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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

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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

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(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.

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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)

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The basic sensory equipment involved in human vision

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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.

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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.

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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

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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.

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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.

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Schematic diagram of a typical trial in Sperling’s experiments

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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.

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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.

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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

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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

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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

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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

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Geons (components) and the objects they make

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Nonrecoverable objects

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Recoverable Objects

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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.

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Top-down effects in pattern recognition

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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.

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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.

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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?

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

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

word units.