Mental workload and models of cognition

Grasha, a psychologist who was interested in the relationship between MW and dispensing errors made in pharmacies proposed a framework called the cognitive systems performance model (see Figure 2 below) (Grasha, 2001b; Grasha & O'Neill, 1996) which could be used to study the relationship between MW and dispensing errors. This model demonstrates how human information processing and

subsequent task or work performance is adversely affected by a variety of given psychosocial factors. The psychosocial factors included in the cognitive systems performance model include the subjective and objective features of the task (e.g.

task complexity, time allotted to complete the task), the characteristics of the person carrying out the task (e.g. age, gender, personality traits), interpersonal relationships (e.g. at work and outside of work), organisational characteristics (e.g. organisational roles and norms, supervisory practices), extra-organisational influences (e.g.

interfaces with boards of pharmacy, governmental and commercial pressures on pharmacy) and the physical environment (e.g. levels of illumination and noise) (Grasha, 2001b).

11 Included within the cognitive systems model are the key aspects of our information processing system; the sensory register, long term memory and working memory.

Figure 3 below shows a more detailed model of our information processing system (Wickens, Lee, Liu, & Gordon Becker, 2004a). Importantly this model of information processing also includes attentional resources which are not included in the cognitive systems performance model, but are very important to the understanding of MW and the functioning of our information processing system.

Figure 2: Cognitive systems performance model (With Permission,Grasha, 2001b;

Grasha & O'Neill, 1996)

Cognitive Systems Model

Correct and incorrect responses/decisions Beliefs, attitudes, values & emotional responses

Task Demands

Long Term Memory Sensory

Register

Working Memory

Extra-organizational

influences

Organizational influences

Environmental influences Interpersonal

influences

Personal influences

12 Figure 3: A model of human information processing (with permission from Wickens, et al., 2004a, pp.122)

Using this model of human information processing we can begin to understand the mental processes that are involved when a pharmacist carries out an accuracy checking task. First the pharmacist uses their senses to gather information about the dispensed item and prescription they are checking. Their eyes providing information on the visual appearance of the prescription and dispensed item, and as they hold the medicine somatosensory information about how the medicine feels (e.g. weight).

This raw un-coded sensory information hits the sensory register where it is stored very briefly (1-4 seconds) (G. Cohen, 1993) and filtered to identify what information will be processed (this filtering happens in two ways, firstly, certain sensory

information will capture your attention (e.g. telephone ringing) and other information will be selected as it is related to the task at hand. In the case of checking sensory information relating to the prescription and medicine is selected. Sensory information that is not selected decays. The information selected for processing is then

perceived, i.e. our brain produces a meaningful interpretation of the sensory information through interaction with the long-term memory stores, where our prior knowledge is stored. Perception can lead straight to response selection and execution (i.e. the pharmacist decides that the medicine and label match what has

SENSORY REGISTER

PERCEPTION

ATTENTION RESOURCES

THOUGHT DECISION MAKING

WORKING MEMORY

RESPONSE SELECTION

RESPONSE EXECUTION

LONG TERM MEMORY PERCEPTUAL ENCODING

CENTRAL

PROCESSING RESPONDING

FEEDBACK

13 been requested on the prescription) most often however the response selection and execution is delayed whilst the perceived information is manipulated in working memory (Baddeley, 2003) and paired with other knowledge and experience to form a decision. For example the pharmacist may pause to consider has the patient had this medicine before in this dose? Working memory underlies many of our conscious thought processes e.g. rehearsing, planning, understanding. Working memory² is a temporary store that interacts with our perception and long-term memory and it is therefore also involved in the process of converting new information into memories to be stored in our long term memory (Baddeley, 2003). Once the pharmacist has decided they have considered all the information they will then select a response and execute it. A feedback loop is also included as we routinely monitor and perceive our own actions (Wickens, et al., 2004a).

Figure 3 above shows that all the stages of information processing rely on attention resources and they are generally considered to be a pool of resources which can be allocated and divided between tasks as required. Two types of attention are

distinguished in the literature. Selective attention relates to what we are purposefully attending to or focusing on at any one time, and is required for (but does not

guarantee) perception. Divided attention relates to our ability to attend to more than one thing at once (Wickens, et al., 2004a). Both of these characteristics of our attentional resources are particularly important to consider when designing interventions to improve safety.

Two aspects of this information processing model are capacity or resource limited, working memory and attention. Tasks will feel effortful when we are using most or all of our working memory or attention resources, this directly relates to the concept of mental overload, and our mental workload. Having considered in detail how a pharmacists’ cognitive processes might be working when carrying out a final accuracy check task, it is clear to see how the psychosocial factors identified in Grasha’s cognitive systems model (see figure 2 above) may interact and impact on the amount of mental workload experienced by the pharmacist. For example a one item prescription may require less working memory space compared to a multi-item prescription to accuracy check. A noisy working environment will lead to more divided attention and possibly working memory space being used if the pharmacist is

monitoring or thinking about the noise around them.

2 Working memory is often referred to as our short-term memory

14