MHP and Time Scales Flashcards
Humans as Information Processors
- In cognitive science, humans are viewed in terms of information processing
- Perception
- Cognition
- Motor action
What does it mean by “Perception” in humans as Information Processors
We gain information from the world through sensors
What does it mean by “Cognition” in humans as Information Processor
- We process information based on existing knowledge
- We gain new knowledge, and make decisions
What does it mean by “Motor action” in humans as Information Processors
- We have ‘information output’ into the world
- Speaking, gesturing, writing, drawing, navigating the world, manipulating objects,…
Information Processing & Action control
Model Human Processor
A model to describe human performance as it relates to human-computer interaction
- Eyes and ears for input
- Arm-hand-finger for output
- Brain with processors and memories
- Each with performance parameters and connections
What are the 3 interacting subsystems in MHP?
- Perceptual system
- Motor system
- Cognitive system
Processors and Memories
Perceptual System
- Composed of perceptual memory and processor
- Responsible for transforming external events into a form that the cognitive system can process
What is Perceptual Memory
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
- The incoming data is represented as “raw data”
- Low-level features of images, sound, …
Perceptual Processor
Content in perceptual memory is processed to be symbolically encoded
Cycle time: Tp = 100ms
- Variable rate, shorter for features that “pop out” or are more intense
What is the Cycle time in the Perceptual Processor?
Tp = 100ms
What is the formula on Bloch’s Law:
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
- If 20 clicks per second are played for 5 seconds, about how many clicks could a person hear?
- If 30 clicks per second are played for 5 seconds, about how many clicks could a person hear?
- How many frames per second must a video be played to give illusion of motion?
- In a talking head video, how far off can the audio and video be before a person perceives the video as unsynchronized?
FIND THE ANSWER ON LECTURE RECORDING
How does Perceptual Processor work?
The processor cannot code all information before the next stimulus arrives.
- There is more buffered in Perceptual Memory that can be coded before it is replaced by new sensations
- The way something is encoded impacts on how it is stored in memory and how it can be retrieved from memory
What is the Order of coding in Perceptual Processors influenced by?
Attention
(What we focus on, what we are looking for, what draws our attention)
What are the types of coding in Perceptual Processors influenced by?
- Gestalt perception of patterns, shapes and structure
- Associations triggered (e.g. faces seen before)
Cognitive System
- Composed of working memory, long-term memory and the cognitive processor
- Responsible for processing perceived information and deciding how to act upon it
Cognitive Processor
the cognitive processor works on symbolic information that is available in working memory, as a result of perceptual coding
What is Cognitive processing 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)
- Recognition is highly parallel, but Acting is serial: one decision at a time
- Cycle time: Tc = 70ms
- Uncertainty Principle
What is the Uncertainty Principle:
Decision time increases with the uncertainty about the judgment to be made, requires more cognitive cycles
How do the Cycle time of the Cognitive Processor can be impacted?
- Cycle time can be shorter when a greater effort is induced by the task
- Cycle time also diminishes with practice
Motor System
Translating thought into action
- Cycle time: Tm = 70ms, time required to issue a motor command (Between 30-100ms depending on task)
Motor System 2
Rate of repetitive movement
- Drumming
- Drum solo in Whiplash
- Increasing to 900 BPM -> 1800 movements per min.
- 30 movements / sec.
- 33.3 ms for a movement
- Typing
- Advanced professional 120 wpm -> 2 words/sec
- 4.7 characters/word -> 9.4 characters/sec
- 106 ms per character
- 53 ms for finger-down / finger-up
Applying the MHP model to HCI
A user sits in front of a computer screen, finger on the button.
Whenever a symbol appears, they must press the button.
What is the reaction time?
- Perception of stimulus -> 100ms
- Recognition of stimulus as trigger for action -> 70ms
- Executing the motor command -> 70ms
= 240ms.
Time Scales of Human Action
- Model of human action in different timeframes
- Time on a logarithmic scale
- Interactive systems support human goals and activities
- Goals are achieved through the completion of tasks
- Tasks are broken down into “unit tasks”, small enough to complete in one pass in working memory
- User interface enables low-level operations and perceptions
Time Requirements for HCI
- Time is a critical factor in HCI
- For interaction to be successful, systems need to responsive
- A system is perceived as responsive if it complies with human time requirements
