This project deals with one of the oldest issues in psychology: the relationship between mental experience (our sensations) and the magnitude of the physical stimulus. The participant in this experiment estimates how many dots are present in an array of dots. The experimenter can study the relationship between the perceived and the actual number of dots, under different conditions and in different kinds of tasks. The experimenter can assess the effect of the regularity of dot placement, the relationship between dot number and screen area, and the nature of control/display information and trial feedback. It is interesting to compare the results obtained with numerosity estimation in this task with the functions obtained using sensory modalities such as brightness, loudness, weight, and shock.