Stimulus frequency alone can account for the size effect in number comparison

Abstract

In a number comparison task, the size effect (i.e, smaller values are easier to compare than larger values) is usually attributed to a psychophysics-based representation. However, alternative models assume that the size effect is a frequency effect: Smaller numbers are easier to process because they are observed more frequently. Previous studies have demonstrated that the frequency of the digits fundamentally influences the comparison size effect: In new number symbols, the frequency entirely determines the size effect. In contrast, in Arabic notation, the size effect aggregates the frequency in the actual session and the previous regular size effect. Here, we investigate whether the previously acquired regular size effect can depend on the frequency of the stimuli as well or on a psychophysics-based representation that is not yet active in new symbols. Participants in the study compared numbers that were denoted with new symbols, with the frequency of the symbols being changed throughout the session. We found that the frequency of the stimuli in both halves of the session was aggregated in the size effect. In addition, no psychophysics-based size effect was found throughout the session. These results confirm that the size effect can be created and shaped purely by the frequency of the symbols, while a psychophysics-based representation is not necessary to account for these size effect-related phenomena.

Keywords

• Symbolic number comparison
• Size effect
• Distance effect
• Approximate number system
• Discrete semantic system