Sensation and Perception Flashcards
modalities
sensory brain region that process different components of the perceptual world.
define psychophysics
scientific method for investigation of relationships between physical stimuli and psychological experience
what is the absolute threshold
the minimum stimulus discriminated reliably from no stimulus. need to respond yes 50% of the time for a trial to be successful
what are the 5 senses thresholds
on picture
what is the difference threshold / just noticeable difference
the minimum difference in stimulus intensity necessary to tell the two apart
what is webers law
that the just noticeable difference is a constant proportion despite variations in the stimulus
what is the aim in detection experiments
for the ppt to discriminate the presence of a stimulus from background noise
how does a ppt do this
adopt a response criterion (= attitude to the decision)
what is signal detection theory
an observation that the response to stimulus depends on a persons sensitivity to the stimulus in the presence of noise and on a persons response criterion
Signal detection theory allows us to measure sensitivity and bias separately how?
using hits and false alarms.
describe the ways in which a ppts response could be categorised
hit = said yes was yes
miss = said no but was there
false alarm = said yes wasnt there
correct rejection = was no said no
what effects response criterion
your evaluation of the costs and benefits of the different possible outcomes e.g is there a tumour said no but it is there = death
what is d prime
a statistic that gives a relatively pure measure of the observers sensitivity or ability to detect signals
what is sensory adaptation
sensitivity to prolonged stimulation tends to decline over time as an organism adapts to current conditions
what is visual acuity
ability to see fine detail
what is visible light
the portion of the electromagnetic spectrum that can be seen
how we see
see picture
describe the retina
the surface of the retina is composed of photoreceptor cells the rods and cone beneath a layer of transparent neurons the bipolar and retinal ganglion cells
describe the world on your retina
inverted as has passed through the lens
topographic - reflects real world spatial relationships
much of view common to both retina but also sees parts the other doesnt
what happens from the retina to the brain
visual signals relay to primary visual cortex (V1) via the lateral geniculate nucleus
prior to this half the optic nerve fibres from either eye cross over at the optic chiasm so Right visual field to left hemisphere
what is a receptive field
region of the sensory surface that when stimulated causes a change in firing rate of thay neuron - on centre cells off center cells
receptive field info
each photoreceptor receives light from a specific part of the visual field so its receptive field corresponds to a specific part of the visual field
what is the receptive field of the ganglion determined by
the positions of the photoreceptors to which it connects
describe the parts of the receptive fields
functional and spatial characteristics - most are center surround type. ganglion cell is sensitive to differences between illumination in the centre and surround portions of its receptive field
describe simple cells
larger receptive fields than ganglion cells they respond to edges of a certain orientation in a certain position
describe complex cells
combine input from many simple cells with the same orientation turning and adjacent receptive fields. can respond to an edge of a particular orientatopn st any position in their receptive field
describe hypercomplex cells
combine input from many complex cells to respond to increasingly refined features
bottom up hierarchy of feature detectors see phone
see picture
what is motion
a powerful cue for alerting and orientating and for form perception
what is space constancy
we factor out self generated movement to perceive only movement arising in the world
what are the two possibilities for space constancy
monitoring eye muscle systems for sensory (afferent) or motor (efferent) signals
observations linked to space constancy
the world does not stay stable when the eye is moved passively (sensory signal but no motor signal = space constancy fails)
the world seems to move when we try to move a paralysed eye (motor signal but no sensory signal = space constancy maintained)
what can we conclude from the space constancy observations
the brain automatically factors out from the image motion signal(IMS), the corollary discharge signal (CDS) which is an exact copy of the motor signal sent to the eyes
describe evolutionary utility
dont experience the world directly, through the filter of own perceptual system. do not present objective reality, they have evolved to reconstruct reality in a way that is biologically useful
how does colour vision help
classify and identify objects
important signalling mechanism in nature. facilitates perceptual organisation of scene into distinct objects
what determines the colour
the wavelength of light that it reflects. most objects reflect a mixture of wavelengths
what are the two types of photoreceptor
rods and cones
describe rod cells
very light sensitive but all contain same photopigment (rhodopsin) they provide low light acuity, light sensitive peripheral vision which is monochromatic
describe cone cells
they are tightly packed in the central fovea giving high acuity colour vision. cones come in three varieties depending on the photopigment they contain
what are the three absorption spectra of the cone cells
blue = S and 419 nm wavelength green = m 531 red = L 559 nm
how do the cone cells work together to produce images
the combination of responses from the S M and L cones leads to perception of all colours
what is colour transduction
trichromatic
describe the neural coding of colour
it is an opponent process. the signals from the red green and blue cones are coded as opponent pairs. a retinal ganglion cell may be excited by firing of red cone and inhibited by firing of green
describe colour constancy by chromatic adaptation
wavelenghts reflected by object are determined by objects reflectancy + wavelengths in illumination. colour constancy reduces sensitivity to the dominant wavelengths in the light with our current environment. same colour across changes in illumination
describe perceptual constancies
means we can see real unchanging properties in the world despite large changes in stimulation
what is the problem with vision
recovering a 3d world from a 2d one. no unique solution so do it by piecing together as much info as is available and making assumptions about the world
what is the depth cues table on
my phone
what is binocular disparity
two eyes have slightly different views. by sensing the disparity between the objects image in the two eyes the brain can calculate depth
what is the process of matching up disparate images as seeing in depth called?
