Basic Visual Functioning

To build a coherent knowledge base of the world.
- Necessary information must be obtained.
- Information must be integrated appropriately for the age of the learner.
- The integrated information is then used to act in the environment.

The world is composed of objects, each made up of distinct features.
It is essential to see these features before one can synthesize them to perceive an entire object.

Rapid development occurs in the processing of information during infancy.
The capacity for input is limited by sensory processes that extract information from the environment.
- These sensory processes are linked to the development of the nervous system.

Tested using two primary methods:
- Preferential Looking: Observing where infants gaze implies preference, indicating better acuity.
- Visual Evoked Potential (VEP): A neurological test that provides objective measures of visual acuity and development.
VEP typically yields more accurate acuity measurements than preferential looking.

Acuity is often recorded in Snellen Units, where the pattern observed is as follows:
- At age 0 months: Acuity begins lower at approximately 20/400.
- Acuity progresses with age and levels off after 6 months, reaching adult levels by 1 year.

The trends regarding visual acuity measures: 20, 120, 220, 320, 420,… and continues to improve as age increases.

In infancy, grating acuity (ability to detect lines or stripes) is better than vernier acuity (ability to detect alignment of specific points).
After about 1 year, the development of vernier acuity accelerates, and by 5 years, it surpasses grating acuity.
Reference: ZANKER ET AL. (1992)

Differs from acuity in that it focuses on how well differences between light and dark are perceived (brightness differences).
Assessment shows that overall contrast sensitivity improves during early infancy.
- Peak sensitivity transitions towards higher spatial frequencies which represent finer details.
Performance metrics across ages:
- Neonates, 4 months, 6 months, 8 months, and adults demonstrate increasing sensitivity levels.

Cone density in the fovea (central part of the retina) in infants is only 1/3 of what adults have, and their cone length is only 1/10 of adult size.
Initial cone density at 1 month vs. at 6 months indicates development.

Lens in infants does not adjust effectively for distance changes.
Myelination of the axons from retinal ganglion cells is ongoing, affecting optic nerve function.
The lateral geniculate nucleus (LGN) in the visual cortex matures, progressively better responding to higher frequencies of details.

Acuity and contrast sensitivity offer only rudimentary patterns of light and dark.
To utilize this information, the visual system must extract significant properties from these patterns.
- Evidence suggests organizational grouping of neurons in the early visual cortex responds specifically to certain patterns.
Research by Braddick, Wattam-Bell, & Atkinson (1986) employed visual evoked potentials to test these patterns, especially orientation.
- Changes in orientation of a striped pattern elicited measurable brain activity via VEP.

Findings indicated that VEP responses change specifically at the point of orientation shift as early as 6 weeks of age.
Additionally, habituation studies (Maurer & Martello, 1980) show that 6-week-olds exhibit orientation discrimination behaviorally.

Slater (1989) utilized a novelty-preference paradigm to provide evidence that newborns show some form of orientation discrimination.

There are two primary types of eye movements:
- Saccades: Quick movements that localize stationary objects.
- Pursuit: Smooth tracking movements used to follow moving objects.

By 1 month, infants can localize intended targets but with limited accuracy and slow speed.
By 6 months, saccadic movements become more adult-like.
Infants can perform predictive saccades by 3 months, anticipating target movement.

Research (Canfield, Smith, Brezsnyak, & Snow, 1997) reported typical minimum latency for adults at approximately 133 ms across various ages of infants (0-8 months).

Aslin (1981) studied pursuit movements and found detection challenging in infants under 2 months as they relied on saccades.
By 6 months, infants demonstrate reliable tracking ability similar to adults.

Phillips, Finocchio, Ong, & Fuchs (1997) observed that infants younger than 2 months can show smooth pursuit if the target moves slowly (at 10 degrees/second).
The frequency and effectiveness of tracking performance improve significantly by 6 months.