 The positive part of the modest modularity hypothesis is that input systems are modular. By ‘input system’ Fodor (1983) means a computational mechanism that “presents the world to thought” (p. 40) by processing the outputs of sensory transducers. A sensory transducer is a device that converts the energy impinging on the body’s sensory surfaces, such as the retina and cochlea, into a computationally usable form, without adding or subtracting information. Roughly speaking, the product of sensory transduction is raw sensory data. Input processing involves non-demonstrative inferences from this raw data to hypotheses about the layout of objects in the world. These hypotheses are then passed on to central systems for the purpose of belief fixation, and those systems in turn pass their outputs to systems responsible for the production of behavior.