Hunnius (2007). The early development of visual attention and its implications for social and cognitive development.” – Article summary

Looking behaviour forms the basis for cognitive and social development in the life of an infant. Looking is one of the most important methods of communicating for infants.

The preferential looking paradigm consists of presenting infants with two stimuli and checking whether infants discriminate between them by evaluating the looking duration. The visual habituation procedure consists of evaluating looking duration to an unfamiliar stimulus after habituation to another stimulus. It is based on the infant’s tendency to look at novel stimuli. These two methods, however, are not very precise.

Electro-oculography (EOG) measures the change in electrical potential caused by the rotation of the eye. It is a very precise method for measuring eye movements. However, it can be sensitive to artefacts (1) and requires electrodes to be attached to the subject’s face (2). Corneal-reflection photography measures the reflection of the front surface of the eyeball using infrared. This reflection changes when the subject moves fixation and this information is used to determine whether eye movement took place. It can determine the location of fixation but requires individual calibration.

Heart rate is associated with the cerebral cortex (i.e. higher level cognitive processes). This means that changes in heart rate occur in association with changes in attentional status and sensory and cognitive processing. Therefore, heart rate measures could be used to investigate attentional processes during visual tasks.

Marker tasks make use of behavioural tasks. It checks the performance on the same tasks at different ages and in different contexts to provide insight in the interrelations between developmental changes in observable behaviour and brain structure. However, it is difficult to generalize results as the results might be mediated by different neurological structures at different stages of development.

Electro-encephalography (EEG) can be used to measure event-related potentials regarding visual processing in infants. Functional magnetic resonance imaging (fMRI) and near infrared spectroscopy (NIRS) can be used to measure infant’s brain activity.

New-borns prefer looking at faces and spend more time looking at faces than at other stimuli. Overt orienting refers to shifting one’s gaze from one location to the other. Covert orientation refers to shifting attention without shifting gaze or body. Exogenously controlled shifts of attention refers to automatic shifts of attention (e.g. shift of attention due to salient stimulus; loud noise). Endogenously controlled shifts of attention refers to voluntary shifts of attention (e.g. voluntary shift of attention to location of interest). However, initiation of attention shifts includes both endogenous and exogenous components.

The visual grasp reflex (i.e. attention getting reflex) refers to automatic saccades as the result of the sudden onset of a stimulus in the peripheral visual field.

Overt orienting becomes more efficient during the first months of life. Infants start making one large eye movement rather than a series of small movements. However, adult-like performance in the visual field is not attained until the end of infancy.

Infants alternate intense inspections with short looks away. Arousal is controlled by regularly shifting their gaze away from an interaction partner. If an infant is already looking at something (e.g. toy), looking away is preceded by the disengagement of attention and gaze. Young infants (i.e. 1 month – 4 months) have difficulty looking away from a stimulus once their attention has been engaged. This expresses itself in periods of long staring. This is also called obligatory fixation.

Infants are especially unlikely to shift their gaze to a target in the periphery when their attention is actively engaged by the central stimulus, although they still detect and process peripheral stimuli.

The degree of disengagement difficulty varies between situations as the probability and latency of infant’s shifts of gaze from a stimulus currently under attention to a target in the periphery are influenced by higher order characteristics of the two stimuli.

During fixation of a stimulus, rapid shifts of covert attention take place to select the next location to look at. Covert attention to a spatial location affect subsequent responses to a target at this location. Perceptual processing of stimuli at the previously attended location is enhanced for 300ms. If the interval is longer than 300ms, the response facilitation effect is reversed and the processing of targets in the vicinity of the cue is impaired. This is the response facilitation effect. Processing of targets in the vicinity of the cue is impaired for a few seconds afterwards. This the inhibition of return (IOR).

There appears to be a gradual development of the ability to shift attention covertly throughout the first months of infancy. It is possible that looking behaviour is initially determined by environment-based inhibition of return before object-based inhibition of return starts to emerge. Processing of an object at which another person is looking is enhanced.

Young infants will scan a stimulus after orienting to it. However, their scanning patterns differ from those of older infants and adults. Young infants examine limited parts of the stimulus to spend long periods fixating a few single locations and to ignore other stimuli in the visual field. Young infants will also look at the most salient parts of a stimulus (e.g. edges) rather than the inner parts of the stimulus (i.e. externality effect) Young infants develop the ability to tailor their scanning behaviour to the characteristics of the stimuli under examination around 3 months of age.

Around 4 or 5 months of age, eye movements are generated in accordance with the strategic demands of ongoing information processing. The externality effect in young infants does not appear to occur when a face is behaving naturally (i.e. moving, talking).

In Schiller’s model, the anterior eye movement control system is responsible for saccades that are voluntary or planned. The posterior eye movement control system is responsible for fast, reactive eye movements and orienting responses. Both systems control the activity of the superior colliculus.

The visual and attentional behaviour of an awake, alert infant is largely determined by the developmental status of the brain structures that form the visual system. Changes in behaviour can be the result of maturation or experience. Maturation lays the foundation for experience and depends on experience. Bronson’s model states that the early development of visual attention can be viewed as a shift from subcortical to cortical processing as subcortical processing is the most mature at birth (e.g. superior colliculus).

Several comparatively independent cortical streams of visual processing exist. They undergo rapid development during infancy. Eye movements are controlled by striate networks early in life and these areas are highly responsive to stimulus salience. Salient areas close to fixation produce higher levels of striate activity and highly salient stimuli produce long-lasting striate activity, which explains the long fixations in infants. The poststriate networks become more effective after 6 weeks of age. Older infants can draw on the poststriate capacities to override salience effects and move their eyes intentionally to locations of interest.

Modulation of the subcortical orienting system by cortical processes is necessary to end infants’ disengagement difficulties.

Attention patterns in early infancy are related to later cognitive functioning. Infants’ looking duration during habituation shows continuity with cognition in later childhood. Differences in scanning patterns are related to perceptual and cognitive competences.

Shifting attention is connected to self-regulatory competences. Infants’ ease of disengagement is associated with their level of distress when faced with limitations. Orienting away during a stressful situation was associated with a decrease in negative affect in 5-month-old infants. Attentional processes affect infants’ regulatory skills and social behaviour.