What are the shapes of response time distributions in visual search?

J Exp Psychol Hum Percept Perform. 2011 Feb;37(1):58-71. doi: 10.1037/a0020747.


Many visual search experiments measure response time (RT) as their primary dependent variable. Analyses typically focus on mean (or median) RT. However, given enough data, the RT distribution can be a rich source of information. For this paper, we collected about 500 trials per cell per observer for both target-present and target-absent displays in each of three classic search tasks: feature search, with the target defined by color; conjunction search, with the target defined by both color and orientation; and spatial configuration search for a 2 among distractor 5s. This large data set allows us to characterize the RT distributions in detail. We present the raw RT distributions and fit several psychologically motivated functions (ex-Gaussian, ex-Wald, Gamma, and Weibull) to the data. We analyze and interpret parameter trends from these four functions within the context of theories of visual search.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Eye Movements / physiology
  • Humans
  • Middle Aged
  • Normal Distribution
  • Photic Stimulation
  • Reaction Time / physiology*
  • Reference Values
  • Visual Perception / physiology*
  • Young Adult