Judging Total Volumes of Silhouetted Spheres in Different Numerosities.

Volume and number are addressed separately rather than combined in perception research. Yet, our everyday problems often involve summed continuous volumes of countable solid objects with partial depth cues (e.g., food items). The participants were presented with a set of black-and-white silhouettes of spheres that independently varied in numerosity (from 1 to 6) and total volume (2, 4, 6, or 8), and an adjacent silhouette of a partially filled cylinder. They judged how much the silhouetted sphere(s) in the set would raise the level of the cylinder content if the spheres were immersed into that content. Higher total volumes and numerosities of the spheres were judged slower and underestimated. Lower total volumes and numerosities were judged faster and overestimated. These effects strongly reflected the total silhouette area of the spheres in a set. The discontinuous effect of numerosity on judgment accuracy and speed suggested separate judgment modes below and above Numerosity 3.