Psychophysics: The Fundamentals

By George A. Gescheider | Go to book overview

2
Psychophysical Measurement of Thresholds: Absolute Sensitivity

The measurement of the absolute threshold, though perhaps not as important for the development of psychology as Fechner's insights into difference thresholds, has led to many significant advances in understanding sensory systems. Before considering in detail the various psychophysical methods for measuring DL's and RL's, let us consider examples of how measuring absolute thresholds has facilitated our understanding of vision, audition, touch, and olfaction.


The Absolute Sensitivity of the Eye

The eye is an extremely light-sensitive instrument capable of responding to almost unbelievably small amounts of light energy. However, a simple answer cannot be given to the question: How sensitive is the eye to light? The absolute sensitivity of the eye cannot be gauged by a single threshold value, since the minimum amount of light necessary for vision has been found to depend on the conditions of stimulation. Therefore, the absolute sensitivity of the visual system is best understood by examining the functional relationships between the absolute threshold and the conditions that determine its value.

The value of the absolute threshold depends upon previous stimulation. Exposing the eye to intense light greatly decreases the absolute sensitivity of the eye. Sensitivity is recovered gradually if the eye is subsequently kept in darkness. Nearly complete recovery of sensitivity occurs after about one hour in the dark. The dark adaptation curve is traced out by measuring an observer's absolute threshold periodically

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Psychophysics: The Fundamentals
Table of contents

Table of contents

  • Title Page iii
  • Contents vii
  • Preface ix
  • Acknowledgments x
  • 1- Psychophysical Measurement Of Thresholds: Differential Sensitivity 1
  • 2- Psychophysical Measurement Of Thresholds: Absolute Sensitivity 16
  • 3- The Classical Psychophysical Methods 45
  • 4- Classical Psychophysical Theory 73
  • 5- The Theory of Signal Detection 105
  • 6- Further Considerations of Tsd 125
  • 7- Procedures of Tsd 142
  • 8- Some Applications of Tsd 166
  • 9- The Measurement of Sensory Attributes And Discrimination Scales 183
  • 10- Partition Scales 207
  • 11- Psychophysical Ratio Scaling 231
  • 12- Evaluation of Ratio Scaling Methods 264
  • 13- The Psychophysical Law 296
  • 14- Some Fundamental Issues In Psychophysical Scaling 327
  • Conclusion 369
  • Appendix 371
  • Glossary 392
  • References 408
  • Author Index 425
  • Subject Index 431
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