PSYC 213 Chapter Notes - Chapter 3: Optical Flow, European Credit Transfer And Accumulation System, Parahippocampal Gyrus
28 May 2018
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Chapter 3: Perception
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Introduction
• Visual agnosia: unable to identify objects visually even though able to identify using other
senses (i.e. touch)
• Perception: processing of sensory information such that produces conscious experiences and
guides action in world
Physiology of Visual Perception
• Visual perception involves processing of info conveyed by light energy
• Cornea: outer transparent tissue of the eye
• Pupil: small opening through which light enters --size controlled by iris, which gives eye its
color
• Retina: sheet at the back of the eye on which light is focused
o Contains photoreceptors, packed in fovea
• Primary visual cortex: region responsible for early processing of visual signal
o Retinotopic: information falling on adjacent regions of retina processed in adjacent
areas of V1
• Initially thought that this was only region responsible for visual info processing
o Later shown that interacts with other areas of the brain
• Highly modular --some areas for motion, some color, etc.
• Achromatopsia: selective damage resulting in color perception deficit
• Akinetopsia: inability to perceive motion (motion blindness)
Visual Pathways
• Ventral pathway: what pathway, inferior temporal lobe
o Processing characteristics of objects and assigning meaning
o Visual agnosia
• Dorsal pathway: where pathway, parietal lobe
o Processing spatial aspects & motion/location
o Akinetopsia
• Connections between brain areas are bi-directional
• Feedforward sweep: propagation info V1 --> dorsal & ventral pathways
o Bottom-up influence
• Re-entrant feedback connections: connections allowing propagation of information from
endpoints of ventral & dorsal pathways back to V1
o Expectations influence early processing, biasing perception
o Top-down influence
• Perception relies on both bottom-up and top-down influences
Ventral Pathway & Object Recognition
• V1 processes basic features of objects; cells in ventral stream process complex aspects
o Inferior temporal cortex (IT) identify entire objects
• i.e. Fusiform face area responds selectively to faces
• Prosopagnosia is deficit in recognizing faces, due to damage to FFA
• Unable to combine features into complete percept
o Temporal lobe
• Parahippocampal place area for recognizing places
• Extrastriate body area for body parts other than faces
Object Recognition
• Pattern recognition: ability to recognize an event as an instance of a particular category of
events
o From computer science; computer able to identify configurations
o i.e. recognize words as meaningful and not just scribbles, recognize object with handle
as coffee mug
• Recognizing configuration requires interaction between perception and memory
o Memory trace: trace that experience leaves behind in memory
o Hoffding function: process by which perception contacts memory trace
Feature Detection
• Feature detection theory: detecting patterns based on their features / properties
o Selfridge
o Objects and events made of features that are used to identify them
o A lot simplified, but influential
• Pandemonium is simple version of this model
o 3 levels:
o Bottom = image or cluster of data in which pattern of features presented
• Features: size, color, shape, etc.
o Next level is cognitive demons who examine pattern
• Each demon looking to detect particular pattern (i.e. one for apples, one for
baseball, etc.)
• When demon sees pattern similar to one looking for, it shouts; the more similar, the
louder it shouts
o Top is decision demon who selects cognitive demon shouting the loudest
• Choice determines what pattern recognizes
• Pelli, Farell & Moore: looked at effect of contrast between letters in word and background
o Black letters on white background have more contrast energy
• Experiment where vary word length (2-16 letters) & contrast energy
o Shown word for 200ms, then must identify which one was from list of 26 words of same
length
• The longer the word, the higher the contrast energy required to identify word
o Letters (unlike overall patterns) are crucial features of visual system
o Too difficult to identify large number of letters in short time when signal is low
• Squelching: tendency of NS to inhibit processing of unclear features
o Visual system focuses on reliability --doesn’t want to "guess" when not sure
Recognition by Components
• Explains how feature analysis applies to real world objects (how breakdown 3d images into
simple components)
• Recognition by components (RBC) theory: assume that image on retina is segmented --breaks
it down at points of concavity where curvature is discontinuous (corner) into basic components
called geons
o Biederman
o Then geons compared with geon configurations stored in memory, and when match,
recognize the object
• Experiment where vary number of geons used to depict given object & varied complexity of
object
o Show object quickly and then ask to name
o More geons = better recognition (more details)
• 80% for 2-3 geons; quite good
• More complex obtains recognized more efficiently --counterintuitive since contain
more information so should take more time to process
o Show that breaking down objects into geons is crucial for object recognition
Template Matching
• Template: guide used to bring piece of work into desired shape
• Store templates in memory corresponding to standard forms of configurations seen
o Compare current configuration with representative/prototypical forms that have in
memory
• i.e. Can recognize letter written with different fonts
o Involves comparing each a with the prototypical a that have in memory
o If match good enough, recognize the letter
• Difficult to explain specific characteristics of model --template matches with identical and
similar enough patterns (not fixed)
o Criticized
o But good idea in that recognize thing because are similar to underlying prototype that
have
• Hintzman: multiple-trace memory model
o Record traces of each individual experience in memory --No matter how often particular
event experienced, memory trace is recorded every time
• Distinguishes between primary & secondary memory
o Achieve secondary memory using a probe
• Snapshot of info / active representation of experience in primary memory that
activate memory traces in secondary memory
• Probe goes from primary --> secondary memory, activating memory traces similar
to the probe (current experience)
o Activated memory traces return as echo to primary memory
• Echo made from all activated memory traces, like choir
• Get general impression, lose individual memory trace's properties
• Theory used to explain results of study by Posner
• Posner: participants shown distortions of prototypical patterns ("concept")
o Dots randomly moving away from position in prototype
o Do not see prototype themselves
• Later shown prototypes, original distortions and some new distortions of prototypes
o Asked to classify these into various concepts
• Results: participants good at classifying prototypical patterns even though had not seen them
before
o Sometime misidentified prototypes as patterns previously seen, even though only had
seen distortions of it
