Attention represents an essential and crucial basic resource of the brain for all activities, particularly in the domain of vision and cognition (e.g. Berman and Colby 2009). Van Zomeren and Brouwer (1994) have found it useful to distinguish between two dimensions of attention: intensity and selectivity, which are both regulated and controlled by a superordinate (executive) function that monitors and adapts attentional resources to the actual task demands. In both dimensions, several components can be identified, which are, however, closely interconnected within a common network. The dimension intensity comprises alertness (activation of global attentional resources), sustained attention (maintenance of a given level of attention over time), information processing and mental speed. The dimension selectivity includes the ability to focus on just one stimulus or stimulus configuration without being distracted by other stimuli or tasks (concentration), the ability to divide attention between two or more stimuli or stimulus configurations (divided attention), and the ability to shift attention between stimuli (attentional flexibility). In their taxonomy of attention, Chun et al. (2011) rely on targets, i.e. the types of information that attention is operating over. External attention refers to the selection and modulation of spatial and temporal properties and modality of sensory input, while internal attention refers to the selection, modulation, and maintenance of internally generated ‘information’, i.e. responses, task rules, working and long-term memory. Posner and Peterson (1990) have proposed a model of attentional brain systems comprising three components: alerting (brain stem) subserving alertness, orienting (thalamus and posterior parietal cortex) for attention in space, and executive control (pre-frontal cortex) for selective and divided attention, including multi-tasking, and the control of alertness and spatial attention. The original model has been extended to include self-regulation (prefrontal cortex; cingulate cortex), i.e. self-control of attentional responses (Petersen and Posner 2012). Spatial attention comprises the global distribution of attention over a wide or narrower part of the surroundings or a scene (field of attention) and the shift of attention to particular regions/locations in space (spatial attentional shifts).

In early child development, the various attentional functions show different trajectories. Components of intensity and simple functions of selectivity develop earlier, while components with higher sharing of executive function develop later and are not available before the age of 3 years (Colombo 2001; Jones et al. 2003; Kannass et al. 2006). Attention plays an important role in the development of vision, in particular visual search and object processing (Amso and Johnson 2006) and recognition memory (Rose et al. 2001), but also social interaction (Elam et al. 2010).

These developmental trajectories are briefly described and summarised below (after Anderson et al. 2001b; Colombo 2001; Klenberg et al. 2001; Anderson 2002; Ruff and Cappozoli 2003).

1st year. Wakefulness changes more and more into alertness with guided attention to external stimuli. In the first year, periods of wakefulness, and thus of alertness, increase in both frequency and duration; during such periods attention to visual stimuli can systematically be elicited and thereby improved. At the end of the third year, longer periods of alertness are well established within the circadian rhythm of the child. At the age of 10 months, children show less concentration when more than one stimulus (toy) is present in their field of attention. At the end of their first year, children show faster habituation to novel stimuli; consequently stimulus salience has to be increased in order to elicit a reliable response. This manifests a kind of a milestone in the development of attention: a change takes place, from predominantly externally (bottom-up) guided attention, to an increasingly stronger internal (intentional, top-down) guidance of attention that allows more independence from external events and thus more personal autonomy.

2nd–4th year. All attentional functions improve, in particular sustained attention and attentional capacities involving higher executive components. Multi-tasking however, still remains limited.

5th–16th year. Information processing and mental speed, sustained attention, concentration, attentional control and flexible adaptation to changing stimulus and task conditions increase further. Multi-tasking performance also improves, but complex multi-tasking is not fully developed until early adulthood.

Learning is the fundamental basis for recalling visual (and other) facts and experiences from memory. There exist various forms of learning, which differ with respect to the degree of ‘conscious’ control involved (implicit vs. explicit) and the more declarative or non-declarative character (Gabrieli 1998; Squire and Wixted 2011). Classical conditioning refers to the association of a neutral stimulus with a particular significance (the baby learns to associate the view of the little white bottle with ‘food’). Operant conditioning denotes a form of learning through the outcomes of particular behaviours, whether they are pleasant and rewarding, or otherwise. Learning by imitation (so-called model learning or observational learning) denotes the type of learning when children acquire a behavioural response or even a complex type of behaviour by observing this behaviour as shown by another person. Trial and error learning may be taken literally and typically takes place in a new or very unfamiliar task condition, when subjects just try and test again and again until the outcome eventually fits. Of course, the processes of planning, problem solving and monitoring, as well as knowledge gained from experience are also involved in this type of learning. Learning by insight means that the outcome is gained by systematic consideration and testing of ideas based on previous experiences and inductive and deductive reasoning.

