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Chapter 3

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Carleton University
PSYC 2700
Chris Herdman

Lecture 3 Chapter 3: pattern recognition I. Pattern recognition Recap: sensory memory - SM codes are primitive (features) • Ex: lines and dots - SM duration is short (~250ms) • Memory trace does not last long.Approximately 250 milliseconds - How can we recognize patterns? • SM has large capacity that allows us to recognize large amounts of information and then interpret it by:  Recognizing patters...  THEN selecting certain things for further processing A. Template models - Match stimulus to template in memory • Pattern recognition consists of matching stimulus to a template or model stored in your mind • Matching process involves: stimulus template - Support for idea: computers • Pattern matching with computers emerged to begin  Store in computer representation “templates”  Ex: when you go shopping there is a bar code on each item. This barcode (stimulus) is scanned and matched to a template in the computer which brings up the correct price - Limits: • Inefficient  This theory would not be very efficient for massive amounts of information (which is what we intake) • Irregular world  Our world is ever-changing. Each person you see, each sounds you hear, etc... it is all very complex • Strict match - The template model is therefore constrained B. Feature models - Feature more regular than patterns • Features are more common - Complex objects composed of simple features - Gibson (1969) • Features of letters • Maybe this is how we read see letters as features and then letters combine to become words - Neisser (1964) (see figure 3-8 p.96) • High-speed scanning  Features extracted and noted  When looking at an object, features are extracted from SM and noted  Then, compared to store items from experience  “count” (compare) “Z” to item  In class ex: Z stands out due to the fact that it’s features are different from surrounding features :curvy letters”  Takes a lot longer to find Z amongst letters than have similar features (straight and horizontal lines)  This occurs because each similar feature activates many of the same letters so longer reaction times and recognition • Harder (slower) if target (Z) shares features with distracters - Pritchard (1961) • Physiological nystagmus (jitter 30-70/sec)  Refreshes retinal receptors  Your eyes jitter back and forth even if you are focused on one single point to refresh your receptors, so you can constantly see an image  Researchers wondered what would happen if they stabilized the image to make it stay in the exact spot the eyes were moving  Researchers hooked up participants to an eye tracking device that keeps images on the same spot as receptors • What if stabilize image?  Image fades away because receptors could not fire anymore  The image faded in chunks (lines, curves)  The fading is related to features (perceptive level) • Suggests higher-order features detectors  This suggests that we keep image features at a higher level of cognition - Lettvin et al (1959) • Inserted microelectrodes into cells of frog retina • Recorded activity... found certain receptors which only responded to:  Edge detectors (would only fire when recognized an edge)  Moving edge  Dimming (lowering of luminous)  Convex edge (small, circular dot moves) (fly or bug)  Small circular dot moving • Shows existence of feature detectors - Hubel & Wiesel (1963) • Recorded cells in cats in visual cortex • Simple cells:  Only simple patterns of light in certain location of visual field (Edge, slit, line) • Complex cells:  Same as simple, but NOT location specific • Hypercomplex cells:  Moving lines • W, x, y cells:  How fast something is moving along the visual field  Speed of transmission  Y (movement speed) Beyond features: top-down (conceptually driven) pattern recognition - Pattern recognition is NOT just bottom-up system • Our knowledge has an impact on how we recognize features • Our knowledge influences how we perceive our world - Pattern recognition is influenced by knowledge • UNIVERSITY is easier to memorize the letters than when the same letters are scattered - Avant & Lydall • Masking of BOY vs. YOB  Energy masking flash a bulb at same time as stimulus  Pattern masking features, lines, pound signs in between stimulus • Used backwards pattern masking  Would present target for 50 ms (YOB or BOY)  Then intervals of 100ms for each would be presented the mask  To effectively mask out target ha
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