Model Human Processor

Question 1

Model Human Processor

Answer 1

A model to describe human performance as it relates to
human-computer interaction

Introduced in a 1983 book on Psychology applied to HCI

Question 2

Three interacting subsystems

Answer 2

• Perceptual system
• Motor system
• Cognitive system

Question 3

Perceptual System

Answer 3

• Composed of perceptual memory and processor
• external factors from the eyes and ears
• Responsible for transforming external events into a form that the cognitive
  system can process

Perceptual memory is like a buffer for sensor data

• For each sensor, incoming stimuli are stored for a short time
• Visual image store: ~200ms
• Audio store: ~1500ms

these data are known as raw data

Question 4

Perceptual Processor calc

Answer 4

• When multiple similar events occur in the same
  cycle, then they are integrated
• Bloch’s Law: R = I x t
• e.g. perceiving two short stimuli as one of twice the intensity

Cycle time: TP = 100ms

Question 5

Perceptual memory

Answer 5

The processor (brain) can’t fully encode all incoming information before new stimuli arrive. This means more data is stored temporarily in Perceptual Memory than can be processed.

What gets coded first depends on attention — what we focus on, expect, or what stands out.

The way we code information is influenced by:

Gestalt principles (how we perceive patterns and structures)

Past associations (like familiar faces)

Finally, how something is encoded affects how it’s stored and how easily it can be retrieved from memory later.

Question 6

Cognitive System

Answer 6

• Composed of working memory, long-term memory and the cognitive processor
• Responsible for processing perceived information and deciding how to act upon it

Cognitive processing is based on a recognize-act cycle:
* Recognize: activate associations stored in long-term memory

• Act: decide what to do next, modifying working memory (“loading” the next task)
• Cycle time: TC = 70ms
• Recognition is highly parallel, but Acting is serial: one decision at a time

Uncertainty Principle: decision time increases with the uncertainty about the judgment
to be made, requires more cognitive cycles
* Cycle time can be shorter when greater effort is induced by the task
* Cycle time also diminishes with practice

Question 7

Motor System

Answer 7

Translating thought into action

• Cycle time: TM = 70ms, time required to issue a motor command
• Between 30-100ms depending on task

Rate of repetitive movement