Nonverbal counting in humans: The psychophysics of number representation

In a nonverbal counting task derived from the animal literature, adult huma n subjects repeatedly attempted to produce target numbers of key presses at rates that made vocal or subvocal counting difficult or impossible. In a s econd task, they estimated the number of flashes in a rapid randomly timed sequence. Congruent with the animal data,,mean estimates in both tasks were proportional to target values, as was the variability in the estimates. Co nverging evidence makes it unlikely thar subjects used verbal counting of t ime durations to perform these tasks. The results support the hypothesis th at adult humans share with nonverbal animals a system for representing numb er by magnitudes that have scalar variability (a constant coefficient of va riation). The mapping of numerical symbols to,mental magnitudes provides a formal model of the underlying nonverbal meaning of the symbols (a model of numerical semantics).