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Lab 3.1 Exercises

3.1.1. Understand the Human Information Processor

Using the analogy with a computer, Card and colleagues proposed the model human processor.

a) User interface designs can employ the parameter values of Table 3.2 when deciding on physical aspects of the interface design. Discuss how designers might use this information.

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A1:

Answer: This information can be used when determining such things as font and image size, frequency of change, and the type and duration of sounds. Human touch is utilized in the latest force-feedback joysticks and steering wheels used for computer games. Balance, too, is being exploited in some sophisticated simulation rides in theme parks.

One concrete example would be the storage capacity in items. Interface designers could use this parameter as the number of items stored in working memory. This could be quickly retrieved and displayed before another group of characters is retrieved.

In general, these parameters can guide user interface designers in the volume of visual and auditory information to present to the user at each stage in the interaction. In the most recent computer hardware with the extended GUI interaction devices, human speech and full audition are exploited to the fullest. Human speech input is becoming commonplace, and the personal computer now threatens the traditional stand-alone audio systems with sophisticated 3D sound output.

From the processing point of view, the actions and performance of humans during interaction with computers are regarded as a series of processing stages. Each stage involves a different processor or processors, which will transfer information to and from a variety of memories. For example, when typing a key on the keyboard, the visual processor will start with the transfer of the current state of the screen near to the location where the user expects the new character to appear. Next, the cognitive processor assesses the state information and forms a decision to press a particular key in working memory. Finally, the motor processor enacts the decision by guiding the finger to press the required key.

b) One subsystem of the model human processor is memory. Describe the three processing subsystems and discuss how they are modeled in computer systems.

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A2:

Answer: The perceptual system perceives or senses the world around you. The computer perceives you through tactical inputs (keyboard, mouse), auditory inputs (microphone), and even visual (cameras, scanners).

The motor subsystem is responsible for movement. Motion can be perceived by the computer through a mouse, joystick, and even a camera. Motion can also be generated by a computer by hooking it up to any number of devices. Examples of this abound in the manufacturing industry.

The cognitive subsystem is typically equated with memory. From a human perspective there is more to it than just memory. For humans it can also be knowing. A computer can take a number of inputs and compare it to its memory. If the input is close to what it has in memory, it “guesses” that the input matches what is in memory. For example, a computer can be programmed to “recognize” people either from photos or videos. However, it does not know that a particular photo is a specific person. On the other hand, a human knows. In addition, humans can make this kind of identification with much less input (e.g., a fuzzy picture) and still be able to accurately identify the person.

c) Discuss the three types of memory.

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A3:

Answer: Short-term sensory stores hold data received from the external world. The stores are split into visual, auditory, and tactile material (although tactical input can also be received from inside the body). The lifetime of the stored material is extremely short, just a few tenths of a second. In computer terminology, sensory stores are called buffers. A very small percentage of this buffered information is passed on to the working memory. That is, you only become “aware” of a very small percent of the information your sensors receive.

As you are reading these words, you are only aware of the words you are reading (how many depends on the individual). Although the photons from other words, the margins, your hands, and many other things around you are reaching your visual receptors (your eyes). You are not aware of them.

Short-term (working) memory is where information is processed, or “chunked,” into small pieces of useful information. This is where you actually become aware of the input. The number of chunks is normally limited to the 7 we discussed early (although some people can get up to 10). These chunks typically have a lifetime of up to 15 seconds. Some chunks are passed on to the long-term memory.

Long-term memory is assumed to hold information indefinitely, although not all information can be retrieved evenly. The storage capacity appears to be very large indeed, with no sensible upper limit yet discovered. Name the human input/output channels that are typically used for the user interface of a general-purpose personal computer and discuss how this input is provided?

d) Name the human input/output channels that are used for the user interface of a general-purpose personal computer and discuss how this input is provided.

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A4:

Answer: The two human input channels are vision (sight) and audition (sound); these are used for the user interface of a general-purpose personal computer.

e) Looking at the response time of the human motor processor, what is the theoretical maximum upper limit to typing speed in words per minute? Assume the average word is five characters. Could a human input information faster?

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A5:

Answer: According to Card, Moran, and Newell's experiments the motor processor response is 70 msec, that is, just over 14 keys per second. This gives a typing speed of 171 words per minute. Fast professional typists can sustain up to 140 words per minute.

Although this is the (theoretical) limit for tactical input, you could choose another input method such as speech. However, speaking 171 words a minute would probably be extremely difficult to maintain, if not impossible. The catch is that the human does not need to speak that fast to be able to input at a faster rate. Dragon Systems, the makers of the Naturally Speaking voice recognition software, have developed a product that you use like a tape recorder or dictation machine. It is then hooked up to the computer and is able to input the speech at a far faster rate than you could speak it.


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