Perception
Organisation, identification and interpretation of sensory information
-how we interpret info affects how we interact with the world
Bottom up pathway
Perceptions are built from sensory input
-feed forward
-Receives info from what/where pathways
Top-down processing
Interpretation of sensations are influences by available knowledge, experiences and thoughts
-regions at end of what/where pathways move to V1
Factors affecting perception (8)
- Sensory adaption
—not perceiving stimuli that remains relatively constant over prolonged periods of time - Motivation
- Attention
—concentration on specific parts of our environment (often at the exclusion of others) - Beliefs/values/prejudices/expectations
- Inattentional blindness
—failure to notice something completely visible because of lack of attention - Change blindness
- Colour perception
- Life/cultural bias
Retina
Internal surface of eye that contains photoreceptors that convert light into neural signals
-Relayed to the brain via optic nerve
Blind spot
Point at which optic nerve leaves the eye
-no rods or cones are present here
Rods
Specialised for level of low light intensity
-located primarily in periphery
Cones
Specialized for levels of high light intensity and detection
-packed more densely in center of retina (fovea)
Transduction of light
- Light enters though cornea
- Passes through pupil
- Refracted through the lens
- Focused on retina tissue at back of eye
- Captured by photoreceptors in fovea and converted into neural signals
- Neural signal transmitted to brain through optic nerve
Primary visual cortex (V1
Area at back of brain responsible for early processing of visual signals (how light something is, color, movement, etc)
-signals travel to here via processing station called lateral geniculate nucleus
-V1 cells respond to light into particular orientations, lengths, etc.
Dorsal pathway
“Where” pathway
Ventral pathway
“What” pathway
Word superiority effect
Easier to identify a letter if it appears in a word rather than alone or in a non-word
V4
Region associated with color perception
-acheomatopsia is the failure to perceive color
V5
Region associated with motion perception
-akinestopsia is the failure to perceive visual motion
Stages of object recognition
- Initial stage
-detection of basic visual elements (colors, edges, etc) - Intermediate stage
-grouping basic elements into higher units that code depth cues and segregate surfaces into figure and ground - Advanced/final stage
-recognising the object and attributing meaning to it
Feature detection
Detecting patterns on the basis of their features or properties
Slefridges pandemonium model (3 levels)
- Features
-property of stimulus (color, shape, size) - Cognitive demons
-decides whether stimulus matches its particular patterns - Decision demons
Decides which pattern is being recognized based on cog demon input
Recognition by components
Decomposing objects into fundamental 3D geometric shapes and comparing with existing memory representations
-explains why we can recognize objects from different viewpoints
Gestalt grouping principles
Perception is holistic rather than atomistic
-grouping of visual features to form a whole
-follows certain organisational principles
Template matching
Comparing configuration of current sensory input with standard configuration we have
-we have a prototype/template
Apperception agnosia
Failure to understand meaning of objects
-deficit at level of object perception
Associative agnosia
Failure to understand meaning of objects
-deficit at level of semantic memory
Integrative agnosia
Failure to integrate parts into wholes