Once processed, information is stored and has to be recalled for use, in forming experiences and in guiding and regulating behaviour. Information in short-term memory can be kept for only a few seconds without further processing, while in working memory, information can be maintained and processed over minutes. Information important for the individual is then transmitted to long-term memory, from where it can be recalled even decades later. Long-term memory is organised as a store-house with separate compartments for events (episodic memory), facts and knowledge (semantic memory), and procedures (procedural memory). Episodic memory comprises autobiographical and public events of one’s life, including details about who, what, where, when, and why and how. Semantic memory contains facts and knowledge. In procedural memory procedures are stored, i.e. how things are done. Most of these procedures are actions and complex motor activities, for example, walking, swimming, and skiing, but also waving a hand for a good bye, writing and drawing. In a more general sense, there also exist procedures in the domains of perception and cognition, for example, how to scan a scene for fast and complete comprehension, how to regulate attention when performing a task, how to learn a language, or how to monitor a complex action to avoid errors. After considerable practice such procedures usually become routine, and less cognitive (and sometimes also physical) effort is needed to carry out the activity in question. Interestingly, learning ‘by looking’ plays an important role in the infants’ transition from crawling to walking (Clearfield et al. 2008). Episodes and facts can be easily put into words and communicated through language; in contrast, procedures and skills are very difficult to declare. Thus, episodic and semantic memory is also called declarative memory, while procedural memory is known as non-declarative memory (Squire and Wixted 2011). Episodes from the first 2–3 years can only imprecisely be recalled in childhood, and most cannot be remembered into adulthood, which is not explained by the time elapsed between event and time of recall but relates to the very young age of the brain at the time of storage (Eacott and Crawley 1999; Hayne 2004; Picard et al. 2009). Conditioning and procedural (‘implicit’) learning are already operating after birth, while ‘pre-explicit’ working and long-term memory develop in the first months after birth, and improve within the first year of age; whereas working memory shows a protracted course of development (Nelson 1995). A special type of memory is prospective memory, which plays a major role in organising everyday life activities (Maylor and Logie 2010). Prospective memory refers to events and actions in the future. It entails forming a particular intention, keeping this intention in memory, and recalling it when needed, with initiation and execution of the intended action at the foreseen time or associated with future events or with persons. Thus prospective memory works at the intersection of memory and executive functions (Kliegel et al. 2008). Temporal lobe cortical structures, the hippocampus and thalamus appear crucial for episodic and semantic verbal (left hemisphere) and non-verbal (right hemisphere) memories; basal ganglia serve habit learning, and premotor/supplementary structures and basal ganglia process procedural memory (Squire and Wixted 2011), while prefrontal structures accord prospective memory (Burgess et al. 2011). Brain injury does not usually cause global memory impairment due to this functional and anatomical segregation of the memory systems.

The main developmental trajectories for the various forms of learning and memory are summarised below (after Reese 2002; Courage and Howe 2004; Barrouillet et al. 2009; Schwenck et al. 2009; Maylor and Logie 2010).

1st year. Classical and operant conditioning exist already at birth. In addition, basal capacities for the reception, processing and coding of olfactory, gustatory, somatosensory and acoustic stimuli are also developed. Within the first 12 months, vision develops rapidly such that learning through this modality can take place. At the age of 6 months, visual observation learning is possible. At 9 months children can learn through imitation, one, or a series of two actions; by the age of 12 months this increases to 4, and by the age of 3 years, children can learn up to 25 action steps.

2nd–4th year. By the end of the second year of life, children can learn by insight. At the age of 2 years, children have access to episodic memory independent of the context. This flexible recall is a milestone in memory development because it demonstrates the detachment of the memory from the external world. The child is no longer dependent on external cues but can intentionally and voluntarily retrieve information from memory. However, at this age memories are still bound by their episodic context, i.e. memory for facts and procedures/actions are more or less coloured by the events in which they have been learned. The social context appears to play an important role, particularly the style of interactions with parents, brothers and sisters, and other relevant persons. Children need self-conception for the formation and development of an autobiographical memory; conversations with the mother or another relevant person support the building of the child’s own experiences in proper order and context. Language capacities also play an important role in reporting episodes.

4th–6th year. At this age children possess reliable knowledge concerning similar and repeatedly occurring events, for example, regular journeys and restaurant visits (so-called script knowledge). In addition, children use learning strategies; these strategies are, however, still simple and cannot be improved so much by practice as at a later stage.

6th–16th year. Episodic memory shows a distinct increase in performance from the sixth year on, possibly from using more efficient strategies for encoding and recall. Working memory also improves markedly in terms of greater efficiency in parallel processing of information and flexible attentional control. At the age of 11 years children can report recent experiences (events) in great detail. At about the same age efficient and skilful learning strategies have been adopted and can be used, however, prospective memory is still developing until adulthood.

Reasoning, planning and problem solving are among the most complex human mental abilities. The various cognitive processes and functions underlying these abilities are subsumed under the umbrella term ‘executive functions’ and represent a variety of components for guidance, regulation, control and monitoring of behaviour. These components render possible and ensure that actions can be adapted to particular stimulus and task conditions, involving changes in the various domains of perception, attention, memory, action and communication, modulated by motivation and emotion (Ardila 2008). Table 3.1 gives a summary of executive functions and their role in human behaviour. As can be seen, planning and problem solving consist of several components, which facilitate imagination of situations and tasks leading to action to solve problems, or a plan in mind before executing the action (thereby avoiding effortful, and largely frustrating, trial and error behaviour). Anticipation of real or possible difficulties and impediments, detection and correction of errors, development and actual use of alternatives, monitoring of provisional and final outcomes with respect to the intended goal, and learning from errors are also functions of the executive system. This rather complex structure and organisation of mental operations of the executive system is required to cope with its many roles. Relevant information is processed and coded by the perceptual systems, is maintained in working memory, attentional resources are allocated to the various executive action steps, irrelevant and false responses and actions are inhibited, while relevant and correct responses and actions are initiated and executed. It is still unclear, whether the executive system is in fact one big system, which comprises a high diversity of functions/capacities, or whether sub-systems act more or less independently. Each alternative appears possible (for a review, see Jurado and Rosselli 2007), although the dissociated nature of executive impairments tends to favour regional sub-systems, which despite a high degree of autonomy, interact closely with each other (Stuss and Alexander 2007). It is important to note that executive function influences the mapping of sensory information to motor activities via attentional bias toward rewarding stimuli and actions (Deco and Rolls 2005).