Problem 1 - DONE Flashcards
measuring Perception
perceptual processes
- journey from stimuli to responses
- continuously changing process
7 steps of perceptual processes
- environmental stimulus
- light is reflected and transformed
- receptor processes
- neural processing
- perception (knowledge)
- recognition (knowledge)
- action
step 1 - environmental stimulus
what person observes (tree)
step 2 - stimulus on receptors
light is reflected and transformed
principle of transformation
stimuli and responses created by stimuli are transformed/changed between the environmental stimulus and perception
- central principle of perception
first transformation
light hits object (tree) –> reflected from object to the person’s eyes
nature of reflected light depends on
- properties of the light energy hitting the tree
- properties of the tree
- properties of the atmosphere through which the light is transmitted
second transformation
reflected light reaches the eye –> focused by the eye’s optical system –> form an image on the receptors of the retina
step 3 - receptor processes/transduction
transduction = transformation of one form of energy to another form
receive light reflected from tree –> (1) transduction + (2) shape perception by the way they respond to stimuli
step 4 - neural processing
neural processing = changes in signals that occur as they are transmitted through network of neurones
transduction –> electrical signals –> signals enter interconnected network of neurones –> retina –> out the back of the eye –> brain
step 5 - perception
- person perceives object (tree)
- conscious awareness of object (tree)
step 6 - recognition
- recognises object (tree)
- playing an object in a category that gives meaning
step 7 - action
- action that involves motor activities
knowledge
any information that perceiver brings to situation; acquired years ago or just recently acquired
- can affect a number of steps in perceptual processes
bottom-up processing
(data-based processing)
- processing that is based on stimuli reaching the receptors
- stimuli provide starting point for perception
- -> everything that comes from the outside to the inside
top-down processing
(knowledge-based processing)
- processing that is based on knowledge
- -> anything that we add (prior knowledge/experience/memory)
method 1: measuring thresholds
- Gustav Fechner
- psychophysical methods
- -> absolute threshold
- Fechner’s law
- Ernst Weber
- -> difference threshold
- Weber’s law
method 2: scaling - measure private experience
- S. S. Stevens
- -> magnitude estimation
- Stevens’ power law
other methods to measure perception
- phenomenological method = person is asked to describe what he or she is perceiving or to indicate when a particular perception occurs
- visual search = observer’s task is to find one stimulus among many, as quickly as possible
- -> reaction time = time between presentation of the stimulus and the observer’s response to the stimulus
Gustav Fechner
- German scientist-philosopher
- psychophysics = methods and theory to formally describe the relationship between sensation (mind) and the energy (matter)
- absolute threshold = minimum stimulus intensity that a subject can detect a given proportion of the time (50% or 75%)
psychophysical methods
- how to measure an absolute threshold
- method of constant stimuli
- method of limits
- method of adjustment
method of constant stimuli
- repeatedly present stimuli
- stimuli ranging from rarely to almost always perceivable
- stimuli are presented one at a time –> participants respond to each presentation ‘yes/no’, ‘same/different’
- weaknesses: time consuming, relies on subjects’ reports
method of limits
- present stimulus far below/above threshold –> increase/decrease intensity until subject responds differently (reports detection/no detection of stimuli)
- weaknesses: time consuming, relies on subjects’ reports
method of adjustment
- experimenter/observer adjust amplitude of a stimuli until observer can just barely detect the stimulus
- method of limits in which the subject can control the change
Fechner’s law
- principle describing the relationship between the stimulus and resulting sensation
–> says the magnitude of subjective sensation increases proportionally to the logarithm of the stimulus intensity
y = k*log(S) - began with Weber’s law
- calculation based on some assumptions about how sensation works
- assumes that all JNDs are perceptually equivalent –> incorrect
- indirect scaling = based on discrimination ability
Ernst Weber
- German anatomist, physiologist
- two-point touch threshold = minimum distance at which two stimuli are just perceptible as separate
- difference threshold = JND (just-noticeable difference) = smallest detectable difference between two stimuli
Weber’s law
- principle describing the relationship between stimulus and resulting sensation
–> says the JND is a constant ratio of the standard stimulus - Weber fraction = constant of proportionality in Weber’s law
k = JND/S - involves clear objective measurement —> we know how much we varied the stimulus
- observers can tell that the stimulus changed or they cannot
S. S. Stevens
- psychologist
- magnitude estimation = psychophysical method; participant assigns values according to perceived magnitudes of the stimuli –> ask observer to rate experience
Stevens’ power law
- principle describing the relationship between stimulus and resulting sensation
–> says the magnitude of subjective sensation is proportional to the stimulus magnitude raised to an exponent
estimation = k S^p - describes rating data quite well –> rating data are qualitatively different from the data that supported Weber’s law
- can record the subjects’ ratings
- direct scaling = have subjects produce numbers proportional to the magnitude of a given stimulus dimension
how do we measure perception?
lecture
- psychophysics
- electrophysiology
- neuropsychology
- cognitive neuroscience
- psychophysics
lecture
stimulus –> perception
- present a stimulus and determine the person’s response
- first task (laws)
- electrophysiology
lecture
stimulus –> brain processes
- present a stimulus and measure direct brain activity
- in animals (invasive) –> watch neural firing due to stimulus
- neuropsychology
lecture
brain processes –> perception
- study the effects of brain damage on behaviour
- how does brain damage influence perception?
- cognitive neuroscience
lecture
stimulus –> brain processes –> perception
- present a stimulus and measure both brain activity and perceptual responses
- fMRI (where in the brain?; passively measure)
- EEG (when in the brain?)
- TMS (local, temporary disturbance of brain function; actively measure)
sensation
= process by which our senses (vision, hearing, smell, taste, touch) receive and relay outside stimuli
- more basic level than perception not really perceive consciously
perception
= way our brains organise and interpret sensory information and put it into context
- consciously perceive something
- active process
- -> bottom-up processing
- -> top-down processing
