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Chapter 1

PSYB51H3 Chapter Notes - Chapter 1: Étienne Bonnot De Condillac, Detection Theory, Gustav Fechner


Department
Psychology
Course Code
PSYB51H3
Professor
Matthias Niemeier
Chapter
1

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PSYB51: Sensation and Perception Clara Rebello
1
PSYB51 Chapter 1: Introduction
Sensation and Perception
Sensation: the ability to detect a stimulus and, perhaps, to turn that detection into a private
experience
Perception: the act of giving meaning to a detected sensation
Everything we feel, think, and do depends on our sensations and perceptions
18th century French philosopher Etienne Bonnot de Condillac
o Asked his readers to imagine the mental life of a statue with no sense
o Concluded that the statue has no mental life because it lacks senses
o Thought that if the statue had a ose, all of the statue’s etal life ould osist of the
thigs he’d sell
o More senses and experience A real mental life would develop
Methods Used in the Study of Senses
Studies of sensation and perception can be found in psychology, biology, computer science,
medicine, neuroscience, etc
o The study of sensation and perception needs scientific methods
Method 1: Thresholds
o For example; the loudest/faintest sound you can hear without causing damage
Method 2: Scaling Measuring Private Experience
o Qualia: (Singular: Quale) In philosophy, the private conscious experiences of sensation
or perception
o The qualia you experience would be much different from others
o We hae o diret a to eperiee soeoe else’s eperiees
Method 3: Signal Detection Theory Measuring Difficult Decisions
o Perceptual decision Based on your knowledge and experiences, you perceive a
decision in an event/situation to be the most effective to take
o Experts like radiologists can make perceptual decisions that turn out to be incorrect and
has real consequences
o This type of decision can be studied scientifically
Method 4: Sensory Neuroscience
o Sensory receptors and nerves provide a firm basis of your perceptual experience
Method 5: Neuroimaging An Image of the Mind
o Binocular rivalry The effect caused by the two images (one seen by each eye
separately) that compete to dominate your perception
o Binocular rivalry represents a dissociation of the stimuli, presented to the eyes, and your
private perceptual experience
o Methods of neuroimaging let us see traces of experiences as it takes place in the brain
Thresholds and the Dawn of Psychophysics
The study of the senses was always a mix of experimental science and philosophy
19th century German scientist-philosopher Gustav Fechner
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PSYB51: Sensation and Perception Clara Rebello
2
o Sometimes considered to be the true founder of experimental psychology
Sometimes that title is given to Willhelm Wundt
o Suffered extreme eye damage from gazing too much at the sun while performing visual
experiments
Fell into deep depression until one day when his vision began to recover quickly
Suddenly got very absorbed with the relationship between mind and matter
This placed him in the middle of a philosophical debate between dualism and
materialism
Dualism: the idea that the mind has an existence separate from the material
world of the body
Materialism: the idea that the only thing that exists is matter, and that all
things, including the mind and consciousness, are the results of interaction
between bits of matter
Fechner supported panpsychism: the idea that the mind exists as a property of
all matter that is, that all matter, including inanimate things, has
consciousness
o Goal Formally describe the relationship between sensation (mind) and the energy
(matter) that gave rise to that sensation
Called both his methods and theories psychophysics
Psychophysics: the science of defining qualitative relationships between
physical and psychological (subjective) events
Anatomist and physiologist Ernst Weber
o Very interested in touch
Tested the accuracy of our sense of touch by using a device to measure the
smallest distance between two points that was required for a person to feel
touch on two points instead of one
Two-point touch perspective: the minimum distance at which two stimuli (ex.
Two simultaneous touches) are just perceptible as separate
o Feher as er iterested i Weer’s fidigs iolig judgeets of lifted eights
Weer’s test to differetiate etee a stadard eight ad a differed
comparison weight
Comparison weight would change after each trial
Found that the ability to differentiate the weights depended greatly on the
standard weight
Just noticeable difference (JND) or difference threshold: the smallest
detectable difference between two stimuli, or the minimum change in a
stimulus that enables it to be correctly judged as different from a reference
stimulus
Noticed that JNDs changed in a systematic way
A constant ratio between the change and what was being changed could
describe the threshold of detectable change quite well
Weber fractions: ostat of proportioalit i Weer’s la sas that the ratio
rule above is true except when intensities, size, etc. are very small/very large,
nearing the min. or max. of our senses
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PSYB51: Sensation and Perception Clara Rebello
3
Weer’s La: the principle describing the relationship between stimulus and
resulting sensation that says the JND (I) is a constant fraction (K) of the
comparison stimulus (I)
o Feher foud i Weer’s oseratios hat he as lookig for: a a to desrie the
relationship between mind and matter
Fechner assumed that JND (I) could be considered a unit of the mind because
this is the sallest it of hage that’s pereied
Eteded Weer’s La to eoe Fehner’s La: a principle describing the
relationship between stimulus and the resulting sensation that says the
magnitude of subjective sensation increases proportionally to the logarithm of
the stimulus intensity
Feher’s La S = k log R
S psychological sensation
Log R logarithm of the physical stimulus level
k constant
This equation describes how our psychological experience of the intensity of
light, sound, touch, etc. increases less quickly than the actual physical stimulus
increases
Absolute threshold: the minimum amount of stimulation necessary for a person to detect a
stimulus 50% of the time
o Example of a threshold that Fechner would try to determine through his methods of
measuring senses
Psychophysical Methods
Method of constant stimuli: a psychophysical method in which many stimuli, ranging from
rarely to almost always perceivable (or rarely to almost always perceivably different from a
reference stimulus), are presented one at a time
o Example A hearing test, where you would report when you could or could not hear a
tone played by the audiologist
Subtle perceptual judgements are variable
o The stimulus varies for physical reasons
o Thus, one measure is almost never enough
The intensity at which a stimulus would be detected 50% of the time would be chosen as your
threshold
Method of constant stimuli Simple, but can be inefficient
o Much of subject’s tie is spet ith stiuli that are learl ell aoe or elo
threshold
o More efficient approach is method of limits: a psychophysical method in which the
particular dimension of a stimulus, or the difference between two stimuli, is varied
incrementally until the participant responds differently
o With this method, the experimenter puts the stimuli in order of increasing/decreasing
intensity instead of random presentations
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