Shape Your Imagination: Iconic Gestural-Based Interaction (Marsh 1998)

Summary:
Iconic gestures are a natural, intuitive, and effective way to convey spatial information. This paper separates iconic gestures into virtual and substitutive categories. Virtual depiction is defined as using the spatial relationship between the hands as an outline or tracing the picture of an object or shape. Substitutive depiction is defined as shaping the hands to match the form of an object as if it were being held or grasped in the hands.
A user study is performed to determine if humans use iconic hand gestures during non-verbal communication of shapes and objects, and if so, what kind of gestures are used with what frequency, and how many hands are involved in the gestures. Twelve volunteers were seated in a room and asked to non-verbally describe fifteen shapes and objects using hand gestures. Care was taken not to influence the volunteers' descriptions or otherwise influence their gestures by providing images of the objects.
Subjects used two-handed gestures 88.1% of the time, preferring virtual depiction. 75% of gestures were performed using purely virtual depiction, 17.9% were performed using purely substitutive depiction, and 7.1% used a combination of both. Only one object, the circle, was performed using primarily one-handed virtual depiction gestures.

Discussion:
The results of this paper were not surprising. I suppose it was still good to confirm the ideas experimentally, although a larger group of subjects could have been used to obtain more statistically significant results. Also, since the goal was to see how gestures are used naturally, an experiment could be designed to observe when gestures accompany certain spoken words or phrases. Telling the subjects that they must communicate completely non-verbally does not seem like a situation in which the most natural gestures would be made.
In general, users found describing 2D shapes easier than 3D shapes. I think an analogy to this insight exists in the recognition realm. Sketch recognition in two dimensions is an easier problem than gesture recognition in three dimensions.