Cognitive Functions

Various cognitive architectures have been proposed in the literature that attempt to describe the information processing sub-systems involved in cognition, such as ACT-R, SOAR, and EPIC (Adams, Langdon, & Clarkson, 2002; Byrne, 2003; Proctor & Vu, 2003; Wickens &

Hollands, 1999). Mainstream cognitive psychology attempts to generalise the architecture of the mind for broad application, and a distinction can be drawn between the architecture of the

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cognitive system and the contents of the cognitive system at different points in time (Payne, 2003). Wickens describes a model of human information processing stages shown in Figure 5-4 (Wickens & Hollands, 1999).

Figure 5-4 A model of human information processing stages (Wickens & Hollands, 1999)

The model is a stage based model i.e. it consists of a series of operations on information. In addition, the processing may begin at any stage by external input or intentions to act (Wickens & Hollands, 1999). The various stages of the model will be discussed in the following sections.

5.4.1 Sensation and Perception

Starting at the left of the diagram, sensory information is transmitted to the brain via initial sensory processing. There is a short-term sensory store (STSS) associated with this stage that stores the sensory input for a short time. The quality of information reaching the brain depends on the state of the sensory receptors. As previously discussed, if there are reductions in visual and auditory capabilities, the raw sensory information reaching the brain is

degraded, and this impacts on the stages that follow.

Raw sensory input is decoded and interpreted in the next stage of perception. Perception is both bottom-up and top-down in that characteristics of the input signal together with

expectations from long term memory are used to rapidly categorise the incoming information.

The process is rapid and requires less mental effort and processing time than cognitive operations using working memory. The bottom-up and top-down perceptual processing is

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adaptive, so that if the incoming sensory information is poor for example, more weight will be given to the top-down processing utilising stored experiences in long term memory.

5.4.2 Working Memory

Working memory can be considered as a temporary store for activated information (Baddeley, 2000). Baddeley proposes that it is structurally organised by different modalities of storage (Baddeley, 2000; Baddeley, 2002). This working memory model is shown in Figure 5-5. It consists of three subsystems: the visuospatial sketchpad, the episodic buffer and the phonological loop. The central executive is responsible for attentional control and coordination of the working memory subsystems. The working memory subsystems are linked to long term memory where learned information is retrieved. The working memory system is responsible for cognitive tasks such as rehearsal, reasoning, image transformation, planning and problem solving (Wickens & Hollands, 1999).

Figure 5-5 A model of working memory

Working memory has been found to have a limited capacity for stored information with a duration of 10-15 seconds. The general capacity of the working memory system has been estimated to be around five to nine chunks of information (Baddeley, 2000). However, more complex items such as sentences, procedures, or images can be remembered as if they were individual elements when chunked. This is after prolonged use has caused them to become well established in the more permanent store of long term memory. Another important characteristic of working memory is that the central executive is assumed to have limited resources of attention. This can be overloaded by either increasing the volume of individual items to deal with or the number of simultaneous activities that require attention. Therefore working memory and attentional capacities are the limiting factors when interacting with

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products. Thus two important performance measures for the working memory system are storage capacity in terms of the number of chunks that can be held and speed and accuracy of processing.

5.4.3 Long Term Memory

Long term memory is a permanent store for knowledge gathered from experience. The type of knowledge stored can be classified into various types including semantic memory, episodic memory and procedural memory. It is useful to distinguish between knowledge of product features and how the product works, versus knowledge on how to use the product in terms of action sequences that will achieve goals. These two types of knowledge are inter-related, and are both used when interacting with products. Therefore, recognition and recall capabilities are the limiting factors in the performance of long term memory. Measures of recognition capability are required when comparing visible product features to information stored in long term memory. Recall capability measures are needed for determining users’ ability to retrieve stored knowledge about product features and behaviour.

5.4.4 Mental Models

Users are assumed to construct mental models in working memory based on previous knowledge cued by current environmental characteristics and use this representation as they proceed through the interaction (Cañas, Antolí, & Quesada, 2001; Van der Veer & Melguizo, 2003). These models may reflect their understanding of the behaviour of the product and how it is to be used (Norman, 1983; Van der Veer & Melguizo, 2003). The concept of mental models has received significant attention in the HCI and applied cognitive science literature.

It has been found that mental models can be incomplete, unstable, unscientific, and

parsimonious while varying in complexity depending on the degree of previous experience (Norman, 1983). Because of this dependence on previous experience and continuous

modification through successive interactions, mental models can be difficult to capture (Van der Veer & Melguizo, 2003).

From a practical standpoint, the concept of a mental model could be used to enable the operational estimation of cognitive information processing demands. Mental models could be embodied in a representation that captures a demanded mental model of device usage.

Cognitive processes therefore could be assumed to act on this representation during the guidance of action. A mental model representation consists of knowledge of the various interface features and how they work, and a representation of the action sequences necessary for moving from an initial state to a goal state. Because working memory is limited, there will

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be a limit to the complexity of the mental model in mind and the mental operations that can be performed on it at any one time. In summary, interaction involves retrieving previous knowledge of a particular product’s features and how the product works, and using this knowledge together with task demands and product perception to form and operate on mental models in working memory (Van der Veer & Melguizo, 2003).

5.4.5 Response Selection and Execution

Cognitive processing results in the selection of a response that would move a user toward a goal. Response selection is distinct from response execution, as execution involves the coordination of movement. Even though a given response selection may be correct, the execution may be erroneous (Wickens & Hollands, 1999). Successful execution also depends on the state of the effectors i.e. the motor capabilities of the user.

5.4.6 Language and Communication

Language and communication capabilities involve the comprehension and expression of verbal and written language. An assessment of language comprehension capability is necessary when performing tasks such as reading labels and product manuals. It is also employed to interpret verbal messages from a product or system. An assessment of language communication capabilities is important for giving spoken commands to a product. For product evaluation, the primary concern is with linguistic communication in speech and sentence construction as these are most commonly employed in product design. Language and communication capabilities depend on the perceptual, working memory and long term

memory systems (Wickens & Hollands, 1999).

5.4.7 Age Related Effects

The literature shows that ageing is in general accompanied by declines in the cognitive capabilities mentioned above including attention, memory, reasoning and problem solving.

However, certain forms of crystallised intelligence, for example vocabulary, do not show decline with age (Park, 1999). The effects of conditions such as dementia, Alzheimer’s, brain injury, cerebral palsy, and amnesia are such that cognitive decline is either accelerated, or certain cognitive capabilities are lost. The aforementioned cognitive capabilities form the infrastructure on which cognitive task performance is based, and therefore should constitute the set of limiting factors to successful product interaction.

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