PATTERN RECOGNITION & SENSORY MEMORY

• PATTERN RECOGNITION is the ability to identify objects in the environment--a necessary first step in all cognitive processses. Incoming sensations are combined/compared with patterns stored in LTM.
• It is related to SENSORY MEMORY, where incoming stimuli are held for further processing following their initial detection.

TEMPLATE-MATCHING MODELS

• Template: exact internal representation of a pattern to be recognized.
• Incoming patterns are compared "as is" to existing, stored patterns in LTM.
• Example: a computer scanning the bottom numbers on checks looks for an exact match, or the use of UPC codes.
• Template-matching theory as a theory of pattern recognition:
•     1.) assumes that a retinal image is faithfully encoded in the brain.
•     2.) assumes that an attempt is made to compare the retinal image directly to various stored patterns, or templates.
•     3.) may be a mechanism for the sensory register--allows extra time to hold information for processing, but with a questionable application for real life--when do we have stimuli changing every 250 ms on a consistent basis?
• Problems with template matching theories:
•     1.) Requires an all or none judgment.
•     2.) Gives no room for context.
•     3.) Symbols must always be the same size, orientation position as the pattern to be identified.
•     4.) Things can go wrong with the template--assumes a precise retinal image.
•     5.) Does not show how two patterns may vary, e.g. P vs R, or E vs F
•     6.) Does not allow for alternate descriptions of the pattern, e.g., sting ray versus sail--ambiguous stimuli.
•     7.) That a precise, standardized system is needed for template matching to work reduces the credibility of this process as a model for human pattern recognition, which is highly complex and would require an almost infinite store of patterns.
•     8.) Very few researchers today view template matching as an adequate model.

FEATURE ANALYSIS MODELS

• Feature analysis as a theory of pattern recognition:
•     1.) Requires the recognition of critical features rather than reading an exact template.
•         Stimuli are thought of as combinations of elemental features. Can describe a pattern by listing its parts.
•         Like bottom-up processing in that there is a feature-by-feature comparison. Individual units are used to build a whole.
•     2.) Key component: contrasts/ differentiates between patterns and looks for distinctive features, i.e., the lowest horizontal line in E, differentiate it from F.
• Advantages over template matching:
•     1.) Features are simpler units.
• At the visual level there is strong evidence that the nervous system indeed extracts such features as lines (e.g., Hubel & Weisel, 1962).
•     2.) "Critical" features, those relationships among features which are most critical to a pattern, can be identified: i.e., for the letter ‘A’ the critical point is that two approximately 45-degree lines intersect as near to the top as possible and the cross bar intersects both lines as nearly as possible, bisecting both lines.
•     3.) Reduces the number of stored units: you do not need a template for each possible pattern but only for each feature. Since the same features tend to occur in many patterns this would mean a considerable savings in storage.
•     4.) Sensitivity to context: small variations in relationships can be overcome by taking account of the context--top-down processing is taken into account-- expectations and internal schemata play a part in perception.
•     5.) Problem: Fails to explain relationships between features.

STRUCTURAL THEORIES

•     A.)     Extend feature theories by specifying how features are related. This is a follow-up step to feature identification.
•     B.)     Also called ‘analysis-by-synthesis’.
•     C.)     Makes use of Gestalt principles--rules for initial form organization. The Gestalt principles seem to function so that one can quickly segment a stimulus into a set of objects and to organize these objects into larger configurations.
•         In some situations this segmentation seems quite successful: i.e., in a written page the principle of proximity serves to identify the letters and words, the principles of proximity and good continuation identify the line of text.
•         Theoretically more efficient than template models: They allow a single set of rules for determining relations among features to apply to a wide range of objects and scenes.

IMPORTANCE OF CONTEXT OR TOP-DOWN PROCESSING Context:

• 1.) The use of existing knowledge to guide processing.
• 2.) At the earliest, top down processing can take place at the level of visual or auditory short term memory.
• 3.) Top-down processing becomes more important as you degrade bottom-up. We compare what we see with past experiences and use this to interpret what is being seen.

Auditory example of verbal context
effect on pattern recognition

• Have you seen the new display?
• Have you seen the nudist play?

