Attention
Attention is defined by Chaplin (1968. P 42) as "the process of preferentially responding to a stimulus or range of stimuli", although a universally accepted definition has yet to appear in the literature (Lezak, 1995). Attention is generally viewed as "a system in which processing occurs sequentially in a series of stages within different brain systems involved in attention "Lezak, 1995 p.39).
Five different types of attention have been identified. They are as follows: Sustained attention which is the ability to maintain concentration on a task. Focused attention which is the ability to attend to the task at hand.
Selective attention which is the ability to exclude distractions.
Divided attention which is the ability to respond to two or more tasks at once. Alternating attention which is the ability to switch from one task to another (Lezak, 1995).
22
The neuroanatomy of attention is very complicated. The main cortical areas involved are the inferior parietal cortex which is involved in spatial selective
attention plus the frontal cortex which has a role in response selection and control, and also in sustained attention (Lezak,1995). Sustained attention also involves the frontal and cingulate cortex and basal ganglia (Marrocco and Davidson, 1998). The sub-cortical thalamic nuclei have a function in selective attention. The arousal
and activation functions of the mesencephalic reticular system are also important in attention. Limbic system structures involved include the amygdaloid and septal nuclei which help establish salience (Cohen et al., 1998).
The main neurotransmitters involved in attention are acetylcholine and noradrenalin. Other neurotransmitter systems implicated include dopamine, histamine and serotonin. Noradrenalin and acetylcholine play key roles in pure attentional tasks and tasks that don't include changes in arousal or perceptual processing (Marrocco and Davidson, 1998).
The attention task used in this research involves the ability to pick out a target among a page of distractors. This requires the abilities of sustained attention and visual search. Theories of visual search mclude the notion of 'pop-up' in which attention is suddenly drawn to a target. According to Nakayama and Joseph
23 This spread of attention combined with a narrowing appears a contradiction but can be explained in that two distinct processes are occurring simultaneously. Easy visual search, such as the location of a number or word on a page, is comprised of a "global attentional allocation to the whole array (useful to do the rapid search task) followed by a narrowing of attention to the target (Nakayama and Joseph, 1998, p.291)
Memory
"Memory is a process that results in a relatively permanent change in behaviour. It is never observed and is always inferred" Kolb and Whishaw, 1985. p.476) . There is no one brain 'memory centre' that houses memories. Memory is a
function of several brain systems working together (Emilien et al., 2004).
However, different parts of the brain have more importance for certain types of memory. For example, the inferior temporal lobe is important for facial
recognition.
Lesion studies from humans and animals have provided information on brain systems involved in memory. The role of the hippocampus in memory has been well known. Damage to the hippocampus results in mild amnesia, but damage that includes the entorhinal and parahippocampal areas results in severe amnesia. Lesions to the temporal lobes produces deficits in long-term memory (Kolb and Whishaw, 1985). The medial temporal lobe and medial thalamic structures work together in the establishment of new memories (O'Connor and Morin, 1998). Parietal lobe lesions result in deficits in short-term memory, particularly the ability to recall digits. Frontal lobe lesions are not associated with specific memory deficits, but effect the ability to resist interference (Kolb and Whishaw, 1985). The prefrontal role in working memory is in the mediation of problem solving strategies. Tasks that require subjects to rehearse verbal material activates a part of the parietal cortex whereas different parietal areas are activated during
visuospatial processing (Marrocco and Davidson, 1998).
There are five processes involved with memory. The first is attention. The second involves encoding the information so it can go into storage (the third process). Memories are stored in two primary formats; as declarative memory for
language accessible information and as habits or procedural memory that is non language based. Once memories are stored they are consolidated. The last
There are three types of memory. Registration or sensory memory holds large amounts of information for 1-2 seconds in sensory store. Short term memory lasts a few seconds to one hour and includes working memory. Long-term memory or secondary memory refers to the ability to store information and includes
semantic, reference and episodic memory (Lezak, 1995; Emilien et al., 2004 ). The tasks used in this research involve working memory. The concept of working memory includes a capacity for performing mental operations. The model was formulated in the 1970's by Baddeley and Hitch (cited Gazzaniga et al, 1998) and is constructed of a central executive that controls the two subsystems of a
phonological loop and visuospatial sketch pad. The phonological loop is a system for processing language. The visuospatial sketch pad provides for visuospatial processing . Working memory is a form of declarative memory as the processing goes on in consciousness (Eichenbaum and Cohen, 2001). The central executive of Working Memory is associated with the prefrontal cortex which also has a role in problem solving, personality, effect, motor control and language processing (Eichenbaum and Cohen, 2001).