Doherty Threshold
Conceived by Walter Doherty and Ahrvind Thadani, the Doherty threshold is an objective for keeping the user thoroughly engaged when interacting with a computer. If a response appears after the 400 ms threshold, users eventually become disinterested according to a study done in the late 1970s.
Origin
In 1982, Walter J. Doherty and Ahrvind J. Thadani published "The Economic Value of Rapid Response Time" in the IBM Systems Journal, challenging the then-accepted 2-second standard for computer response time. Drawing on productivity data gathered at IBM, they argued that systems responding within 400 milliseconds kept users in sustained mental flow, while slower systems caused measurable drops in output — reframing response time as an economic issue, not merely a technical one. The threshold became a foundational benchmark in human–computer interaction and remains a standard citation in UX design guidelines today.