SENSORY REGISTERS; VISUAL & ACOUSTIC STORES: OVERVIEW

• There appear to be sensory registers, or stores, which can hold incoming stimulus information for very short periods of time. These sensory registers are a first step in establishing a more permanent memory.
• Each sensory system has its own, apparently independent store:
• Iconic (vision) Auditory (hearing)
• Haptic (touch) Gustatory (taste)
• Olfactory (smell)

THE INFORMATION AVAILABLE IN BRIEF VISUAL PRESENTATIONS

• Brief visual information is gathered by use of a tachistoscope--stimuli can be viewed for a precise duration and a brightness.
•      A.) The Span of Apprehension
•         the amount of information we can attend to at any one time. Defined as 50% accuracy in detecting the information available in a visual display. This amount is limited, and the limit can be assessed by using a t-scope.
•     B.) The Partial Report Procedure
•         Sperling (1960) devised a procedure in which letters and numbers appeared in a 4 x 3 matrix. In a control, whole report condition, stimuli were exposed and subjects reported as many letters and numbers as they could--average was between 4 & 5.
•         This suggests there is a limited ability which is linked to a perceptual limit.
•         In the experimental, or partial report condition a tone of high, medium or low pitch was sounded, cueing the subject to report the stimuli from either the top, middle or bottom row.
•         All three rows were randomly tested, and the results showed a mean recall of 3 stimuli per row--on any one trial 9 stimuli (3 x 3) were available for recall, about twice as many as were available with whole report.
•         Thus, there appears to be a brief visual sensory store which can hold a fair amount of information but which is quickly lost if not immediately attended to.
•         This suggests there is a limited ability linked to a memory capacity limit.
•         The question remains which is it: Perceptual or Mnemonic limit?
•     C.) Properties of Iconic Memory
•         Iconic memory is the name given to the visual sensory register--the memory for a rapidly fading visual image.
•         Unlike an afterimage, which is thought to be a retinal (eyeball) event, the icon is thought to be a central (nervous system) event--thus making a true psychological event and not a physiological one.
•         It is short-lived, less than about 500 ms., and is limited to about 75% of a display, or about 9 - 12 items, depending on the experimental paradigm.
•         It is serial--processing is on an item-by-item basis.
•         It is controlled--requires mental effort.
•         It is limited to physical information, such as color, but not to higher cognitive processes such as category membership.
•         It is not conscious--all information enters the system.

ECHOIC MEMORY

•     A.) Dichotic Listening
•         The auditory sensory store has been inferred by the technique of dichotic listening.
•         Subjects wear stereo headphones through which different information is presented to each ear, simultaneously. If you present three digits to the left ear and three digits to the right ear simultaneously, then ask for recall, subjects typically recall first all of the digits from one ear and then all of the digits heard in the other.
•         This implies that the second set must be held while the first is being recalled.
•         Another dichotic technique involves shadowing, where a subject is presented two different stories, one to each ear, and the subject is asked to repeat aloud the story in one ear.
•         When the two messages are identical, but offset, subjects become aware of that fact when they shadow the leading message, with the nonshadowed message offset by up to 13 words. When the shadowed message is the lagging one, then subjects only become aware of them being identical when they are offset by up to 6 words. This is evidence that there must be some brief storage for the nonshadowed message as well.
•     B.) Partial Report
•         Darwin, Turvey & Crowder (972) applied Sperling's partial report technique to the auditory modality.
•         They found that by cuing recall with a visual marker the partial report was superior to the whole report.
•         For whole report the span of auditory apprehension is between 4 and 5 items, just as for the visual store. However, by partial report auditory apprehension increased, even for delays up to 4 secs, although the increase was not as large as for the visual technique.
•         The findings suggest there is an auditory store in which echoic memory persists longer than iconic memory, but which is more limited in its capacity.
•     C.) Word Superiority Effect:
•         Iconic memory studies show that a letter is recognized more quickly when it is part of a word than when it is considered by itself, or as a part of a nonword.
•         This suggests that prior knowledge about words leads us to expect particular letters to appear in particular locations, providing evidence for interaction between sensory and long term memory stores.
•         Also provides evidence for a parallel processing model in which features, letters and words are processed simultaneously.