Productivity soars when computer response times remain below 400 milliseconds, creating immediate-feeling interactions that maintain continuous user engagement eliminating disruptive waiting periods—systems achieving sub-400ms responses enable users to maintain flow state concentration producing 10-15% higher productivity compared to systems with 1-2 second delays while creating "addictive" interaction patterns where users remain engaged continuously rather than context-switching during wait times. Doherty and Thadhani's groundbreaking IBM research (1982) established this 400ms threshold through controlled productivity experiments revealing that when neither human nor computer waits for the other, interaction becomes continuous and highly efficient—participants using sub-400ms systems completed 25-30% more transactions per hour while reporting significantly higher satisfaction and engagement compared to systems with conventional 2-second response times demonstrating quantifiable business value of rapid response.
Doherty and Thadhani's landmark 1982 research "The economic value of rapid response time" challenged prevailing assumptions that 2-second response times represented acceptable performance. Their comprehensive productivity study at IBM involved hundreds of users across diverse computing tasks (data entry, programming, analysis) comparing system performance at varying response time thresholds. Critical breakthrough: productivity did not plateau at 2 seconds as industry assumed—dramatic gains continued down to 400-millisecond responses where productivity peaked before diminishing returns below 100ms. This 400ms threshold emerged as optimal balance between technical feasibility and maximum productivity benefit.
Their economic analysis quantified rapid response value through cost-benefit modeling—calculating total cost of ownership including hardware investment, operating costs, and user productivity. Results demonstrated that investing in faster systems achieving sub-400ms responses produced 3:1 to 5:1 ROI through productivity gains alone, even accounting for higher hardware costs. This economic validation transformed response time from aesthetic preference to business imperative. Research revealed sub-400ms systems enabled users to complete 25-30% more transactions hourly, with quality maintained or improved through reduced errors stemming from maintained concentration. Users described sub-400ms systems as "immediate" and "addictive," remaining continuously engaged versus context-switching during wait periods.
Miller's foundational 1968 research "Response time in man-computer conversational transactions" provided theoretical framework explaining why response time thresholds matter through human temporal perception and task disruption analysis. Miller established three critical response time categories: 0.1 seconds (100ms) represents perceived instantaneous response where users experience direct manipulation with no conscious delay—cause and effect feel simultaneous. 1.0 seconds marks user flow maintenance limit where attention remains focused on task without conscious waiting or wondering about system status. 10 seconds defines maximum attention span without feedback where users begin wondering whether systems froze, considering alternative activities, or losing task context entirely.
Miller's research demonstrated that response times between these thresholds create qualitatively different user experiences beyond simple quantitative differences. Sub-100ms enables fluid manipulation, 100ms-1s maintains focus but introduces slight hesitation, 1-10s requires explicit progress indication to prevent abandonment, >10s demands comprehensive status communication or risks complete task abandonment. These thresholds derive from fundamental human cognitive architecture—working memory decay rates, attention span limits, temporal perception granularity—making them universal across cultures and individuals rather than learned preferences.
Nielsen's extensive usability research (1993) in Usability Engineering synthesized decades of HCI response time studies into practical design guidelines validating Doherty Threshold while providing nuanced guidance for different interaction types. Nielsen distinguished between different operation categories requiring different response thresholds: typing and cursor movement (sub-50ms for perceived real-time), simple commands (100-400ms Doherty range), system operations (1-2s with visual feedback), complex calculations (2-10s with progress indication). His research demonstrated that response time requirements scale with operation perceived complexity—users tolerate longer waits for objectively complex operations (database queries, report generation) but demand instant response for simple operations (button clicks, form submissions).
Seow's contemporary research (2008) "Designing and engineering time" extended response time understanding into web and mobile contexts where network latency, device capabilities, and battery constraints create new performance challenges. His studies demonstrated Doherty Threshold principles remain valid in modern contexts but require sophisticated implementation strategies—perceived performance optimization through optimistic UI updates, skeleton screens, progressive loading enables sub-400ms perceived response even when actual processing requires longer. Research showed users evaluate perceived response time (interaction initiation to first meaningful feedback) more than actual completion time, enabling design strategies that acknowledge actions instantly while processing continues asynchronously.