The haptic cues humans use to sense small numbers of objects in a box

Humans can acquire behaviorally relevant information about the contents of a container through their sense of touch. A container poses a challenge to the haptic sense as it creates an intermediary between its contents and the observer. Despite this challenge, several studies have shown that individuals are particularly adept at estimating small numbers of objects in an opaque box solely through tactile interaction. This study aimed to identify which physical cues contribute to this ability by systematically attenuating (Experiment 1) or augmenting (Experiment 2) the cues of rolling vibrations, impact, and weight. Rolling cues were manipulated by varying the friction between the objects and the container's floor. Impact cues were manipulated by softening or hardening the container's internal wall. Weight cues were controlled by equalizing the total weight of the contents, regardless of the number of objects. The findings suggest that rolling vibrations are the primary cues, followed by impact cues, while weight plays only a minor role.