Pattern Recognition


Explain with reference to the relevant experimental evidence the main models of pattern recognition.


Adaptation of Sperling’s model of Information processing explores the third process after Sensory Input, Pattern Recognition. Pattern recognition is the process by which we identify the various stimuli which have been encoded by our sensory systems. Evidence of the processes of how individuals assess stimuli is determined by establishing the main theoretical models and determing the patterns that arise of the stimuli of written and spoken word and objects. The investigation of these two stimuli involves recognising written and spoken letters, how individuals recognise words made up of these letters, and the recognition and semantic development of sentences made up of these words.


Three model types provide experimental evidence of Pattern recognition these being; Template Models, Feature Models, and Structural Models. The Template theory argues that we recognise patterns by comparing them to stored representations. There are three basic assumptions of the theory behind Template models;
1) Memories are represented as holistic unanalyzed entity (a template).


2) An input pattern is compared to the stored representation.


3) Identity is determined by selection of the template with the greatest amount of overlap and we recognise a given pattern by the template which matches that stimulus most closely. For example the numbers on a check are recognized by a Template system.


Although effective, a number of problems can occur with the template model of Pattern recognition. One of the main problems is that a given object may be represented by a range of different physical patterns, which suggests there is intolerance to deviations. The second problem is a number of templates may be required.


Due to the shortcomings of the Template theory, an alternative explanation of pattern recognition was developed. This explanation, known as Feature-Detection theory. It was designed to accommodate pattern variability by focusing on common elements across different instances of an object. The theory proposes that we break a stimulus down into its component features and then use these features to infer the identity of the stimulus. It also proposes that patterns are identified in terms of the set of features which define them. Supported by Gibson (1969), this model suggests individuals learn to identify patterns by learning which particular set of features allows us to discriminate that pattern. Feature theory Pattern Recognition theories work on three basic premises. The first premise is that stored representation is a description of past inputs in terms of list of attributes or features. The second premise is that inputs are broken down into a small list of constituent features, and the third premise is that identity is determined by selecting the feature list most similar to the input.


One of the most influencive Features theory model was identified by Selfridge (1959) developed a feature based model of pattern recognition called Pandemonium. Pandemonium explored four key areas of Pattern recognition. Pandemonium consists of four separate layers: each layer is composed of \'\'demons\'\' specialized for specific tasks




The first type of demons is Image demons, these acquire a neural representation of the stimulus, and they also store and pass on the data. The second Type of Demons is Feature Demons. Feature demons extract the features of the stimulus. The third type is Cognitive demons and they try and match feature demons feature components to known stimuli. The fourth type, the decision demon decides what the pattern is based on the strength of the output of the cognitive demons.


How did Selfridge come up with this pattern recognition methodology? He demonstrated the effectiveness of Pandemonium via two different tasks.


(1) He went about distinguishing dots and dashes in manually keyed Morse code


(2) He tested the ability to recognizing 10 different hand-printed characters


Gibson (1969) expanded upon Selfridge’s model by proposing a set of features which could be used to discriminate upper case letters. He assessed four criteria for choosing these features.


For example, features should be critical ones which are not present in all members, for example the Horizontal line in the A is critical for the A as it differentiates it from other letters. The features should remain intact regardless of changes in the in size, perspective or any other features. For example the features of the B are that it has a vertical line, with closed curves, an