3 Processes of Pattern Recognition

1. 3 Processes of Pattern Recognition • Sensation – you have to detect or see the pattern • Perception – you have to organize the features into a whole • Memory – you have recognize you have seen this pattern before and remember its label

2. Agnosia • Agnosia: A failure or deficit in recognizing objects • Prosopagnosia: A disruption in face recognition. • Apperceptive Agnosia: A form of agnosia in which individual features cannot be integrated into a whole percept or pattern; a basic disruption in perceiving patterns. • Associative Agnosia: A form of agnosia in which the individual can combine perceived features into a whole pattern but cannot associate the pattern with meaning or identify it

3. (a) Left and right hemispheres of the brain, showing apperceptive agnosia usually is limited to posterior regions of the right hemisphere parietal lobe. (b) Both left and right hemispheres have cross-hatched regions at the junction of the temporal and occipital lobes, the region usually damaged in associative agnosia.

4. Implications for Cognitive Science 1. Detecting the features in a visual stimulus is a separate (and later) process from the sensory steps that encode a stimulus into the cognitive system. (sensation) 2. Detecting the visual features is critical in constructing a perceived pattern, a percept. (perception) 3. There is a separate step involved in hooking up the pattern with its meaning and name, involving the visual association from the pattern to the knowledge stored about it in memory. (memory)

5. The basic sensory equipment involved in human vision

6. Binocular pathways of information flow from the eyes into the visual cortex of the brain. The patterns of stimulus-to-brain pathways demonstrate the contralaterality of the visual system.

7. Gathering Visual Information • Saccades: The voluntary sweeping of the yes from one fixation point to another. • Fixations: The pause during which the eye is almost stationary and is taking in visual information; also the visual point on which the eyes focus during the fixation pause. • Change Blindness: The failure to notice changes in visual stimuli (e.g. photographs) when those changes occur during a saccade. • Inattentional Blindness: We sometimes fail to see an object we are looking at directly, even a highly visible one, because our attention is directed elsewhere.

8. Visual Sensory Memory • First two perspectives on how to study perception and pattern recognition • Largest group – sees the importance of laboratory studies and highly controlled experiments • Second group – an ecological approach. The laboratory is too artificial and has little relevance to how humans perceive the real world

9. Visual Sensory Memory • Visual Persistence: The apparent persistence of a visual stimulus beyond its physical duration. • Visual Sensory Memory (iconic memory): The short-duration memory specialized for holding visual information, lasting no more than about 250 to 500 ms.

10. Amount and Duration of Storage The classic cognitive research on the characteristics and processes of visual sensory memory was reported by Sperling and his coworkers. Sperling used a special apparatus for presenting visual stimuli, the tachistocope, commonly known as the T-scope.

11. Schematic diagram of a typical trial in Sperling’s experiments

12. Erasure and Interference • Backward Masking: Whereby a later visual stimulus can drastically affect the perception of an earlier one. • Erasure: When the contents of visual sensory memory are degraded by subsequent visual stimuli, the loss of the original information is called erasure, a specific kind of interference.

13. The Argument About Iconic Memory The “Ecological Validity” Challenge Based on the work of Haber, ecological validity refers to the fact that methodologies and tasks should resemble the real-work ecology of cognitive processing.

14. The Template Approach • Templates: Stored models of all categorizable patterns. • Acts like a computer reading numbers on your checks • Problem: Our brain can’t store enough templates

15. Visual Feature Detection • Feature analysis/feature detection: all patterns made up of a limited number of features • We detect these distinctive features and use them to recognize the pattern

16. Feature Integration Theory • Two stages • 1st preattentive stage – object is broken down into its basic features prior to conscious awareness • 2nd focused attention features combined into whole objects that is now perceived. Top-down processing determines what features are combined (expectation and Context

17. Biederman’s Recognition by components • All objects are composed of one or more basic geometric components called geons • 36 basic geons • Perception involves recognizing these geons

18. Geons (components) and the objects they make

19. Nonrecoverable objects

20. Recoverable Objects

21. Beyond Features: Conceptually Driven Pattern Recognition • Data-driven processing system: Processing is driven by the stimulus pattern, the incoming data. • Conceptually-driven processing effects: Context and higher-level knowledge influence lower-level processes.

22. Top-down effects in pattern recognition

23. Beyond Features (con’t.) • Pattern recognition starts by processing the incoming pattern, a bottom-up process; this bottom-up emphasis slights the contribution made by the cognitive system. It misses the effect of context, the influence of surrounding information and your own knowledge. • Repetition Blindness: The tendency to not perceive a pattern, whether a word, a picture, or any other visual stimulus, when it is quickly reported.

24. Connectionist Modeling • Connectionist Modeling: A theoretical and computational approach to cogntion. Computational refers to the ways in which the human cognitive system performs in mental operations.

25. Connectionist Modeling (con’t.) • Input Units: In a model of a simple connectionist framework, input units are basic “cells” that receive inputs from the environment. • Hidden Units: This level in the framework is completely internal, always one step removed from an input output. • Output Units: The units that report the system’s response, say to the question “What is this word?

26. A portion of the PDP network for recognizing four-letter words. The bulk of the illustration involves identifying the first letter of the word.

27. A possible display that might be presented to the connectionist model of word recognition and the resulting activations of selected letter and word units.