Visual Search

Method and Analysis

Visual search is a common activity in daily life and in many cognitive activities: looking for a word on a page while reading, trying to find a friend in a crowded room, examining an X-ray for anatomical abnormalities in a hospital, or searching the ground for fossils and artifacts. The scientific study of visual search often examines much simpler tasks that afford greater experimental control. Of primary interest for many scientists interested in visual search is why some search tasks are fast and efficient and others are slow and inefficient.

Figure 1 displays an example of the sort of task a participant in a visual-search study would commonly see. Here the target is the letter T among nontarget letter F s. A typical experiment would require the participant to look for the target and to press one button if it is present and another if it is absent; half of the trials would have a target and half would not. The items would generally appear to the participant and remain visible until the response. The speed (or reaction time) and the accuracy of the search would be recorded for each trial.

Figure 1 Look for the Ts among the Fs. The large, white T can be found efficiently; however, the small black one requires an inefficient search.

The data are summarized commonly in a plot of reaction time as a function of the number of items displayed. Other variables, such as presence or absence of the target, are plotted as different functions or groupings of data points in the graph. Each group of data points can be summarized by a slope and intercept of the linear function that fits those points. The slope provides information about the rate of visual search, and the intercept summarizes the amount of time required for all other aspects of the search task (such as the motor preparation for the response).

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