3 Processes of Pattern
• Sensation – you have to detect or see the
• Perception – you have to organize the features
into a whole
• Memory – you have recognize you have seen
this pattern before and remember its label
• 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
(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.
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)
The basic sensory equipment involved in
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.
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.
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
– Second group – an ecological approach. The
laboratory is too artificial and has little
relevance to how humans perceive the real
Visual Sensory Memory
• Visual Persistence: The apparent
persistence of a visual stimulus beyond its
• Visual Sensory Memory (iconic memory):
The short-duration memory specialized for
holding visual information, lasting no more
than about 250 to 500 ms.
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.
Schematic diagram of a typical trial in
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.
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
The Template Approach
• Templates: Stored models of all
• Acts like a computer reading numbers on
• Problem: Our brain can’t store enough
Visual Feature Detection
• Feature analysis/feature detection: all
patterns made up of a limited number of
• We detect these distinctive features and
use them to recognize the pattern
Feature Integration Theory
• Two stages
– 1st preattentive stage – object is broken down
into its basic features prior to conscious
– 2nd focused attention features combined into
whole objects that is now perceived. Top-
down processing determines what features
are combined (expectation and Context
Biederman’s Recognition by
• All objects are composed of one or more
basic geometric components called geons
• 36 basic geons
• Perception involves recognizing these
Geons (components) and the objects they make
Beyond Features: Conceptually
Driven Pattern Recognition
• Data-driven processing system: Processing is
driven by the stimulus pattern, the incoming
• Conceptually-driven processing effects:
Context and higher-level knowledge influence
Top-down effects in pattern recognition
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.
• Connectionist Modeling: A theoretical
and computational approach to cogntion.
Computational refers to the ways in which
the human cognitive system performs in
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
A portion of the PDP network for recognizing four-letter words. The
bulk of the illustration involves identifying the first letter of the word.
A possible display that might be presented to the connectionist model
of word recognition and the resulting activations of selected letter and