With reference to 'Learning Curves', when in a learning process the speed of learning is extremely slow in the initial phase, but as practice increases, the speed of learning starts increasing rapidly and finally it tends towards a definite plateau, what is this specific type of learning curve psychologically known as?

Under child development and pedagogy, 'Learning Curves' is an important topic. A Concave Curve or 'Positive Acceleration Curve' is that curve in which the speed of learning is slow in the beginning because the learner is unfamiliar with the subject matter, but upon continuing practice, the speed of learning starts increasing rapidly. In contrast, in a Convex Curve, the speed is fast in the beginning and slow later. The 'S-shaped' curve includes both stages. Therefore, the correct option is A.