Perception. Indirect approaches: the inferential approach Author: Elena Pasquinelli [INSTNICOD] Contributors: none Current version (on 2006-01-20) The inferential approach to perception can be traced back to H. von Helmholtz’s notion of perception as a process involving unconscious inferences: perception is only indirectly related to objects in the world; data signalled by the senses are fragmentary and often hardly relevant, so that perception requires inferences from knowledge to make sense of the sensory data. Indirect approaches to perception affirm that it is not directly the objects that we perceive, but intermediates. The inferential approach is a variation of the indirect approach: “Following von Helmholtz’s lead we may say that knowledge is necessary for vision because retinal images are inherently ambiguous (for example for size, shape and distance of objects), and because many properties that are vital for behaviour cannot be signalled by the eyes, such as hardness and weight, hot or cold, edible or poisonous. For von Helmholtz, ambiguities are usually resolved, and non-visual object properties inferred, from knowledge by unconscious inductive inference from what is signalled and from knowledge of the object world.” [Gregory, 1997, p. 1121] One of the most important applications of knowledge to perception regards the vision of scenes and object in a threedimensional way. In the indirect perspective, in fact, threedimensional vision is not straightforward, even if we normally perceive a three-dimensional world because the bottom-up information the visual system disposes of is just “flat ghostly images in the eyes” [Gregory, 1997, p. 1122] To read reality from images is to solve a problem. And when the problem is quite difficult errors are to happen. Marr’s researches about vision go into this same direction [Marr, 1982] We can reconstruct the main argument for this position as follows:
1. stimuli are ambiguous (such as visual size) or insufficient for specifying object properties (such as for weight by sight) 2. nevertheless, the final percept is unambiguous and specified 3. some process must have taken place which has solved the ambiguity and allowed specification of object properties 4. in addition to present information, the subject disposes of previously acquired knowledge about objects of the world 5. knowledge can be used to disambiguate present stimuli and to specify incomplete information through a process of inference 6. inference is a mechanism that allows the use of past knowledge for producing new knowledge, thus the final percept is the result of an inference based on the content of actual experience and the content of past knowledge. As a consequence, errors might arise at different moments in the course of the inferential process. The argument of the inferential approach has been contested at different levels. As we will better see in what follows, the type of direct perception approach represented by Gibson and others (ecological approach) contests the first point, that is, the assumption that information is ambiguous or insufficient. As a consequence there is no need for additional, cognitive processes as stated at point three in order to obtain a coherent, informative final percept. Points two and three are discarded by [O'Regan & Noë, 2001], who endorses another type of direct approach to perception and sustains that there is no need for internal mechanisms because the final percept is not complete and the coherence of the final percept is simply warranted by the unity of the motorperceptual experience. Finally, point five of the argument can be contested because inference is not considered as the proper process at stake (as in the case of the application of Bayesian inference).
References: Gregory, R. L. (1997). Knowledge in perception and illusion. Philosophical Transactions of the Royal Society of London, B 352, 1121-1128. Marr, D. (1982). Vision. New York: W. H. Freeman and Co.
O'Regan, K., & Noë, A. (2001). A sensorimotor account of vision and visual consciousness. Behavioral and Brain Sciences, 24(5), 939-1011. Gibson, J. J. (1966). The senses considered as perceptual systems. Boston: Houghton Mifflin Company. Knill, D. C., & Richards, W. (1996). Perception as Bayesian inference. Cambridge: Cambridge University Press.
Related items: Perception. Direct and indirect approaches Perception. Bayesian inference Perception. Direct approaches
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