1 Information Input and Processing Information Theory: Some times called cognitive psychology, cognitive engineering, and engineering psychology. Information is defined as the reduction of uncertainty. The occurrence of highly certain events do not convey much information (such as fasten seat belt sign). But the occurrence of highly unlikely events convey more information (such as high temperature warning in a car). The fasten seat belt sign conveys less information because it is expected. Although it is an important message, the importance is not directly considered in the information definition. Because this message comes on every time the car is started, it contains little (or no) information in the context of information theory.

2 Measuring Information: Information is measured in bits (symbolised by H). A bit is the amount of information required to decide between two equally likely alternatives. If the probabilities of N alternatives are equal, then the amount of information in bits is calculated according to the following formula: When the alternatives are not equally likely, the information conveyed by event i having a probability of pi is calculated as follows: The average information conveyed by a series of events having different probabilities is:

3 The maximum possible information occurs when all the alternatives have equal probability. Information decreases from maximum as the difference between the probabilities of the events is increased. The reduction in information from the maximum due to unequal probabilities of events is called REDUNDANCY. Percentage of redundancy is calculated according to the following formula: Reaction time to a stimulus increases as the number of equally likely alternatives is increased. When the number of stimuli is converted to bits and the mean reaction time is plotted as a function of information (bits), the function was linear (Hick’s experiment). But is the reaction time a function of the number of alternatives only? What if the probabilities of events are changed?

4 Hyman altered stimulus information without changing the number of alternatives simply by changing the probability of occurrence of the alternatives and found that reaction time was still a linear function of stimulus information when it was measured in bits. Choice reaction time is a linear function of stimulus information (Hick-Hyman law) DISPLAYING INFORMATION Human information input and processing depends on the sensory reception of relevant external stimuli which contain the information. The original source of information (the distal stimulus) is some object, event, or environmental condition. Information from the distal stimulus may come to us directly or indirectly.

5 In the case of indirect sensing, the new distal stimuli may be coded stimuli or reproduced stimuli. In both cases the coded or reproduced stimuli become the actual distal stimuli to the human sensory receptors. Human factors are needed when indirect sensing applies. Display is a term that applies to any indirect method of presenting information.

6 Types of information presented by displays Information presented by displays can be dynamic or static. Dynamic information changes continuously or is subject to change through time. Examples are: traffic lights, radar displays, temperature gauges. Static information remain fixed over time. Examples are: alphanumeric data, traffic signs, charts, graphs, labels. Note that static information presented through VDT is being considered as static information. The above classification is general. A detailed classification is presented below:  Quantitative: such as temperature or speed.  Qualitative: represents approximate value, trend or rate of change.

7  Status: reflects the condition of a system (such as on or off, and traffic lights).  Warning and signal: indicating danger or emergency.  Representational: pictorial or graphical representation of objects, areas, or other configurations. Such as photographs, maps, heartbeat oscilloscope.  Identification: used to identify a condition, situation or object. Such as traffic lanes and coloured pipes.  Alphanumeric and symbolic: such as signs, labels, printed material and computer printouts.  Time-phased: display of pulsed or time- phased signals. The duration and inter- signal intervals are controlled.

8 Selection of display modality Visual or auditory displays? Tactual sense? The selection of the sensory modality depends on a number of considerations. Table 3.1 in page 53 gives reasons for making a decision to use visual or auditory presentation of information. Coding of information Coding takes place when the original stimulus information is converted to a new form and displayed symbolically. Examples are: radar screens where the aircrafts are converted and presented as dots on the screen, maps displaying cities with different kinds and populations with different symbols and sizes.

9 Information is coded along many dimensions. Examples:  varying the size, brightness, colour and shape of targets on a computer screen.  Varying the frequency, intensity, or on-off pattern of an audio signal. Each of the above variations constitutes a dimension of the displayed stimulus, or a stimulus dimension. The convenience of any stimulus dimension to convey information depends on the ability of people to: 1.Identify a stimulus based on its position along the stimulus dimension (such as identifying a target as bright or dim, large or small). This is an example of absolute judgment OR 2.Distinguish between two or more stimuli which differ along the stimulus dimension (such as indicating which of the two stimuli is brighter or larger). (relative judgment example)

10 Characteristics of a good coding system 1.Detectability of codes: the used stimulus most be detectable by human sensory mechanisms under the present environmental conditions. 2.Discriminability of codes: every code symbol must be discriminable from other symbols. In this case, the number of coding levels is important. 3.Meaningfulness of codes: A coding system should use codes meaningful to the user. Meaning could be inherent in the code or learned. The meaningfulness is related to the concept of conceptual compatibility which will be discussed later. 4.Standardisation of codes: When a coding system is to be used by different people in different situations, it is important that the codes be standardised and kept the same. The meaning of the colour red to different populations.

11 5.Use of multidimensional codes: this can increase the number and discriminabilty of coding stimuli used.

12 Compatibility It is the relationship between the stimuli and the responses to human expectations. A major goal in any design is to make it compatible with human expectations. It is related to the process of information transformation. It is thought that the greater the degree of compatibility, the less recording must be done to process the information. This leads to fast responses and learning, less errors and reduced mental workload. People like things that work as they expect them to work. There are four types of compatibility: 1.Conceptual compatibility: it is related to the degree to which codes and symbols correspond to the conceptual associations people have. It relates to how meaningful the codes and symbols are to the people who use them.

13 Examples of conceptual compatibility: An airplane symbol is used to denote an airport on a map would mean much more than a square or circle. 2.Movement compatibility: It relates to the relationship between the movement of the displays and controls and the response of the system being displayed or controlled. Example: to increase the volume on the radio, we expect to turn the knob clockwise. 3. Spatial Compatibility: Refers to the physical arrangement in space of controls and their associated displays. 4.Modality compatibility: it refers to the fact that certain stimuli-response modality combinations are more compatible with some tasks than with others. Example: responding to a verbal command that needs verbal action is faster than responding to a written or displayed command requiring the same verbal action.