Davis & Pérusse’s Classification of Numerical Competence Davis and Pérusse (1988) distinguish several types of numerical competence and suggest that different cognitive or perceptual processes underlie each type. They divide numerical competence into the categories of relative numerousness judgments, subitizing, estimation, and counting. They assume that relative numerousness judgments involve the simplest decision processes since no knowledge of absolute number is required. Instead an animal judges numerical inequalities that are ordered in magnitude (e.g. "more" vs. "less" decisions). In this chapter, the term "numerosity discrimination" is used instead of relative numerousness judgments. Subitizing is a form of pattern recognition that is used to rapidly assess small quantities of items. A label is then assigned to the perceived array. For instance, a glimpse of several dots arranged at the angles of an imaginary triangle leads to a judgment about the specific quantity. For us, that quantity would be labeled "3" because we know that triangles have three corners. For an animal, that quantity might simply be labeled "correct amount – peck it!" without the animal necessarily knowing how this quantity relates to other numerical values. Other researchers doubt there is a separate subitizing process however (see section VI on Models and Mechanisms for Numerical Processing). Estimation refers to the ability to assign a numerical label to an array of large numbers of items without having to count or enumerate each one. When we judge at a glance that there are about 50 ducks on a lake we are "estimating". Animals’ judgments of large number arrays have not been systematically studied yet. Counting is the ability to discriminate the absolute number in a set by a process of enumeration. This involves tagging each item in a set, and applying a series of ordered labels as these items are ‘counted off’. To count the number of peanuts in a packet of mixed nuts, for instance, we might put each peanut to one side, at the same time labelling them "1", "2", "3", etc. The numerical label we apply to the last peanut we find is the absolute or cardinal number of peanuts in the packet. The criteria for counting behavior have been defined by Gelman and Gallistel (1978) (see section IV on Cardinal Numbers and Counting). Davis and Pérusse regard counting as a more complex process than the ones involved in relative numerousness judgments or subitizing (and presumably estimation too). They also discuss the concept or sense of number as an attribute of counting. This term implies an ability to transfer numerical discriminations across sensory modalities (e.g. 5 sound pulses are equivalent to 5 light flashes) or across modes of presentation (e.g. 4 red squares shown simultaneously on a computer screen are equivalent to 4 red squares presented one after the other).