This document provides an overview of psychophysics, which quantitatively examines the relationship between physical stimuli and the resulting sensations and perceptions. It discusses the origins of psychophysics, key areas of investigation such as thresholds and psychological scaling, classical methods utilized in psychophysical experiments, and major influencing factors affecting perception. Additionally, it touches on the deficits of traditional methods and introduces adaptive psychophysical methods for more accurate measurement.

1. Psychophysics
PSY103 Cognitive Psychology – 1
Presented to: Asst Prof Hemlata Joshi
HOD: Prof L. N. Bunker
Presented by:
A Siddhartha
MA (Psychology) 1st Sem
Jai Narayan Vyas University

2. Contents
1. What is Psychophysics?
2. Origins of Psychophysics
3. Thresholds
4. Detection
5. Discrimination
6. Psychological Scaling
7. Classical Methods of Psychophysics
8. Major Influencing Factors
9. Deficits
10.Adaptive Psychophysical Methods

3. What is Psychophysics?
 Psychophysics quantitatively investigates
the relationship between physical stimuli
and the sensations and perceptions they
produce.
PerceptionSensationStimulus

4. Origins of Psychophysics
 Works of German physiologist Ernst Heinrich Weber on sense of touch and
light in the early 1830s inspired Fechner.
 Theories of psychophysics were formulated in 1860 when Gustav Theodor
Fechner in Leipzig published Elemente der Psychophysik (Elements of
Psychophysics).
 He coined the term "psychophysics", describing research intended to relate
physical stimuli to the contents of consciousness such as sensations

5. Three main areas of investigation
Absolute
Thresholds
Discrimination
Thresholds
Psychological
Scaling

6. Thresholds
 A threshold (or limen) is the
point of intensity at which the
participant can just detect the
presence of a stimulus (absolute
threshold) or the presence of a
difference between two stimuli
(difference threshold).
Threshold
Absolute Differential

7. Detection
 An absolute threshold is the level
of intensity of a stimulus at which
the subject is able to detect the
presence of the stimulus some
proportion of the time.
 Also often referred to
as detection threshold.

8. Discrimination
 A difference threshold (or just-
noticeable difference, JND) is the
magnitude of the smallest
difference between two stimuli of
differing intensities that the
participant is able to detect some
proportion of the time (the
percentage depending on the
kind of task).

9. Psychophysical scaling
 It refers to the process of quantifying psychological events, especially
sensations and perceptions.
 Scaling requires both a set of empirical operations and a theoretical
framework to derive the quantitative values or representations

10. Classical Methods of Psychophysics
 Psychophysical experiments have traditionally used three methods for
testing subjects' perception in stimulus detection and difference
detection experiments:
the method of limits,
the method of constant stimuli and
the method of adjustment.

11. Major Influencing Factors
Sensitivity
Response Bias
Attention
Memory
Motivation

12. Deficits
 In general, each of these three methods suffers from one or more of the
following deficits:
absence of control over the subject's decision criterion;
the estimates may be substantially biased;
no theoretical justification for important aspects of the
procedure;
a large amount of data is wasted since the stimulus is often
presented far from threshold where little information is
gained

13. Adaptive Psychophysical Methods
 Staircase procedures
 Bayesian and maximum-likelihood
procedures
 Magnitude estimation

14. Thank You