Thus, a letter can take any one of many different form: a a a a a a a We would compare each “a” with the prototypical “a” that we have in memory, and, if the match is sufficient, we would then recognize the letter. • Template matching is a difficult process to spell out in detail. o The prototypical pattern must differ somewhat from the particular patterns we perceive, just as each “a” shown above differs from the others. Problem is to specify how a template can match not only patterns that are identical to it, but also patterns that are similar enough to it. Hintzman propsed a multiple-trace memory model which accounts that traces of each individual experience are recorded in memory. No matter how often a particular kind of event is experienced a memory trace of the event is recorded each time. • In this model, there are two types of memory o Primary memory refers to what people are experiencing at any point in time. o Secondary memory refers to all of the memory traces created out of all the experiences that a person has had. Secondary memory can be activated by means of a probe from primary memory. The activated memory traces are said to return an echo to primary memory. • Choir example – can’t hear individual voices, but general impression of what is in common • Hitntzman used his theory to account for the results of classic studies by Posner et al. • Prototypes:
Chapter 3 – Perception Pattern Recognition 20:58 • Distortions: o Participants were shown the distortions but did not actually see the prototypes. Subsequently, participants were required to classify another set of patterns consisting of the prototypes, the original distortions, and some new distortions of the prototypes. The result was that the prototypical patterns were quite well classified even though they had never been seen before. o Hitzman explained Posner’s findings as memory traces of the set of distorted patterns produce an echo. The echo contains what the different distortions have in common, and not the peculiarities of each individual distortion. Consequently, the prototype is recognized, even though it has never been seen before. Feature Detection Feature detection theory proposed by Selfridge is detecting patterns on the basis of individual features. • Pandemonium is a model of pattern recognition consisting of three levels: data, cognitive demons, and decision demons. o Features might be things like size, colour, shape, and so on. o Cognitive Demons is a feature detector that decides whether the stimulus matches its pattern. o Decision demon is a feature detector that determines which pattern is being recognized. • Pelli et al. investigated the effect of the contrast between the letters in a word and the background on which they are printed.
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- Winter '08