Introduction to psychophysics (English)

The branch of psychological science that study relationship between psychological phenomenon and physical properties of a stimulus

1. Introduction to
Psychophysics
Dr Rajesh Verma
Asst. Prof in Psychology
FGM Govt. College Adampur, Hisar, Haryana

2. Meaning
ThewordPsychophysicsismadeupofPsychology
andPhysics.
Psychology=Psychologicalvariables(Specially
SensationandPerception)ofanindividual.
Physics=PhysicalPropertiesofStimulus
Meansstudyingthe
relationshipbetween
psychologicalphenomenon
andphysicalproperties
ofstimulus.

3. Definition
Thebranchofpsychologicalsciencethatstudy
relationshipbetweenpsychologicalphenomenonand
physicalpropertiesofastimulus.
Therelationshipbetweenstimuliandthesensations
theyevokehasbeenstudiedinadiscipline,called
psychophysics(NCERT,XI).
“Theanalysisofperceptualprocessesby
studyingtheeffectonasubject's
experienceorbehaviourof
systematicallyvaryingthepropertiesof
astimulusalongoneormore
physicaldimensions”(Bruceet.al.,
1996quotedbyWikipedia).

4. Introduction
ThetermpsychophysicswascoinedbyGustav
TheodoreFechnerin1860todescribemathematically
therelationshipbetweenbodyandmind.Hewas
Germanphysicistandphilosopherwhousedthisina
book(inGerman)namedas‘Elementsof
Psychophysics’.Priortohiswork
whileworkingatLeipzigUniversity,
ErnstHeinrichWeberproposedthe
conceptofJNDbaseduponthesenses
oftouchandlightwhichiscommonly
referredasWeber’slaw.

5. Itstatesthattheamountrequiredto
produceJNDisaconstantproportionofthe
valueoftheoriginalstimulusorreference
intensity.TheconceptofmodernPsychophysics
isbasedontheworkWeberandFechner.
Inpsychophysicstheintensityofstimuli
thatactivatethefive
sensesareobjectively
quantified.

6. Thetwoimportantconceptsofpsychophysics:-
(i)Absolutethresholdorlimen(AL)–Itis
alsoknownasDetectionThreshold.The
minimumamount,intensity,valueorweightof
thestimulustogetnoticedorperceivedby
humansensorysystem.ALvariesacross
individualsandsituationsdependingupon
variouspsycho-
physicaland
situational
factors.

7. SotomeasureALthenumberoftrials
formsthebase.Whenthestimulusisperceived
correctlyin50%oftotaltrialsthanthe
particularintensityorvalueofthestimulusis
referredasAL. Ear drum, and three tiny bones
(Ossicles)

8. (ii)Differentialthresholdoflimen(DL)–Itisalso
knownasJustNoticeableDifference(JND)or
DiscriminationThreshold.Thesmallestdifferenceinthe
valuesofthetwostimulithathelpsindetectingthe
differencebetweenthem.AsAL,DLalsomeasured
usingnumberoftrialsi.e.theminimumamountof
changeinthevalueofastimuluswhichiscapable
enoughtobedetected
correctlyin50%of
thetrials.

9. Methods of Psychophysics
Tomeasuretherelationshipbetween
intensityofstimulusandperceptionFechner
developedfollowingthreemethods.:-
(i)MethodsofLimits
(ii)Methodof
ConstantStimuli

10. (iii)MethodofAdjustment
Thesemethodsareusedtomeasurethe
thresholdoftheintensityofthestimulus
requiredtoperceiveitwhichisknownas
AbsolutethresholdorAbsoluteLimen(AL).

11. References:
1. NCERT,XIPsychologyTextbook.
2. Bruce.V.,Green,P.R.&Georgeson,M.A.(1996).Visual
perception(3rded.).PsychologyPress.
3. https://www.britannica.com/science/Webers-law.
4. https://en.wikipedia.org/wiki/Psychophysics.
5. https://www.britannica.com/science/psychophysics.

12. Next Discussion
Problems of
Psychophysics

13. Meet You Soon
With Next Video
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