Chapter 3 - Perception and Mental Imagery Flashcards
Distal and Proximal Stimuli
outside world (objects) - physical world
what we experience - perceptual world
distal stimulus: actual object
ex: a tree
proximal stimulus: energy from object reaching our senses
ex: pattern of light falling on retina reflected from trees
perceptual system creates representation of what the distal stimulus is based on information in the proximal stimulus
Constructive Process
perceptual system must often fill in information
perceptual system uses available information to make best guess about most likely cause of sensory input
sometimes people make different inferences - results in different perceptual experiences
Transduction
conversion of proximal stimulus into neural signals
Sensation
the detection of sensory signals and beginning of perception
Bottom-Up Processing
incoming sensory information
Top-Down Processing
knowledge and experience
Bottom-Up Information in Vision
transduction & sensory receptors: light falling on retina converted into neural signals
specialized neurons
rods: low light
cones: high light - color
optic nerves carry information out of eyes
right visual field to left hemisphere
left visual field to right hemisphere
eventually reaches primary visual cortex
neurons respond to basic visual features
spatially organzied, more cortex devoted to central vision
Predictions
brain uses experiences and context to anticipate or predict
incoming information often ambiguous, experience helps to resolve ambiguity
Perceiving Objects
vision begins with mosaic of light falling on each retina
need to be able to parse the visual array into different areas corresponding to different objects
object segmentation: group areas into different objects, edges and contours define boundaries of objects
Figure-Ground Observation
boundaries indicate where objects end, boundaries belong to Figure
the Ground appears to continue on behind figure
rules of figure-ground segregation:
enclosure
symmetry
convexity
meaningfulness
Occlusion
blocked views of objects
have to recognize objects without complete view and fill in missing information
in order to complete objects behind occlude – must assign edges to surfaces
amodal completion: completing surfaces behind an occluder
boundary extension: remember seeing more that what was actually present
Binocular Depth Clues
our two eyes at slightly different positions in space
two eyes see slightly different views of the world
difference gives us information about depth, gives rise to steropsis, impression of depth based on retinal disparity
Monocular Depth Clues
cues for depth that we can use with a single eye
linear perspective
texture gradient
relative size
height in particular plane
occlusion
Object Constancy
retinal image changes with different viewpoints of object
able to still recognize from these different views
input changes, but we experience the same object
Size Constancy
size of retinal image changes with distance
still perceive objects to be same size
Color Constancy
visual system takes color/wavelength of light source into account
perceive object as the same color although inputs are different
Lightness Constancy
similar to color constancy
visual system takes amount of light into account when judging lightness of a surface
perceive object as the same lightness although different amounts of light are reaching the eyes under different illuminations
Object Recognition
low-level (early) vision: analyzing basic visual features (color, orientation, motion)
high-level (visual) vision: combines features into object representations, compares these representations with memory
Agnosia
inability to recognize objects by sight
apperceptive agnosia: impairments in early vision, unable to construct coherent object representations, unable to draw objects right in front
associative agnosia: impairments in later vision, can create representations, problems matching that representation to memory
Holistic Processing
most everyone has the same facial features
we process faces holistically
relationships between features
relative size of features
Face Inversion Effects
inverting faces affects recognition more than objects
inversion disrupts holistic processing
Composite Effect
perceiving half a face is more difficult when it appears against a different complementary half
effect is reduced if face halves are offset – disrupting holistic processing
Holistic Processing and Fusiform Face Area (FFA)
Gauthier et al. (2000)
used fMRI to compare activity in FFA of car and bird experts
increased FFA activity when car experts viewed cars and bird experts viewed birds
Perception and Action: What and Where
separate visual streams/pathways
- what? stream: identifying an object
- where/how stream: identifying the object’s location
Mental Imagery
internal representation of items that are not currently being sensed
may be old, new, imaginary
Imagery and the Brain
brain activity in response to imagery
evidence: correlational in nature
indicates something is happening
Imagery Debate
Kosslyn’s view of imagery is imagery is depictive in nature and uses much of the same “machinery” as perception
imagery: activates these areas in a top-down fashion
perception: initially activates these areas in a bottom-up fashion
