Ensemble perception of size in 4-5-year-old children.

Groups of objects are nearly everywhere we look. Adults can perceive and understand the 'gist' of multiple objects at once, engaging ensemble-coding mechanisms that summarize a group's overall appearance. Are these group-perception mechanisms in place early in childhood? Here, we provide the first evidence that 4-5-year-old children use ensemble coding to perceive the average size of a group of objects. Children viewed a pair of trees, with each containing a group of differently sized oranges. We found that, in order to determine which tree had the larger oranges overall, children integrated the sizes of multiple oranges into ensemble representations. This pooling occurred rapidly, and it occurred despite conflicting information from numerosity, continuous extent, density, and contrast. An ideal observer analysis showed that although children's integration mechanisms are sensitive, they are not yet as efficient as adults'. Overall, our results provide a new insight into the way children see and understand the environment, and they illustrate the fundamental nature of ensemble coding in visual perception.

Sensitive perception of a person's direction of walking by 4-year-old children.

Watch any crowded intersection, and you will see how adept people are at reading the subtle movements of one another. While adults can readily discriminate small differences in the direction of a moving person, it is unclear if this sensitivity is in place early in development. Here, we present evidence that 4-year-old children are sensitive to small differences in a person's direction of walking (∼7°) far beyond what has been previously shown. This sensitivity only occurred for perception of an upright walker, consistent with the recruitment of high-level visual areas. Even at 4 years of age, children's sensitivity approached that of adults'. This suggests that the sophisticated mechanisms adults use to perceive a person's direction of movement are in place and developing early in childhood. Although the neural mechanisms for perceiving biological motion develop slowly, they are refined enough by age 4 to support subtle perceptual judgments of heading. These judgments may be useful for predicting a person's future location or even their intentions and goals.

An aftereffect of adaptation to mean size.

The visual system rapidly represents the mean size of sets of objects. Here, we investigated whether mean size is explicitly encoded by the visual system, along a single dimension like texture, numerosity, and other visual dimensions susceptible to adaptation. Observers adapted to two sets of dots with different mean sizes, presented simultaneously in opposite visual fields. After adaptation, two test patches replaced the adapting dot sets, and participants judged which test appeared to have the larger average dot diameter. They generally perceived the test that replaced the smaller mean size adapting set as being larger than the test that replaced the larger adapting set. This differential aftereffect held for single test dots (Experiment 2) and high-pass filtered displays (Experiment 3), and changed systematically as a function of the variance of the adapting dot sets (Experiment 4), providing additional support that mean size is adaptable, and therefore explicitly encoded dimension of visual scenes.