stereoscopic vision
describe stereoscopic vision
slightly different images to each eye - images compared computed and vivid depth is experienced
what is motion parallax
a dynamic monocular retinal depth cue
when are static (pictoral) depth cues available
when viewing a static scene such as a picture through even one eye
what are the pictorial depth cues
height in scene blur and interposition
explain size perspective and texture gradient as a pictorial depth cue`
size - retinal image projected by an object reduces in proportion to distance from the eye
perspective - brain assumes parallel edges
texture gradient - the braini assumes a constant grain size
explain size and distance in more depth
how far away, interpret image size, tells us how big the object is. depth is a cue to object size
what is size constancy
tendency to take distance into account when estimating object size. far objects not as small as they should because we size them up
how does familiar size relate to depth perception
familiar with real size use it to infer distance
what are extra retinal depth cues
do not come from visual image but from movement of the eyes
how do extra retinal depth cues work
monitoring the convergence angle of the eyes the brain can calculate the distance to a point of fixation - trigonometry
what did the gestalt psychologists propose
the whole is other than the sum of the parts
what are the proposed laws of perceptual organisation also called
heuristics
how is the problem of vision solved
all of the depth cues and heuristics (assumptions)
what are the laws of perceptual organisation
pragnanz to prox
simplicity Law of pragnanz - stimulus patter is seen such that the resulting structure is as simple as possible
similarity - similar things group together
proximity - near things group together
rest of the laws of perceptual organisation
good continuation - points on straight or smooth lines belong together
closure - often aided by cues of good continuation we tend to see object as complete despite occlusion.
common fate - things that move together belong together
meaningfulness/ familiarity - things are more likely to form groups is those are familiar
how do heuristics work in the real world
make perception more efficient under normal conditions but mislead us when normal conditions dont apply.
what is figure ground segregation
figure is the thing in the scene with ground out uniformly behind it. figure ground border belongs to thing. regions w symmetry tend to be seen as the figure. smaller regions tend to be seen as figure
is lower or upper part the figure - what else
lower in 84% of free viewing
meaningful shapes are seen as the figure.
how does figure ground segregation link to object reognition
recognition interacts with and influences FGS
top down or bottom up
perception doesnt just come from sensory data (bottom up) actively constructed using context knowledge and expectation (bottom down)
how do bottom up combine
the predictions about the world (top down) are continuously refined by comparing them to sensory data (bottom up). the predictions and prediction errors are what we experience.
how is perceptual inference bayesian
his work on conditional probabilities describes how we should adjust our beliefs according to new evidence. prior prob.(how much we expect something) and sensory data (how much evidence we have for it)
what is synaesthesia
person experiences sensations in one modality when a second modality is stimulated
what are some characterisctics of synaesthesia
cross modal pairings are stable over time. can show automatic interference or pop out effects. grapheme - colour synaesthete slowed by letters in wrong colour
is synaesthesia result of memories of coloured letters and numbers
a learned association between colour and grapheme doesnt explain historical reports. other types of the condition and martian colours
are synaesthetes on drugs
LSD - pharmacologically induced may not based on the same neural mechanisms as the congenital synth.
not everyone who uses LSD experiences it
low and high level
low level only letter not number
high level letter and number
costs of synaesthesia
can not be switched off. can be distracting can be intrusive and unpleasant
benefits of synaesthesia
can confer mental advantages. richer sensory associations = enhanced memory
pruning
synaptic pruning
what is the mcgurk effect
if a person sees lip movements of one speech sound while a different is spoken they hear a third sound
we use visual info whilst we listen
people with hearing loss do this more accurately
