Cognitive reliability of the sense of touch confronted with the thinning effect

The dependence of the cognitive function of the sense of touch of the area sensorium was investigated by means of the thinning illusion produced by rotating the cylindrical rod between the thumb and the forefinger. The genetic phases of this illusion were traced from sensations to perceptions and to meaningful cognition converting the rod's objective convexity into an apparent concavity, running seemingly around the rod. Adult subjects (N = 52) experimentally checked all variables on their optimum degree for producing this illusion, which showed an effective way for using illusions for a thorough investigation of mental synthetic processes.