Frequency effects in distributions of stimuli with or without standards

Category ratings of stimulus intensities are affected by the skewing of frequency distributions of stimuli. According to Parducci’s theory, frequency effects are due to the tendency of participants to use all the categories with the same frequency. According to Haubensak’s theory, these effects are due to the tendency of participants to use all categories during the initial presentations. Frequency effects should be reduced by the presentation of stimuli with extreme intensities as standards before each variable stimulus. In this experiment, participants rated brightnesses of squares or lengths of lines using integers from 1 to 5. Target stimuli were presented with or without standards and, for each of these two conditions, frequency distributions were negatively or positively skewed. Results show that the skewing of frequency distributions strongly affected subjective scales independently of the presence or absence of standards. This finding indicates that, in spite of the standards, participants used previous stimuli rather than the standards as a frame of reference for their judgments.