title:  Intersection Decisions and Reaction Time
Creators: name: Beckman, Orhan Earle
Publisher: name: Old Dominion University
Year: 1993

description: Reaction time (RT) as a dependent variable can be used to assess human performance and identify variables influencing performance. Donders (reprinted in English as Donders, 1969) defined three types of reaction time (RT). Simple RT is defined as RT in a situation involving one stimulus and one response. The selective reaction time (SRT) is defined by a situation involving two or more stimuli with only one possible response. Choice reaction time (CRT) is defined by a situation with more than one stimulus category and an equal number of possible responses.

The Hick-Hyman law defines CRT as a logarithmic function of stimulus information. The Hick-Hyman law was founded on searches using union decisions. A union decision requires that a decision be based on an 'or' rule. An intersection decision requires that a decision be based on an 'and' rule. The relationship between intersection decision making and RT is examined in the present research. A specific question this research attempted to answer is whether a linear/logarithmic relationship, similar to Hick's law, exists between RT and the number of elements that are found in conjunction.

Subjects consisted of 96 undergraduate students, 48 males and 48 females. A six factor mixed model design was employed to compare the RT for males and females measured in the intersection and union decision conditions. Four levels of difficulty, varying the number of positive set items, were used. Reaction time, the dependent variable, was measured a total of 480 times for each subject. The design uses 10 blocks of 48 trials, two display set sizes (6 or 8) and two decision types (positive or negative) as within subject variables.

There were two main conditions. In the Union Decision condition subjects were required to decide whether ~an member of the positive set was represented in the display set. In the Intersection Decision condition subjects were required to decide whether ~a I of the members of the positive set were contained in the display set. The response set for all conditions contained two possibilities: 1) a positive response, or, 2) a negative response.

The stimuli were presented on a 12 inch monochrome monitor driven by an IBM compatible computer. The display sets were presented at the center of the screen in a single row with no spaces separating the characters. As a memory aid, the positive set appeared at the bottom of the screen. Each subject responded to 480 display sets which were randomly generated for each trial from the set of 26 characters (A to Z) . The positive set, consisting of 2, 3, 4 or 6 characters appeared at the bottom of the screen on the far left in a single row with spaces separating each character. RT in milliseconds was measured for each trial and recorded by the computer.

The RT data were analyzed with a 4 x 2 x 2 x 2 x 2 x 10 (Positive Set Size [2,3,4 or 6] x Type of Decision [Union or Intersection] x Type of Trial [Positive or Negative] x Gender x Display Set Size [6 or 81 x Block). Five main effects and 16 interaction effects reached statistical significance at the p &.05 level. The results are discussed in terms of the roles the independent variables played in determining and predicting human information-processing performance. The degree to which the RT data agree with the Hick-Hyman and Sternberg models of human information processing is also examined.