Title: qdm: Dealing with violations of regular minimality in
psychophysical judgments

Authors: Nora Umbach and Florian Wickelmaier

Affiliation: University of Tuebingen

Abstract: The R package qdm will be introduced which allows us to fit a
model to discrimination data obtained with same-different judgments.  When
collecting discrimination data in psychophysical experiments, it is
plausible to assume that stimuli are most often judged to be the same when
they are physically identical.  This property is called regular minimality
in canonical form.  In experiments, regular minimality is often violated
due to measurement error.  Dzhafarov & Colonius (2006) introduce the
quadrilateral dissimilarity model that makes predictions which are regular
minimality compliant in canonical form.  This model was implemented with
different specifications in the qdm package.  Fitting this model to
discrimination data allows us to obtain predicted same-different judgments
which are regular minimality compliant.  These predictions can then be used
for further analysis like MDS or Fechnerian scaling which require regular
minimality to hold.

Dzhafarov, E. N., & Colonius, H. (2006). Regular Minimality: A
  fundamental law of discrimination. In H. Colonius & E. N.
  Dzhafarov (Eds.), Measurement and representation of sensations
  (pp. 1–46). Hillsdale, NJ: Lawrence Erlbaum Associates.