their own. This ability is later narrowed to their own native language. Infants prefer motherese or infant-directed speech, the speech that adults use when addressing an infant.

Piaget stated that infants were not born with knowledge of the world, but gradually constructed knowledge and the ability to represent reality mentally. According to Piaget, prior to the age of 9 months, infants do not exhibit object permanence. It does not develop fully until near the end of the second year of life. The A, not B error is an object-searching error that is often made by 8-12-month-olds. Infants making this error will look for an object where they have most often found the object, rather than where they last saw it being hidden.

A limitation of Piaget’s work was that it relied on the infant’s ability to act upon the object. The violation of expectation technique is a technique where infants are shown an event and then shown two new events, one of which is consistent with reality and the other is inconsistent with reality. The infants will typically look longer at the impossible events because it violates their expectancies. This leads to the conclusion that 5-month-olds have object permanence. Even 2-month-olds have the ability of some sorts.

Spelke and Baillargeon argue that infants possess core knowledge of the world, which is basic information about the world. Infants reason about the number of objects involved in an action, as shown by research. Infants are able to discriminate between arrays in terms of numerosity, though only in the case of small numbers. Numerical competence was based on subitising, the ability to perceive directly the number of items without consciously counting. This only applies to small numbers and thus this ability disappears with larger numbers. Infants are also able to make very simple additions and subtractions, as shown by the time they looked at impossible events.

The idea that a lack of motor skill leads to not searching for an item seems false, given that infants will try to look for it when it is placed behind a transparent screen, but not behind a non-transparent screen. This shows that infants do not understand the relationships between objects and occluders, but this does not mean that infants do not have object permanence.

A possible explanation for the A, not B error is response preservation, which is repeating a previously learned response usually when it is no longer appropriate. Another possible explanation is a memory explanation, that there is interference between the location A and the location B and that the already existing memory predominates over the new memory. The problem with this explanation is that errors even occur when the object is in view in the new location. Another possibility is that through seeing an object hidden and finding it, infants quickly learn to treat place A as a container and that this knowledge, rather than knowledge about the object, prevents them from finding the object. There is a link between success and continued attention to location B during the delay. When attention is distracted, more preservative behaviour occurs. Another possible explanation is that the frontal cortex, which is involved in planning and guidance of actions and executive functions is still too immature to fully process the event. Successful B trials are positively associated with greater frontal EEG activation.

It is possible that infants do have knowledge about things such as object permanence and the movement of objects, but that they are not able to convert this knowledge to action. It is likely that Piaget’s model has to be remodelled by stating that infants do not gain knowledge by actively acting upon the world, but that they have the knowledge and by actively acting upon the world they create links between that knowledge and action.