World wide web : means graphics, & network congestion effect response time.
Lengthy or unexpected system response time can produce:
- Frustration
- Annoyance
- Eventual anger
- learning less
- reading with lower comprehension
- making more ill-considered decisions
- committing more data-entry errors
Models of response-time impacts
Response time
- The number of seconds it takes from the moment users initiate an activity until the computer presents results on the display
User think time
- The number of seconds the user thinks before entering the next action
- Designers of response times and display rates in HCI must consider:
- complex interaction of technical feasibility
- cost
- task complexity
- user expectations
- speed of task performance
- error rates
- error handling procedures
- Overall majority of users prefer rapid interactions
- Lengthy response times (15 seconds) are detrimental to productivity
- Rapid response times (1 second or less) are preferable, but can increase errors for complex tasks
- Display Rate
- Alphanumeric displays: The speed in characters per second at which characters appear for the user to read
- World Wide Web Applications: Display rate may be limited by network transmission speed or server performance
- Reading textual information from a screen is a challenging cognitive and perceptual task
- Cognitive human performance would be useful for :
- making predictions
- designing systems
- formulating management policies
Limitations of short-term and working
memory
- Any cognitive model must emerge from an understanding of human problem-solving abilities
- Magic number seven - plus or minus two
- The average person can rapidly recognize seven chunks of information at a time
- Short-term memory and working memory are used in conjunction for processing information and problem solving
- Short-term memory processes perceptual input
- People learn to cope with complex problems by developing higher-level concepts using several lower-level concepts brought together into a single chunk
- Short term and working memory are highly volatile
- Solutions to problems must be recorded to memory or implemented.
- When using an interactive computer system users may formulate plans and have to wait for execution time of each step
- Long (1976) found unskilled and skilled typists worked more slowly and made more errors with longer response times
Conditions
for optimum problem solving
- Longer response time causes uneasiness in the user because the penalty for error increases
- Shorter response time may cause the user to fail to comprehend the presented materials
- Progress indicators shorten perceived elapsed time and heighten satisfaction:
- graphical indicators
- blinking messages
- numeric seconds left for completion
- Rapid task performance, low error rates, and high satisfaction can come from:
- Users have adequate knowledge of the objects and actions necessary for the problem-solving task
- The solution plan can be carries out without delays
- Distractions are eliminated
- User anxiety is low
- There is feedback about progress toward solution
- Errors can be avoided or handled easily
- Other conjectures in choosing the optimum interaction speed
Users have adapted a working style and
expectation based on responses within a fraction of a second. People can detect 8% changes in a 2-4
second response time
Response-time
choke
- A system is slowed down when the load is light and potential performance high
- Makes the response time more uniform over time and across users, avoiding expectations that can’t always be met
It effects user interest and quality
assessment.
Three
things influence response-time:
- Previous experiences
- The individual's tolerance for delays
- Task complexity
User
productivity
- Repetitive tasks
- Nature of the task has a strong influence on whether changes in response time alter user productivity
- Shorter response time means users responds more quickly, but decisions may not be optimal
- Goodman and Spence (1981) – reduced response time lead to more productivity
- Teal and Rudnecky (1992) – slower response time lead to more accuracy
- Problem solving tasks
- Users will adapt their work style to the response time
- Users will change their work habits as the response time changes
- Grossberg, Wiesen, and Yntema (1976) – the time to solution was invariant with respect to response time
Variability
- People are willing to pay substantial amounts of money to reduce the variability in their life, e.g. insurance
- Goodman and Spence (1981)
- Subjects took more advantage of fast response time by making their subsequent commands immediately and balancing the time lost in waiting for slower responses
(Ceaparu
et al., 2004) 46% to 53% of users’ time was seen as being wasted
- Recommendations include improving the quality of service and changes by the user
- Poor quality of service is more difficult in emerging markets and developing nations
- User training can help
- Email a common application, but also a common source of frustration
- Viruses also a problem
- Since frustration, distractions, and interruptions can impede smooth progress, design strategies should enable users to maintain concentration.
- Three initial strategies can reduce user frustration:
- Reduce short-term and working memory load
- Provide information abundant interfaces
- Increase automaticity
- Automaticity in this context is the processing of information (in response to stimuli) in a way that is automatic and involuntary, occurring without conscious control.
- An example is when a user performs a complex sequence of actions with only a light cognitive load, like a driver following a familiar route to work with little apparent effort.
Tidak ada komentar:
Posting Komentar